(300 HZ TO 300 GHZ)

    This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Radiation Protection Association, or the World Health Organization.

    Published under the joint sponsorship of
    the United Nations Environment Programme,
    the International Radiation Protection Association,
    and the World Health Organization

    World Health Orgnization
    Geneva, 1993

    WHO Library Cataloguing in Publication Data

    Electromagnetic fields (300 Hz to 300 GHz)

          (Environmental health criteria: 137)

    1. Electromagnetic fields - adverse effects  2. Environmental
    exposure    I.Series

          ISBN 92 4 157137 3         (NLM Classification QT 34)
          ISSN 0250-863X

          The World Health Organization welcomes requests for permission
    to reproduce or translate its publications, in part or in full.
    Applications and enquiries should be addressed to the Office of
    Publications, World Health Organization, Geneva, Switzerland,
    Which will be glad to provide the latest information on any changes
    made to the text, plans for new editions, and reprints and
    translations already available.

    (c) World Health Organization 1993

          Publications of the World Health Organization enjoy copyright
    protection in accordance with the provisions of Protocol 2 of the
    Universal Copyright Convention.  All rights reserved.

          The designations employed and the presentation of the material in
    this publication do not imply the impression of any opinion whatsoever
    on the part of the Secretariat of the World Health Organization
    concerning the legal status of every country, territory, city, or area
    or of its authorities, or concerning the delimitation of its frontiers
    or boundaries.

          The mention of specific companies or of certain manufacturers'
    products does not imply that they are endorsed or recommended by the
    World Health Organization in preference to others of a similar nature
    that are not mentioned.  Errors and omissions excepted, the names of
    proprietary products are distinguished by initial capital letters.



         1.1. Summary
              1.1.1. Physical characteristics in relation to biological
              1.1.2. Sources and exposure
              1.1.3. Biological effects
              1.1.4. Laboratory studies
              1.1.5. Human studies
              1.1.6. Health hazard assessment
                Thermal effects
                Pulsed fields
                Amplitude-modulated RF fields
                RF field effects on tumour induction and
                RF-induced current densities
                RF contact shocks and burns
              1.1.7. Exposure standards
                Basic exposure limits
                Occupational exposure limits
                Exposure limits for the general
                Implementation of standards
              1.1.8. Protective measures
         1.2. Recommendations for further studies
              1.2.1. Introduction
              1.2.2. Pulsed fields
              1.2.3. Cancer, reproduction, and nervous system
              1.2.4. Weak-field interactions
              1.2.5. Epidemiology

         2.1. Introduction
         2.2. Electric field
         2.3. Magnetic field
         2.4. Waves and radiation

         3.1. General
         3.2. Natural background
              3.2.1. Atmospheric fields
              3.2.2. Terrestrial emissions
              3.2.3. Extraterrestrial fields
         3.3. Human-made sources
              3.3.1. General
              3.3.2. Environment, home, and public premises
              3.3.3. Workplace
              3.3.4. Medical practice

         4.1. Introduction
         4.2. Theoretical estimation
         4.3. Measurements
              4.3.1. Preliminary considerations
              4.3.2. Near-field versus far-field
              4.3.3. Instrumentation
              4.3.4. Measurement procedures

         5.1. General
         5.2. Low frequency range
              5.2.1. Magnetic fields
              5.2.2. Electric fields
         5.3. High-frequency range
         5.4. Derivation of exposure limits from basic quantities

         6.1. General
         6.2. Electrical properties of cells and tissues
              6.2.1. Permittivity
              6.2.2. Non-linear effects
              6.2.3. Induced fields at the cellular level
              6.2.4. Body impedance
         6.3. Direct interactions - strong fields
              6.3.1. Interactions with excitable tissues
              6.3.2. Thermal interactions
         6.4. Direct interactions - weak fields
              6.4.1. General
              6.4.2. Microelectrophoretic motion
              6.4.3. Ion-resonance conditions
              6.4.4. Calcium ion exchange
         6.5. Indirect interactions

         7.1. Introduction
         7.2. Macromolecules and cell systems
              7.2.1. Effects on cell membranes
              7.2.2. Effects on haematopoietic tissue
              7.2.3. Isolated cerebral tissue, peripheral nerve tissue,
                       and heart preparations
              7.2.4. Mutagenic effects
              7.2.5. Cancer-related studies
              7.2.6. Summary and conclusions:  in vitro studies
         7.3. Animal studies
              7.3.1. Nervous system
              7.3.2. Ocular effects
              7.3.3. Auditory perception
              7.3.4. Behaviour
                Activity (spontaneous movement)
                Learned behaviours
              7.3.5. Endocrine system
              7.3.6. Haematopoietic and immune systems
              7.3.7. Cardiovascular system
              7.3.8. Reproduction and development
                kHz studies
                MHz and GHz studies
              7.3.9. Genetics and mutagenesis
              7.3.10. Cancer-related studies
              7.3.11. Summary and conclusions

         8.1. Laboratory studies
              8.1.1. Cutaneous perception
              8.1.2. Other perception thresholds
              8.1.3. Auditory effects
              8.1.4. Induced-current effects
              8.1.5. Thermoregulation
              8.1.6. Contact currents
         8.2. Epidemiological and clinical comparative studies
              8.2.1. Mortality and morbidity studies
              8.2.2. Ocular effects
              8.2.3. Effects on reproduction
              8.2.4. VDU studies
              8.2.5. Conclusions
         8.3. Clinical case studies and accidental overexposures

         9.1. Introduction
         9.2. Thermal effects
         9.3. RF contact shocks and burns
         9.4. Induced current densities
         9.5. Pulsed RF fields
         9.6. RF fields amplitude modulated at ELF frequencies
         9.7. RF effects on tumour induction and progression

         10.1. General considerations
         10.2. Present trends
         10.3. Recommendations by the IRPA
         10.4. Concluding remarks

         11.1. Engineering measures 
         11.2. Administrative controls
         11.3. Personal protection
         11.4. Medical surveillance 
         11.5. Interference with medical devices and safety equipment




    Prof J. Bernhardta       Federal Office of Radiological 
                             Protection, Institute for Radiation Hygiene,
                             Munich-Neuherberg, Germany

    Dr C. F. Blackman        US Environmental Protection Agency, Health
                             Effects Research  Laboratory, North
                             Carolina, USA

    Dr L.A. Courta           Département de Protection Sanitaire,
                             Centre d'Etudes Nucléaires,
                             Fontenay-aux-Roses, France

    Mme A. Duchênea          Scientific Secretary, International
                             Non-ionizing Radiation Committee, 
                             Fontenay-aux-Roses, France

    Prof M. Grandolfoa       Istituto Superiore di Sanità, Rome,

    Dr M.H. Repacholia       Royal Adelaide Hospital, Adelaide,
                             Australia  (Chairman)

    Dr R.D. Saunders         National Radiological Protection Board,
                             Didcot, United Kingdom  (Co-Rapporteur)

    Prof M.G. Shandalaa      AN Marzeev Research Institute of General
                             and Communal Hygiene, Kiev, USSR

    Dr J.A. Stolwijka        Department of Epidemiology and Public
                             Health, Yale University, New Haven, USA

    Dr M.A. Stuchlya         Bureau of Radiation and Medical Devices,
                             Ottawa, Canada

    Dr M. Swicord            Centre for Devices and Radiological Health,
                             Food and Drug Administration, Rockville, USA

    Dr L.D. Szaboa           National Research Institute for
                             Radiobiology and Radiation Hygiene,
                             Budapest, Hungary

    Dr S. Szmigielski        Centre for Radiobiology and Radiation
                             Safety,Warsaw, Poland  (Vice-Chairman)


    Dr A. McKinlaya          National Radiological Protection Board,
                             Didcot, United Kingdom

    a From the International Non-Ionizing Radiation Committee of IRPA.


         Every effort has been made to present information in the criteria
    monographs as accurately as possible without unduly delaying their
    publication. In the interest of all users of the environmental health
    criteria monographs, readers are kindly requested to communicate any
    errors that may have occurred to the Director of the International
    Programme on Chemical Safety, World Health Organization, Geneva,
    Switzerland, in order that they may be included in corrigenda, which
    will appear in subsequent volumes.


    This monograph is dedicated to:

    Professor Przemyslaw A. Czerski, a charter member of International
    Non-ionizing Radiation Committee, who died on 15 April 1990 in Silver
    Spring, MD (USA). He was a pioneer investigator into the effects of
    non-ionizing radiation on biosystems and the assessment of the
    potential hazards associated with such exposure. As a fervent promoter
    of international cooperation, Professor Czerski played an active part
    in the establishment of the International Non-Ionizing Radiation
    Committee and in the development of its activities. His broad
    scientific knowledge and his tireless energy made him a major
    contributor to the present publication.


    The International Radiation Protection Association (IRPA) initiated
    activities concerned with non-ionizing radiation by forming a Working
    Group on Non-Ionizing Radiation in 1974. This Working Group later
    became the International Non-Ionizing Radiation Committee
    (IRPA/INIRC), at the IRPA meeting held in Paris in 1977. The
    IRPA/INIRC reviews the scientific literature on non-ionizing radiation
    and makes assessments of the health risks of human exposure to such
    radiation. On the basis of Environmental Health Criteria monographs,
    developed in conjunction with the World Health Organization, Division
    of Environmental Health, the IRPA/INIRC recommends guidelines on
    exposure limits, drafts codes of safe practice, and works in
    conjunction with other international organizations to promote safety
    and standardization in the non-ionizing radiation field.

    A WHO/IRPA Task Group to review the final draft of the Environmental
    Health Criteria on Electromagnetic Fields (300 Hz-300 GHz) met at the
    WHO Collaborating Centre for NIR in Ottawa, Canada, from 22 to 26
    October 1990. Dr A.J. Liston, Assistant Deputy Minister, Health
    Protection Branch, opened the meeting on behalf of the Minister for
    Health and Welfare Canada. Mr J.R. Hickman, Director General,
    Environmental Health Directorate, welcomed the participants. The
    support of Health and Welfare Canada and the local organization by the
    Environmental Health Directorate are gratefully acknowledged.

    The first draft of this publication was compiled by Professor J.
    Bernhardt, Professor P. Czerski, Professor M. Grandolfo, Dr A.
    McKinlay, Dr M. Repacholi, Dr R. Saunders, Professor J. Stolwijk, and
    Dr M. Stuchly. An editorial group comprising Professor J. Bernhardt,
    Professor P. Czerski, Professor M. Grandolfo, Mr C. Hicks, Dr A.
    McKinlay, Dr R. Saunders, Mr D. Sliney, Professor J. Stolwijk, and Dr
    M. Swicord met at the US Army Environmental Hygiene Agency, Edgewood,
    MD, in February 1990 to revise the draft. A second editorial group
    comprising Professor J. Bernhardt, Mme A. Duchêne, Dr A. McKinlay
    (Chairman), Professor B. Knave, Dr R. Saunders, and Dr M. Stuchly met
    at the National Radiological Protection Board, Didcot, United Kingdom,
    in May 1990 to collate and incorporate the comments received by IPCS
    Focal Points, IRPA Associate Societies, and individual experts. Dr M.
    Repacholi was responsible for the scientific editing of the text and
    Mrs M.O. Head of Oxford for the language editing.

    This publication comprises a review of the data on the effects of
    electromagnetic field exposure on biological systems pertinent to the
    evaluation of human health risks. The purpose of the document is to
    provide an overview of the known biological effects of electromagnetic
    fields in the frequency range 300 Hz to 300 GHz, to identify gaps in
    this knowledge so that direction for further research can be given,
    and to provide information for health authorities, regulatory, and
    similar agencies on the possible effects of electromagnetic field
    exposure on human health, so that guidance can be given on the
    assessment of risks from occupational and general population exposure.

    Most radiofrequency (RF) field standards are based on the premise that
    there exists a threshold specific absorption rate (SAR) of RF energy
    (for frequencies above about 1 MHz) of 1-4 W/kg, above which there is
    increasing likelihood of adverse health effects. Below about 1 MHz,
    standards are based on induced currents in the body, causing shocks
    and burns. The purpose of updating the original Environmental Health
    Criteria monograph on radio frequency (WHO, 1981) is not only to
    provide a description of more completely developed RF dosimetry in
    humans, but to critically review more recent scientific literature, to
    determine if the threshold SAR on which standards are based is still
    valid. With the frequency range covered by the document extended down
    to 300 Hz, more emphasis is placed on induced currents and other
    possible mechanisms of interaction.

    In conducting the literature review, earlier reports are not
    necessarily included, since these were reviewed in UNEP/WHO/IRPA
    (1981). Every effort has been made to distinguish clearly between
    biological effects that have been established and those that have been
    reported as preliminary or isolated results, or as hypotheses proposed
    to explain observed results. The conclusions of this document are
    based on peer reviewed and established knowledge of interactions of
    electromagnetic fields with biological systems.

    Subjects reviewed include: the physical characteristics of
    electromagnetic fields; measurement techniques; applications of
    electromagnetic fields and sources of exposure; mechanisms of
    interaction; biological effects; and guidance on the development of
    protective measures, such as regulations or safe-use guidelines.
    Health agencies and regulatory authorities are encouraged to set up
    and develop programmes that ensure that the maximum benefit occurs
    with the lowest exposure. It is hoped that this criteria document will
    provide useful information for the development of national protection
    measures against electromagnetic fields, as well as serving as a
    reliable basis for such reports as environmental impact statements
    necessary for proposed electromagnetic field emission facilities.

    The WHO Regional Office for Europe has published a second edition of
    the book entitled  Nonionizing radiation protection, which includes
    a chapter on radiofrequency radiation (Suess & Benwell-Morison, 1989).


    1.1  Summary

    1.1.1  Physical characteristics in relation to biological effects

         This monograph is concerned with the health effects of
    electromagnetic fields in the frequency range of 300 Hz-300 GHz, which
    includes the radiofrequency (RF) range (100 kHz-300 GHz) covered in
    the earlier publication (WHO, 1981). For simplicity, RF is the term
    used in this document for electromagnetic fields of frequency 300
    Hz-300 GHz. Within these frequencies are microwaves, having
    frequencies of between 300 MHz and 300 GHz.

         Exposure levels in the microwave range are usually described in
    terms of "power density" and are normally reported in watt per square
    metre (W/m2), or milliwatt or microwatts per square metre (mW/m2,
    µW/m2). However, close to RF sources with longer wavelengths, the
    values of both the electric (V/m) and magnetic (A/m) field strengths
    are necessary to describe the field.

         Exposure conditions can be altered considerably by the presence
    of objects, the degree of perturbation depending on their size, shape,
    orientation in the field, and electrical properties. Very complex
    field distributions can occur, both inside and outside biological
    systems exposed to electromagnetic fields. Refraction within these
    systems can focus the transmitted energy resulting in markedly
    non-uniform fields and energy deposition. Different energy absorption
    rates can result in thermal gradients causing biological effects that
    may be generated locally, difficult to anticipate, and perhaps unique.
    The geometry and electrical properties of biological systems will also
    be determining factors in the magnitude and distribution of induced
    currents at frequencies below the microwave range.

         When electromagnetic fields pass from one medium to another, they
    can be reflected, refracted, transmitted, or absorbed, depending on
    the conductivity of the exposed object and the frequency of the field.
    Absorbed RF energy can be converted to other forms of energy and cause
    interference with the functioning of the living system. Most of this
    energy is converted into heat. However, not all electromagnetic field
    effects can be explained in terms of the biophysical mechanisms of
    energy absorption and conversion to heat. At frequencies below about
    100 kHz, it has been demonstrated that induced electric fields can
    stimulate nervous tissue. At the microscopic level, other interactions
    leading to perturbations in complex macromolecular biological systems
    (cell membranes, subcellular structures) have been postulated.

    1.1.2  Sources and exposure  Community

         In comprehensive community surveys of background levels of
    electromagnetic fields in the USA, a median exposure of the order of
    50 µW/m2 was found. Very high frequency broadcasts were identified
    as the main contributors to ambient electromagnetic fields. No more
    than 1% of the population was exposed to ambient power densities in
    excess of 10 mW/m2. Exposure in the immediate vicinity (at a
    distance of the order of one half wavelength of the incident fields)
    of transmitting facilities, can be higher, and can be enhanced by
    nearby conducting objects. Such conditions should be evaluated for
    each specific situation.  Home

         RF sources in the home include microwave ovens, induction heating
    stoves, burglar alarms, video display units (VDUs), and television
    receivers. Leakage from microwave ovens can be up to 1.5 W/m2 at 0.3
    m and 0.15 W/m2 at a distance of 1 metre. Exposure to radiation from
    domestic appliances is best limited by design and by monitoring at the
    point of manufacture.  Workplace

         Dielectric heaters for wood fabrication and the sealing of
    plastics, induction heaters for the heating of metals, and video
    display units, are widely used in a variety of occupational settings.
    VDUs create electric and magnetic fields at frequencies in the 15-35
    kHz range and frequencies modulated in the ELF range. Personnel
    working on, or near, broadcasting towers or antennas can be exposed to
    substantial fields of up to 1 kV/m and 5 A/m, respectively. Workers
    near radar installations can be exposed to substantial peak power
    densities, if they are in the RF beam a few metres from radar antennas
    (up to tens of MW/m2). Usually, the average power density in the
    vicinity of air traffic control radars, for example, is of the order
    of 0.03-0.8 W/m2.

         In the occupational environment, the protection of workers is
    best assured by referring to the emission specifications for
    individual items of equipment, and, where necessary, by monitoring and
    surveillance using appropriate instrumentation.

         A special case of exposure occurs in the medical environment with
    the use of diathermy treatments for pain and inflammation in body
    tissues. Diathermy operators are likely to be exposed occupationally
    to stray radiation at relatively high levels, which can be reduced by
    appropriate shielding or machine design. Field strengths of 300 V/m
    and 1 A/m at 10 cm from the applicators have been measured. Similarly,
    surgeons using electrosurgical devices operating at frequencies near
    27 MHz may be exposed to levels above recommended limits. These field

    strengths decline very rapidly with increasing distance from the

         Most magnetic resonance imaging (MRI) systems use static magnetic
    fields with flux densities of up to 2 T, low-frequency gradient fields
    up to 20 T/s, and RF fields in the 1-100 MHz frequency range. Although
    power deposition in the patient can be substantial, staff exposures
    are much lower and are determined by equipment characteristics.

    1.1.3  Biological effects

         Electromagnetic fields in the frequency range of 300 Hz-300 GHz
    interact with human and other animal systems through direct and
    indirect pathways. Indirect interactions are important at frequencies
    below 100 MHz, but are specific to particular situations. When
    metallic objects (such as automobiles, fences) in an electromagnetic
    field have electrical charges induced in them, they can be discharged
    when a body comes into contact with the charged object. Such
    discharges can cause local current densities capable of shock and

         A major interaction mechanism is through the currents induced in
    tissues, so effects are dependent on frequency, wave shape, and
    intensity. For frequencies below approximately 100 kHz, the
    interactions with nervous system tissue are of interest, because of
    their increased sensitivity to induced currents. Above 100 kHz, the
    nervous tissue becomes less sensitive to direct stimulation by
    electromagnetic fields and the thermalization of energy becomes the
    major mechanism of interaction.

         There is evidence from a number of studies that weak-field
    interactions also exist. Different mechanisms for such interactions
    have been postulated, but the precise mechanism(s) has not been
    elucidated. These weak-field interactions result from exposure to RF
    fields, amplitude modulated at lower frequencies.

    1.1.4  Laboratory studies

         Many of the biological effects of acute exposure to
    electromagnetic fields are consistent with responses to induced
    heating, resulting either in rises in tissue or body temperature of
    about 1 °C or more, or in responses to minimizing the total heat load.
    Most responses have been reported at specific absorption rates (SARs)
    above about 1-2 W/kg in different animal species exposed under various
    environmental conditions. The animal (particularly primate) data
    indicate the types of responses that are likely to occur in humans
    subjected to a sufficient heat load. However, direct quantitative
    extrapolation to humans is difficult, given species differences in
    responses in general, and in thermoregulatory ability, in particular.

         The most sensitive animal responses to heat loads are
    thermoregulatory adjustments, such as reduced metabolic heat

    production and vasodilation, with thresholds ranging between about
    0.5-5 W/kg, depending on environmental conditions. However, these
    reactions form part of the natural repertoire of thermoregulatory
    responses that serve to maintain normal body temperatures.

         Transient effects seen in exposed animals, which are consistent
    with responses to increases in body temperature of 1 °C or more
    (and/or SARs in excess of about 2 W/kg in primates and rats), include
    reduced performance of learned tasks and increased plasma
    corticosteroid levels. Other heat-related effects include temporary
    haematopoietic and immune responses, possibly due to elevated
    corticosteroid levels. The most consistent effects observed are
    reduced levels of circulating lymphocytes, increased levels of
    neutrophils, and altered natural killer cell and macrophage function.
    An increase in the primary antibody response of B-lymphocytes has also
    been reported. Cardiovascular changes consistent with increased heat
    load, such as an increased heart rate and cardiac output, have been
    observed, together with a reduction in the effect of drugs, such as
    barbiturates, the action of which can be altered by circulatory

         Most animal data indicate that implantation and the development
    of the embryo and fetus are unlikely to be affected by exposures that
    increase maternal body temperature by less than 1 °C. Above these
    temperatures, adverse effects, such as growth retardation and
    post-natal changes in behaviour, may occur, with more severe effects
    occurring at higher maternal temperatures.

         Most animal data suggest that low RF exposures that do not raise
    body temperatures above the normal physiological range are not
    mutagenic: Such exposures will not result in somatic mutation or
    hereditary effects. There is much less information describing the
    effects of long-term, low-level exposures. However, so far, it does
    not appear that any long-term effects result from exposures below
    thermally significant levels. The animal data indicate that male
    fertility is unlikely to be affected by long-term exposure to levels
    insufficient to raise the temperature of the body and testes.

         Cataracts were not induced in rabbits exposed at 100 W/m2 for
    6 months, or in primates exposed at 1.5 kW/m2 for over 3 months.

         A study of 100 rats, exposed for most of their lifetime to about
    0.4 W/kg, did not show any increased incidence of non-neoplastic
    lesions or total neoplasias compared with control animals; longevity
    was similar in both groups. There were differences in the overall
    incidence of primary malignancies, but these could not necessarily be
    attributed to the irradiation.

         The possibility that exposure to RF fields might influence the
    process of carcinogenesis is of particular concern. So far, there is
    no definite evidence that irradiation does have an effect, but there
    is clearly a need for further studies to be carried out. Many

    experimental data indicate that RF fields are not mutagenic, and so
    they are unlikely to act as initiators of carcinogenesis; in the few
    studies carried out, the search has mainly been for evidence of an
    enhancement of the effect of a known carcinogen. Long-term exposure of
    mice at 2-8 W/kg resulted in an increase in the progression of
    spontaneous mammary tumours, and of skin tumours in animals treated
    dermally with a chemical carcinogen.

          In vitro studies have revealed enhanced cell transformation
    rates after RF exposure at 4.4 W/kg (alone or combined with
    X-radiation) followed by treatment with a chemical promoter. The
    latter data have not always been consistent between studies. It is
    clear, however, that studies relevant to carcinogenesis need
    replicating and extending further.

         A substantial body of data exists describing biological responses
    to amplitude-modulated RF or microwave fields at SARs too low to
    involve any response to heating. In some studies, effects have been
    reported after exposure at SARs of less than 0.01 W/kg, occurring
    within modulation frequency "windows" (usually between 1-100 Hz) and
    sometimes within power density "windows"; similar results have been
    reported at frequencies within the voice frequency (VF) range (300
    Hz-3 kHz). Changes have been reported in: the electroencephalograms of
    cats and rabbits; calcium ion mobility in brain tissue  in vitro, and
     in vivo; lymphocyte cytotoxicity  in vitro; and activity of an
    enzyme involved in cell growth and division. Some of these responses
    have been difficult to confirm, and their physiological consequences
    are not clear. However, any toxicological investigations should be
    based on tests carried out at appropriate levels of exposure. It is
    important that these studies be confirmed and that the health
    implications, if any, for exposed people, are determined. Of
    particular importance would be studies that link extremely low
    frequency, amplitude-modulated, RF or microwave interactions at the
    cell surface with changes in DNA synthesis or transcription. It is
    worth noting that this interaction implies a "demodulation" of the RF
    signal at the cell membrane.

    1.1.5  Human studies

         There are relatively few studies that address directly the
    effects of acute or long-term exposures of humans to RF fields. In
    studies in the laboratory, cutaneous perception of fields in the 2-10
    GHz range has been reported. Thresholds for just noticeable warming
    have been reported at power densities of 270 W/m2 - 2000 W/m2,
    depending on the area irradiated (13-100 cm2) and the duration of
    exposure (1-180 s). When human volunteers are exposed to SARs of 4
    W/kg for 15-20 minutes their average body temperature rises by 0.2-0.5
    °C, which is quite acceptable in healthy people. The impact that this
    added thermal load would have on thermoregulatory impaired individuals
    in environments that minimize the perspiration-based cooling
    mechanisms is not known.

         The few epidemiological studies that have been carried out on
    populations exposed to RF fields have failed to produce significant
    associations between such exposures and outcomes of shortened life
    span, or excesses in particular causes of death, except for an
    increased incidence of death from cancer, where chemical exposure may
    have been a confounder. In some studies, there was no increase in the
    incidence of premature deliveries or congenital malformations, while
    other studies produced indications that there was an association
    between the level of exposure and adverse pregnancy outcome. Such
    studies tend to suffer from poor exposure assessment and poor
    ascertainment and determination of other risk factors.

    1.1.6  Health hazard assessment

         The following categories of health hazard have been identified in
    an overall assessment of the health hazards associated with RF
    exposures.  Thermal effects

         The deposition of RF energy in the human body tends to increase
    the body temperature. During exercise, the metabolic heat production
    can reach levels of 3-5 W/kg. In normal thermal environments, an SAR
    of 1-4 W/kg for 30 minutes produces average body temperature increases
    of less than 1°C for healthy adults. Thus, an occupational RF
    guideline of 0.4 W/kg SAR leaves a margin of protection against
    complications due to thermally unfavourable environmental conditions.
    For the general population, which includes sensitive subpopulations,
    such as infants and the elderly, an SAR of 0.08 W/kg would provide an
    adequate further margin of safety against adverse thermal effects from
    RF fields.  Pulsed fields

         It has been shown, under a number of conditions, that the
    thresholds for biological effects at frequencies above several hundred
    MHz are decreased when the energy is delivered in short (1-10 µs)
    pulses. For example, auditory effects occur when pulses of less than
    30 µs duration deliver more than 400 mJ/m2 per pulse. A safe limit
    for such pulses cannot be identified on the basis of available
    evidence.  Amplitude-modulated RF fields

         The effects described for this type of field at the cellular,
    tissue, and organ levels cannot be related to adverse health effects.
    No dose-effect relationships can be formulated that demonstrate
    threshold levels; thus, the available information cannot lead to
    specific recommendations.  RF field effects on tumour induction and promotion

         It is not possible, from the reports of the effects of RF
    exposure in certain cell lines, on cell transformation, enzyme
    activity, and tumour incidence and progression in animals, to conclude
    that RF exposure has any effect on the incidence of cancer in humans,
    or, that specific recommendations are necessary to limit such fields
    to reduce cancer risks.  RF-induced current densities

         In the frequency range of 300 Hz-100 kHz, the induction of fields
    and current densities in excitable tissues is the most important
    mechanism for hazard assessment. The thresholds for the stimulation of
    nerve and muscle tissue are strongly dependent on frequency, ranging
    from 0.1-1 A/m2 at 300 Hz to about 10-100 A/m2 at 100 kHz.
    However, with regard to other effects, reported to occur below these
    thresholds, there is not sufficient information available to make
    specific recommendations.  RF contact shocks and burns

         Conducting objects in an RF field can become electrically
    charged. When a person touches a charged object or approaches it
    closely, a substantial current can flow between the object and the
    person. Depending on the frequency, the electric field strength, the
    size and the shape of the object,and the cross-sectional area of
    contact, the resulting current can cause shock through stimulation of
    peripheral nerves. If the current is strong enough, burns can result.
    Protective measures include the elimination or enclosure of conductive
    objects in strong RF fields, or the limiting of physical access.

    1.1.7  Exposure standards  Basic exposure limits

         To protect workers and the general population from the possible
    health effects of exposure to electromagnetic fields, basic exposure
    limits have been determined on the basis of knowledge of biological
    effects. Different scientific bases were used to develop the limits
    for frequencies above and below about 1 MHz. Above 1 MHz, biological
    effects on animals were studied to determine the lowest value of the
    whole body average SAR that caused detrimental health effects in
    animals. This value was found to be in the 3-4 W/kg range.

         The vast majority of results pertained to exposures in the low
    GHz region. Thus, to determine the effects at lower frequencies
    requires an assumption concerning the frequency dependence of the
    biological response. Since the observed bioeffects in the 1-4 W/kg
    range are believed to be thermal, the SAR threshold was assumed to be
    independent of frequency. It was considered that exposure of humans to

    4 W/kg for 30 minutes would result in a body temperature rise of less
    than 1°C. This body temperature rise is considered acceptable.

         A safety factor of 10 is introduced, in order to allow for
    unfavourable, thermal, environmental, and possible long-term effects,
    and other variables, thus arriving at a basic limit of 0.4 W/kg. An
    additional safety factor should be introduced for the general
    population, which includes persons with different sensitivities to RF
    exposure. A basic limit of 0.08 W/kg, corresponding to a further
    safety factor of 5, is generally recommended for the public at large.
    Derived limits of exposure are given in Tables 34 and 35 of this

         The limitations for the whole body average SAR are not
    sufficiently restrictive, since the distribution of the absorbed
    energy in the human body can be very inhomogeneous and dependent on
    the RF exposure conditions. In partial body exposure situations,
    depending on frequency, the absorbed energy can be concentrated in a
    limited amount of tissue, even though the whole body average SAR is
    restricted to less than 0.4 W/kg. Therefore, additional basic limits
    of 2 W/100 g are recommended in any other part of the body, in order
    to avoid excessive local temperature elevations. The eye may need
    special consideration.

         At frequencies below about 1 MHz, exposure limits are selected
    that will prevent stimulation of nerve and muscle cells. Basic
    exposure limits refer to current densities induced within body
    tissues. Exposure limits should have a sufficiently large safety
    factor to restrict the current density to 10 mA/m2 at 300 Hz. This
    is the same order of magnitude as natural body currents. Above 300 Hz,
    the current density necessary for excitation of nervous tissue
    increases with frequency, until a frequency is reached at which
    thermal effects dominate. For frequencies around 2-3 MHz, the basic
    limit for current density is equivalent to the limit for the peak SAR
    of 1 W/100g. Since SAR or induced current density values cannot be
    measured easily in practical exposure situations, exposure limits in
    terms of conveniently measurable quantities must be derived from basic
    limits. These "derived limits" indicate the acceptable limits in terms
    of the measured and/or calculated field parameters that allow
    compliance with the basic limits.  Occupational exposure limits

         The occupationally-exposed populations consist of adults exposed
    under controlled conditions, who are aware of the occupational risks.
    Because of the wide frequency range addressed in this publication, a
    single limit number for occupational exposure is not possible.
    Recommended derived occupational limits in the frequency range 100 kHz
    to 300 GHz are provided in Table 34. A conservative approach is
    recommended for pulsed fields where electric and magnetic field
    strengths are limited to 32 times the values given in Table 34, as
    averaged over the pulse width, and the power density is limited to a

    value of 1000 times the corresponding value in Table 34, as averaged
    over the pulse width.  Exposure limits for the general population

         The general population includes persons of different age groups,
    different states of health, and pregnant women. The possibility that
    the developing fetus could be particularly susceptible to exposure to
    RF deserves special consideration.

         Exposure limits for the general population should be lower than
    those for occupational exposure. For example, recommended derived
    limits in the frequency range of 100 kHz-300 GHz are provided in Table
    35, which are generally a factor of 5 lower than the occupational
    limits.  Implementation of standards

         The implementation of RF field occupational and public health
    protection standards necessitates the allocation of responsibility for
    measurements of field intensity and interpretation of results, and the
    establishment of detailed field protection safety codes and guides for
    safe use, which indicate, where appropriate, ways and means of
    reducing exposure.

    1.1.8  Protective measures

         Protective measures include workplace surveillance (exposure
    surveys), engineering controls, administrative controls, personal
    protection, and medical surveillance. Where surveys of RF fields
    indicate levels of exposure in the workplace in excess of limits
    recommended for the general population, workplace surveillance should
    be conducted. Where surveys of RF fields in the workplace indicate
    levels of exposure in excess of recommended limits, action should be
    taken to protect workers. In the first instance, engineering controls
    should be applied, where possible, to reduce emissions to acceptable
    levels. Such controls include good safety design and, where necessary,
    the use of interlocks or similar protection devices.

         Administrative controls, such as limitation of access and the use
    of audible and visible warnings, should be used in conjunction with
    engineering controls. The use of personal protection (protective
    clothing), though useful under certain circumstances, should be
    regarded as a last resort to ensure the safety of the worker. Wherever
    possible, priority should be given to engineering and administrative
    controls. Where workers could be expected to incur exposures in excess
    of the limits applicable to the general population, consideration
    should be given to providing appropriate medical surveillance.

         Prevention of health hazards related to RF fields also
    necessitates the establishment and implementation of rules to ensure:
    (a) the prevention of interference with safety and medical electronic

    equipment and devices (including cardiac pacemakers); (b) the
    prevention of detonation of electroexplosive devices (detonators); and
    (c) the prevention of fires and explosions due to the ignition of
    flammable material from sparks caused by induced fields.

    1.2  Recommendations for further studies

    1.2.1  Introduction

         There are concerns about the possible effects of RF fields in the
    areas of promotion and progression of cancer, of reproductive
    failures, such as spontaneous abortions and congenital malformations,
    and of effects on central nervous system function. Knowledge in all
    these areas is inadequate to determine whether such effects exist, and
    therefore, there is no rational basis for recommendations to protect
    the general population from possible adverse effects.

         Future research efforts in the areas of weak-interaction
    mechanisms on the one hand, and studies of effects on carcinogenesis
    and reproduction in animals and humans on the other hand, should be
    coordinated to a high degree. This coordination can be brought about
    by focusing funding on research proposals of a multidisciplinary and
    multi-institutional nature. Studies on RF field effects could well be
    coordinated with similar programmes addressing ELF (50/60 Hz) field
    effects. A high priority should be placed on research that emphasizes
    causal relationships and dose-effect thresholds and coefficients.

         The following is a list of priority areas identified by the Task
    Group as needing further study.

    1.2.2  Pulsed fields

         There is a major deficiency in the understanding of the effects
    of pulsed fields in which very high peak power densities occur,
    separated by periods of zero power. Only a few isolated reports of
    pulsed field effects are available and it is not possible to identify
    either the frequency or the peak power domain of importance. Data to
    assess human health hazard in terms of pulse peak power, repetition
    frequency, pulse length, and the frequency of the RF in the pulse, are
    urgently needed in view of the widening application of systems
    employing high power pulses, (mostly radar), and involving both
    occupational and general population exposures.

    1.2.3  Cancer, reproduction, and nervous system studies

         There is increasing concern about the possibility that RF
    exposure may play a role in the causation or promotion of cancer,
    specifically of the blood forming organs or in the CNS. Similar
    uncertainties surround possible effects on reproduction, such as
    increased rates of spontaneous abortion and of congenital

         Effects of RF exposure on CNS function, with resulting changes in
    cognitive function, are also surrounded by uncertainties. In view of
    the potential importance of these interactions and the disruptive
    effects of the uncertainty on society, a high priority should be
    placed on research in this area. It is important that research efforts
    be coordinated to clarify rather than increase the level of
    uncertainty. Research on possible mechanisms, such as weak-field
    interactions, should be closely coordinated with appropriately
    designed animal toxicology studies and with human epidemiology.

    1.2.4  Weak-field interactions

         Very few people are exposed to thermally significant levels of
    RF; the vast majority of exposures occur at levels at which weak-
    field interactions would be the only possible source of any adverse
    health response. A substantial amount of experimental evidence
    implicates responses to amplitude-modulated RF fields, which show
    frequency and amplitude windows; some responses are dependent on
    co-exposure to physical and chemical agents. Establishing the
    significance of effects for human health and their dose-response
    relationships is of paramount importance. Studies are necessary that
    identify biophysical mechanisms of interaction and that extend the
    animal and human studies, in order to identify health risks.

    1.2.5  Epidemiology

         Epidemiological studies on the association between cancer and
    adverse reproductive outcomes and RF fields are made difficult by a
    number of factors:

    -    Most members of any population are exposed to levels of RF that
         are orders of magnitude below thermally significant levels.

    -    It is very difficult to establish RF exposure in individuals over
         a meaningful period of time.

    -    Control of major confounders is very difficult.

    Some, but not all, of the sources of difficulties can be overcome by
    a suitably designed and implemented case-control study. Such studies
    are in progress and being planned to study childhood cancer and any
    effects of ELF fields. It is important that such studies evaluate any
    exposures to RF radiation.


    2.1  Introduction

         The study of the biological effects of electromagnetic fields is
    multidisciplinary; it draws from physics, engineering, mathematics,
    biology, chemistry, medicine, and environmental health. For this
    reason, background information has been included in this publication
    that may appear elementary to some readers, but is essential for those
    from a different discipline. Much of the confusion and the
    controversies that exist in the field today arise from individuals of
    one discipline not fully appreciating the basic facts or theories of

         In this section, the aim is to summarize briefly the basic
    physical characteristics of electric, magnetic, and electromagnetic
    fields in the frequency range 300 Hz-300 GHz. The corresponding
    wavelengths extend from 1000 km to 1 mm. At low frequencies (below
    about 10 MHz) and for near-field conditions (see section 4), the
    electric (E) and magnetic (H) fields must be treated separately.

         The quantum energies at these frequencies are extremely small and
    are not capable of altering the molecular structure or breaking any
    molecular bonds. The maximum quantum energy (at 300 GHz) is 1.2
    millielectronvolts (meV), while disruption of the weakest hydrogen
    bond requires 80 meV; for comparison, the thermal motion energy at 30
    °C is 26 meV.

         Although there are other definitions of the radiofrequency (RF)
    spectrum, its use in this document covers 300 Hz-300 GHz. The region
    between 300 MHz and 300 GHz is called microwaves (MW).

    2.2  Electric field

         Electric charges exert forces on each other. It is convenient to
    introduce the concept of an electric field to describe this
    interaction. Thus, a system of electric charges produces an electric
    field at all points in space and any other charge placed in the field
    will experience a force because of its presence. The electric field is
    denoted by E and is a vector quantity, which means that it has both
    a magnitude and a direction. The force, F, exerted on a point
    (infinitely small) body containing a net positive charge q placed in
    an electric field E is given by:

         F = qE                                               (Equation 2.1)

    Various units of the electric field strength are in use; the SI unit
    is newton per coulomb (N/C). It is frequently easier and more useful
    to measure the electric potential, V, rather than the force and
    charge. This is because the potential is much less dependent on the

    physical geometry of a given system (e.g., location and sizes of

         The potential difference V between two points in an electric
    field E is defined by V = W/q, where W is the work done by the field
    in moving a charge q between the two points. The work done is W = Fd,
    where d is the separation between the two points; or using equation
    2-1, W = qEd. From V = W/q, it follows that:

         E = V/d                                          (Equation 2.2)

    In practice, the unit of volt per metre (V/m) is used for the electric
    field strength.

         Electric fields exert forces on charged particles. In an
    electrically conductive material, such as living tissue, these forces
    will set charges into motion to cause an electric current to flow.
    This current is frequently specified by the current density, J, the
    magnitude of which is equal to the current flowing through a unit
    surface perpendicular to its direction. The SI unit of current density
    is ampere per square metre (A/m2). J is directly proportional to
    E in a wide variety of materials. Thus:

         J = deltaE                                           (Equation 2.3)

    where the constant of proportionality delta is called the electrical
    conductivity of the medium. The unit of delta is siemens per metre

    2.3  Magnetic field

         The fundamental vector quantities describing a magnetic field are
    the magnetic field strength H and the magnetic flux density B
    (also called the magnetic induction).

         Magnetic fields, like electric fields, are produced by electric
    charges, but only when these charges are in motion. Magnetic fields
    exert forces on other charges but, again, only on charges that are in

         The magnitude of the force F acting on an electric charge q
    moving with a velocity v in the direction perpendicular to a magnetic
    field of flux density B is given by:

         F = qvB                                          (Equation 2.4)

    where the direction of F is perpendicular to both those of v and
    B. If, instead, the direction of v were parallel to B, then F
    would be zero. This illustrates an important characteristic of a
    magnetic field: it does no physical work, because the force, called
    the Lorentz force, generated by its interaction with a moving charge

    is always perpendicular to the direction of motion. The basic unit of
    the magnetic flux density can be deduced from Equation 2.4 to be
    newton second per coulomb metre [N s/C m]. According to the
    International System of Units (SI), this unit is called the tesla (T).
    In the literature, both mks and cgs units are also used to express
    flux density values. The conversion between the gauss (G), the cgs
    unit of flux density, and the tesla is 1 T = 104 G.

         The magnetic field strength H is the force with which the field
    acts on an element of current situated at a particular point. The
    value of H is measured in ampere per metre (A/m).

         The magnetic flux density B, rather than the magnetic field
    strength, H (where B = µH), is used to describe the magnetic field
    generated by currents that flow in conductors. The value of µ (the
    magnetic permeability) is determined by the properties of the medium.

         For most biological materials, the permeability µ is equal to
    µ0, the value of permeability of free space (air) (1.257 × 10-6
    H/m). Thus, for biological materials, the values of B and H are
    related by the constant µ0.

    2.4  Waves and radiation

         Maxwell's equations form the theoretical foundation for all
    classical electromagnetic field theory. These equations are very
    powerful, but for complex systems, such as biological bodies, they are
    difficult to solve.

         One class of their solutions results in wave descriptions of the
    electric and magnetic fields. When the source charges or currents
    oscillate and the frequency of oscillation is high enough, the E and
    H fields produced by these sources will radiate from them. A
    convenient and commonly used description of this radiation is wave

         The basic ideas of wave propagation are illustrated in Fig. 1.
    The distance from one ascending, or descending, node to the next is
    defined as the wavelength, and is usually denoted by lamda.

         The wavelength and the frequency (the number of waves that pass
    a given point in unit time), denoted by f, are related and determine
    the characteristics of electromagnetic radiation. Frequency is the
    more fundamental quantity and for a given frequency, the wavelength
    depends on the velocity of propagation and, therefore, on the
    properties of the medium through which the radiation passes.

         The wavelength normally quoted is that in a vacuum or in air, the
    difference being insignificant. However, the wavelength can change
    significantly when the wave passes through other media. The linking
    parameter with frequency is the speed of light as expressed in
    Equation 2.5 (v = 3 × 108 m/s in air):

         lamda = v/f                                      (Equation 2.5)

    When RF traverses biological material, its speed is reduced and its
    wavelength becomes shorter than in air.

    FIGURE 1

         Two idealizations of wave propagation are commonly used:
    spherical waves and plane waves (Stuchly, 1983; Grandolfo & Vecchia,
    1988). A spherical wave is a good approximation to some
    electromagnetic waves that occur. Their wavefronts have spherical
    surfaces and each crest and trough has a spherical surface. On every
    spherical surface, the E and H fields are constant. The wavefronts
    propagate radially outwards from the source and E and H are both
    tangential to the spherical surfaces.

         A plane wave is another model that approximately represents some
    electromagnetic waves. Plane waves have characteristics similar to
    spherical waves because, at points far from the source, the curvature

    of the spherical wavefronts is so small that they appear to be almost

    The defining characteristics of a plane wave are:

    (a)  E, H, and the direction of propagation are all mutually

    (b)  The quotient E/H is constant and is called the wave
         impedance. For free space E/H = 377 OMEGA. For other media and
         for sinusoidal steady-state fields, the wave impedance includes
         losses in the medium in which the wave is travelling.

    (c)  Both E and H vary as 1/r, where r is the distance from the

         In RF plane wave propagation (far-field), the power crossing a
    unit area normal to the direction of wave propagation is usually
    designated by the symbol S. When the electric and magnetic field
    strengths are expressed in V/m and A/m, respectively, S represents
    their product, which yields VA/m2, i.e., W/m2 (watts per square

         In free space, electromagnetic waves spread uniformly in all
    directions from a theoretical point (isotropic) source. As the
    distance from the point source increases, the area of the wavefront
    surface increases as a square of the distance, so that the source
    power is spread over a larger area.

         As power density S corresponds also to the quotient of the total
    radiated power and the spherical surface area enclosing the source, it
    is inversely proportional to the square of the distance from the
    source, and can be expressed as:

         S = P/4pi r2                                       (Equation 2.6)

    where P is the total radiated power and r is the distance from the

         In the case of plane waves, frequently called far-field
    conditions, the power density can be derived from E2/377 or from 377
    H (see Table 1). Therefore, in many practical applications only the
    E field or the H field needs to be measured when the point of
    measurement is at least one wavelength from the source. In this case,
    measurement of E makes possible the determination of H and vice-versa.

    Table 1.  Comparison of power densities in the more commonly used
    units for free-space, far-field conditions (Note: values have been
    rounded to one or two significant figures, based on the relationships
    W/m2        mW/cm2        µW/cm2     V/m      A/m

    10-2        10-3          1          2        5 10-3
    10-1        10-2          10         6        1.5 10-2
    1           10-1        102          20       5 10-2
    10          1           103          60       1.5 10-1
    102         10          104          2 102      5 10-1
    103         102         105        6 102      1.5
    104         103         106        2 103      5

         The region close to a source is called the near-field. In the
    near-field, the E and H fields are not necessarily perpendicular;
    in fact, they are not always conveniently characterized by waves. They
    are often nonpropagating in nature and are sometimes referred to as
    fringing fields, reactive near-fields, or evanescent modes.
    Near-fields often vary rapidly with distance; the inverse square law
    of the dependence with distance does not apply, and the impedance
    (E/H) may differ from 377 OMEGA. Objects located near sources may
    strongly affect the nature of the fields. For example, placing a probe
    near a source to measure the fields may change the characteristics of
    the fields considerably (Dumansky et al., 1986).

         When RF fields are incident on a conductive object, RF currents
    are induced in the object. These currents produce surface fields that
    are highly localized to the object and are often referred to as RF hot
    spots. RF hot spots are better characterized as electric and magnetic
    fields rather than radiation, since, for many conditions, the fields
    leading to the hot spot never propagate away from the object. At
    higher frequencies, the electric and magnetic fields maintain an
    approximately constant relationship in propagating waves. In general,
    the lower the frequency, the less coupled the fields become. This is
    particularly so when the wavelength is very large with respect to the
    physical size of the source. In practice, the fields of concern from
    a hazard perspective will be near-fields at frequencies below about 1


    3.1  General

         In the last few decades, the use of devices that emit
    electromagnetic fields has increased considerably. This proliferation
    has been accompanied by an increased concern about possible health
    effects of exposure to these fields (Grandolfo et al., 1983;
    Repacholi, 1988; Shandala & Zvinyatskovski, 1988, Franceschetti et
    al., 1989). As a result, throughout the world, many organizations,
    both governmental and nongovernmental, have established safety
    standards or guidelines for exposure (see section 10).

         Electromagnetic devices already in use and the continuous
    addition of new sources result in the expansion to new frequencies in
    the spectrum and the increasing presence of RF fields. Comprehensive
    data on existing emission systems, and evaluation of present levels of
    exposure, are essential for the assessment of potential radiation
    hazards (Repacholi, 1983a; Shandala et al., 1983; Savin, 1986; Stuchly
    & Mild, 1987).

         In this section, sources of electromagnetic fields, both natural
    and human-made, in the 300 Hz-300 GHz frequency range are surveyed.
    The human-made electromagnetic environment consists of fields that are
    produced either intentionally or as by-products of the use of other

         Human-made sources in the spectrum considered here, however,
    produce local field levels many orders of magnitude above the natural
    background. Therefore, for the practical purposes of hazard
    assessment, the electromagnetic fields on the earth's surface arise
    from human-made sources. According to the treaty of the International
    Telecommunications Union (ITU, 1981), the electromagnetic spectrum up
    to 3 THz is subdivided into 12 frequency bands. These bands are
    designated by numbers as shown in Table 2; only the bands referred to
    in this publication are given.

    3.2  Natural background

         The natural electromagnetic environment originates from processes
    such as discharges in the earth's atmosphere (terrestrial sources) or
    in the sun and deep space (extra-terrestrial sources).

    Table 2.  Frequency bands of the electromagnetic spectrum in the
              frequency range 300 Hz-300 GHz a
    Band    Frequency range   Metric        Description and symbol
    number  subdivision
    3       0.3 to 3 kHz      -             voice frequency [VF]

    4       3 to 30 kHz       myriametric   very low frequency [VLF]

    Table 2 (continued)
    Band    Frequency range   Metric        Description and symbol
    number  subdivision
    5       30 to 300 kHz     kilometric    low frequency [LF]

    6       0.3 to 3 MHz      hectometric   medium frequency [MF]

    7       3 to 30 MHz       decametric    high frequency [HF]

    8       30 to 300 MHz     metric        very high frequency [VHF]

    9       0.3 to 3 GHz      decimetric    ultra high frequency [UHF]

    10      3 to 30 GHz       centimetric   super high frequency [SHF]

    11      30 to 300 GHz     millimetric   extremely high frequency [EHF]
    a From: ITU (1981).

    3.2.1  Atmospheric fields

         Atmospheric fields of frequencies of less than 30 MHz originate
    predominantly from thunderstorms. Their strengths and range of
    frequencies vary widely with geographical location, time of day, and
    season. Some of these variations are systematic and some are random.
    Overall, atmospheric fields have an emission spectrum with the largest
    amplitude components having frequencies of between 2 and 30 kHz.
    Generally, the atmospheric field level decreases with increasing
    frequency. The geographical dependence is such that the highest levels
    are observed in equatorial areas and the lowest in polar areas.

    3.2.2  Terrestrial emissions

         The earth emits electromagnetic radiation (black-body radiation),
    as do all media, at a temperature T that is different from that at
    absolute zero. In the RF range, the black-body radiation follows the
    Rayleigh-Jeans law and the thermal noise from the earth (T about 300
    K) is 0.003 W/m2 (0.3 µW/cm2), when integrated up to 300 GHz
    (Repacholi 1983).

    The human body also emits electromagnetic fields at frequencies of up
    to 300 GHz at a power density of approximately 0.003 W/m2. For a
    total body surface area of about 1.8 m2, the total radiated power is
    approximately 0.0054 W.

    3.2.3  Extraterrestrial fields

         The atmosphere, ionosphere, and magnetosphere of the earth shield
    it from extra-terrestrial sources of nonionizing electromagnetic
    energy. Electromagnetic waves that are able to penetrate this shield

    are limited to two frequency windows, one optical and the other
    encompassing radiowaves of frequencies from about 10 MHz to 37.5 GHz.
    The short-wave boundary of the RF-window is due to energy absorption
    by molecules contained in the atmosphere (primarily O2 and H2O),
    whereas the long-wave boundary is related to the shielding action of
    the ionosphere.

         RF radiation of cosmic origin observed with earth satellites
    ranges in magnitude from 1.8 × 10-20 W/m2/Hz at 200 kHz to 8 ×
    10-20 W/m2/Hz at 10 MHz (Struzak, 1982).

         There are three main types of solar emission. The first is the
    so-called background, which is the constant component of the emission
    observed during periods of low solar activity. The second is the
    component that displays long-term changes, associated with variations
    in the number of sunspots. Its main contribution is in the frequency
    range from 500 MHz to 10 GHz. The third type of emission arises from
    isolated radio flares or radio emission bursts. The intensity of such
    emission can exceed the average intensity of the quiet radiation by a
    factor of one thousand or more; its duration varies from seconds to

         Natural sources of lesser intensity also exist and include the
    moon, Jupiter, Cassiopeia-A, the universal thermal background
    radiation at 3 K, hydrogen emissions from ionized clouds, line
    emissions from neutral hydrogen, the OH radical and, most recently
    observed, from ammonia.

    3.3  Human-made sources

    3.3.1  General

         Radio and television transmitters are examples of human-made RF
    sources that intentionally produce electromagnetic emissions for
    telecommunication purposes. At frequencies of 3 kHz-3 MHz, normal
    service coverage is provided by ground-wave propagation. At VLF,
    propagation over distances of thousands of km is possible using this
    method. At LF and MF, during night-time, reflections from the
    ionosphere make propagation up to 2000 km possible with little
    attenuation. At HF, other propagation modes are also possible. At
    frequencies of 30 MHz-30 GHz, service coverage is provided by
    line-of-sight (short paths), diffraction (intermediate paths), or by
    forward scattering (long paths) propagation.

         Broadcasting systems vary greatly in terms of their design. This
    diversity results in somewhat different approaches in evaluating human
    exposure and potential problems. The situations are significantly
    different for workers and for the general population. In the case of
    some workers, such as those maintaining equipment on broadcasting
    towers, there is a potential for exposure to strong RF fields. Workers
    may also be exposed to strong fields in the close vicinity of towers
    and particularly broadcasting antennas in the VLF, LF, and MF. In

    contrast, it is rare for the general population to be exposed to
    strong RF fields from broadcasting. However, there is simultaneous
    exposure to more than one source.

         Some insight on the levels of exposure of the general population
    may be gained from data collected in the USA, indicating that, in
    large cities, the median exposure level is about 50 µW/m2 (Tell &
    Mantiply, 1980). SAR values ranging from 0.05 to 0.3 µW/kg are
    expected in the frequency range 170-800 MHz.

         There are also human-made sources of electromagnetic fields used
    for non-communication purposes, in industry (I), science (S), and
    medicine (M). ISM applications are intended to transport and
    concentrate electromagnetic energy in a restricted working area to
    produce physical, chemical, and/or biological effects.

         The frequency bands for ISM applications designated by the ITU
    are shown in Table 3. However, in individual countries, different
    and/or additional frequencies may be designated for use by ISM
    equipment (ITU, 1981; Metaxas & Meredith, 1983).

    Table 3.  Centre frequencies and frequency bands agreed
              internationally and assigned for ISM applications a
    Centre frequency     Frequency bands    Area permitted
    70 kHz               60-80 kHz          USSR

    6.780 MHz            6.765-6.795 MHz    subject to agreement
    13.560 MHz           13.553-13.567 MHz  worldwide

    27.120 MHz           26.957-27.283 MHz  worldwide

    40.68 MHz            40.66-40.70 MHz    worldwide

    42;49;56;61;66 MHz   approx. 0.2%       United Kingdom

    84;168 MHz           approx. 0.005%     United Kingdom, Austria,
    433.92 MHz           433.05-434.79 MHz  Liechtenstein,
                                            The Netherlands, Portugal,
                                            Switzerland W. Germany

    896 MHz              886-906 MHz        United Kingdom

    915 MHz              902-928 MHz        North and South

    2.375 GHz            2.325-2.425 GHz    Albania, Bulgaria,
                                            Hungary, Romania,
                                            and USSR

    Table 3 (continued)
    Centre frequency     Frequency bands    Area permitted
    2.45 GHz             2.4-2.5 GHz        worldwide, except
                                            where 2.375 GHz is

    3.39 GHz             3.37-3.41 GHz      The Netherlands

    5.8 GHz              5.724-5.875 GHz    worldwide
    6.78 GHz             6.74-6.82 GHz      The Netherlands

    24.125 GHz           24.0-24.05 GHz     worldwide
    40.68 GHz            40.43-40.92 GHz    United Kingdom

    61.25 GHz            61.0-61.5 GHz      subject to agreement
    122.5 GHz            122-123 GHz        subject to agreement
    245 GHz              244-246 GHz        subject to agreement

    a Adapted from: ITU (1981) and Metaxus & Meredith (1983).

         Because of unavoidable imperfections in the construction,
    production, and use of ISM equipment, and of fundamental physical
    laws, there is always unintentional leakage of electromagnetic energy
    from such equipment. As a result, each ISM generator acts as an
    unintentional source producing signals capable of causing harmful
    effects, depending upon the amount of leakage.

         To date, the total number of ISM installations in the world is
    estimated at 120 million (Struzak, 1985). The number of ISM generators
    constantly increases at a rate of about 3-7% per year. With such
    growth, the number of ISM generators expected by the year 2000 will be
    2-4 times greater than it is now.

         ISM equipment is usually designed at minimum cost, and,
    typically, is reduced to the essentials necessary for operation.
    Frequency stability and spectral purity of the power delivered to the
    work piece are not normally major objectives. In almost every case,
    the work piece is strongly coupled to the oscillator/amplifier, and
    since the electromagnetic characteristics of the material change
    during the work cycle, the magnitude, phase, and frequency of the
    radiation may be affected by these changes.

         Electromagnetic energy leaks from ISM equipment mainly from the
    applicator and associated leads (e.g., RF heaters and sealers), the
    oscillator body/cabinet, and also from surrounding structures in which
    RF currents are induced. The amount of energy radiated from the
    applicator and associated leads depends on the particular arrangement
    of the devices and the work piece, which together act like an antenna
    the radiation efficiency of which is usually very low. However, the

    radiated power may be considerable if the nominal power is high.

         Stray fields are also associated with currents flowing over the
    surface of the body/cabinet and over the surrounding structures. The
    equipment acts as a complex antenna system consisting of coupled
    radiating surface elements resonating at some unspecified frequencies.
    Often all the power and control wires are situated close to RF power
    circuits with no shielding. As a result, a considerable amount of RF
    energy may be fed into these leads and is conducted outwards at a
    distance and then reradiated.

    Table 4.  Typical applications of equipment generating electromagnetic
              fields in the range 300 Hz-300 GHz
    Frequency   Wavelength   Typical applications
    0.3-3 kHz   1000-100 km  Broadcast modulation, medical applications,
                             electric furnaces, induction heating,
                             hardening, soldering, melting, refining

    3-30 kHz    100-10 km    Very long range communications, radio
                             navigation, broadcast modulation, medical
                             applications, induction heating, hardening,
                             soldering, melting, refining, VDUs

    30-300 kHz  10-1 km      Radionavigation, marine and aeronautical
                             communications, long-range communications,
                             radiolocation, VDUs, electro-erosion
                             treatment, induction heating and melting of
                             metals, power inverters

    0.3-3 MHz   1 km-100 m   Communications, radionavigation, marine
                             radiophone, amateur radio, industrial RF
                             equipment, AM broadcasting, RF excited arc
                             welders, sealing for packaging, production
                             of semiconductor material, medical

    3-30 MHz    100-10 m     Citizen band, amateur radio broadcasting,
                             international communications, medical
                             diathermy, magnetic resonance imaging,
                             dielectric heating, wood drying and gluing,
                             plasma heating

    30-300 MHz  10-1 m       Police, fire, amateur FM, VHF-TV, diathermy,
                             emergency medical radio, air traffic
                             control, magnetic resonance imaging,
                             dielectric heating, plastic welding, food
                             processing, plasma heating, particle

    Table 4 (continued)
    Frequency   Wavelength   Typical applications
    0.3-3 GHz   100-10 cm    Microwave point to point, amateur, taxi,
                             police, fire, radar, citizen band,
                             radionavigation, UHF-TV, microwave ovens,
                             medical diathermy, food processing, material
                             manufacture, insecticide, plasma heating,
                             particle acceleration

    3-30 GHz    10-1 cm      Radar, satellite communications, amateur,
                             fire, taxi, airborne weather radar, police,
                             microwave relay, anti-intruder alarms,
                             plasma heating, thermonuclear fusion

    30-300 GHz  10-1 mm      Radar, satellite communications, microwave
                             relay, radionavigation, amateur radio

         Typical uses of equipment generating electromagnetic fields in
    the frequency range 300 Hz-300 GHz are shown in Table 4.

    3.3.2  Environment, home, and public premises

         A comprehensive evaluation of general population exposure to RF
    has been performed by the USA Environmental Protection Agency (Tell&
    Mantiply, 1980). Broadcasting services, particularly those usingthe
    VHF and UHF bands, have been identified as the main sources of ambient
    RF fields (Karachev & Bitkin, 1985). Measurements performed in 15
    large cities in the USA led to the conclusions that the median
    exposure level was 50 µW/m2 and that approximately 1% of the
    population studied was potentially exposed to levels greater than 10

         The presence of conducting objects can give rise to field
    strengths higher than those expected from theoretical considerations,
    since they act as diffracting elements for the electromagnetic fields.
    Consequently, the presence of such objects in the near-field zone of
    radio stations makes the area between the radiator and the object
    potentially more hazardous and indicates that problems of safety
    should be considered carefully (Bernardi et al., 1981).

         Although measurements as well as theory indicate that there is no
    high-level exposure from broadcasting stations, the existence of
    limited areas of relatively high irradiation close to the sources
    should be checked (Dumansky et al., 1985a). Such situations can exist
    in proximity to very powerful, ground-level transmitters. In several
    cases, urban areas are served locally by low-power, in-town repeaters.
    These are placed, for convenience, on the top of tall buildings;
    unless properly designed, this creates the possibility of stray fields

    in a densely populated area directly below the RF source. A typical,
    high-power, MF transmitter can have a carrier power of 100 kW, plus up
    to 50 kW in the sidebands of the propagated field. This is an example
    of how high field strengths can occur in a space open to the public.

         Although a broadcasting station's property is usually fenced to
    keep out unauthorized individuals, the fence may be close to the tower
    base and people may be able to get as close as a few tens of metres or
    less from the antenna. Because the wavelengths involved are so long,
    a near-field exposure situation may exist and a field strength
    considerably greater than the theoretical ground-wave field strength
    is to be expected (Bini et al., 1980).

         Local MF transmitters find widespread use in cities, where they
    provide coverage on "blind spots" or other low-signal receiving areas.
    Powers range from 100 to 1000 W at the amplifier output and much less
    than that can be expected to be radiated into space. In a typical
    arrangement, the transmitting module is located at the top of a
    stucture. The radiating system is fed via a coaxial cable. It consists
    of a dipole over a ground plane or counterpoise laid directly on the
    roof. More than one transmitter can serve the same radiator. Currents
    can set up fields in a complicated pattern inside the building (Bini
    et al., 1980).

         When RF fields are incident on conductive objects, RF currents
    are induced in the objects. Because of these currents, the objects
    become sources of additional fields that are highly localized and in
    some situations can constructively add to original fields.

         Among the general population, the most popular application of
    microwave power is in the cooking of food. Power levels range from 300
    W to 1 kW in consumer microwave models, at a frequency of 2.45 GHz. In
    a properly designed microwave oven, a very small fraction of this
    power escapes from the oven housing through various leakage paths.
    When leakage occurs, it is most frequently through the door seal. It
    may increase with use or mechanical abuse of the oven. Small amounts
    of leakage can also occur through the viewing screen (Osepchuk, 1979).

         Personal exposure from microwave ovens is extremely small because
    of the rapid decrease of the power flux density with increasing
    distance from the oven. For worst case leakage from the microwave oven
    of 5 mW/cm2, the power density at a distance of 0.3 m is less than
    0.15 mW/cm2 and, at 1 m it is about 10 µW/cm2. Typical leakage
    values, therefore, imply exposure values well below the most
    conservative RF exposure standards in the world (Stuchly, 1977;
    Dumansky et al., 1980).

         Recently, the induction heating stove, a new appliance for
    domestic use, has been introduced on the market. This appliance
    operates in the kilohertz range. Exposure levels at distances greater
    than 0.5 m are low compared with existing exposure limits, being less

    than 5 V/m and 0.5-10 A/m, respectively, at a distance of 0.3 m
    (Stuchly & Lecuyer, 1987).

         Microwave anti-intrusion alarms are typical of low-power devices.
    These operate continuously to avoid thermal drift or switching
    problems, thus exposing people in the protected area. With a typical
    power of 10 mW, power densities of the order of 10 µW/cm2 are
    measured at a distance of about 0.5 m. Population exposure to RF
    fields from commonly encountered sources, such as airport, marine, and
    police radar, is similarly very low (Stuchly, 1977; Dumansky et al.,
    1980, 1985b, 1988).

    3.3.3  Workplace

         Levels of occupational exposure vary considerably, and are
    strongly dependent upon the particular application. While most
    communication and radar workers are exposed to fields of only
    relatively low intensity, some can be exposed to high levels of RF.
    Workers climbing FM radio or TV broadcasting towers may be exposed to
    E fields up to 1 kV/m and H fields up to 5 A/m (Repacholi 1983a; Mild
    & Lovstrand, 1990).

         Radar systems produce strong RF fields along the axis of the
    antenna. However, in most systems, average field strengths are reduced
    typically by a factor of 100-1000, because of antenna rotation and
    because the field is pulsed. With stationary antennas, which represent
    the worst case, peak power flux densities of 10 MW/m2 may occur on
    the antenna axis up to a few metres away from the source.

         In areas surrounding air traffic control radars (ATCRs), workers
    can be exposed to power flux densities of up to tens of W/m2, but
    are normally exposed to fields in the range 0.03-0.8 W/m2. In an
    exposure survey of civilian airport radar workers in Australia, it was
    found that, unless working on open waveguide slots, or within
    transmitter cabinets when high voltage arcing was occurring, personnel
    were, in general, not exposed to levels of radiation exceeding the
    specified limits in the Australian and IRPA radiofrequency exposure
    standards (Joyner & Bangay, 1986a).

         Dielectric or RF heaters are widespread in many industries. RF
    energy produces heat directly within the processed material. This
    unique characteristic is commonly used for such purposes as sealing
    plastics or drying glue for joining wood. All RF heaters have a higher
    efficiency in comparison with conventional ovens. According to several
    surveys (Conover et al., 1980; Stuchly et al., 1980; Grandolfo et al.,
    1982; Bini et al., 1986; Joyner & Bangay, 1986b; Stuchly & Mild,
    1987), the sealing or welding of polyvinyl chloride (PVC) is the most
    common use for RF dielectric heaters. Two pieces of plastic are
    compressed between electrodes and RF power is applied. The plastic
    material heats, partially fuses, and forms a bond. Plastic heaters
    frequently operate at the ISM frequency of 27.12 MHz. However, during

    the operating cycle, this value may vary by several megahertz. The RF
    output power ranges from fractions of a kilowatt to about 100 kW.

         Since the exposure of heater sealer operators and other personnel
    working in the same area takes place in the near-field, both E and H
    field strengths must be measured to evaluate exposure levels. However,
    to demonstrate compliance with basic limits of RF exposure, the
    development of body current measurement techniques should prove to be
    useful (Allen et al., 1986). In the vicinity of RF sources,
    measurements of fields must be made with the operators absent from the
    positions that they normally occupy. The stray fields are localized in
    the immediate vicinity of the sealers, so that exposure of the body is
    highly inhomogeneous.

         RF industrial heaters (plastic sealers and other devices) have
    been found to produce exposure fields exceeding the limits recommended
    in various countries and by the IRPA. Furthermore, direct current
    measurements have confirmed coupling of the RF energy from the device
    to its operator. Various methods have been developed to ameliorate the
    situation, such as shields, grounding strips, and others. Potential
    overexposure to RF radiation is probably one of the most common
    occurrences in the case of RF heaters, unless protective measures are

         Magnetic fields below a few tens of megahertz are used in
    industry for the induction heating of metals and semiconductors and in
    arc welding. Surveys of the magnetic field strength to which the
    operators are exposed have shown that these exposures are, in many
    instances, high compared with recommended exposure limits (Stuchly &
    Lecuyer, 1985; Conover et al., 1986; Stuchly, 1986; Andreuccetti et
    al., 1988; Stuchly & Lecuyer, 1989).

         In many practical situations, exposure can be reduced either by
    administrative measures (Eriksson & Mild, 1985) or by the use of
    protective screening. Screening may be intentional (wire fences) or
    incidental (walls of buildings) and may function by reflection or by
    absorption. In general, both contribute to the total attenuation

         Thin metal sheets are adequate for the attenuation of RF electric
    fields. However, in many cases, it is usual to use wire screens or
    perforated sheets, since these have the advantages of transparency,
    ventilation, light weight, etc. In all cases, surveys are desirable to
    verify the integrity of such screens or shields. Faults in screens
    could, in some circumstances, be secondary sources of significant
    radiation or reactive fields (White, 1980).

         The applications of video display units (VDUs) are numerous and
    their use widespread. Even more applications are anticipated in the
    future. In the RF region, they emit electric and magnetic fields from
    the cathode ray tubes (CRTs). The dominant sources are the horizontal
    and vertical sweep generators (fly-back transformers) operating at

    frequencies of some 15-35 kHz. VDUs produce fields that have complex
    waveforms. Typical electric field stengths at the operator position
    (0.5 m from the screen) range from less than 1 to 10 V/m (RMS).
    Magnetic flux densities range typically from less than 0.01 µT to 0.1
    µT (RMS). In most VDUs, both fields are produced at the lower end of
    these ranges. VDUs also produce weak, electric and magnetic fields at
    the power line frequency (50 or 60 Hz) and its harmonics. All surveys
    have concluded that VDUs do not present any hazard for human health
    within the context of existing guidelines for exposures to
    non-ionizing electromagnetic fields (see section 10) (BRH, 1981;
    Stuchly et al., 1983b; Harvey, 1984; Repacholi, 1985; Elliott et al.,

         A statement has been published by the International Non-Ionizing
    Radiation Committee of the International Radiation Protection
    Association (IRPA, 1988b). Conclusions in this and other documents
    (WHO, 1987; ILO, 1991) are that, on the basis of current biomedical
    knowledge, there are no health hazards associated with radiation or
    fields from VDUs and that there is no scientific basis to justify
    radiation shielding or regular monitoring of the various radiations
    and fields emitted by VDUs.

    3.3.4  Medical practice

         Shortwave and microwave diathermy treatments are used to relieve
    pain through the non-invasive application of non-ionizing
    electromagnetic energy to body tissues. Several surveys have been
    published (EHD, 1980; Ruggera, 1980; Grandolfo et al., 1982; Stuchly
    et al., 1982; Delpizzo & Joyner, 1987), with the primary purpose of
    measuring the field strengths to which diathermy operators are exposed
    during typical treatments. Measurements of the magnitude of fields
    near diathermy electrodes (applicators) were made from shortwave
    diathermy units operating at 27.12 MHz, and from microwave diathermy
    units operating at 434 MHz and 2.45 GHz. They indicate emissions of
    high field and radiation levels in directions other than those
    intended for treatment. Operators, physiotherapists, and personnel
    performing service and maintenance tasks are exposed to stray fields
    and radiations. Reduction of unnecessary exposure of both operator and
    patient during microwave and shortwave diathermy treatments is
    technically achievable through adequate shielding of existing units,
    careful design of new equipment, and judicious planning of the
    treatment area (Bonkowski & Makiewicz, 1986).

         Hyperthermia devices are used in cancer adjuvant therapies (Storm
    et al, 1981; Stuchly et al., 1983a; Hagmann et al., 1985). Treatments
    have been based on biological studies that suggest hyperthermia
    effectiveness in conjunction with radiotherapy and with chemotherapy.
    The evaluation of hyperthermia efficacy is proceeding through the
    development of therapeutic trials for specific tumours (Arcangeli et
    al., 1985; Perez et al., 1991). A few international and national
    organizations have independently determined and developed randomized
    trials (Lovisolo et al., 1988). For the purposes of safety evaluation,

    hyperthemia devices can be classified as: (a) those irradiating
    external to the body and intended for superficial and deep
    hyperthermia, and (b) those irradiating from inside the body and
    intended for interstitial and endocavitary hyperthermia.

         All devices present, to a greater or lesser extent, problems of
    patient health protection. Adverse effects on patients have included
    pain, discomfort, burn, ulceration, and, for deep hyperthemia,
    tachycardia and faintness. These are due to an overheating of
    superficial tissues, tissues surrounding the tumour, and, in deep
    hyperthermia, other tissues far from the tumour and irradiated region
    (Myerson et al., 1989; Petrovich et al., 1989). The magnitude of the
    electromagnetic field around superficial, interstitial, and
    endocavitary applicators is relatively low and does not cause any
    health risk to the operators, though the possibility of leakage of RF
    energy from generators and connecting cables has to be considered in
    some models. Capacitive and phase array devices, however, may leak RF
    energy (Storm et al., 1981).

         Hagmann et al. (1985) measured the stray electric and magnetic
    fields of angular phased array and helical coil applicators for limb
    and torso hyperthermia at 70.93 MHz. Field strengths were measured in
    excess of 300 V/m and 1A/m, respectively, at a distance of about 10 cm
    from the applicator. At 0.5 m, these values were reduced to 14 V/m and
    0.1 A/m, respectively. In general, manufacturers of hyperthermia
    devices pay too little attention to minimizing the leakage of RF
    fields from generators, cables, and applicators, and each new model
    generator should be tested for RF emissions.

         Magnetic resonance imaging (MRI) is now an established diagnostic
    technique while  in vivo spectroscopy is undergoing rapid
    development. The complexity of exposure associated with MRI requires
    the safety consideration of three different fields (Tenforde &
    Budinger, 1986; Budinger, 1988). During clinical imaging, patients or
    volunteers, and operators are exposed to static magnetic fields,
    time-varying magnetic fields, and radiofrequency electromagnetic
    fields. RF fields in the frequency range 1-100 MHz, are deposited in
    patients, principally as heating associated with eddy currents induced
    by the RF magnetic field (Grandolfo et al, 1990). For MRI systems with
    static magnetic flux densities below 2 T, power deposition from
    electric fields associated with RF transmitter coils is relatively
    low, when efficient transmitter coil designs are employed. The power
    deposited by transient magnetic field gradients is similarly low
    (Bottomley et al., 1985). Staff operating the equipment are
    intermittently exposed to weaker fields that are present in the
    vicinity of the imaging equipment. Guidelines on "Protection of the
    patient undergoing magnetic resonance examinations" have been
    published by the International Non-Ionizing Radiation Committee of the
    International Radiation Protection Association (IRPA, 1991).


    4.1  Introduction

         Exposure evaluation provides information necessary to perform
    risk assessments. Two methods are available: (i) a theoretical
    estimation; and (ii) measurements of the fields or related parameters,
    such as energy absorption rates and currents.

         Estimates of exposures are necessary before an installation is
    constructed. Whenever possible, estimates of radiation fields should
    be made before detailed surveys of potentially hazardous exposures are
    carried out. This procedure is needed to select suitable survey
    instruments, and to determine whether potentially hazardous exposure
    of the surveyor could occur, if the choice of the instrument were
    inappropriate or if the instrument were faulty.

    4.2  Theoretical estimation

         Electromagnetic waves may be harmonic, i.e., the electric and
    magnetic fields oscillate as sine waves, and power is generated as a
    continuous wave (CW) at essentially a single frequency. The waves may
    be also modulated, i.e., the amplitude, phase, or frequency may be
    changed in a chosen manner, for example, if pulse modulation,
    short-duration electromagnetic pulses are emitted at certain time
    intervals. The duration of the pulse (pulse length or pulse width),
    which may be of the order of small fractions of a second, is
    designated by t. Its reciprocal, the pulse repetition frequency (pulse
    repetition rate), is expressed in hertz. The product of pulse length
    and repetition rate is referred to as the duty cycle, D. In case of
    pulsed-wave generation, the emitted power increases rapidly, reaches
    a peak pulse power, and rapidly decreases.

         This may be averaged for pulse length or per unit time, which
    introduces the concept of mean (average) power emitted, according to:

         Pp = Pa/tfr or Pa = Ppfr t                           (Equation 4.1)

    where Pp is the peak power, Pa the average power, fr the
    repetition frequency, and t the pulse length.

         In practice, average power is usually measured, and, for safety
    purposes, mean power density is used. The peak pulse power may be many
    times higher than the average power output. The average and peak power
    flux densities (Sa and Sp) are given by:

         Sa = DSp                                             (Equation 4.2)

    Universally used sources with moveable antennas and/or beams, such as
    scanning or rotating radars, introduce an additional complication from
    the safety viewpoint. Electromagnetic power from such installations
    arrives intermittently.

         The power flux density for a scanning antenna in motion can be
    estimated from the power flux density measured with the antenna
    stationary using the expression:

         Wm = ksWs                                          (Equation 4.3)

    where Wm is the power flux density for the antenna in motion, ks
    is the antenna rotational reduction factor, and Ws is the power flux
    density measured on the axis of the stationary antenna at a given

         In most radar installations, the antenna rotates and therefore an
    occupied position is exposed only when the radar beam sweeps it. The
    average exposure level is obtained by multiplying the measured or
    estimated level from a stationary antenna by the rotational reduction
    factor (RRF). In the far-field, RRF equals the ratio of the half power
    beam width to the antenna scan angle.

         The rotational reduction factor (ks) for the near-field region
    is equal to:

         a/Rk                                               (Equation 4.4)

    where "a" is the dimension of the antenna in the scan (rotation) plane
    and Rk is the circumference of the antenna scan sector at the given
    distance r, at which the measurements have been made.

         The region close to a source antenna is called the near-field. As
    shown in Fig.2, the near-field can be divided into two subregions: the
    reactive near-field region and the radiating near-field region. The
    region of space surrounding the antenna in which the reactive
    components predominate is known as the reactive near-field region. In
    the radiating near-field region, the radiation pattern varies with the
    distance from the antenna. The near-fields often vary rapidly with
    distance and mathematical expressions generally contain the terms 1/r,
    1/r2, ...., 1/rn, where r is the distance from the source to the
    point at which the field is being determined. At greater distances
    from the source, the 1/r2, 1/r3, and higher-order terms are
    negligible compared with the 1/r term and the fields are called
    far-fields. These fields are approximately spherical waves that can,
    in turn, be approximated in a limited region of space by plane waves.
    Measurements and calculations are usually easier in far-fields than in

         When the longest dimension (L) of the source antenna is greater
    than the wavelength (lamda), the distance from the source to the
    far-field is 2L2/lamda. For L<lamda, this distance is lamda/2pi
    (see Fig. 2). In practice, the distance from the source that
    represents the boundary between the near-field and far-field regions
    is often taken to be the greater of the two quantities, lamda and
    2L2/lamda. However, the appropriate empirical relationship depends
    on the type of aperture of the source and, for example, for a circular

    aperture, such as on a microwave relay tower, the relationship
    L2/lamda may be more appropriate. In this case, with a frequency of
    2 GHz (lamda = 15 cm), L is approximately 3 m and, consequently, the
    quantity L2/lamda = 60 m. Because 60 m is much greater than 15 cm,
    this is the distance that can be assumed as a boundary between the
    near- and far-field regions.

         The boundary between the near-field and far-field regions,
    however, is not sharp, because the near-fields gradually become less
    as the distance from the source increases.

         In free space, electromagnetic waves spread uniformly in all
    directions from a theoretical point source. In this case, the
    wavefront is spherical. As the distance from the point source
    increases, the area of the wavefront surface increases as a square of
    the distance, so that the source power is spread over a larger area.

    FIGURE 2

         If the exposure takes place in the far-field of a well
    characterized antenna in free space, then S is calculated by the

         S = GPt /4pi r2 (W/m2)                               (Equation 4.5)

    where G is the far-field power gain, Pt is the power transmitted (W)
    and r is the distance (m) from the antenna.

         For a horn or reflector type antenna:

         G = 4pi Ae/lamda2                                    (Equation 4.6)

    where Ae is the effective area of the antenna.

         If G is not known, a useful approximation of S can be obtained by
    substituting the physical area A for Ae in equation 4.6. This gives
    a somewhat larger value for S, since A is generally larger than Ae.

         Although the equations are far-field relationships, i.e., correct
    for distances greater than approximately 2L2/lamda (L > lamda),
    they can be used with an acceptable error for distances greater than
    0.5 L2/lamda. The error is on the safe side, since the equations
    predict greater values of S. However, at distances closer than 0.5
    L2/lamda, the values of S predicted by the equations become
    unrealistically large and radiating near-field estimates must be used.
    For commonly encountered horn and reflector type antennas, the maximum
    expected radiating, near-field, power flux density Sm can be
    estimated (Hankin, 1974) from:

         Sm = 4Pt/A                                           (Equation 4.7)

         Unfortunately, there are no equivalent reactive near-field
    formulae for small radiators. The radiating near-field behaviour of
    horn and reflector type antennas is discussed in detail elsewhere
    (Bickmore & Hansen,1959; SAA, 1988). A detailed discussion of the
    reactive near-field of small radiators can be found in Jordan &
    Balmain (1968).

         In the near-field, the situation is somewhat complicated, because
    the maxima and minima of E and H fields do not occur at the same
    points along the direction of propagation as they do in the the case
    of the far-field. In this region, the electromagnetic field structure
    may be highly inhomogeneous and typically, there may be substantial
    variations from the plane wave impedance of 377 OMEGA; i.e., in some
    regions, almost pure E-fields may exist and, in other regions, almost
    pure H-fields. Field strengths in the near-field are more difficult to
    specify, because both the E and H fields must be measured and because
    the field patterns are more complicated; the power density tends to
    vary inversely with r instead of r2 (as in the far-field), and may
    display interference patterns. Near-field exposures become
    particularly important when considering fields from microwave
    diathermy equipment, RF sealers, broadcasting antennas, and microwave
    oscillators under test.

    4.3  Measurements

    4.3.1  Preliminary considerations

         Several steps are necessary for the accurate assessment of RF
    exposure. The source and exposure situation must be characterized, so
    that the most appropriate measurement technique and instrumentation
    can be selected (ANSI, 1990; Tell, 1983). The correct use of this
    instrumentation requires knowledge of the quantity to be measured and
    the limitations of the instrument used. A knowledge of relevant
    exposure standards is essential.

         In the following sections, information is given concerning
    preliminary RF survey considerations, measurement procedures, and
    calibration facilities.

         Prior to the commencement of a survey, it is important to obtain
    as much information as possible about the characteristics of the RF
    source and the exposure situation. This information is required for
    the estimation of the expected field strengths and the selection of
    the most appropriate survey instrumentation.

    Information about the RF source should include:

    -    frequencies present, including harmonics;
    -    power transmitted;
    -    polarization (orientation of E field);
    -    modulation characteristics (peak and average values);
    -    duty cycle, pulse width, and pulse repetition frequency;
    -    antenna characteristics, such as type, gain, beam width and scan

    Information about the exposure situation must include:

    -    distance from the source;
    -    existence of any scattering objects. Scattering by plane surfaces
         can enhance the E field by a factor of 2, hence, S, by a factor
         of 4. Even greater enhancement may result from curved surfaces,
         e.g., corner reflectors.

    4.3.2  Near-field versus far-field

         For the practical purposes of measurement, the reactive
    near-field exists within 0.5 lamda from the source with a practical
    outer limit of several wavelengths (Jordan & Balmain, 1968). Both E
    and H field components must be measured within the reactive
    near-field. At present, no instruments are available commercially for
    the measurement of H-fields above 300 MHz, which imposes a de facto
    frequency limit on the measurements.

    4.3.3  Instrumentation

         An electric or magnetic field-measuring instrument consists of
    three basic parts; the probe, the leads, and the monitor. To ensure
    appropriate measurements, the following instrumentation
    characteristics are required or are desirable:

    -    The probe must respond to only the E field or the H field and not
         to both simultaneously.
    -    The probe must not produce significant perturbation of the field.
    -    The leads from the probe to the monitor must not disturb the
         field at the probe significantly, or couple energy from the
    -    The frequency response of the probe must cover the range of
         frequencies required to be measured.
    -    If used in the reactive near-field, the dimensions of the probe
         sensor should preferably be less than a quarter of a wavelength
         at the highest frequency present (see next section).
    -    The instrument should indicate the root mean square (rms) value
         of the measured field parameter.
    -    The response time of the instrument should be known. It is
         desirable to have a response time of about 1 second or less, so
         that intermittent fields are easily detected.
    -    The probe should be responsive to all polarization components of
         the field. This may be accomplished, either by inherent isotropic
         response, or by physical rotation of the probe through three
         orthogonal directions.
    -    Good overload protection, battery operation, portability, and
         rugged construction are other desirable characteristics.
    -    Instruments provide an indication of one or more of the following

         (a)  Average power density (W/m2, mW/cm2);
         (b)  Average E field (V/m) or mean square E field (V2/m2);
         (c)  Average H field (A/m) or mean square H field (A2/m2).

         However, no instrument actually measures average power density
    and this quantity is not useful in the near-field of antennas. Power
    density is measured in the far-field by E-field or H-field probes. The
    surveyor should be aware of the field parameter (E or H) to which the
    instrument responds, and that exposure standards generally stipulate
    limits corresponding to both field parameters. Equivalent plane wave
    power density is certainly a convenient unit, but in the reactive
    near-field, E and H field components must be measured and compared
    with the corresponding exposure limits.

         Some factors that can influence the signal levels of the
    instruments (e.g.,influence of multiple signals, pulse modulation,
    lead pick-up, coupling into probes) are discussed in detail in ANSI
    (1981) and Joyner (1988).

    4.3.4  Measurement procedures

         If information on the RF source and exposure situation is well
    defined, then a surveyor, after making estimates of the expected field
    strengths and selecting appropriate instruments, may proceed with the
    survey using a high-range probe to avoid inadvertent probe burnout and
    a high-range scale to avoid possible over-exposure.

         In the reactive near-field of radiators operating at frequencies
    of less than 300 MHz, an electrically small (largest dimension <0.25
    lamda) probe sensor is required since large gradients in field
    components exist. Spatial resolution is critical (large probes will
    yield spatially averaged values) and the use of an isotropic probe is
    strongly recommended. E and H field measurements should not be made
    closer than a distance of 20 cm from metallic objects. In some such
    cases, it may be possible to assess compliance with exposure standards
    by making contact current measurements.

         Non-uniform field distributions result from reflections from
    various structures. Peaks in the field distribution are separated by
    at least one-half wavelength with the maximum levels of E and H fields
    occurring in different locations. Temporal variations occur also as a
    result of scanning antennas, scanning radiation beams, and changes in
    frequency. Therefore, it is imperative that any survey include a
    sufficiently large sample of data to preclude omission of hazardous
    combinations of conditions. When surveying sources of leakage
    radiation, such as waveguide flanges, equipment cabinet doors, and
    viewing or shielding screens, a "sniffing" procedure in the immediate
    vicinity of the equipment is required. A low-power probe and
    high-range setting should first be used to determine leakage sources
    from a distance, and lower-range settings used as a closer approach is
    made. Usually, leakage power varies as the inverse square of the

         When surveying radar antennas, it is necessary to have the
    antenna or the beam stationary, because the response time of the
    instruments is generally not short enough to indicate the maximum
    levels for common beam sweep and scan speed. It is important to
    estimate the peak exposure level, in order to ensure that the probe
    chosen can withstand such a peak level. Also, instruments that
    time-sample the field at insufficiently low sample rates should not be
    used for radar applications (Tell, 1983). Appropriate equations are
    then used to convert back to time-averaged levels for a rotating

         All occupied and accessible locations should be surveyed. The
    operator of the equipment under test and the surveyor should be as far
    away as practicable from the test area. All objects normally present,
    which may reflect or absorb energy, must be in position. The surveyor
    should take precautions against RF burns and shock, particularly near
    high-power, low-frequency systems.

         With careful measurement techniques and the correct choice of
    instrument, overall measurement uncertainties that are acceptable can
    be achieved. Direct field measurements frequently do not provide
    reliable means for exposure evaluation at distances from the field
    source (an antenna, or a re-radiating surface) of less than about 0.2
    m or lamda/2, whichever is smaller. In such a case, it may be
    necessary to evaluate the specific absorption rates (SARs) in a model
    of the human body using one of the dosimetric measures (Stuchly &
    Stuchly, 1986), or to measure directly the RF current flowing through
    the person (Blackwell, 1990; Tell, 1990a).


    5.1  General

         Time-varying electric and magnetic fields induce electric fields
    and corresponding electric currents in biological systems exposed to
    these fields. The intensities and spatial distribution of induced
    currents and fields are dependent on various characteristics of the
    exposure field, the exposure geometry, and the exposed biological
    system. The exposure field characteristics that play a role include
    the type of field (electric, magnetic, or electromagnetic radiation),
    frequency, polarization, direction, and strength. Important
    characteristics of the exposed biological body system include its
    size, geometry, and electrical properties. The electrical properties
    of biological systems described by the complex permittivity and
    electrical conductivity differ for various tissues.

         The biological responses and effects due to exposure to
    electromagnetic fields generally depend on the strength of induced
    currents and fields. However, only the external fields can be measured
    easily and dosimetry has been developed to correlate the induced
    currents and fields with the exposure conditions. Induced currents, as
    a measure of dose, have been used in the quantification of
    experimentally induced effects in animals and the results have been
    extrapolated to humans.

         In the broad range of frequencies considered in this publication,
    i.e., 300 Hz-300 GHz, two different, but interrelated, quantities are
    commonly used in dosimetry. At lower frequencies (below approximately
    100 kHz), many biological effects can be quantified in terms of the
    current density in tissue. Therefore, this parameter is most often
    used as a dosimetric quantity. At higher frequencies, where many (but
    not all) interactions are due to the rate of energy deposition per
    unit mass, the parameter specific absorption rate (SAR) is used. The
    SAR is defined as "the time derivative of the incremental energy, dW,
    absorbed by, or dissipated in, an incremental mass, dm, contained in
    a volume element, dV, of a given density, rho" (NCRP 1981). The SAR is
    most often expressed in units of watts per kilogram (W/kg).

    5.2  Low frequency range

         At frequencies below approximately 0.1-1 MHz, interactions of
    electromagnetic fields with biological systems can be considered in
    terms of induced currents and their density. This approach is
    particularly well suited for calculations at frequencies for which the
    dimensions of the object are small compared with the wavelength. Under
    these circumstances, quasi-static approximations are valid, i.e., the
    effects of the electric and the magnetic field can be considered
    separately. The advantages of considering induced currents are
    twofold. First, the current densities induced in humans can be

    compared with those known to produce physiological responses, e.g.,
    nerve or muscle stimulation, or they can be compared with endogenous
    body currents. Second, consideration of induced currents in ungrounded
    metallic objects can be used to assess thresholds for shocks and burns
    for people, who are fully or partially grounded and come in contact
    with such objects. Maximum current densities and the resulting maximum
    SARs, in some parts of the human body under certain exposure
    conditions, can be conveniently evaluated using the induced current
    approach. The direct evaluation of the internal electric fields would
    be much more complex and difficult. Under these conditions, limits of
    exposure may be expressed more appropriately in terms of induced
    currents rather than external field strengths.

         The use of induced currents or current densities is appropriate
    for the assessment of acute, immediate, safety hazards, while it may
    have limitations for the complete evaluation of long-term effects.
    This has yet to be determined.

    5.2.1  Magnetic fields

         In accordance with Faraday's law, magnetic fields that vary in
    time induce the movement of electrical charge and cause potentials and
    circulating (eddy) currents in biological systems. These currents can
    be estimated using the following equation, provided that the current
    paths are circular:

         J = sigma E = 0.5 r sigma dB/dt                    (Equation 5.1)


    J = current density (A/m2)
    E = induced electric field strength (V/m)
    r = radius of the loop (m) (usually several cm up to 20 cm)
    sigma = tissue conductivity (S/m)
    dB/dt = rate of change of magnetic flux density B (T/s).

         For sinusoidal fields of frequency f, equation 5.1 reduces to:

         J = pi r sigma fB0                                 (Equation 5.2)

    where B0 is the magnetic flux density peak amplitude.

         The current density, internal electric field, and SAR, at any
    location in an exposed biological body, are inter-related as follows:

         SAR = sigma E2/rho                                 (Equation 5.3)

    where rho is the physical density (kg/m3) and

         SAR = J2/sigma rho                                 (Equation 5.4)

         Because of the paucity of experimental data on the biological
    effects of electromagnetic fields at frequencies below a few tens of
    megahertz, consideration of the following effects of induced current
    densities provides a useful alternative.

         The magnitude of the magnetically induced electric fields and
    current densities is proportional to the radius of the induction loop
    in the body, to the tissue conductivity, and to the rate of change of
    magnetic flux density. The dependence of the induced field and current
    on the radius of the loop through which magnetic flux linkage occurs
    is an important consideration for biological systems. The induced
    current density is greatest at the periphery of the body, where the
    conducting paths are longest, whereas microscopic current loops
    anywhere within the body would have proportionally smaller current
    densities dependent on the loop size. The magnitude of the current
    density is influenced also by tissue electrical conductivity. In
    biological bodies, the exact paths of the current flow depend in a
    complicated way on the electrical conducting properties of the various

         It is difficult to calculate the complex current distributions in
    biological bodies. Therefore, the treatment of this problem is
    restricted, at present, to relatively simplified situations.

         Typical values for the low-frequency electrical conductivity are
    0.1-0.35 S/m for cardiac muscle and 0.1-0.3 S/m for nerve tissue.
    Additionally, high ratios of transverse to longitudinal impedance up
    to 7:1 have been observed (Epstein & Foster, 1983).

         There is very little experimental or theoretical work dealing
    with the coupling of magnetic fields to models of living organisms
    (e.g., Spiegel (1976) described magnetic field coupling with spherical
    models, Gandhi et al. (1984) calculated induced current densities in
    the torso of a human using a multidimensional lattice of impedance
    elements). Bernhardt (1979, 1985, 1988) performed calculations, using
    "worst case" assumptions, to estimate the order of magnitude for
    "safe" and "dangerous" values of magnetic field strengths and their
    frequency dependence. Considering the cardiac region and the brain as
    "critical" organs, approximate "worst case" calculations can be made
    (Bernhardt, 1979, 1985). For the purpose of these calculations, both
    regions can be considered as homogeneous spheres of different radii.
    Differences in electrical conductivity of the white and grey cerebral
    matter, and the anisotropic nature of conductivity at frequencies
    below approximately 10 kHz are not considered. A value of sigma =
    0.2S/m is used for the specific electrical conductivity of the

    cerebral substance, and a value of 0.25 S/m is used for the myocardial
    tissue. When a radius r of 7.5 cm of the induction loop is assumed for
    the head, and 6 cm for the heart, the product sigma r is the same for
    both the heart and head.

         Therefore, approximately the same current densities are
    calculated to result in the peripheral regions of the heart and brain
    for a vertical magnetic field. Because of the uncertainties of the
    current loops and of the values for the electrical conductivities, the
    accuracies of these calculations are limited to about one order of
    magnitude. For larger effective current loops and electrical
    conductivities, smaller values of magnetic flux density may induce the
    same current densities.

         The waveform is an important factor to be considered in the
    response of biological systems to a time-varying magnetic field. Many
    different waveforms of magnetic field are used in medicine and
    industry, including sinusoidal, square-wave, saw-tooth, and pulsed.
    For these fields, the parameters of key importance are the rise and
    decay signal times. These determine the maximum rates of change of the
    field (dB/dt) and the maximum instantaneous current densities induced
    in tissues. In order to provide an "effective" value for a variety of
    waveforms, root-mean-square (rms) values are often used. However, peak
    instantaneous field strengths appear to be important in considering
    nerve and muscle cell stimulation, and for perturbing cell functions.
    The effects depend strongly on frequency.

    5.2.2  Electric fields

         Exposure of a living organism to electric fields is normally
    specified by the unperturbed electric field strength. The fields that
    actually act on an exposed organism include electric fields acting on
    the outer surface of the body and electric fields and current
    densities induced inside the body. These fields can be different from
    the exposure, because of perturbations caused by placing the body in
    the external field. They must, however, be determined in order to
    specify exposure at the level of living tissues or to relate exposure
    levels and conditions from one species to another.

         The electric fields that act directly on an exposed subject can
    be categorized as follows:

     (a) Electric fields acting on the outer surface of the body.
    These fields can cause hair to vibrate and thereby can be perceived;
    they may also be able to stimulate other sensory receptors in the

     (b) Electric fields induced inside the body.
    These fields act at the cellular level, and their presence is
    accompanied by electric currents because of the electrically
    conductive nature of living tissues.

    Secondary short-term effects must also be considered when evaluating
    health risks resulting from electric field exposure. Hazardous
    thresholds for some indirect effects are lower than the thresholds for
    biological effects due to the direct influence of electric fields. In
    this case, the following points are important:

    *    Contact currents enter a person through electrical conductors in
         contact with the skin.

    *    For static and low-frequency fields, spark discharges introduce
         transient currents into the body via an arc gap, when the
         electrical breakdown potential of air is exceeded.

    *    Electric or magnetic fields may interfere with the performance of
         unipolar cardiac pacemakers.

         Therefore, a clear distinction is necessary between effects
    caused by the direct influence of electric fields and indirect effects
    caused by approaching or touching electrically charged objects, or by
    electromagnetic interference with implanted electromedical devices.

         Within the body, the current and the current density are the two
    main quantities of interest. The total current is more easily measured
    or calculated, but the current density is more directly relevant to
    electric field effects in a particular tissue or organ. The electrical
    complexity of the interior of the human body, due to the presence of
    insulating membranes and tissues of various impedances, has so far
    frustrated confident analysis of precise interior current densities
    (Kaune & Phillips, 1980; Spiegel, 1981).

         Electric field coupling occurs through capacitive and conductive
    mechanisms. A body is coupled to an electric field in proportion to
    its capacitance to the ground as one equipotential surface, such that
    the greater the capacitance the greater the current flow in the body.
    By definition, in capacitive coupling, the body, according to its
    capacitance C, "acquires" a certain amount of surface charge Q and
    attains a potential V = Q/C. The capacitance, and, thus, the induced
    current, decreases for a body separated from the ground and not close
    to an energized electrode. The capacitance is dependent on the size
    (especially on the surface area), the shape, and the orientation of
    the body. Internal currents will differ between fat and thin persons,
    between persons standing and reclining, and between persons walking

    barefoot and those wearing shoes or standing on a non-conductive
    platform. In all cases, it is necessary, to define the conditions
    under which the capacitance has been measured.

         A short-circuit current, Isc, flows in a body placed in an
    electric field and connected to the ground through a low resistance
    path (paws, bare feet, a hand grasping an earthed pole). This current
    is the sum of all the displacement currents collected over the surface
    of the body. The only place on the body where a current of the
    magnitude of the short-circuit current flows is where there is
    connection with the ground. The total current induced in the body is
    simply the Maxwell's displacement current density multiplied by the
    effective area of the body. Since the body is highly conducting, this
    current is completely independent of the body's dielectric parameters.
    Deno (1977) determined this effective area by measuring the surface
    currents induced in hollow metal mannequins exposed to 60 Hz electric
    fields. He characterized the complete current distribution and
    determined the total short-circuit current to ground.

         The equivalent area for an adult human corresponds to an
    effective surface area of 5.08 m2 for a 1.77 m-tall subject. This
    results in a total short circuit to ground current Isc (mA) for a
    grounded person given by:

         Isc = 0.09 h2Ef                                      (Equation 5.5)

    where h(in m) is the height of the person, E (in kV/m) is the electric
    field strength, and f (in kHz) is the frequency.

         From measurements by Guy & Chou (1982) and Tell et al. (1982),
    the values of short-circuit current obtained by Deno for the metal
    foil models were confirmed to be the same for humans at frequencies of
    up to 1 MHz.

         The results are shown in Fig. 3, normalized to an exposure level
    of 614 V/m. Since the threshold for RF burns was found by Rogers
    (1981) to be 200 mA, it is clear that an exposure level of 614 V/m
    does not protect humans against RF burns resulting from contact with
    grounded objects.

         Deno's current distributions can be used to calculate spatial
    distributions of SAR as well as average SAR for real human bodies
    exposed to electric fields of wavelengths that are large compared with
    the size of the body.

         To make accurate calculations of the SAR distributions from the
    body current distributions for various exposure conditions, it is

    necessary to determine the electrical conductivity and resistance per
    unit length along the axis of the body and limbs. At frequencies
    between approximately 60 kHz and 3 MHz, this can be simply achieved by
    passing a known very low-level (VLF-MF) current through the whole body
    and measuring the potential at various points.

    FIGURE 3

         Calculations of SAR for exposure levels of 614 V/m, based on
    measured electrical conductivity and current distribution, are
    illustrated in Fig. 4 for exposure conditions where the feet are
    grounded. The maximum SAR values were obtained from the average values
    in each elliptical element by assuming that the current would be
    shunted through fat, bone, and muscle tissues, according to the ratios
    of the electrical conductivity of each tissue to the average
    electrical conductivity of the entire elliptical element.

    FIGURE 4

         The peak SAR occurring in the muscle and blood vessels of the
    ankle, when the feet are grounded, reaches a value of 100 W/kg. Gandhi
    (1985) was the first to draw attention to this problem. Although these
    SAR values are quite high, they occur in a relatively small volume and
    the thermal consequences are difficult to predict.

         In studies on the distribution of the electric field or the
    absorbed power in different parts of the human body, it has been
    demonstrated that, for fields of frequencies below 10 MHz, the
    internal field strength increases in direct proportion to the

    frequency for a given external electric field strength. Therefore, a
    simple relationship exists between the internal and the external
    electric field strengths, depending on the body part or organ
    considered, on the electrical conductivity, and on the exposure

         A detailed evaluation of current density thresholds as a function
    of frequency for various interactions, and an estimation of maximum
    current densities in models of humans exposed to electric and magnetic
    fields of frequencies of less than 100 kHz, have been reported
    (Bernhardt, 1985). Envelope curves of current densities that are
    required for cell stimulation, and those associated with endogenous
    currents in brain tissue have been established for fields of
    frequencies up to 100 kHz.

         The current densities induced within the body by an external
    electric field E and frequency f were calculated using the formula
    J=KfE. The constant K depends on the part of the body considered
    (Bernhardt, 1985). The longitudinal axis of the body parallel to the
    external E field represents optimum coupling geometry and must be
    considered as the "worst case".

         The K values can be determined by two different methods. Data
    from studies by different authors on absorption within the
    quasi-static range can be used, or K can be determined by calculating
    the current densities on the basis of the field strength measured on
    the body-surface at 50/60 Hz. The K values, determined by entirely
    different methods, coincide satisfactorily. The same value K=3.10-9
    S/(Hz m) was obtained for the cardiac region and head, however for
    other parts of the body the values of K may be larger (Kaune &
    Phillips, 1980; Guy et al., 1982; Kaune & Forsythe, 1985). The surface
    E field and current density data derived from human measurements
    (Deno, 1977) and animal data (Kaune & Phillips, 1980) demonstrate that
    the external unperturbed fields, which are almost always used to
    specify exposure, must be scaled to equalize internal current
    densities or surface E fields. This must be done in order to
    extrapolate biological data from one species to another. This process
    is complicated by the fact that the actual value of the scaling factor
    depends on the internal quantity that is being scaled.

         Currents in electrically-grounded people exposed to fields at
    frequencies below 50 MHz have been measured (Guy & Chou, 1982; Gandhi
    et al., 1985b, 1986). The resulting SARs in a small volume within the
    ankle were estimated to be in the range of 200-540 W/kg for E fields
    of 61.4 V/m in the range of frequencies 40-62.5 MHz. However, lower
    values were found in a quantitative analysis by Dimbylow (1987, 1988).

         The SAR in the wrist for contact with isolated metallic objects
    in an RF field has been calculated as a function of contact current
    for various frequencies used in broadcasting (Tell, 1990). The maximum
    contact currents to maintain the SARs below 8 W/kg and 20 W/kg are

    given in Table 5. The values in Table 5 are based on an assumed
    effective wrist cross section of 11.1 cm2.

    Table 5.  Maximum contact currents to keep SARs in the wrist below
              8 and 20 W/kga
    Broadcast band                Limiting current to control SAR (mA)
                                  <8 W/kg         <20 W/kg
    AM (0.55-1.6 MHz)             75.1           119

    Low VHF (54-88 MHz)           84.1           133

    FM (88-l08 MHz)               87.3           138

    High VHF (176-216 MHz)        93.6           148

    Channel 14 (470-476 MHz)      99.7           158

    Channel 20 (506-512 MHz)      100            159

    Channel 66 (782-788 MHz)      124            197
    a From: Tell (1990).

    5.3  High-frequency range

         The interaction of RF fields with matter can be described in
    terms of its electrical properties, which are the macroscopic
    reflection of interactions at the molecular or cellular level. The
    basic interaction mechanisms, which are discussed in section 6,
    involve relaxation phenomena due to the rotation of polar molecules,
    such as water, amino acids, protein, lipids, interfacial space-charge
    polarization due to non homogeneous structures (e.g., cell membranes),
    and ionic conduction.

         The internal fields can be quantified in various ways. The
    magnetic permeability of tissue is practically equal to that of free
    space, and all known and anticipated interactions occur through
    mechanisms involving the electric field (including the current induced
    by the magnetic field). Therefore, the electric field vector, or its
    distribution throughout the exposed body, fully describes the exposure
    field-tissue interactions. Some additional information may be needed
    for full quantification, e.g., the frequency characteristics of the
    exposure field, such as modulation characteristics and modulation

         A direct calculation of the expected temperature rise (DELTA T in
    kelvin) in tissue exposed to RF fields for a time (t seconds) can be
    made from the equation:

         DELTA T = (SAR) t / C                            (Equation 5.6)

    where C is the specific heat capacity expressed in J/kg K. This
    equation, however, does not include terms to account for heat losses
    via processes such as thermal conduction and convection. Although it
    expresses the rate at which the electromagnetic energy is converted
    into heat through well established interaction mechanisms, it provides
    a valid quantitative measure of all the interaction mechanisms that
    are dependent on the intensity of the internal electric field in a
    non-linear manner. Some additional information may be relevant. For
    instance, since some effects of RF fields modulated in amplitude at
    ELF (extremely low frequencies) are dependent on the electric field
    intensity (Adey, 1981), they could probably be expressed in terms of
    the SAR, modulation characteristics, and the "zones" or windows of
    amplitudes of the SAR that are biologically effective.

         The SAR concept has proved to be a simple and useful tool in
    quantifying the interactions of RF fields with living systems. It
    enables comparison of experimentally observed biological effects for
    various species under various exposure conditions and it provides the
    only means, however imperfect, of extrapolating animal data to
    potential hazards for humans exposed to RF. It also facilitates
    planning and effective execution of therapeutic hyperthermic

         Dosimetry in bioelectromagnetic research has been developing in
    two parallel but interacting complementary ways, the theoretical and
    the experimental. RF dosimetry calculations can be performed by
    solving Maxwell's equations for a given configuration approximating
    the exposed object (an animal, a human being, a part of a human body)
    and for given exposure conditions (e.g., a plane wave at a given
    frequency, incident from a given direction). These data have been
    collected and discussed in the  Radiofrequency radiation dosimetry
     handbook (Durney et al., 1986). However, even analyses of greatly
    simplified models provide valuable information for quantifying
    interactions of electromagnetic fields with biological systems. The
    results obtained from simple models often provide valuable insight and
    qualitative understanding that can facilitate the analysis of more
    complex models.

         Fig. 5 illustrates the average SAR as a function of frequency for
    an average man exposed to a plane wave for three polarizations (Durney
    et al., 1978; Durney, 1980). Various models used in the calculations
    are also indicated.

    From these data, the following conclusions can be drawn:

    -    the average SAR is a function of frequency;
    -    the average SAR depends on the wave polarization, and is greatest
         for the E polarization (electric field is parallel to the long
         axis of the body), except at higher frequencies, where it is
         slightly greater for the H polarization (magnetic field (H) is
         parallel to the long axis of the body);
    -    the average SARs for the E or K polarizations (when electric
         field (E) or wave propagation direction (K), respectively, are
         parallel to the long axis of the body) exhibit a maximum at
         certain frequencies, called the resonant frequencies.

    FIGURE 5

    FIGURE 6

         The frequency-dependent behaviour is illustrated in Fig. 6 for
    several human sizes. The average whole-body SAR in W/kg is plotted as
    a function of electromagnetic field frequency (MHz) for an incident
    average power density of 1 W/m2.

         Based on the absorption characteristics in the human body, the
    radiofrequency range can be subdivided into four regions (IRPA,
    1988a), as shown in Fig. 7:

    (a)  The sub-resonance range, less than 30 MHz, where surface
         absorption dominates for the human trunk, but not for the neck
         and legs, and where energy absorption increases rapidly with
         frequency (in the neck and the legs significantly larger
         absorptions may occur).

    (b)  The resonance range, extending from 30 MHz to about 300 MHz
         for the whole body, and to even higher frequencies if partial
         body resonances, more particularly in the head, are considered.

    (c)  The "hot-spot" range, extending from about 400 MHz up to about
         3 GHz, where significant localized energy absorption can be
         expected at incident power densities of about 100 W/m2; energy
         absorption decreases when frequency increases and the sizes of
         hot spots range from several cm at 915 MHz to about  1 cm at 3

    (d)  The surface absorption range, greater than about 3 GHz, where
         the temperature elevation is localized and restricted to the
         surface of the body.

         The average SAR varies with species, as illustrated in Fig. 8.
    These data are of importance in extrapolation of the results from
    experimental animal studies to human exposures. The average SAR varies
    within one order of magnitude in the subresonance range, depending on
    the separation of an average person from the electric ground plane
    (with the highest SAR for a person on a ground plane).

         Whole-body-average SARs have been measured for humans (Hill,
    1984a,b,c; Hill & Walsh, 1985), and the spatial distribution of the
    SARs in full-scale, realistic models of the human body (Kraszewski et
    al., 1984; Stuchly M. et al., 1985, 1986; Stuchly S. et al., 1985).
    The whole-body average SAR was measured for human volunteers exposed
    to RF at a few frequencies between 3 and 41 MHz, which are below and
    close to the resonant frequencies of adult humans. The exposure
    conditions simulated free-space and grounded conditions in the
    orientation that results in the greatest SARs (Hill, 1984a, b, c). At
    all frequencies, the measured SARs exceeded the calculated values by
    a factor of 2.7-3.9 in free space, and 4.3-4.4 for the grounded

    FIGURE 7

    FIGURE 8

         Similar differences between the calculated and measured SAR for
    simple models were found on scaled-down models at 5-10 MHz (Guy,
    1987). Spatial distributions of the SAR in models of the human body
    have been investigated experimentally (Guy et al., 1984; Kraszewski et
    al., 1984; Stuchly M. et al., 1986; Stuchly S. et al., 1987). Large
    differences, typically by a factor of 10-30, between the measured SAR
    values and those previously calculated using a block model, have been
    observed (Stuchly M. et al., 1986) at frequencies above resonance.
    However, despite the differences in spatial distributions, the ratios
    of peak to whole-body average SARs predicted theoretically and
    measured, were relatively small, except for the SAR at the body
    surface. With reference to developing human exposure limits, these
    results underscore the limitations of the theoretical methods of
    prediction available at present.

         The measurements on a full-scale model (Olsen, 1982; Stuchly S.
    et al., 1986 ), on a scaled-down model of man (Guy et al., 1984), and
    on a full-scale model of a monkey (Olsen & Griner, 1982) all indicated
    that, for free space and the most absorbing orientation

    (E-polarization), measured values are close to those predicted from
    calculations at, and above, the resonant frequency (up to about 450

         Changes to the average SAR for important practical exposure
    conditions (e.g., separation between the subject's feet and the ground
    plane, the body position, articulations of the limbs, and two-body
    interactions) have been investigated using human volunteers (Hill,
    1984b, 1984c). Footwear reduces the average SAR with the degree of
    reduction depending on the type of footwear and the frequency of the
    exposure field.

         Similar effects have been observed in body currents measured in
    people exposed to HF and VHF antennas (Allen et al., 1988).

         High local SARs also occur at frequencies around and below the
    resonant frequency at locations such as the ankles (Gandhi et al.,
    1985b, 1986) and the wrist (Guy & Chou, 1982). At frequencies above a
    few GHz (millimetre waves), high local SARs are produced at the body
    surface (Gandhi & Riazi, 1986). Exposures corresponding to 10 W/m2
    may result in perception of heating.

         Data have also been collected on the SAR distribution for
    near-field exposures (Stuchly M. et al., 1985, 1986, 1987; Stuchly S.
    et al., 1985, 1986). One of the most important findings is that the
    SAR distributions are highly non-uniform, with typical ratios between
    spatial peak and whole-body average SARs of the order of 150:1 to
    200:1 (Stuchly S. et al., 1985). At all frequencies investigated, the
    maximum SAR is at the body surface, with lower magnitude "hot spots"
    located inside the body. Practically all the energy, however, is
    deposited within about 20% of the body volume closest to the antenna.
    Knowledge of these SARs can be used in specifying, for instance, the
    maximum output power of portable transmitters that would be allowed
    under a selected limit of the SAR.

    5.4  Derivation of exposure limits from basic quantities

         For the assessment of the possible health effects of
    electromagnetic fields, it is useful to differentiate between basic
    limits and derived limits.

         Basic limits may be directly correlated with biological effects.
    Using experimental data or related studies, a threshold exposure level
    can be determined, above which adverse health effects are increasingly
    likely, but below which no adverse effect occurs. The basic exposure
    limit is based on this threshold level.

         Since basic limits in terms of SAR or induced current density
    cannot be measured easily in practical exposure situations, exposure
    limits in conveniently measured quantities are derived from the basic
    limit. These derived limits then indicate the acceptable limits in
    terms of measured and/or calculated field parameters.

         Three categories of basic limits have been identified and
    quantitatively established.

    1.   The specific absorption rate (SAR) averaged over the whole body
         or over parts of the body:
         Whole body SAR is a widely accepted measure for relating adverse
         effects to RF exposure, especially for frequencies above about 10
         MHz. Local SAR values are necessary to evaluate and limit
         excessive energy deposition in small parts of the body and to
         avoid hot spots resulting from special exposure conditions.
         Examples of such conditions are: a grounded individual exposed to
         RF in the low MHz-range; individuals exposed in the near-field of
         an antenna or individuals exposed at the higher end of the
         frequency range, where the penetration depth of the RF is low.

    2.   The induced electric field strength or current density:
         RF fields can induce sufficiently high current densities to
         stimulate excitable tissue (nerve or muscle) or to produce other
         potentially harmful effects, especially at frequencies below 100
         kHz. The thresholds for biological effects are expressed in terms
         of current density and are strongly frequency dependent.

    3.   Contact current between a person and a charged object:
         A conductive object in an electric field can be energized by the
         field. For field frequencies below 100 kHz, contact between the
         object and a person may result in stimulation of electrically
         excitable tissue with pain and more severe effects (burns), if
         the current density is sufficiently high. For frequencies between
         about 100 kHz and 100 MHz, the hazard of burns from contact
         current will predominate.

         Derived limits are necessary to provide a practical method to
    evaluate a given RF exposure. Derived limits obtained from one of
    these basic limits above include, e.g., electric and magnetic field
    strength, power density, contact voltage of the conductive objects,
    and short-circuit currents. The derived limits have to be calculated
    in such a way that, even under worst-case conditions of field
    exposure, the basic limits will not be exceeded. In many special
    exposure conditions, e.g., in the near-field, very close (less than
    0.5 wavelength) to an antenna, the assessment of possible health
    effects may require separate measurements or calculations to
    investigate whether the basic limit is exceeded.


    6.1  General

         Electromagnetic fields in the frequency range 300 Hz-300 GHz
    interact with biological systems (humans and other animals) through
    direct and indirect mechanisms. A direct interaction produces effects
    in the exposed organisms directly from exposure to the electromagnetic
    field. An indirect interaction is mediated through the presence of
    other bodies in the electromagnetic field, and occurs as a result of
    an interaction (usually physical contact) between the biological body
    and another object, such as an automobile, fence, or even another
    biological body.

         Direct interactions that are well understood can be quantified in
    terms of dosimetry, and can be considered as resulting from induced
    currents and internal electric fields. The macroscopic spatial
    distribution of these currents and fields within an exposed biological
    body is of importance and is determined by theoretical and
    experimental dosimetry. The spatial distributions of the currents and
    fields within, and around, the cell are also important. As outlined
    earlier, the patterns of induced currents and fields within biological
    systems usually are highly non-uniform and depend on the geometry and
    electrical properties of the exposed system, as well as on the field
    frequency, and, for lower frequencies, the type of field, whether
    electric or magnetic (where spatial separation of the electric and the
    magnetic field is realistic). The extent to which the electric or
    magnetic field plays a role is uncertain. However, apart from
    differences due to different current distributions, the frequency of
    the field clearly establishes the type of mechanism for the mechanisms
    that are well understood.

         For frequencies below about 100 kHz, an established interaction
    mechanism is the stimulation of excitable tissues by induced currents.
    For higher frequencies, thermal interactions predominate. At the lower
    frequencies, much less of the electromagnetic field is absorbed by
    biological systems. Thermal interactions occur at energy levels much
    higher than interactions due to induced currents. Therefore, thermal
    interactions are usually of little interest for fields at levels at
    which people are exposed. Additionally, at frequencies below
    approximately 1 kHz and at higher frequencies amplitude modulated at
    extremely low frequencies (1-300 Hz), there is experimental evidence
    that interactions occur through mechanisms other than thermal or cell
    excitation. These mechanisms are not understood.

         In the context of direct and indirect interaction mechanisms, the
    electrical properties of tissues have to be considered. Macroscopic
    electrical properties of tissues play a major role in defining induced
    currents and fields and their patterns inside the body. Microscopic
    electrical properties provide an insight into events at the molecular
    and cellular level that result from exposure of the biological body to
    an electromagnetic field.

         A brief review of tissue electrical properties is presented in
    this section, together with a discussion of direct and indirect
    interaction mechanisms.

    6.2  Electrical properties of cells and tissues

    6.2.1  Permittivity

         The interactions of an electric field with matter are described
    in terms of the complex permittivity, epsilon*:

    epsilon* = epsilon' - j epsilon"                          (Equation 6.1)

    where epsilon' is the dielectric constant, epsilon" is the loss
    factor, and j = square root -1.

         Equation 6.1 is a representation in the complex plane of a
    physical property, in this case the permittivity. Such representation
    indicates two distinct properties. The dielectric constant, epsilon'
    is a measure of the ability to store electric field energy. The loss
    factor, epsilon", describes a fraction of energy dissipated in the
    material per cycle.

         The permittivity represents a combined macroscopic effect of
    various molecular phenomena causing electrical polarization. It
    includes contributions from relaxation phenomena due to molecules,
    cells, and ion layers surrounding molecules. For convenience, it also
    includes the contribution from ionic conductivity (movement of ions).
    The contribution of each of the phenomena varies with frequency.

         Frequently, the relative permittivity is used, i.e., the
    permittivity normalized to that of free space (vacuum):

         epsilon*r =
         epsilon'r - j epsilon"r =
         epsilon*/epsilono =
         epsilon'/epsilono - j epsilon"/epsilono              (Equation 6.2)

    where epsilono is the permittivity of free space, 8.85 × 10-12 F/m.

    The loss factor, epsilon"r, is related to the electrical
    conductivity of the material, sigma, in the following way:

         epsilon"r = sigma/omega epsilono                     (Equation 6.3)

    where omega = 2pi f, f is the frequency. The unit of electrical
    conductivity is siemens per metre (S/m). The electrical conductivity
    consists of two terms, the static electrical conductivity due to ionic
    conduction, and the electrical conductivity due to various

         Electrical properties of tissues change over a few orders of
    magnitude with frequency in the range as shown in Fig. 9 (note the
    logarithmic scale).

    FIGURE 9

         Biological tissues exhibit three strong relaxation phenomena (the
    alpha-, ß-, and gamma-dispersion) and one weak (the delta-dispersion)

    (Foster & Schwan, 1986, 1989). The molecular phenomena responsible for
    the alpha-dispersion are the least understood.

         Relaxation of counter-ions about the charged cellular structure,
    intracellular structures, e.g., the tubular apparatus in muscle cells,
    relaxational behaviour of membranes themselves, may all contribute to
    this dispersion to various degrees. The ß-dispersion is mostly due to
    membranes, which separate regions having different dielectric
    constants and electrical conductivities, resulting in an interfacial
    polarization causing the Maxwell-Wagner type relaxation. Smaller
    contributions result from the relaxation of proteins. The
    gamma-dispersion is due to free water relaxation and the
    delta-dispersion results from relaxation of bound water, amino acid,
    and charged side groups of proteins.

         The alpha-dispersion occurs at frequencies that are usually below
    10 kHz, the ß-dispersion at about 20 kHz-100 MHz, the delta-dispersion
    at 100-1000 MHz, and the gamma-dispersion at 25 GHz (at 37 °C).

         All the dispersions in most tissues occur over a broad range of
    frequency, because of the highly non-uniform structure of tissues, and
    usually with more than one specific interaction mechanism contributing
    to the dispersion (Foster & Schwan, 1986, 1989; Stuchly & Stuchly,

         The permittivity of cells and tissues has been extensively
    studied and comprehensive reviews can be found (Foster & Schwan, 1986,
    1989; Stuchly & Stuchly, 1990). A detailed description on the
    molecular/cellular level of all the relaxation phenomena is provided
    in a review by Foster & Schwan (1989).

         Resonant dielectric absorption was reported in DNA solutions at
    1-10 GHz (Edwards et al., 1984, 1985). Various theoretical hypotheses
    were proposed to explain the resonances (Scott, 1985; Van Zandt,
    1986). However, more careful measurements were performed by three
    other research teams (Foster et al., 1987; Gabriel et al., 1987;
    Maleev et al., 1987 ) and a part of the original team that found the
    resonance (Rhee et al., 1988). None of the groups found resonant
    behaviour of DNA in aqueous solutions. A lack of resonant behaviour is
    in agreement with the earlier experimental data on the dielectric
    properties of DNA (Takashima et al., 1984).

    6.2.2  Non-linear effects

         The bulk dielectric properties of tissues reflect the passive
    properties of cells, e.g., the capacitance of cell membranes (Foster

    & Schwan, 1989). The physiological response of the membrane to the
    changes in the membrane potential, due to the applied field, results
    in nonlinearity. These phenomena include changes in the membrane
    conductance associated with gating and action potentials. An induced
    potential across the membrane of the order of 10 mV or more is
    required to produce firing of a resting nerve cell, which for a
    membrane thickness of, for example, 50 nm corresponds to an electric
    field strength of 200 kV/m. However, substantially lower electric
    field strengths can induce changes in the firing pattern of pacemaker
    cells (Sheppard et al., 1980; Wachtel, 1985). At high field strengths
    (voltages across the membrane), pores are formed in the membrane, and,
    eventually, at a few hundred mV across the membrane, breakdown occurs
    (Foster & Schwan, 1989).

         Muscle cells exhibit an anisotropic excitation, which is
    consistent with the following phenomenon. The maximum voltage across
    the membrane for spherical cells is related to the electric field
    strength by the following relationship (Foster & Schwan, 1989):

         Vm = 1.5 rE                                        (Equation 6.4)

    where r is the cell radius, and E is the electric field strength in
    extracellular fluid (Fig. 10). For ellipsoidal cells, similar
    equations have been derived by Bernhardt & Pauly (1973). Their results
    show that electric fields axial to a cell induce a voltage across the
    membrane that is proportional to the length of the cell and to the
    extracellular electric field strength. Thus, asymmetrical muscle cells
    exhibit dimension-dependent induced voltages, when exposed to electric

         Gradients in the induced surface charge can also affect molecules
    and cells in solution. Polar molecules (e.g., water, proteins) align
    themselves with the field at high electric field strengths of the
    order of 106 V/m. Also, non-spherical cells align themselves with
    the field and form "pearl chains". The larger the cell, the lower the
    field strength required for orientation and formation of pearl chains.
    For instance, for a cell of radius 1 µm, an electric field of 10 kV/m
    is required (Foster & Schwan, 1989).

         Counter-ion polarization is likely to produce a nonlinear
    dielectric response at moderate field strengths of the order of a few
    hundred V/m in tissue for large cells, but the response is slow to
    develop, and the relaxation frequency is a fraction of a hertz. There

    have been relatively few studies on the nonlinear responses of the
    counter-ion relaxation (Foster & Schwan, 1989).

    6.2.3  Induced fields at the cellular level

         Knowledge of the electric fields acting on specific parts of the
    cell due to a certain electric field in tissue is important in
    predicting cell stimulation. It is also important to evaluate the
    possibility of interaction with the genetic apparatus, when fields of
    sufficient strength are acting at the cell nucleus. A general analysis
    of these fields was performed by Schwan (1984) and Foster & Schwan
    (1989). The results of the analysis are illustrated in Fig. 11 showing
    the plasma-membrane potential, the cytoplasm field strength, and the
    nuclear membrane potential, as a function of frequency.

    FIGURE 10

         Data shown in Fig. 11 can be summarized as follows: below the
    ß-dispersion for the cells, the plasma membrane shields the interior
    of the cells; above the ß-frequencies for the plasma membrane and the

    nucleus, the induced voltage drop across both membranes falls off as
    the inverse of the frequency. The greatest potential is induced on the
    nuclear membrane at frequencies between the ß-dispersion frequencies
    for the plasma and the nuclear membranes, and this potential is
    approximately equal to the product of the external electric field and
    the nuclear radius (Foster & Schwan, 1989). Table 6 gives a summary of
    induced fields in various parts of the cell and Fig. 11 gives the
    induced membrane potentials and electric fields in various
    compartments (Schwan, 1985).
    Table 6.  Summary of the coupling properties of external fields to cellular
    membranes and compartments. fr is the beta-dispersion frequency of the plasma
    cell membrane, where fn is the beta dispersion frequency of the nucleus and
    other organelles. Approximate values of relaxation frequencies are given in
    brackets. a


                 f<fr              fr<f<fn                 f>fn
                 (approx 1 MHz)    (approx 10 MHz)


     Membranes   Polarized         Not polarized         Not polarized
     Interior    Doubly shielded   Shielded              Exposed


     Membranes   Not polarized     Partially polarized   Not polarized
     Interior    Doubly shielded   Shielded              Exposed


     Membranes   Polarized         Not polarized         Not polarized
     Interior    Not exposed       Exposed               Exposed


    a From: Schwan (1985).
    FIGURE 11

    6.2.4  Body impedance

         To determine the currents that flow when a person in an
    electromagnetic field comes into contact or close proximity with an
    isolated conducting object, it is important to consider the impedance
    of the human body. The human body impedance can be considered as a
    composite of the impedances of various parts through which the current
    is flowing. For instance, for a finger contact with an automobile and
    a current flowing to ground, the total impedance is the sum of the
    following: the contact impedance, the finger impedance, the arm
    impedance, the body (trunk plus legs) impedance and the capacitance to
    ground. All these impedances are frequency dependent. Furthermore the
    contact impedance depends on the surface area and condition (dry or
    wet) of the contact surface, and at least at low frequencies probably
    on contact voltage as documented by measurements at 60 Hz (Tenforde &
    Kaune, 1987).

         The complete body impedance can be represented by an equivalent
    circuit consisting of a number of resistive and capacitive components,
    some of them frequency dependent. Measurements of body impedance have
    been performed at 60 Hz (Tenforde & Kaune, 1987) and from 10 kHz to 3
    MHz (Gandhi et al., 1985a).

    6.3  Direct interactions - strong fields

         Well established interaction mechanisms for the direct effects of
    electric and magnetic fields can be divided into two types, each
    dependent on the field frequency. For frequencies below approximately
    100 kHz, the interactions (stimulation) with excitable tissue are of
    primary interest. Above about 100 kHz, the current density thresholds
    for stimulation and other effects due to interactions with excitable
    tissue are higher than those required to produce energy deposition
    rates of about 1 W/kg. At such rates of energy deposition in tissue,
    thermal interactions become important. In both frequency ranges, other
    forms of interactions are also observed for induced currents and
    fields below those associated with stimulation or heating.

    6.3.1  Interactions with excitable tissues

         In tissues, the induced electric fields are amplified across the
    cell membranes. At sufficiently high field strengths, these affect the
    electrical excitability of nerve and muscle cells. This inter-action
    occurs up to hundreds of kilohertz (Lacourse et al., 1985), but
    increasingly stronger fields are required above the ß-dispersion.
    Changes in the membrane potential cause changes in the permeability to
    ions, conformational changes in the embedded proteins, a number of ion
    gates open, and eventually membrane depolarization results in an
    action potential. Threshold current densities for subtle modulations
    of excitable cells, and their biological significance, are less well
    understood. There is a substantial amount of data on tissue
    stimulation, extra-systole elicitation, and ventricular fibrillation.
    These data, as summarized by Bernhardt (1985, 1986, 1988), are shown

    in Fig. 12. The ventricular fibrillation thresholds are above those
    needed for stimulation. Thresholds for the stimulation of excitable
    tissue depend not only on the current density and frequency, but also
    on the waveform. In the case of pulsed fields, they depend on pulse
    duration and other parameters (Reilly, 1988).

    FIGURE 12

    6.3.2  Thermal interactions

         As described in section 5, exposure to an electromagnetic field
    can result in a spatially nonuniform SAR in the body. The initial rate
    of temperature increase, when heat losses are neglected, is directly
    proportional to the SAR:

         dT/dt = SAR/C                                    (Equation 6.5)

    where T is the temperature, t is time, and C is the specific heat
    capacity of tissue.

         At the molecular level, the phenomena involved in a conversion of
    RF energy into thermal energy are the relaxation processes described
    earlier. Deposition of RF energy in the body may not necessarily lead
    to a proportional increase in its temperature, because of

    thermoregulatory responses. Various mathematical models for human
    thermoregulation have been applied to evaluate thermal interactions of
    RF energy (Emery et al., 1976; Spiegel et al., 1980; Way et al., 1981;
    Spiegel, 1982).

         The rapid rate at which heating can occur, and a uniquely
    non-uniform spatial pattern of energy deposition are important and
    unique to thermal interactions of electromagnetic energy. The rate of
    initial heating appears to be very important for pulsed fields. These
    two features make biological responses due to electromagnetic thermal
    loading unlike those due to other thermal agents. Thermal interactions
    are not necessarily accompanied by significant local or whole-body
    temperature increases.

         In some thermal interactions, biological responses depend on the
    temperature-time profile, where such a profile is achieved by RF
    heating. In some other biological responses, the rate of temperature
    change is the critical parameter while the total temperature rise may
    be very small. Here again, RF energy (pulsed) can be very effective.

         One of the most prominent, thermally-induced effects, where the
    temperature increases are very small, is the microwave hearing effect
    (Guy et al., 1975a; Lin, 1978). Exposure to one pulse of
    electromagnetic energy results in the perception of a click, and
    exposure to repeated pulses in a buzzing or hissing sound. The energy
    threshold for human beings is very low (16 mJ/kg) and the resulting
    temperature increase is estimated to be only about 5 × 10-6 °C (Guy et
    al., 1975a). The simplified mechanism of interaction is as follows:
    absorption of electromagnetic energy causes a rapid temperature
    increase, which, in turn, produces thermal expansion pressure
    initiating an acoustic wave that is detected by cochlea (Guy et al.,
    1975a; Lin, 1978).

    6.4  Direct interactions - weak fields

    6.4.1  General

         There is a growing body of data from studies indicating that
    extremely low frequency fields (ELF) (Tenforde & Kaune, 1987; WHO,
    1987) and RF amplitude modulated at ELF (Adey, 1981, 1988) interact
    with various biological systems at energy levels significantly lower
    than those needed for the stimulation of excitable tissues or for
    thermal interactions. The mechanisms of these interactions are not
    understood. Several mechanisms have been hypothesized, but these need
    further development and testing, and possibly still other
    considerations need to be taken into account to unravel the rather
    complex mechanisms behind the observed interactions.

         Pericellular currents induced by electromagnetic fields produce
    electrochemical alterations in components of the cell membrane
    surface. These changes are hypothesized to cause signals across the
    cell membrane and produce intracellular alterations (Adey, 1981, 1988;
    Tenforde & Kaune, 1987).

         Weak field interactions are sometimes criticized and dismissed on
    the grounds that the field intensities induced in the biological
    systems that produce them are lower than those associated with thermal
    noise. A recent analysis of noise and electric fields induced on a
    simple model of cell membranes by Weaver & Astumian (1990) indicates
    that induced fields of the order of 0.1-0.01 V/m are theoretically
    detectable above the broad band noise level. Much smaller fields, of
    the order of 10-4 V/m, are estimated to be detectable if only a narrow
    frequency band response of the membrane or signal averaging are
    assumed. The assumption of the narrow frequency band response is
    consistent with some experimental data on biological responses. The
    signal averaging is also supported by experimental work on
    enzyme-catalysed reactions.

         A description of some hypothetical interaction mechanisms for ELF
    fields, which possibly also applies to the lower frequencies of
    concern here (probably below 1000 Hz) and to RF fields modulated at
    ELF can be found in Tenforde & Kaune (1987) and WHO (1987).

         The hypothesized scheme of transductive coupling between induced
    electric currents in the extracellular medium and the intracellular
    events occurring in living cells is illustrated schematically in Fig.

         An alternative model involving magnetic-field induced changes in
    specific molecular species associated with the plasma membrane has
    been proposed by Blackman et al. (1988). In this model, as in others,
    an amplification step must be involved. Conditions for the cellular
    response may involve the induction of a weak electric field in the
    extracellular fluid, a molecular change in the membranes to "trigger"
    cooperative events within the cell membrane. The basic premise is that
    the cell membrane exists in a metastable, non-equilibrium state that
    can be significantly perturbed by weak stimuli. The stored energy is
    released by this process as metabolic chemical energy through the
    activation of ion pumps or enzymatic reactions within the membrane
    (Fröhlich, 1968, 1977; Adey, 1981, 1983). This general model may also
    be applicable to the results observed at 41 GHz (Grundler & Keilmann
    1983, 1989). In this case, yeast growth rates have been affected at
    SARs as low as 0.2 W/kg.

    FIGURE 13

    6.4.2  Microelectrophoretic motion

         Recent experimental evidence has given some support to the
    concept that the interactions of ELF fields with living cells occur at
    specific loci on the cell membrane. A model of membrane interactions
    in which a microelectrophoretic motion induced in the cell membrane by
    weak ELF electric fields influences the average distance between
    charged ligands and the cell-surface receptors to which they are bound
    was proposed by Chiabrera et al. (1984). In this theoretical model,
    the effect of the imposed electric field is to decrease the mean
    lifetime of the ligand-receptor complexes on the membrane surface. The
    authors proposed that this effect could influence various biological
    phenomena, such as the activation of lymphocytes by antigens and
    various lectins, and the gating mechanisms that control the membrane
    transport of various types of cations, such as calcium.

    6.4.3  Ion-resonance conditions

         Some experimental evidence suggests that effects occur at
    specific frequencies for ELF fields and static magnetic fields with
    strengths comparable to that of the geomagnetic field. Theoretically
    frequencies up to 1 kHz or higher, depending on the ion involved, can
    be effective under these conditions. It is proposed that the frequency
    of interaction is related to the ion characteristics and the static
    magnetic flux density according to the following relationship:

         f = kBq/m                                        (Equation 6.6)

    where: f is the resonant frequency, k is a constant (integer), q is
    the ion charge, m is the ion mass, and B is the constant magnetic flux
    density. Some of the earlier models, such as the cyclotron resonance
    (Liboff, 1985; McLeod & Liboff, 1986), suffered from serious
    limitations (Halle 1988). Other models appear worthy of closer
    scrutiny (Lednev, 1990; Male & Edwards, 1990).

         Overall, the experimental data for q/m effects on ion binding to
    the membrane or enzyme surfaces and on cation transport through cell
    membrane pores are intriguing, but there is a clear need for
    refinements in the theoretical description of this phenomenon and to
    substantiate the experimental results. Whether, and how, any of the
    resonance models (Chiabrera et al., 1984; Liboff, 1985; McLeod &
    Liboff, 1986; Lednev, 1990; Male & Edmonds, 1990) can be applied to RF
    fields amplitude modulated at ELF has not yet been considered or

    6.4.4  Calcium ion exchange

         An observed change in the EEG pattern of cats exposed to 147 MHz
    fields amplitude modulated at ELF, prompted further investigation with
    an isolated chick-brain tissue preparation, to determine whether the
    presence of the peripheral nervous system was required to elicit a
    change in the central nervous system. Statistically significant

    increases in labelled calcium ion efflux were observed in isolated
    tissues exposed to 10-20 W/m2, 147 MHz fields amplitude-modulated
    at frequencies from 6-20 Hz, but levels remained the same as control
    levels at modulation frequencies of less than 6 Hz or greater than 20
    Hz. No effect on calcium ion efflux was observed from exposure to
    unmodulated RF fields (Bawin et al., 1975). The SAR was less than
    0.004 W/kg. This field-induced effect is of interest because it occurs
    at SARs too low to implicate heating, and because calcium ions play a
    prominent role in the transductive coupling of many cell
    membrane-mediated responses. Thus, this  in vitro result provides a
    means of interrogating the function and processes occurring at the
    cell membrane and of identifying possible subtle mechanisms of
    interaction of RF fields.

         Using 50, 147, and 450 MHz carrier waves, this work has been
    replicated and extended with one or more modulation frequency or power
    density windows being reported (Blackman et al., 1979, 1980a,b, 1985,
    1989; Sheppard et al., 1979). A power density window centred on 8.3
    W/m2 (0.00l4 W/kg) has been reported. Six power density windows were
    observed for 16 Hz modulated 50 MHz, with five of the windows
    separated by a geometric relationship that may reveal a characteristic
    of the underlying mechanism (Blackman 1980a,b, 1985, 1989).

         Lee et al. (1987) reported enhanced release of calcium ions from
    chick-brain tissue exposed in two power density regions of 147 MHz
    fields, modulated at 16 Hz, only when specific temperature conditions
    were instituted in the preparation of the tissue. The temperature
    conditions during sample preparation were also shown to affect the
    relative direction of the efflux and to control the sensitivity of the
    brain tissue samples to ELF signals (Blackman et al., 1991). The
    release of calcium ions from a rat synaptosomal preparation was also
    reported to be affected by 450 MHz, amplitude modulated at 16 Hz, at
    10 W/m2 (Lin-Liu & Adey, 1982).

         Exposures at 315 Hz and at 405 Hz, at intensities of 15 V/m and
    60 nT, were reported to enhance calcium efflux, whereas intensities
    between, above, and immediately below these values did not (Blackman
    et al., 1988). The 315 Hz exposure was dependent on the perpendicular
    flux density and orientation of the DC magnetic field of the earth
    (Blackman et al., 1990). Additional work at lower frequencies suggests
    that the DC magnetic field may have a direct influence on which
    frequencies are effective (Blackman et al., 1985).

         Some investigators have reported null results with brain tissue
    preparations. Shelton & Merritt (1981) did not observe any changes in
    the release of calcium ions from an  in vitro rat brain tissue
    preparation exposed to 1 GHz, pulse modulated at 16 or 32 Hz, at 5,
    l0, 20, or 150 W/m2. Similarly, no effects were observed with rat
    tissue labelled  in vivo and exposed  in vitro or  in vivo to 1 GHz
    or 2.06 GHz, pulse modulated at several ELF and power density
    combinations (Merritt et al., 1982). Null effects were also reported
    by Albert et al. (1987) using chick brain tissue exposed to a few

    power densities of 147 MHz, amplitude modulated at 16 Hz, under anoxic
    and under modified media conditions designed to supply more oxygen to
    the tissue.

         In none of these null-effect experiments did the authors
    reproduce the exposure conditions used by Bawin or Blackman,
    particularly the medium composition, power density, sinusoidal
    modulation, or number of samples per experiment.

         Increases in calcium ion efflux have been reported in two other
    biological preparations. Isolated frog hearts showed enhanced calcium
    ion efflux at SARs of 0.00015 and 0.0003 W/kg when exposed to 240 MHz,
    amplitude modulated at 16 Hz (Schwartz et al., 1990). Human
    neuroblastoma cells exposed in culture to amplitude modulated 147 and
    915 MHz at SARs of 0.005 and 0.05 W/kg displayed maximal calcium ion
    efflux at modulation frequencies around 16 and 60 Hz (Dutta et al.,
    1984, 1989). The latter experiment was conducted under natural,
    cell-culture growth conditions and suggests that anoxia is not an
    absolute requirement for sensitivity of nervous system derived cells
    to RF fields modulated at ELF frequencies.

         Overall, the exposure-induced release of calcium ions from
    tissues should be viewed as contributing to the characterization of
    exposure conditions required to elicit a response, and, thus, to the
    development of an underlying mechanism of action. The efflux assay
    system may ultimately be useful in defining the various aspects of the
    physical and biological exposure conditions that sensitize and affect
    membrane responses to electromagnetic field exposure. It should be
    emphasized that insufficient information is available to define the
    weak field interactions. Furthermore, the reported effects cannot be
    characterized as a potential adverse effect on health, since little or
    no confirmed information has been gathered that suggests this effect
    occurs in animals or humans.

    6.5  Indirect interactions

         Electromagnetic fields, at frequencies below about 100 MHz,
    interact with biological bodies through electrical charges induced on
    ungrounded or poorly grounded metallic objects, such as cars, trucks,
    cranes, wires, and fences.

         Two types of interaction may occur:

    (a) a spark discharge before a person touches the object;

    (b) the passage of current to ground through a person coming into
    contact with such objects; the magnitude of these currents depends on
    the total charge on the object. This charge, in turn, depends on the
    frequency and electric field strength, the object geometry and
    capacitance, and the person's impedance to ground.

         Above a certain threshold, the current to ground is perceived by
    the person as a tingling or prickling sensation in the finger or hand
    touching the charged object, for frequencies below about 100 kHz, and
    as heat at higher frequencies. A severe shock can be experienced at
    levels much higher than this threshold. The threshold currents depend
    on frequency, surface of contact area, and the individual. The
    thresholds for effects (perception, shock, etc.) are generally higher
    for men than for women and children, though there are also individual

         All effects due to induced charges on objects are defined below
    in order of increasing severity:

     Perception - The person is just able to detect the stimulus. There
    is a difference in the current perception threshold for touch and grip

     Annoyance - The person would consider the sensation to be a mild
    irritant, if it were to occur repeatedly.

     Startle - If a person receives one exposure, it is sufficient to
    motivate the person to avoid situations that would lead to a similar

         The remaining reactions apply only to contact of alternating
    currents at frequencies below 100 kHz.

     Let-go - A person cannot let go of a gripped conductor as long as
    the stimulus persists, because of uncontrollable muscle contraction.
    If a person is exposed to prolonged currents, somewhat above the
    let-go level, through the chest, breathing becomes difficult and,
    eventually, the person may become exhausted and die.

     Respiratory tetanus - A person is unable to breathe as long as the
    stimulus is applied, owing to the contraction of the muscle
    responsible for breathing.

     Fibrillation - Uncoordinated asynchronous heart contractions produce
    no blood pumping action.

         Threshold currents for their occurrence are given in Table 7.
    Fig. 14 and 15 show threshold currents for perception and let-go, for
    different percentages of the population at lower frequencies.
    Thresholds for perception and pain (well below the let-go) were
    evaluated for nearly 200 men and 200 women and also estimated for
    10-year-old children (Chatterjee et al., 1986). The thresholds are
    lower for finger contact than for grasping contact. Fig. 16 and 17
    show perception and pain for finger contact (Chatterjee et al., 1986).
    The stimuli in both cases are tingling/pricking at frequencies below
    about 100 kHz and heat/warmth at higher frequencies.

         Currents flowing from an object to ground through a person who
    touches the object can be reduced if shoes are worn (Chatterjee et
    al., 1986). Electric charge induced on various objects and, therefore,
    contact currents for people, can be calculated for a known electric
    field strength. Results of such calculations are shown in Fig. 18 and
    19 for finger contact for males, females, and children, respectively.

         RF burns can occur when current enters through a small
    cross-section of the body, such as a finger, when the finger contacts
    an electrically charged object. Another interaction that may occur at
    lower frequencies is a transient discharge, which occurs between a
    person and a charged object either by direct contact or through an air
    gap (Tenforde & Kaune, 1987).

    Table 7.  Threshold currents (mA) for various effects at frequencies ranging from 50 Hz to 3 MHz
    (experimental data for 50% of men, women, and children)
    Effect                                Subject Threshold current (mA) at various frequencies
                                          50/60   300     1000    10      30     100    300    1      3
                                          Hz      Hz      Hz      kHz     kHz    kHz    kHz    MHz    MHz

    Touch perception            men       0.36    (0.47)  (0.79)  4       15     40     40     40     40
    (finger contact)            women     0.24    (0.31)  (0.53)  3.2     12     35     35     35     35
                                children  0.18    0.24    0.40    2.5     8      25     25     25     25

    Grip perception             men       1.1     1.3     2.2     15      50     300    300    300    300
                                women     0.7     0.9     1.5     10      35     200    200    200    200
                                children  0.55    0.65    1.1      9      30     150    150    150    150

    Shock, not painful          men       1.8     (2.3)   (3.2)   17(10)  (25)   (25)
    (grasping contact)          women     1.2      1.5     2.1    11      16.7   16.7
                                children  0.9     1.1     1.6     8.5     12.5   12.5

    Pain                        men      (1.8)    (2.4)   (3.3)   10      30     55     50     50     50
    (finger contact)            women     1.2     1.6     2.2     6.5    23     47     45     40     40
                                children  0.9     1.2     1.6     6      18     33     30     28     28

    Shock, painful; muscle      men       9      (11.7)  (16.2)   55    (126)  (126)
    control (let-go threshold   women     6       7.8     10.8    37      84     84
    for 0.5% of population)     children  4.5     5.9     8.1     27      63     63

    Burn (finger contact)       men                                                          200    200

    Painful shock,              men       16      18      24      75(88) (224)  (224)
    let-go threshold            women     10.5    12      16      50      150    150
                                children  8       9       12      37      112    112

    Table 7 (contd).
    Effect                                Subject Threshold current (mA) at various frequencies
                                          50/60   300     1000    10      30     100    300    1      3
                                          Hz      Hz      Hz      kHz     kHz    kHz    kHz    MHz    MHz

    Severe shock,               men       23      (30)    (41)    94(126) (320)  (320)
    breathing difficulty        women     15       20      27     63       214    214
                                children  12       15      20.5   47       160    160
     a From Dalziel 1954a,b; Deno, 1974; Guy & Chou, 1982; Guy, 1985; Chatterjee et el., 1986). Data in
      brackets were calculated by using the frequency factors for perception thresholds and for pain end
      let-go thresholds, given in IEC Publication 479. Date in italics were calculated by assuming
      thresholds for women two-thirds of that of men and thresholds for children one-half of that for men
      (IEEE, 1978; Guy, 1985).

    FIGURE 14

    FIGURE 15

    FIGURE 16

    FIGURE 17

    FIGURE 18

    FIGURE 19


    7.1  Introduction

         Numerous reviews and monographs dealing with the biological
    effects of electromagnetic fields have been published including: WHO
    (1981); Grandolfo et al. (1983); USEPA (1984); Akoev (1986); NCRP
    (1986); Polk & Postow (1988); Francescretti et al. (1989); WHO (1989);
    Adey (1989, 1990); Saunders et al. (1991). The purpose of this section
    is to provide an overview of the biological effects that are relevant
    to considerations of the health and safety of exposed people.

         The available scientific data are unevenly distributed within the
    very broad range of frequencies that this publication covers.
    Considerable numbers of  in vitro and experimental animal studies
    have been performed in the mega- and gigahertz range. Relatively few
    scientific reports of effects in the kilohertz range can be found and
    data are particularly sparse for the range between 300 Hz and about 10

    7.2  Macromolecules and cell systems

         Studies of isolated  (in vitro) components of a biological
    system offer possible insights into the mechanisms of RF action.  In
     vitro systems are simple, allowing biological variables to be
    controlled and subtle effects to be identified without being masked by
    the homeostatic responses of the whole organism.

         In addition, the precise control of the temperature of  in vitro
    preparations during exposure should make it possible for thermal and
    athermal interactions to be clearly distinguished, though thermal
    gradients cannot be entirely eliminated from such systems. Effects to
    be tested  in vivo (whole animal) can be identified from these

         From their review of RF effects on macromolecular and cellular
    systems, NCRP (1986) concluded that RF fields, at least continuous
    waves at frequencies above 5 MHz, have little, if any, effect on
    biopolymers, cell organelles, and microorganisms, other than effects
    associated with elevated temperatures. Likewise, they concluded that
    the effects of RF fields on the genetic material of cells have not
    been convincingly demonstrated, unless related to elevations of

         More recently, Cleary (1989) noted that there was strong evidence
    from a number of  in vitro experiments for the involvement of
    non-thermal RF interactions, as well as heating. He concluded that
    effects that may be attributed to RF-specific interactions include
    altered potassium and sodium ion transport across red blood cell
    membranes, changes in membrane calcium ion fluxes, decreased
    non-cAMP-dependent protein kinase activity, inhibition of T-lymphocyte
    cytotoxicity, biphasic effects on lymphocyte proliferation, changes in

    brain cell energy metabolism, altered firing rates and resting
    potentials of neurons, and effects on cell transformation rate. Many
    of these responses are discussed below.

    7.2.1  Effects on cell membranes

         The cell membrane has been suggested as a likely site for the
    interaction of RF fields (Adey, 1981; Cleary, 1987). Several studies
    (summarized in Table 8) have focused on effects on membrane
    permeability and integrity.

         Baranski et al (1971) reported increased cation permeability and
    decreased osmotic resistance in rabbit erythrocytes exposed to 3 GHz
    for up to 3 h at power densities as low as 10 W/m2; higher power
    densities produced effects of greater magnitude. Using thermal
    controls heated in a waterbath to the same temperature as exposed
    cells, Hamrick & Zinkl (1975) were unable to replicate these effects.
    Liu et al. (1979) attributed observed increases in cation permeability
    of erythrocytes to heating.

         More recently however, it has been reported in several studies
    that exposure to RF fields caused specific increases in the cation
    permeability of the cell membrane. The results of these studies have
    been consistent with a sensitivity of the cell membrane at particular
    temperature-dependent energetic states; in some studies, effects have
    been reported only at apparent membrane phase transition temperatures
    (between 8 °C and 36 °C). Membranes loaded with cholesterol to
    eliminate the phase transition were unaffected by microwaves (Liburdy
    & Vanek, 1987). RF-induced changes in the activity of the
    membrane-bound enzyme Na/K ATPase have been suggested as a possible
    mechanism (Allis & Sinha-Robinson, 1987), but similar permeability
    changes have been reported in membranes with no associated protein
    (Liburdy & Magin, 1985).
        Table 8.  Membrane studies (in vitro)
    Exposure condition         Effect                           Reference
    3 GHz (CW) at              Increased K+ efflux              Baranski et al.
    10-100 W/m2, for up        and decreased osmotic            (1974)
    to 3 h                     resistance in rabbit
                               erythrocytes compared
                               with room temperature
                               controls (increased
                               effect at higher
                               power densities)

    2.45 or 3 GHz (CW) at      No effects on K+ efflux          Hamrick & Zinkl
    40-750 W/m2                or osmotic resistance            (1975)
    (3-57 W/kg), for up        in rabbit erythrocytes to 3 h
                               compared with thermal

    Table 8 (continued)
    Exposure condition         Effect                           Reference
    2.45, 3 and 3.95 GHz       Increased K+ ion and             Liu et al. (1979)
    (CW) at up to              haemoglobin release
    200 W/kg (26 - 44 °C)      and osmotic lysis by
                               rabbit, canine, and
                               human erythrocytes;
                               similar effects with
                               conventional heating

    2.45 GHz, at up to         Increased passive                Olcerst et al.
    390 W/kg, for 1 h          efflux of Na22                   (1980)
                               and Rb86 from rabbit
                               erythrocytes compared
                               with thermal controls,
                               only at the transition
                               temperatures for efflux
                               (8-13 °C, 22.5 °C and 36 °C)

    8.42 GHz, CW or pulse      Increased K+ efflux              Cleary et al.
    modulated, for 2 h, at     from rabbit erythrocytes         (1982)
    up to 90 W/kg              relative to thermal (23-28 °C)
                               controls at around 24 °C

    2.45 GHz (CW) at           Increased Na+ efflux             Fisher et al.
    2-3 W/kg for up to         from human erythrocytes          (1982)
    2 h (7-35 °C)              compared with thermal
                               controls at 22-25 °C

    2.45 GHz (CW) at           Increased passive Na+            Liburdy & Penn (1984)
    60 W/kg, for 30 min        transport and protein
    (15-24 °C)                 shedding from rabbit
                               erythrocytes compared with
                               thermal controls, only at
                               membrane phase transition
                               temperatures of 17.7-19.5 °C

    2.45 GHz (CW) up to        Increased Na+                    Liburdy & Vanek
    100 W/kg, for up to        permeability of rabbit           (1987)
    60 min (13-43 °C)          erythrocytes compared
                               with thermal controls, only
                               at 17.7-19.5 °C; response
                               abolished in cholesterol-
                               loaded membranes with no
                               apparent phase transition

    Table 8 (continued)
    Exposure condition         Effect                           Reference
    1.0 GHz (CW) at up to      No effect on membrane            Allis & Sinha (1981)
    15 W/kg, for up to         fluidity of human 5 h (15-40 °C)
                               erythrocytes, as measured by
                               lateral diffusion of
                               lipophilic dye

    2.45 GHz (CW) 6 W/kg,      Inhibition of Na/K               Allis & Sinha-Robinson
    for 20 min (23-27 °C)      ATPase activity in human         (1987)
                               erythrocyte ghosts, only at
                               25 °C
        7.2.2  Effects on haematopoietic tissue

         A summary of  in vitro studies conducted to determine
    haematopoietic and immunological end points is shown in Table 9. In
    general, these studies show that RF exposure, under
    temperature-controlled conditions, at SARs up to 28 W/kg have no
    effects on cell survival or mitogen-stimulated lymphoblastoid

         In some studies, effects are reported at levels too low to
    involve significant heating, or at certain RF modulation frequencies.
    In one unreplicated study, depressed phagocytosis was reported in
    RF-exposed mouse macrophages. A slight rise in temperature in the
    culture medium would have tended to increase activity. T-lymphocyte
    cytotoxicity was depressed during low-level exposure to 450 MHz RF
    modulated at frequencies of 16 and 60 Hz, but not at other
    frequencies. In other studies, a lack of effects of sinusoidal or
    pulse-modulated RF fields on B-lymphocyte capping in mouse spleen
    cells, viability, and DNA synthesis in human mononuclear lymphocytes
    has been reported.
        Table 9.  Haematopoietic and immunological studies (in vitro)
    Exposure conditions          Effect on exposed group        Reference
    Colony-forming ability

    2.45 GHz (CW) up to          Dose-related, reduced          Lin et al.
    2 kW/kg, for 15 min          colony-forming ability of      (1979)
                                 mouse bone marrow
                                 cells - temperature kept
                                 constant; direct effect of RF
                                 on haematopoietic precursor

    Table 9 (continued)
    Exposure conditions          Effect on exposed group        Reference
    2.45 GHz (CW),               cells; spleen colonies in      Rotkovska et al.
    2.4 kW/m2, for 5 min;        radiation-depleted             (1987)
    rise in temperature          recipients rose when tempera-
    of mouse bone marrow         ture rose to between 33 and
    suspension was from          40 °C, but fell above 41 °C
    20 to 45 °C

    Mitogen responses

    2.45 GHz (CW), 19 W/kg,      No changes in cell viability   Smialowicz
    for 1-4 h, temperature       or blastogenic responses       (1976)
    controlled at 37 °C          of mouse spleen lymphocytes
                                 to several mitogens

    2.45 GHz (CW), up to         No effects on spontaneous      Hamrick &
    28 W/kg for up to 44 h,      or mitogen-stimulated          Fox (1977)
    constant temperature. of     transformation of rat
    37 °C                        lymphocytes

    2.45 GHz (CW) up to          No effects on human            Roberts et al.
    4 W/kg, temperature rise     leukocytes viability or on     (1983)
    of 0.9 °C                    unstimulated or
                                 lymphoblastoid transformation

    Modulated RF

    450 MHz, 15 W/m2,            Suppression of mouse T-        Lyle et al.
    sinusoidal-modulated         lymphocyte cytotoxicity,       (1983)
    at 3, 16, 40, 60, 80,        peak at 60 Hz (20%)
    100 Hz

    147 MHz, pulse-              No change in mouse spleen      Sultan et al.
    modulated at 9, 16,          B-lymphocyte capping           (1983b)
    60 Hz, 1.1-480 W/m2          as temperature maintained

    2.45 GHz, pulse-             No effects on human            Roberts et al.
    modulated at 16 or           lymphocyte viability,          (1984)
    60 Hz, up to 4 W/kg          unstimulated or
                                 mitogen-stimulated DNA
                                 synthesis, or total protein

    Table 9 (continued)
    Exposure conditions          Effect on exposed group        Reference
    Pulsed 9 GHz (1000 pps)      Decrease in no. of             Bottreau et al.
    200 W/m2 amplitude-          plaque-forming cells           (1987)
    modulated at 16 MHz          and cytotoxicity of
    (100% mod.) and 16 Hz        NK cells in mice
    (5% mod.) plus 0.8 Hz
    magnetic field 60 mT, 12 h
    per day, for 5 days


    2.45 GHz (CW), 500           Depression of phagocytosis     Mayers &
    W/m2, for 30 min,            in peritoneal mouse            Habershaw
    temperature rise of 2.5 °C   macrophages                    (1973)
    but below optimum
    temperature for phagocytic

    2.45 GHz (CW), for 30 min,   Ability of normal mouse B-     Sultan et al.
    up to 1 kW/m2 (SAR           lymphocytes to form a "cap"    (1983a)
    up to 45 W/kg)               on the plasma membrane of
                                 antigen-antibody complex
                                 reduces with increasing
                                 temperature; if temperature
                                 kept constant, no difference
                                 between exposed and control
        7.2.3  Isolated cerebral tissue, peripheral nerve tissue, and heart

         Studies carried out on calcium ion exchange in chick cerebral
    tissue preparations and other tissues exposed to RF fields, amplitude
    modulated at ELF frequencies, are described in section 6 on
    interaction mechanisms.
        Table 10.  Peripheral nervous tissue studies
    Exposure conditions        Effect on exposed group          Reference
    2.45 GHz (CW or            No effect on compound            Chou & Guy
    pulsed), 1 kW/kg, for      action potential in              (1973);
    several minutes,           functioning isolated frog        Courtney et al.
    temperature controlled     and cat nerves or                (1975)
                               peripheral autonomic
                               ganglia of rabbits

    Table 10 (continued)
    Exposure conditions        Effect on exposed group          Reference
    1.5 or 2.45 GHz (CW),      Reversible changes in            Wachtel et al.
    few minutes above          firing pattern of                (1975)
    threshold of approx.       pacemaker neurons of
    5 W/kg                     Aplysia

    2.45 GHz (CW or            Prolongation of refractory       McRee & Wachtel
    pulsed), temperature       period of isolated frog          (1980, 1982)
    controlled above a         sciatic nerves
    threshold of 5-10 W/kg,
    for 30 min
             Studies conducted on peripheral nerve tissue are summarized in
    Table 10. Most effects of RF exposure on the properties of isolated
    nerve preparations can be ascribed to heating. For example, the
    changes seen in the firing pattern of pacemaker neurons in Aplysia,
    exposed at 5 W/kg or above (Wachtel et al., 1975), were considered to
    be consistent with heating (Seamen, 1977). However, in two studies,
    changes were reported in the properties of frog nerves exposed above
    5-10 W/kg, under constant temperature conditions. These changes were
    not induced by exposure to infrared radiation, suggesting an athermal
    response. The authors noted, however, that, even under
    temperature-controlled conditions, thermal gradients were difficult to

         Several studies (reviewed by Liddle & Blackman (1984) and NCRP
    (1986) have been performed on isolated heart preparations. Decreases
    in heart rate (bradycardia) have been reported in isolated turtle,
    frog, and rat heart preparations exposed to RF at intensities as low
    as 15 W/m2 (NCRP, 1986). However, Clapman & Cain (1975) indicated
    that at least some of the effects observed with these preparations may
    have been caused by currents induced in electrodes in contact with the
    myocardia. Some support for this comes from the work of Yee et al.
    (1984), though a later study (Yee et al., 1988) also implicated the
    low temperatures and oxygen levels used in these experiments.

    7.2.4  Mutagenic effects

         Numerous tests have been carried out to examine the potential
    mutagenic action of RF field exposure. In general, no changes in
    mutation rate have been observed, except in cases where substantial
    temperature increases may also have occurred (USEPA, 1984; NCRP 1986).

         Studies of the chromosomal effects resulting from RF exposure of
    somatic cells are summarized in Table 11. Most well-conducted studies
    report a lack of effect on chromosome aberration frequencies or sister
    chromatid exchange rates, even when RF exposure produces mild
    hyperthermic conditions. Increased aberration frequencies were

    reported in one isolated, long-term study of rat kangaroo cells
    exposed for 50 passages (over 320 days) to 2.45 GHz at 15 W/kg.
    However, these results may have been confounded by temperature and
    senescence (aging) in the cell populations.
        Table 11.  Mutagenic effects in somatic cells
    Exposure conditions        Effect on exposed group          Reference
    20 kHz sawtooth magnetic   Non-significant (P=0.06)         Nordessen et
    field, 16 µT pk-pk,        increase in chromosome           al. (1989)
    for 72 h                   aberration frequency
                               in human amniotic cells,
                               DNA synthesis reduced

    2.45 GHz (CW), up to 200   Human blood lymphocytes          Lloyd et al.
    W/kg, for 20 min           showed no increase in            (1984, 1986)
    temperature rose from      unstable chromosome or
    4 °C or 23 °C to 36 °C     sister chromatid exchanges
    during exposure, second
    experiment temperature
    rose from 37 °C to 40 °C.

    2.45 GHz (CW) 15 W/kg,     Increased chromosome             Yee (1982)
    for up to 320 days         aberrations and polyploidy
    (50 passages)              and decreased growth rate
                               in rat kangaroo RH5 and
                               RH16 cells
        7.2.5  Cancer-related studies

         Experiments on cell systems exposed to RF that have end points
    related to cancer are shown in Table 12. Cellular transformation
    studies are important assays of potential carcinogenicity, in which
    the potential is examined of a suspect carcinogen to abolish contact
    inhibition, an important regulator of cell division. They are,
    however, very susceptible to factors such as variation in growth
    media. Balcer-Kubiczek & Harrison (1985, 1989) reported enhanced
    transformation rates in mouse fibroblasts after RF exposure for 24 h
    at 4.4 W/kg (alone or combined with X-radiation), followed by
    treatment with the chemical promotor TPA. These experiments are not
    conclusive; there were inconsistencies between the studies in plating
    efficiency and in the response to RF combined with X-radiation. The
    authors also noted that the transformation rates were susceptible to
    temperature changes. However, these studies are important and should
    be replicated.

        Table 12.  Cancer-related studies (in vitro)
    Exposure conditions           Effect on exposed group               Reference
    2.45 GHz (CW), 4.4 W/kg       RF reduced plating efficiency of      Balcer -
    for 24 h, temperature         mouse embryo fibroblasts to half,     Kubiczek &
    constant at 37 °C             but no effect on transformation       Harrison
                                  rate was induced by treatment with    (1985)
                                  benzopyrene or X-rays alone. Exposure
                                  of cells to RF and X-rays, then
                                  tumour promotor (phorbal ester TPA),
                                  caused a several-fold increase in
                                  transformation frequency compared
                                  with cells exposed to X-rays and
                                  treated with TPA

    2.45 GHz (CW), 4.4 W/kg       Increased mouse embryo fibroblast     Balcer-
    for 24 h, temperature         transformation rate per surviving     Kubiczek &
    constant at 37 °C             cell, in cells exposed to RF with,    Harrison
                                  or without X-rays, and then treated   (1989)
                                  with TPA. In contrast to 1985
                                  study, no effect on cell plating
                                  efficiency or difference in
                                  transformation response to
                                  combined X-ray, RF and TPA compared
                                  with X-ray & TPA alone

    450 MHz, pulse-               No effect on human lymphocyte         Byus et al.
    modulated at 3-100 Hz,        cAMP-dependent protein kinase         (1984)
    10 W/m2, for up to            activity. cAMP-independent
    60 min                        kinase activity fell to less than
                                  50% of control levels after
                                  15-30 min exposure, then returned
                                  to control levels at 45-60 min.
                                  Reduced enzyme activity occurred
                                  at 16, 40, 60 Hz modulation, not
                                  at 3, 6, 80 or 100 Hz, or
                                  unmodulated carrier

    450 MHz amplitude-            Increased ornithine decarboxylase     Byus et al.
    modulated, 10 W/m2, for       (ODC) at 10, 16, 20 Hz modulation     (1988)
    1 h                           by Reuber H35 hepatoma cells, CHO
                                  cells, and human melanoma cells;
                                  RF (modulated at 16 Hz) exposure of
                                  CHO and hepatoma cells potentiated a
                                  TPA induced increase in ODC, but not
                                  in DNA synthesis in TPA-treated cells
             Protein kinases and ornithine decarboxylase are enzymes important
    in normal and neoplastic cell growth and division. Byus et al. (1984)
    reported an effect of exposure to amplitude-modulated RF on

    cAMP-independent kinase, but no effect on cAMP-dependent kinase,
    normally implicated in cellular responses leading to proliferation.
    Amplitude-modulated RF exposure was also found to enhance ornithine
    decarboxylase activity in several different cell lines (Byus et al.,
    1988), though only by a small amount compared with chemical promotors.
    No effect was seen on DNA synthesis (assayed 14 h after exposure),
    which is a subsequent step in the promotional sequence. It is not
    possible to draw any conclusions with respect to cancer from these

    7.2.6  Summary and conclusions: in vitro studies

         The results of  in vitro studies, conducted so far, suggest that
    the cell membrane is a site of interaction of RF fields and that
    alterations in membrane permeability can result, as well as changes in
    membrane cation fluxes, changes in the activity of certain enzymes,
    and suppression of some immune responses. RF fields are not mutagenic;
    an effect on cellular proliferation, particularly in relation to
    tumour promotion, by interactions other than tisue heating, has not
    been established. Evidence is presented that some effects may result
    from athermal interactions, particularly in response to
    amplitude-modulated fields. However, in many other cases, there is
    great difficulty in eliminating thermal gradients within exposure
    samples exposed at high levels.

    7.3  Animal studies

         While  in vitro studies are important in determining the
    mechanisms of interaction and identifying appropriate biological
    end-points and exposure conditions to be tested in whole animals, they
    cannot serve as a basis for health risk assessment in humans. Whole
    animal studies are necessary in order to evaluate the integrated
    response of various systems of the body that serve to maintain
    homeostasis, the condition necessary for the proper functioning of the
    body. Three bodily systems can be identified as of particular
    importance in this respect: the nervous, endocrine, and immune
    systems. The coordinated interdependent interaction of these systems
    in response to chemical and physical stimuli provides a great capacity
    for adaptation and compensation in response to changes in
    environmental or internal bodily conditions.

         Local hyperthermia, caused by exposure to strong RF fields, and
    damage to morphological structures of the above systems, can lead, in
    turn, to physiological deregulation. Exposure to weaker RF fields with
    minimal thermal loading can result in adaptive and compensatory shifts
    of these homeostatic mechanisms.

         Another important end-point in the consideration of human health
    and safety concerns the possible effects on reproduction, and on
    pre-and post-natal development. In this context, the induction of
    mutagenic changes in germ cells by RF exposure might result in

    hereditary effects in offspring. In somatic cells, such changes could
    be associated with the induction of cancers.

         The effects of exposure to RF fields on these various biological
    end-points is described in the following sections. It is important to
    note that, as far as thermal responses are concerned, experimental
    interpretation can be confounded by differences in ambient
    temperature, relative humidity, and air flow. In addition, the thermal
    load induced by a given SAR is different in different animals,
    generally increasing with body weight in small animal species. These
    two points have been evaluated by Gordon et al. (1986) and Gordon
    (1987), who argue for a conservative extrapolation of thermal effects
    from laboratory animals to humans.

    7.3.1  Nervous system

         Studies of the effects of RF exposure on the nervous system are
    shown in Table 13. Results of early studies suggested that the
    blood-brain barrier (which regulates cerebro-spinal fluid composition)
    was possibly susceptible to RF field exposure. For example, Frey et
    al. (1975) reported the penetration of the blood-brain barrier of
    anaesthetised rats by fluorescein after low-level, pulsed or CW
    exposure. Oscar & Hawkins (1977) reported increased permeability to
    radiolabelled saccharides after exposure of anaesthetized rats to
    low-level RF. However, later work (reviewed by Blackwell & Saunders,
    1986; NCRP 1986) indicated that these responses may have been
    confounded by various factors, including alteration in cerebral blood
    flow, the effect of the anaesthetic, and changes in renal clearance.

         The uptake of horseradish peroxidase by brain tissue is less
    susceptible to these factors. Increased uptake reported in conscious
    Chinese hamsters after exposure at 2 W/kg (Albert, 1977); decreased
    uptake has been reported at higher SARs (Williams et al., 1984b,d).
    More recently, changes in blood-brain barrier permeability have been
    reported after exposure to MRI field conditions; however, the evidence
    for an effect is contradictory, at present (Prato et al., 1990; Ross
    et al., 1990).
        Table 13.  Nervous system effects
    Exposure conditions             Effect on exposed group           Reference
    450 MHz (amp. mod.              Altered exchange rate of Ca++     Adey et al.
    16 Hz), for 60 min, to          during and after exposure of      (1982)
    30 W/m2 (33 V/m, SAR:           cat cortex
    0.29 W/kg)

    2.06 GHz (CW or pulsed          No change in Ca++ mobility        Merritt et al.
    18, 6, 32 Hz), 5-100            in rat cerebral tissue            (1982)
    W/m2 (SAR 0.12-2.4 W/kg)

    Table 13 (continued)
    Exposure conditions             Effect on exposed group           Reference
    2.45 GHz pulsed (2 µs           Decreased choline uptake          Lai et al.
    pulses at 500 Hz) or CW         in the rat brain tissue;          (1988)
    for 45 min (SAR 0.6 W/kg)       effect depended on exposure

    2.45 GHz (pulsed - 2 µs         Decreased choline uptake          Lai et al.
    pulses at 500 Hz) for           in the rat brain tissue at        (1989)
    45 min. (SAR 0.3-1.2 W/kg)      0.45 W/kg and above

    915 MHz (CW), 10-400 W/m2,      Decreased latency of late         Johnson & Guy
    for 15 min exposure of head     components only evoked            (1972)
    (SAR threshold 2.5-5 W/kg)      potentials in thalamus of

    147 MHz (amplitude-modu-        Altered EEG responses in cats     Bawin et al.
    lated 1-25 Hz) 10 W/m2          exposed to field modulated        (1973, 1974)
    (approx SAR 0.015 W/kg)         at EEG frequencies

    2.95 GHz, single or             EEG of rabbits unaffected by      Baranski &
    repeated exposure up to         acute exposure; desynchron-       Edelwejn (1975)
    50 W/m2 (SAR 1 W/kg)            ization of EEG from long-term
    2 h/day for 3-4 months          exposure; pulsed (1 µs pulses
                                    at 1200 Hz) more effective for
                                    changes than CW

    3 GHz (1 µs pulses at           Transient enhancement of EEG      Servantie &
    500-699 Hz) 50 W/m2 (SAR        at frequency of pulse repetition  Etienne (1975)
    1 W/kg) in rats, for            rate, persisted after exposure
    10 days                         ceased

    1-10 MHz (amplitude-modu-       Sustained changes in EEG after    Takashima et
    lated 14-16 Hz) E field         2-3 weeks of exposure of          al. (1979)
    500 V/m, 2 h/day, for           rabbits
    6 weeks

    1-30 MHz (amplitude-modu-       No effect
    lated 60 Hz) single exposure,
    for 3 h

    500 MHz - 3GHz 25-50 W/m2,      No effects on EEG in rats and     Klein
    for 15 days, at 0.5-1 W/kg      monkeys                           et al. (1985)

    4 GHz, CW or amplitude-         Slight changes in EEG pattern,    Mangel et al.
    modulated at 16 Hz              particularly at 16.8 W/kg         (1990)
    (70% mod.), for 30 min          amplitude-modulated RF
    (SAR in cortex 8.4, 16.8,       and 42W/Kg CW
    or 42 W/kg)
         Pulsed RF fields appear to have various effects on the nervous
    system. Exposure to very high peak power pulses is reported to
    suppress startle reflex and evoke body movements in conscious mice
    (Wachtel et al., 1988; 1989). For evoked body movement, each pulse (10
    µs in duration) produced a mid-brain specific absorption of around 200
    J/kg, corresponding to an SAR of 20 MW/kg and was estimated to lead to
    a rise in mid-brain temperature of 0.05 °C. Pulsed fields were only
    about twice as effective as CW suggesting that the effect is unlikely
    to be due to thermoelastic mechanisms.

         Pulsed RF exposure of rats for 45 min at SARs as low as 0.45 W/kg
    has been shown to affect the sodium-dependent, high affinity choline
    uptake (an indicator of cholinergic activity) in different parts of
    the brain (Lai et al., 1989). In a previous study, Lai et al. (1988)
    found that the effect varied with different exposure parameters.
    Further work (Lai et al., 1990) revealed that the concentration of
    benzodiazepine receptor (involved in anxiety and stress responses) in
    the brain of rats exposed for 45 min to pulsed 2.45 GHz or whole body
    SARs of 0.6 W/kg was increased in some parts of the brain, immediately
    after exposure. However, the effect diminished with repeated exposure
    over a 10-day period. The authors suggested that the data support the
    hypothesis that low-level RF exposure is a mild nonspecific stressor.
    There are a number of responses (heat, noise) that can be regarded as
    nonspecific stressors. This set of studies needs further elaboration
    to identify the extent and mechanisms of the stress involved, before
    its implication for health risk can be assessed. High levels of RF,
    sufficient to raise spinal or thalamic temperatures by several degrees
    Celsius, decreased the latency of late components of thalamic evoked

         Exposure to low levels of amplitude-modulated RF has been
    reported to alter brain activity (measured using
    electroencephalography) and to affect calcium ion mobility in the
    cortex. Exposure to 147 MHz fields, amplitude-modulated between 1 and
    25 Hz, has been reported to affect the ability of cats to produce
    selected EEG rhythms. Changes have also been reported in the EEG
    frequency spectrum in rabbits exposed to long-term 1-10 MHz,
    amplitude-modulated at 14-16 Hz.

         Small changes in EEG patterns, particularly earlier studies on
    desynchronisation, were reported in rats and rabbits, after exposure
    to an SAR at around 1 W/kg (Baranski & Edelwejn, 1975; Servantie &
    Etienne, 1975). However, later studies reported a lack of effect.

         The exposure of cats at about 0.3 W/kg to 450 MHz,
    amplitude-modulated at 16 Hz, has been reported to alter calcium ion
    mobility in the cortex (measured as the efflux of labelled calcium
    ions from the cortex surface) (Adey et al., 1982). In contrast,
    exposure at between 0.12 and 2.4 W/kg to 2.06 GHz, pulse-modulated at
    8, 16, or 32 Hz, was reported to have no effect on calcium ion
    exchange in the rat cortex (Merritt et al., 1982).

         Exposure to RF has been shown by several authors to influence the
    effects of various neuroactive drugs (see Table 14). Acute and
    long-term exposure have been reported to potentiate the effects of
    stimulant and convulsant compounds (Baranski & Edelwejn, 1974;
    Servantie et al., 1974). Thermally significant exposures have been
    reported to decrease the period of barbituate-induced anaesthesia in
    mice and rabbits; Blackwell (1980) suggested thermally enhanced
    redistribution from brain tissue as a probable mechanism.

    7.3.2  Ocular effects

         The lens of the eye is potentially sensitive to RF exposure,
    because it lacks a blood supply and so has a reduced ability to
    dissipate heat compared withto other tissues. In addition, the fibres
    that make up the bulk of the lens have only a limited capacity for
    repair and tend to accumulate the effects of minor insults.
        Table 14.  Nervous system effects with drugs
    Exposure conditions        Effect on exposed group          Reference
    1.7 or 2.45 GHz (CW)       Rabbits injected with sodium     Cleary &
    up to 500 W/m2 (up to      pentobarbital and exposed to RF  Wangemann
    10 W/kg)                   showed reduced sleeping times;   (1976)
                               correlated with increased
                               rectal temperature

    2.45 GHz (CW), 250 W/m2    SAR dependent reduction in       Blackwell
    and above (SARs            hexobarbital-induced             (1980)
    >17 W/kg) (rectal          sleeping time in mice during
    temperature rise 3 °C)     RF exposure

    3 GHz (CW) 70 W/m2         Variable effect on               Baranski &
    (1.2 W/kg) for 3 h/day,    chlorpromazine and pentylen-     Edelwejn
    for 200 h exposure         etetrazol changes in EEG         (1974)
                               activity in rabbits

    3 GHz (pulsed 1 µs at      Variable latency of response     Servantie et
    525 Hz), for unspecified   to pentylenetetrazol             al. (1974)
    duration, each day for     induction of convulsion
    8-35 days, at 5 W/kg       activity

    9.3 GHz (CW), 7-28 W/m2    No differences in EEG from       Goldstein &
    0.6 W/kg, for 5 min        normal sodium pentobarbital      Sisko (1974)
                               anaesthetic action
             Most experimental work on the RF induction of cataracts (see
    Tables 15 and 16) has been carried out using near-field exposures at
    2.45 GHz, to selectively irradiate the eye or the side of the head, in
    order to avoid whole-body thermal stress. The intense exposures used

    in these studies have often led to other effects, such as lacrimation
    and oedema of surrounding tissue.

         Exposure has usually been well above perception threshold and the
    animals have usually been anaesthetised. In most studies, the rabbit
    has been used as the experimental animal model, because the dimensions
    of its eye approach those of the human eye.

         Different conditions of exposure can affect the type of opacity
    formed or be ineffective in inducing any permanent change. The
    efficacy with which the applied RF field can induce cataracts depends
    on the depth of penetration and hence the frequency. Below 1.5 GHz,
    the dimensions of the orbit-eye combination are too small to result in
    local field concentration. Above about 10 GHz, penetration decreases
    and power absorption becomes increasingly restricted to the
    superficial tissue (NCRP, 1986).
        Table 15.  Ocular effects from acute exposure
    Exposure conditions           Effect on exposed group       Reference

    2.45 GHz (CW); 4.2 kW/m2,     Posterior cortical            Carpenter &
    for 5 min, or 1.5 kW/m2,      opacities within a            Van Ummerson
    for 60 min                    week; first visible           (1968)
                                  changes (milky bands)
                                  1-2 days after exposure

    2.45 GHz (CW); up to          Ultrastructural changes       Williams et
    2.5 kW/m2 repetitive          in lenses seen with           al. (1975)
    exposure                      microscope; slit lamp
                                  picture appeared normal

    2.45 GHz (CW); single acute   Threshold exposure to         Guy et al.
    exposure of 1.5 kW/m2, for    produce lens cataract         (1975b)
    up to 100 min (SAR peak in
    vitreous of 138 W/kg, 43 °C

    2.45 GHz (CW); SAR 100        Cataract in rabbit            Kramar et al.
    100 W/kg, after >140 min      (1978)

    3 GHz (CW); (far-field)       No lenticular changes,        Appleton
    5 kW/m2, for 30 min           periorbital burns             et al. (1975)

    107 GHz or 35 GHz,            Keratitis in cornea;          Rosenthal
    for 60 min, at 400 W/m2       damage more immediate         et al. (1976)
                                  but recovery quicker
                                  at 107 GHz

    Table 15 (continued)
    Exposure conditions           Effect on exposed group       Reference

    2.45 GHz; 5 kW/m2, for        No cataract in rhesus         Kramar et al.
    60 min                        monkey after 13 months        (1978)
             In general, field intensities associated with the acute induction
    of cataracts in the rabbit are of such magnitude that they are lethal
    if applied to the whole animal. Studies on the acute exposure of
    rabbits' eyes suggest the existence of an RF exposure threshold for
    the production of a cataract. This is best shown in the data of Kramar
    et al. (1978) given graphically in Fig. 20. The threshold power
    density to produce a cataract is approximately 1500 W/m2 for at
    least 1 h.

    FIGURE 20

         The possibility of a cumulative effect of repeated subthreshold
    exposure leading to the development of a cataract has been examined,
    as shown in Table 16. Subthreshold exposures of rabbit eyes caused
    reversible changes, and damage accumulated only when exposure was
    repeated before repair had occurred. However, these exposures were
    only just below the single acute exposure threshold (EPA, 1984).
    Long-term, whole-body exposures in the far-field at lower levels of
    power density have not produced any lens opacities.

         Opacities were induced in the eyes of anaesthetized primates
    after exposures well above threshold levels for rabbits, or after
    long-term exposure of conscious primates (to 9.3 GHz) at up to 1500
    W/m2. It has been suggested that the difference in acute response
    between rabbits and monkeys reflects structural differences in the
    face and lens and, hence, energy deposition and heating in the eye.
        Table 16.  Ocular effects from repeated short-term threshold exposure
    Exposure conditions                  Effect on exposed group      Reference

    2.45 GHz (CW), at 4.2 kW/m2          Various degrees of lens      Carpenter et al.
                                         opacity :                    (1960a,b)
    4 min for 4 days                     - in all rabbits
    4 exposures at 1-week intervals      - in 70% of rabbits
    4 exposures at 2-week intervals      - in 40% of rabbits
    3-min exposure, 5 times in week      - few opacities formed
    3-min exposure, 5 times in 5 weeks   - no opacities formed

    2.45 GHz (CW), at 100 W/m2 (SAR      No lens opacities for up     Ferri & Hagan
    1.5 W/kg), for 8 h/day, 5 days/week  to 3 months after            (1976)
    for 17 weeks                         exposure

    2.45 GHz (CW), 1.8 kW/m2, for        Cataracts in 8 out of        Carpenter et al.
    1 h repeated up to 20 times          10 rabbits                   (1974),

    1.5 kW/m2, for 1 h,                  Cataracts in 4 out of        Carpenter
    repeated up to 32 times              10 rabbits                   (1979)

    1.2 kW/m2, for 1 h,                  Cataracts in 1 out of
    repeated up to 24 times              9 rabbits

    2.45 GHz (CW), 100 W/m2              No changes in rabbits        Guy et al.
    (SAR to head 17 W/kg max),           eyes                         (1980)
    23 h/day for 180 days


    9.3 GHz (CW), 1.5 kW/m2,             No cataract or corneal       McAffee
    10 h/day for over 3 months           lesions found in             et al. (1979)
                                         macaque monkey

    2.45 GHz (pulsed-10 µs pulses        Endothelial cell damage      Kues et al.
    at 100 Hz), 100 W/m2,                to the corneas of            (1985, 1988)
    2.6 W/kg, 4 h/day for 3 days,        monkeys, leakage of iris
    2.45 GHz (CW), 200 W/m2,             vasculature; damage
    6.3 W/kg, 4 h/day for 3 days         greater in timolol
                                         maleate-treated eyes

    Table 16 (continued)
    Exposure conditions                  Effect on exposed group      Reference
    2.45 GHz (10 µs pulses               Leakage of iris vascu-       Monahan et al.
    at 100 Hz), 0-100 W/m2,              lature in timolol maleate-   (1988)
    4 h/day for 3 days                   treated eyes of anaesthet-
                                         ized adult rhesus and cyno-
                                         molgus monkeys; damage
                                         observed at 10 W/m2, but
                                         not at 2 W/m2
             Histological evaluation of the irises of monkeys, exposed  in
     vivo, long-term to 100 W/m2 pulsed 2.45 GHz at an SAR to the eye
    of 2.6 W/kg, indicated an increased vascular leakage (Kues et al.,
    1988). The leakage was increased in exposed animals whose eyes were
    pretreated with the ophthalmic drug timolol maleate (timolol maleate
    is used by people with glaucoma to lower the intraocular pressure by
    reducing the production of aqueous humour). In an extension of this
    study, Monahan et al. (1988) observed vascular leakage in timolol
    maleate-treated monkey eyes at power densities as low as 10 W/m2 (an
    SAR of only 0.26 W/kg).

         The authors suggested that serum protein leakage could have
    contributed to the corneal endothelial lesions observed in an earlier
    paper (Kues et al., 1985). More recently, the authors briefly reported
    that exposure to 50 or 100 W/m2 pulsed 2.45 GHz over a 10-week
    period resulted in degenerative changes in the retinal layer (Kues &
    McLeod, 1990). Timolol maleatic pretreatment increased the severity of
    the responses. Although requiring further study, these results, if
    established, could have important implications for the development of

    7.3.3  Auditory perception

         Auditory perception of pulsed RF exposure by animals is well
    established (see Table 17). For short pulses, thresholds are dependent
    on the energy density per pulse (Guy et al., 1975a, Chou et al., 1985)
    rather than the average power density, indicating a thermo-elastic
        Table 17.  Perception
    Exposure conditions        Effect on exposed group          Reference
    918 MHz (10 µs pulses at   Pulsed RF produced similar       Johnson et al.
    10 Hz), peak SAR           auditory stimulus for rat be-    (1977)
    75 W/kg                    havioural response as a 7.5
                               kHz tone repeated at 10 Hz

    Table 17 (continued)
    Exposure conditions        Effect on exposed group          Reference
    2.45 GHz, pulses with      Threshold auditory percep-       Guy et al.
    width less than 30 µs      tion of pulsed RF fields         (1975a)
        10-16 mJ/kg:           for cats                         Chou et al.
        0.9-1.8 mJ/kg:         for rats                         (1985)

    2.45 GHz (CW), 0.6-2.4     Threshold for perception of      King et al.
    W/kg, for 1 min            the RF field in rats             (1971)
             Threshold specific energy densities for pulses shorter than 30 µs
    were reported as 10-16 mJ/kg for cats and 0.9-1.8 mJ/kg for rats. CW
    fields are ineffective in generating the rapid thermoelastic expansion
    necessary for this effect, but can be perceived if temperature sensors
    in the skin are stimulated; the perception threshold has been reported
    to lie around 0.6-2.4 W/kg (King et al., 1971).

    7.3.4  Behaviour  Thermoregulation

         Exposure to thermally significant levels of RF will induce a heat
    load in addition to metabolic heat production (and other sources of
    heat) and will elicit the various physiological and behavioural
    mechanisms animals use to regulate body temperature. The thresholds
    for such responses, given in Table 18, are dependent on the
    relationships between the total heat load, heat-loss mechanisms, which
    depend on ambient conditions, and small changes in heat storage. In
    cool environments, animals compensate for RF-induced body heating by
    lowering their rate of metabolic heat production. The threshold
    response of squirrel monkeys, exposed for 10-15 minutes to 2.45 GHz,
    varied between about 0.5 and 5 W/kg, depending on ambient temperature.
    Food intake is also reduced in proportion to SAR in animals exposed
    long-term to RF; a threshold response for rats occurs at around 2-3

         Other thermoregulatory responses to RF heating include
    vasodilation, which increases skin thermal conductance, and sweating.
    Thresholds of between about 0.3 and 3 W/kg have been described in rats
    and monkeys. Similar responses have been reported in mice (Stern et
    al., 1979). Thresholds for behavioural thermoregulation, in which
    animals selected cooler environmental temperatures or selected shorter
    durations of infrared heating in response to microwave radiation of
    around 1 W/kg, have been described in rats and monkeys. Mice were
    shown to select a cooler environment by moving along a temperature
    gradient above a threshold SAR of 7 W/kg (Gordon, 1983). The threshold
    SAR necessary to activate a given thermoregulatory response or raise
    body temperature varied inversely with body mass (Gordon 1987). Thus,

    SAR dose-response data must be interpreted carefully when considering
    the extrapolation from experimental animals to humans.
        Table 18.  Thermoregulation
    Exposure conditions        Effect on exposed group          Reference
    Heat production/food intake

    2.45 GHz (CW)              Reduce endogenous heat           Ho & Edwards
                               production to compensate         (1977); Phillips
                               for RF body heating by rats      et al. (1975)

    2.45 GHz (CW), up to       Threshold RF exposure to         Adair & Adams
    1.5 W/kg                   reduce squirrel monkey           (1982)
                               metabolic heat production
                               0.6-0.9 W/kg

    2.45 GHz (CW), 0.7 W/kg,   No change in food or water       D'Andrea et al.
    7 h/day for 98 days        intake or weight in rats         (1986b)

    915 MHz (CW)               Food intake by rats              Lovely et al.
    - up to 2 W/kg             - not reduced                    (1977, 1983)
    - at 3.2 W/kg              - decreased consumption

    918 MHz (CW), 3.6 W/kg,    Decreased food consumption,      Moe et al.
                               but no change in water intake    (1976)
                               or body weight in rats

    Vasomotor/behavioural regulation

    2.45 GHz (CW), 5-min       Threshold for detectable         Adair & Adams
    sessions, 1 W/kg           changes in thermal conduct-      (1980a)
                               ance of skin in squirrel
                               monkeys; power density to
                               cause vasodilation related
                               to ambient temperature

    225 MHz (CW), 1.4 W/kg     Threshold for metabolic and      Lotz & Saxton
                               vasomotor responses in           (1987)
                               rhesus monkeys

    2.45 GHz (CW), 1.2 W/kg    Threshold for sweat response     Adair (1983b)
    (ambient temperature of    from foot in squirrel monkeys;
    36 °C)                     increased threshold with
                               decreased ambient temperature

    2.45 GHz (CW), 10-220      Threshold of approx.             Adair & Adams
    W/m2, for 10 min           1.2 W/kg for initiation of       (1980b)
                               thermoregulatory behaviour
                               in squirrel monkeys

    Table 18 (continued)
    Exposure conditions        Effect on exposed group          Reference
    450 MHz (CW), for          Threshold of approx.             Adair & Adams
    10-180 min                 1.2 W/kg for initiation of       (1988)
                               thermoregulatory behaviour
                               in squirrel monkeys

    2.45 GHz (CW), 1 W/kg      Threshold for initiation of      Stern et al.
                               thermoregulatory behaviour       (1979)
                               in rats

    2.45 GHz (CW) at 7 W/kg    Threshold for movement from      Gordon (1983)
    in waveguide with          preferred normal ambient
    temperature gradient       temperature

    225 MHz (CW), for          Heat poorly dissipated           Lotz & Saxton
    6×10-min exposure or       by rhesus monkeys at             (1988)
    120-min exposure,          255 MHz compared with
    12-100 W/m2,               1.29 GHz
    0.35-2.85 W/kg

    1.2 GHz                    Rats:                            Frey & Feld
        20 W/m2 (CW):          No avoidance of RF field         (1975)
        2 W/m2 (pulsed):       Avoided RF fields
             The thermoregulatory responses elicited by RF exposure have been
    reviewed by Adair, 1988. They were found to be similar to those
    elicited by exposure to conventional radiant or conductive heat
    sources. However, the overall thermoregulatory response of an animal
    to RF exposure will depend on the distribution of RF energy absorption
    and, thus, on the RF frequency. At frequencies below about 10 GHz, RF
    radiation is more deeply penetrating than, for example, infrared
    radiation, and is thus less effective in stimulating the superficial
    temperature sensitive receptors involved in local (and whole-body)
    thermoregulatory responses (Adair, 1983a).

         The effects of the distribution of RF absorption on
    thermoregulatory efficacy is particularly marked during exposure at
    frequencies near whole-body resonance. For example, although
    qualitatively similar, the thermoregulatory responses of squirrel and
    rhesus monkeys were less effective in preventing a rise in skin and
    body temperatures during exposure at resonance than during exposure at
    supra-resonant frequencies (Adair & Adams, 1988; Lotz & Saxton, 1988).  Activity (spontaneous movement)

         Acute and long-term exposure of rats has been reported to reduce
    their spontaneous locomotor activity (e.g., Moe et al., 1976, Mitchell
    et al., 1988). The rats reduced activity to lower their endogenous

    heat production. In a lifetime study, activity levels were also
    reduced after 6 weeks continuous exposure of young rats at up to 0.4
    W/kg, but values returned to control levels during subsequent
    exposure. No other effects on open-field behaviour were reported
    during 25 months exposure. Table 19 includes a summary of reports on
    the activity of RF-exposed rats.  Learned behaviours

         Operant techniques that require behavioural responses, such as
    certain rates of lever pressing in response to a visual or auditory
    cue, provide a means of assessing the performance of specific learned
    tasks in a highly quantified and standardized manner. Such studies are
    summarized in Table 20. It is important to note, however, that
    threshold values for changes in behaviour will depend on many factors,
    such as the complexity of the task being performed. To quote single
    threshold values for a range of tasks is an oversimplification.

         In rodents acutely exposed to RF, thresholds for the disruption
    of operant behaviour have been reported to lie between 2.5 and 8 W/kg,
    with concomitant rises in rectal temperature of around 1 °C. Deficits
    in performance have been reported following long-term exposure to 2.45
    GHz at 2.3 W/kg. The acquisition of a learned task by rats appears
    more sensitive to disruption than performance. Thresholds have been
    estimated of between 0.14 and 0.7 W/kg for long-term exposure to
    continuous wave RF at 2.45 GHz and between 0.7 and 1.7 W/kg for acute
    exposure to pulsed 2.8 GHz RF. Auditory effects were avoided by
    testing after the exposure; however, the data were sometimes variable.

         The responses of primates have been less extensively
    investigated. Operant task performance by rhesus and squirrel monkeys
    has been reduced by acute exposure to above resonant frequencies
    (1.3-5.8 GHz) at SARs of between 4 and 5 W/kg. Exposure of rhesus
    monkeys at whole-body resonance (225 MHz) resulted in reduced task
    performance at only 2.5 W/kg. However, both thresholds corresponded to
    raised body temperatures of about 1 °C; the lower threshold for body
    resonance presumably reflected the deeper heating and less efficient
    thermoregulation noted in the previous section.

         The effects of drugs on behaviour were augmented after
    pulsed-wave RF exposures of 30 min at an average SAR of 0.2 W/kg
    (Thomas et al., 1979).
        Table 19.  Effects on behaviour - activity
    Exposure conditions           Effect on exposed group          Reference
    2.45 GHz (pulsed), 6.3        No differences in the            Hunt et al.
    W/kg, for 30 min              activity of rats                 (1975)

    Table 19 (continued)
    Exposure conditions           Effect on exposed group          Reference
    2.45 GHz (CW), 2.7 W/kg,      Rats less responsive             Mitchell et
    for 7 h                       to novel acoustic stimuli,       al. (1988)
                                  no effect on acquisition or
                                  retention of passive
                                  avoidance task, reduced
                                  locomotion and rearing

    918 MHz (CW), 3.6-4.2         Lower activity and different     Moe et al.
    W/kg, 10 h/night for          temporal distribution of         (1976)
    21 nights                     activity of rats

    2.45 GHz (CW), 1.2 W/kg,      Reduced activity of rats         D'Andrea et
    8 h/day, 5 days/week, for     after exposure, but locomotor    al. (1979)
    16 weeks                      measures unaffected over
                                  long term

    3 or 10.7 GHz (CW), up to     Activity and stereotypic         Roberti et
    approx. 0.3 W/kg, for         behaviour (rearing, sniffing     al. (1975)
    185 h continuously            etc.) of rats unaffected by
                                  RF exposure

    2.45 GHz (CW), 7 h/day for    Decreased activity in rats       D'Andrea et
    up to 14 weeks, 0.7 W/kg      30 days after exposure,          al. (1986b)
    intermittent exposures        increased sensitivity to mild
    (25 W/m2)                     AC shock

    2.45 GHz (10 µs pulses        Except for first session when    Guy et al. square
    at Hz, square wave-           general activity reduced, no     (1985);
    modulated at 8 Hz), up to     difference in behavioural        Johnson et
    0.4 W/kg, from 2 to 27        responses to lifetime            al. (1983)
    months continuous exposure    exposure of rats
        Table 20.  Effects on behaviour - operant performance
    Exposure conditions           Effect on exposed group          Reference

    2.45 GHz (CW), 0.14 W/kg,     Variable changes in rate         D'Andrea et
    7 h/day, for up to 14 weeks   of acquisition of operant        al. (1986a);
    5 W/m2                        tasks, not confirmed by          DeWitt et
                                  DeWitt et al. (1987)             al. (1987)

    Table 20 (continued)
    Exposure conditions           Effect on exposed group          Reference
    2.45 GHz (CW), 2.5-8 W/kg,    Threshold for performance        Sanza &
    for 60 min                    disruption in exposed            de Lorge
                                  rats                             (1977);
                                  de Lorge &
                                  Ezell (1980)

    360, 480, 500 MHz (CW),       Threshold for reduced            D'Andrea et
    >4 W/kg 250 W/m2, for up      performance in rats; rectal      al. (1976)
    to 25 min                     temp rise >1 °C

    600 MHz (CW), >6 W/kg,        Threshold to stop pressing       D'Andrea et
    for up to 55 min              level for food                   al. (1977)

    2.45 GHz (CW), 2.3 W/kg       Impaired operant performance     Mitchell et
    (mean) for 110, 5-h           in exposed rats                  al. (1977)
    sessions over 22 weeks

    2.37 MHz (CW), 10 or          After 10 days exposure,          Shandala et
    50 W/m2, 7 h/day, for         increased learning of            al. (1977)
    up to 90 days                 avoidance task;
                                  up to 90 days decreased
                                  retention and reaquisition

    2.45 GHz (CW) at 100,         Reduced performance              Gage (1979a)
    150, or 200 W/m2, for         fixed ratio alternating
    15 h (SAR 3, 4.5, or 6 W/kg)  operant schedule by rats
    or 300 W/m2 for 55 min
    (ambient temperature, 22 °C)

    2.45 GHz (CW) at 50, 100,     Reduced performance random       Gage (1979b)
    150 W/m2 for 15 h (SAR        interval operant schedule
    1, 2 or 3 W/kg).              by rats
    (ambient temperature, 28 °C)

    2.45 GHz (pulsed, 1 µs        Impaired performance on          Thomas et al.
    pulses at 500 pps), 2-6       discrimination tasks             (1976)
    W/kg, for 30 min

    2.8 GHz (pulsed, 2 µs         Threshold for decreased          Schrot et al.
    pulses at 500 pps),           acquisition of response          (1980)
    1.7 W/kg, for 30 min          sequence schedule


    2.45 GHz (CW), 5 W/kg, for    Reduced performance and          de Lorge (1976)
    up to 2 h                     increased response time,
                                  rectal temperature increased
                                  by 2 °C in rhesus monkeys

    Table 20 (continued)
    Exposure conditions           Effect on exposed group          Reference
    2.45 GHz (CW), > 2.75 W/kg,   Reduced performance of           de Lorge
    for 60 min                    observing task in squirrel       (1979)
                                  monkeys; correlated with
                                  rectal temperature increase

    225 MHz (CW) 2.5 W/kg or      Threshold for impairing          de Lorge
    1.3 or 5.8 GHz (pulsed)       performance of observing-        (1984)
    4-5 W/kg                      response tasks; rectal
                                  temperature rise >1 °C in
                                  rhesus monkey

    1.2 GHz (CW), 1.6 W/kg        Performance of visual            Scholl &
    repeated 120-min exposures    tracking task by rhesus          Allen (1979)
    of head                       monkey unaffected
    7.3.5  Endocrine system

         An extensive literature describes the endocrine responses of
    various species to RF exposure (Table 21). The endocrine responses to
    acute RF exposure are generally consistent with the acute responses to
    non-specific stressors, such as heat, or with changes in metabolism
    caused by hyperthermia (Roberts et al., 1986).

         It has been reported in several papers that plasma corticosterone
    levels in rats were significantly enhanced by exposure above a
    threshold level that decreased with increasing duration of exposure.
    Similar effects were found in cortisol levels in primates. The
    response seems to be modulated in amplitude by the circadian rhythm of
    cortisol (or corticosterone) levels.

         Stressful stimuli are known to depress circulating plasma levels
    of growth hormone and thyroxin hormones in rodents. Plasma levels of
    these hormones have been similarly reduced by whole-body exposure of
    rats to RF. In one study, a threshold response for changes in serum
    growth hormone levels was reported to be as low as 0.2 W/kg. In
    contrast, no significant effects on growth hormone or thyroxin levels
    has been seen in primates.

         No effects on the endocrine system were seen in a lifetime study
    on rats exposed from 2 up to 27 months of age at SARs of up to 0.4

        Table 21.  Endocrine system effects
    Exposure conditions           Effect on exposed group          Reference


    2.45 GHz (CW); 500 W/m2,      Threshold for significant        Lotz &
    up to 10 W/kg, for up         increase in plasma               Michaelson
    to 60 min or                  corticosterone levels;           (1978)
    200 W/m2, 3.2 W/kg, for       Increased (0.7-1.5 °C)
    120 min                       colon temperature needed
                                  for effect

    2.45 GHz (CW), 600 W/m2,      Plasma corticosterone            Lotz &
    9.6 W/kg, for 60 min, or      levels not increased in          Michaelson
    500 W/m2, 8.3 W/kg, for       hypophysectomized rats           (1979)
    60 min for drug-injected      or rats injected with
    rats                          dexamethasone (suppresses
                                  ACTH release)

    2.45 GHz (CW), 100 W/m2,      No change in plasma              Parker
    approx 2.5 W/kg, for 16 h     corticosterone level             (1973)
                                  or rectal temperature

    2.45 GHz (CW), up to          Alteration in normal             Lu et al.
    400 W/m2, up to 8.4 W/kg      circadian elevation in           (1981)
    for 4 or 8 h                  corticosterone levels

    918 MHz (CW), 100 W/m2,       No change in rectal              Moe et al.
    up to 4.2 W/kg,               temperature or in basal or       (1976)
    10 h/day, for 21 days         ether stress-induced serum
                                  corticosterone levels

    918 MHz (CW); 25 W/m2,        No change in rectal              Lovely et
    1 W/kg (ave), 10 h/day,       temperature or serum             al. (1977)
    for 91 days                   corticosterone levels


    1.29 GHz (pulsed),            Increased serum cortisol         Lotz &
    3-4 W/kg, for 4 h             levels and increased rectal      Podgorski
                                  temperature (0.7-1.6 °C)         (1982)
                                  but no change in serum growth
                                  hormone levels or thyroxin in
                                  rhesus monkeys

    Table 21 (continued)
    Exposure conditions           Effect on exposed group          Reference
    1.29 GHz (pulsed) 380 W/m2    Increased serum cortisol         Lotz (1983)
    4.1 W/kg, for 8 h             levels when rhesus monkeys
                                  were exposed during day, but
                                  no change when exposed at night;
                                  rectal temperature rose by
                                  similar amount

    255 MHz (CW), 50 W/m2,        No change in serum               Lotz (1985)
    3.4 W/kg, for 4 h             cortisol level;
                                  rectal temperature increase of
                                  1.5-2 °C in rhesus monkeys

    Growth/thyroid hormones

    2.45 GHz (CW), 90-360 W/m2    Decrease in serum growth         Michaelson et
    SAR up to 7.5 W/kg, for       hormone levels in young          al. (1975)
    10-150 min                    rats only when exposed
                                  to 7.5 W/kg for at least
                                  60 min; colon temperature rose
                                  to more than 40 °C

    2.45 GHz (CW), 500 W/m2,      Threshold to induce changes      Lu et al.
    10.5 W/kg, for 1 h, or        in serum growth hormone levels   (1980b)
    10 W/m2, 0.2 W/kg             was dependent on baseline
    for 2 h                       growth hormone level in rats at
                                  time of exposure; no change in
                                  thyroxin level; no effect with
                                  exposure > 4 h

    2.45 GHz (CW),                Increased thyroxin and tri-      Magin et al.
    58-190 W/kg, for 120 min      iodothyronine secretion          (1977a,b)
                                  when dog thyroid exposed;
                                  increased levels proportional
                                  to temperature increase

    2.45 GHz (CW), 200 W/m2 or    Depressed circulating            Lu et al.
    higher, 4.2-5 W/kg, for       thyroxin and TSH levels in       (1977, 1980b)
    4 or 8 h                      rats; rectal temperature
                                  rose to about 40 °C

    Table 21 (continued)
    Exposure conditions           Effect on exposed group          Reference

    2.8 GHz (CW), 100 W/m2, for   Increased luteinising            Mikolajczyk
    6 h/day, 6 days/week for      hormone, no change in            (1976)
    6 weeks                       follicle-stimulating or
                                  hormone levels in rats;
    2.45 GHz (pulsed),            no differences in plasma         Johnson et al.
    4.8 W/m2, 0.15-0.4 W/kg,      endocrine levels between         (1983)
    continuous exposure of        exposed and control animals      Guy et al (1985)
    rats from 2 to 27 months of
    age (lifetime exposure)
        7.3.6  Haematopoietic and immune systems

         In a large number of studies, haematological effects have been
    found in animals exposed to RF, mainly when a significant rise in body
    temperature has been observed. Few effects have been reported in the
    absence of a detectable increase in temperature, as shown in Table 22.
    Athermal responses have not been established.

         Smialowicz (1984) reviewed earlier studies and did not find any
    consistent effects of RF exposure on peripheral blood cells in
    developing rats. No consistent changes were found in erythrocyte,
    leukocyte, or differential leukocyte cell counts in rats exposed pre-
    and post-natally to RF fields.

         RF exposure has been reported to affect various components of the
    immune system. Whilst both stimulatory and inhibitory responses have
    been reported, these have been mostly transient in nature and usually
    attributable to thermal stress.

         Several authors have noted that exposure to thermogenic levels of
    RF will result in increased levels of circulating neutrophils and
    decreased levels of circulating lymphocytes (see Fig. 21 from Liburdy
    (1979) and Table 23). A lack of effect of low-level exposure on
    circulating blood cell count in rats has been reported in other
    studies. On the basis of his results, Liburdy (1979, 1980) suggested
    that whole-body RF exposure induces heat stress that activates the
    hypothalamic-hypophyseal-adrenal axis to trigger the release of
    adrenal steroids into the blood, leading to the transient changes in
    blood cell counts and other haematopoietic and immunological changes
    associated with RF exposure.

        Table 22.  Haematopoietic system effects
    Exposure conditions            Effect on exposed group        Reference
    Circulating blood cells

    800 MHz, 430 W/m2 (average),   No change in erythrocyte       Spalding et al.
    2 h/day, 5 day/week, for       count, haemocrit, or           (1971)
    35 weeks, SAR estimated        haemoglobin concentration
    at less than 1.5 W/kg          in mice; 4 exposed mice died

    2.95 GHz, 30 W/m2              Decreased erythrocyte          Siekierzynski
    (average), for 158 h           production in rabbits;         (1972)
    (CW or pulsed)                 pulsed exposure more

    2.4 GHz (CW) 100 W/m2          Increased erythrocyte          Djordjevic &
    for 2 h/day, for up to         count; 1 °C rise in            Kolak (1973)
    30 days, SAR approx            rectal temperature in rats
    2 W/kg

    26 MHz(CW) SAR 13 W/kg,        Decreased peripheral           Liburdy (1977)
    for up to 3 h; rectal temper-  lymphocytes, increased
    ature rose by 2-4 °C           neutrophils in mice

    2.45 GHz (CW)                  No effect on peripheral        Smialowicz
    300 W/m2, for 30 min/day       blood cell count in            et al.
    for 22 days, SAR               mice                           (1979a)
    22 W/kg

    2.4 GHz (CW) 50 W/m2,          No effect on peripheral        Djordjevic
    1 h/day for 90 days,           blood cell count in            et al. (1977)
    SAR approx 1 W/kg              rats

    970 MHz (CW) SAR               No effect on blood count       Smialowicz
    2.5 W/kg, 22 h/day for         in rats                        et al. (1981a)
    70 days

    2.45 GHz (CW) SAR              No effect on peripheral        Galvin et al.
    2.2 W/kg, for 8 h              blood cell count in rats       (1982)

    20 MHz (CW) SAR                No effect on blood cells       Wong et al.
    0.3 W/kg, 6 h/day for up       in rats                        (1985)
    to 6 weeks

    2.45 GHz (CW), 5 W/kg          No consistent changes          Smialowicz
    100 MHz (CW), 3 W/kg           in erythrocyte or              et al. (1979b,
    425 MHz (CW), 7 W/kg           leukocyte counts in            1981b, 1982)
                                   rats exposed pre- or           
                                   postnatally, for up            Smialowicz
                                   to 41 days                     et al. (1982)

    Table 22 (continued)
    Exposure conditions            Effect on exposed group        Reference
    Bone marrow cells

    2.95 GHz (CW) 10 W/m2,         Shift in circadian             Czerski et al.
    for 4 h/day for 14 days        rhythm of division of          (1974a);
    in guinea-pig; 4 h at          blast cells in bone            Czerski
    5 W/m2 in mice                 marrow and lymphocytes;        (1975)
                                   no statistical analysis,
                                   hence, response suggestive

    2.45 GHz (CW), 150 W/m2        Reduced ability of             Huang &
    SAR 11 W/kg, 30 min/day        mouse bone marrow cells        Mold (1980)
    for 9 days                     to form myeloid or
                                   erythroid colonies in vitro

    2.88 GHz (pulsed)              Significant but                Ragan et al.
    SAR 4.5 W/kg, 7.5 h/day        inconsistent alterations       (1983)
    for 360 days                   in bone marrow, blood cell
                                   and serum protein values
                                   in mice

    General long-term studies

    2.45 GHz (CW), SAR             41 parameters measured,        McRee et al.
    1.5 W/kg,                      only 3 of which changed;       (1980)
    23 h/day for 180 days          Lower eosinophil, serum
                                   albumin, and calcium
                                   levels in rabbits

    2.45 GHz (pulsed) SAR          No effect on haematology       Guy et al.
    0.15-0.4 W/kg,                 or serum chemistry parameters  (1985)
    for 25 months                  in rats
             Exposure to thermogenic levels of RF fields has been shown to
    cause several effects including a depression of natural killer cell
    activity, implicated, for example, in tumour cell cytolysis, and
    macrophage activation. One group of workers (Wiktor-Jedrzejczak et
    al., 1977a,b, 1980) reported an increase in the number of lymphocytes
    bearing a surface marker (complement receptor) in mice exposed to high
    levels of microwave radiation. Smialowicz et al. (1979a) were unable
    to replicate this effect using a different strain of mouse. This
    difference in response between the two strains may be due to the
    presence of a single gene located on chromosome 5 (Schlagel et al.,
    1980, 1982). At present, this remains an unresolved issue.

        Table 23. Immune system effects
    Exposure conditions           Effect on exposed group          Reference
    Mitogen response - blast transformation

    2.45 GHz (CW) SAR             Transient increase in            Huang et al.
    21 W/kg, 15 min/day,          transformation rate of           (1977)
    for 5 days                    peripheral blood lymphocytes
                                  (to lymphoblasts) in Chinese
                                  hamsters, decreased mitotic
                                  frequency in mitogen-stimulated

    2.45 GHz (CW) up to           Altered mitogen response         Huang &
    150 W/m2 SAR 11 W/kg,         of T- and B- lymphocytes         Mold (1980)
    30 min/day, for 17 days       in Balb/c mice

    2.45 GHz (CW) up to           No effect on mitogen             Smialowicz
    300 W/m2 SAR 22 W/kg,         response of T- and B-            et al. (1979a,
    30 min/day, for               cells in Balb/c mice             1983)
    22 days, or 11 W/kg,          or CBA/J mice
    1.5 h/day, for 9 days

    10.5, 19.27, 26.6 MHz         Enhanced mitogen response        Prince et al.
    (CW) up to 2 W/kg, for        in lymphocytes from rhesus       (1972)
    30 min                        monkeys; rectal temperature
                                  increased up to 2.5 °C.

    Surface (complement receptor) marker

    2.45 GHz (CW) up to           Increased lymphocytes            Wiktor-
    15 W/kg, for 30 min           with surface marker              Jedrzejczak
                                  (complement receptor)            et al.
                                  in CBA/J mice                    (1977a,b,1980)

    2.45 GHz (CW) up to           No increase in complement-       Smialowicz
    22 W/kg, for 30 min           receptor positive lymphocytes    et al. (1979a)
    on 22 consecutive days        in Balb/c mice

    2.45 GHz (CW) 14 W/kg         Increase in complement-          Schlagel et al.
                                  receptor positive lymphocytes    (1980, 1982)
                                  in >12-week-old CBA/J mice;
                                  no effect in BALB/c mice

    2.45 GHz (CW) 28 W/kg         Increase in complement-          Smialowicz
                                  receptor positive lymphocytes    et al. (1981c)
                                  in 16-week-old CBA/J mice

    Table 23 (continued)
    Exposure conditions           Effect on exposed group          Reference
    Lymphocyte circulation

    26 MHz (CW); 5.6 W/kg, for    Reduced mouse peripheral         Liburdy (1979)
    15 min (single or repeated)   lymphocytes; increased neutro-   
    in warm air environment;      phils, T- and B- cells
    rectal temperatures rose      in spleen, elevated
    by 2-3 °C                     corticosteroid levels

    2.6 GHz (CW), for 1 h         Lymphocyte circulation,          Liburdy (1980)
                                  lung, spleen, and bone
                                  marrow - changes only
                                  when rectal temperature
                                  of mice increased;

    at 19 W/kg:                   Altered significantly;
    at 3.8 W/kg:                  Not affected

    Macrophage/NK T-cell activity

    2.45 GHz (CW); SAR            Activation of macrophages        Rama Rao et al.
    13 W/kg                       in hamsters (depressed           (1983)
                                  killer T-cell activity)

    2.45 GHz (CW) for 1 h         Natural killer T-cell            Yang et al.
                                  activity in hamster:             (1983)
                                  (Changes due to heat stress?)

    at 13 W/kg, colon             Transient decrease
    temperature >3 °C:
    at 8 W/kg:                    Unchanged

    2.45 GHz (CW); 21 W/kg;       Transient decrease in            Smialowicz
    Increased rectal              killer T-cell activity;          et al. (1983)
    temperature                   increased macrophage
                                  activity in mice

    2.45 GHz (CW); 22 W/kg        No change in killer              Huang & Mold
    5×30 min; no significant      T-cell activity in mice;         (1980)
    rectal temperature increase   increased macrophage

    Table 23 (continued)
    Exposure conditions           Effect on exposed group          Reference
    Antibody response

    9 GHz (pulsed); 100 W/m2      Stimulation of antibody          Liddle et al.
    (average) SAR 4.7 W/kg,       response and increased           (1980)
    2 h/day for 5 days            survival time of mice
                                  injected with pneumococcal

    2.375 GHz (CW); 0.1,          Appearance of circulating        Shandala &
    0.5, 5.0 W/m2, for            autoantibodies in rats           Vinogradov
    7 h/day for 45 days           against brain and liver          (1982, 1990)
                                  tissue and antibodies against
                                  fetal tissue in pregnant dams
                                  only at 5.0 W/m2

    As above, except SAR          No effect on normal              Liddle et al.
    0.47 W/kg                     antibody response and survival   (1986)

    2.45 GHz (CW), for 1 h        Primary antibody response of     Rama Rao et al.
                                  spleen lymphocytes to sheep      (1985)
                                  RBCs in hamsters:
    8 - 13 W/kg                   increased
    < 8 W/kg                      no change

    Long-term: Juveniles/adults

    2.45 GHz (CW), up to          Increased lymphocyte             Smialowicz
    5 W/kg, for up to 41 days     response to T- and B-            et al. (1979b)
    of age                        mitogens in rats

    425 MHz (CW), up to           Same as above                    Smialowicz
    7 W/kg, for up to 41 days     et al. (1982)
    of age

    100 MHz (CW), SAR             No effect on blood               Smialowicz
    2-3 W/kg, for 4 h/day,        cell count, mitogen              et al. (1981b)
    until 97 days of age          or antibody response in rats

    2.45 GHz (10 µs pulses,       No significant differences       Guy et al.
    800 Hz) 4.5 W/m2,             in immunological                 (1985)
    SAR 0.15-0.4 W/kg,            parameters in rats;
    up to 27 months of age        transient change in lymphocyte
                                  count and responsiveness at
                                  13 months
         The results of studies on the developing immune system, shown in
    Table 23, may indicate an effect of the higher SARs on lymphocyte
    responsiveness. This effect is consistent with other reports and with
    observations of increased lymphocyte activity elicited by conventional
    heating (Roberts, 1979).

         A lifetime exposure study (Guy et al., 1985) in which rats were
    exposed to up to 0.4 W/kg between 2 and 27 months of age did not
    reveal any effects on haematological or immunological parameters,
    except for a transient change in the number and responsiveness of B-
    and T-lymphocytes to specific mitogens after 13 months exposure.

    FIGURE 21

    7.3.7  Cardiovascular system

         The responses of the intact cardiovascular system to exposure to
    RF, as shown in Table 24, are consistent with those associated with
    conventional heating. Hence, depending on the ambient temperature, the
    SAR, and duration of exposure, increases in heart rate (tachycardia),
    no change, or decreases in heart rate (bradycardia) can be induced
    during, and following, RF exposure.

        Table 24.  Cardiovascular system effects
    Exposure conditions           Effect on exposed group          Reference
    During exposure

    2.45 GHz (CW); 100 W/m2,      No heart rate effects in         Birenbaum
    SAR 2 W/kg, for 20 min        rabbits                          et al.(1975)
    applied to heads

    2.45 GHz (CW), 50 or          Increased heart rate only        Chou et al.
    800 W/m2 or 50 W/m2           at 800 W/m2 in                   (1980)
    (pulsed) whole-body SAR       rabbits; normal response
    up to 15 W/kg                 to heating

    2.45 GHz (CW); SAR            No effect on arterial            McRee et al.
    2.3 W/kg for 6 h              blood pressure, but heart        (1988)
                                  rate reduced by 10% in rats

    4 GHz, CW or amplitude-       Transient bradycardia during     Mangel et al.
    modulated at 16 Hz (70%       CW or modulated RF in            (1990)
    mod.), for 30 min, SAR in     anaesthetized rats
    cortex 8.4, 16.8, or 42 W/kg

    After exposure

    2.45 GHz (CW), 30 min to      At 6.5 W/kg, mild bradycardia    Phillips
    SARs up to 11.1 W/kg in       in rats for up to 3 h;           et al. (1975)
    rats; environmental           at 11.1 W/kg, pronounced
    temperature 24 °C             bradycardia for 2 h,
                                  followed by mild tachycardia
                                  and irregular heart rate for
                                  short periods; threshold
                                  between 4.5 and 6.5 W/kg

    915 MHz (CW), SAR             No change in heart weight        D'Andrea
    2.5 W/kg, for 8 h/day,        in rats                          et al. (1980)
    5 days/week, for 16 weeks

    435 MHz (pulsed: 1 µs         No change in resting             Toler et al.
    pulses at 1000 Hz)            heart rate or mean               (1988)
    10 W/m2 whole-body            arterial blood pressure
    SAR approx 0.35 W/kg, for     in rats
    22 h/day over 6 months
             An increase in cardiac output, heart rate, and blood pressure,
    coupled with a decrease in peripheral resistance, has been reported in
    rabbits exposed at SARs estimated at 10-15 W/kg (raising body
    temperatures 0.5 °C) and in anaesthetized rats exposed at levels that
    increased body temperature by about 3.5 °C. Following exposure, heart
    rate decreased; the threshold for this effect was between 4.5 and 6.5

    W/kg. Long-term exposure of rats at SARs of between 0.3 and 2.5 W/kg
    did not affect heart rate or heart weight.

    7.3.8  Reproduction and development

         The assessment of the toxic effects of an agent on fertility and
    the development of the embryo and fetus are of great importance. The
    processes of meiosis, fertilization and implantation, and the high
    rates of cell division and differentiation during development of the
    embryo and fetus tend to be more susceptible to toxic insults than
    many other processes in the tissues of the adult organism.  kHz studies

         Studies in the kHz range are summarized in Table 25. The fields
    used are generally of the type generated by clinical exposure systems
    or by some types of visual display units. These studies have not shown
    consistently reproducible effects. Exposure of developing chick
    embryos to pulsed electromagnetic fields, including a signal of the
    type used clinically for bone healing, for up to a week, had no effect
    on malformation incidence (Sisken et al., 1986). Studies of effects on
    mammals are of greater relevance to human health.

         Two teratological studies (Tribukait et al., 1987; Stuchly et
    al., 1988) on the effects of magnetic fields of the type used in VDUs
    reported increased numbers of malformed fetuses in rodents, but, when
    the results were analysed using the litter rather than the individual
    fetus as the unit of observation, the increases were not significant
    (Stuchly et al., 1988).
        Table 25.  Teratological studies in the kHz region
    Exposure conditions           Effect on exposed group          Reference

    Pulsed magnetic fields        Abnormal development,            Delgado et al.
    10, 100, or 1000 Hz; up       particularly in cephalic         (1982).
    to 1.2 µT, for first          region; effect most
    48 h of development           marked at 100 Hz

    Pulsed electromagnetic        No significant increase in       Sisken et al.
    fields, 3.8 kHz, 50 ms        incidence of abnormalities       (1986)
    burst repeated at 2 Hz
    (0.25 mT peak) or
    4.4 kHz, 5 ms burst
    repeated at 15 Hz
    (1.6 mT) to embryos for
    first 24 h or 7 days of

    Table 25 (continued)
    Exposure conditions           Effect on exposed group          Reference
    20 kHz sawtooth magnetic      No effect on incidence of        Sandstrom et al.
    fields 0.1-16 µT applied      malformation                     (1987)
    to embryos for first 42 or
    47 h of development


    20 kHz sawtooth magnetic      Significant increase in          Tribukait et
    fields 1 or 15 µT applied     number of mouse fetuses          al. (1987)
    to embryos on days 0-14 of    with external malformations
    gestation                     at 15 µT (difference not
                                  significant if analysed by
                                  litter (Stuchly et al.,1988)

    20 kHz sawtooth magnetic      Increased number of implants     Frolen et al.
    fields 15 µT applied to       and post-implantation            (1987)
    embryos on days 0-19 of       deaths in mice; no effect on
    gestation                     incidence of malformation

    19 kHz sawtooth magnetic      No effect on post-implantation   Stuchly et al.
    fields 5.7, 23, for or 66     survival in rats; increase       (1988)
    µT, for 7 h/day, before and   in minor skeletal defects in
    during gestation              highest exposure group, but
                                  only if analysed by individual
                                  fetus and not by litter
                                                                                       MHz and GHz studies

    (a)  Fertility. Most of the studies on reproduction and development
    in small mammals exposed to RF radiation have shown effects that can
    be related to an increase in temperature, and can be produced by
    thermal stress alone. It is well known that, in many species of
    mammal, the development of male germ cells can be adversely affected
    by increased testicular temperatures. The studies shown in Table 26
    indicate that acute RF exposure of anaesthetized animals can, through
    raising testicular temperature, affect the spermatogenic epithelium
    and, thus, male fertility. However, the anaesthesia will have altered
    the animals' abilities to regulate their testicular temperatures
    (usually maintained 3-4 °C below body temperature). The exposure of
    conscious animals has been found to have little effect on testicular
    function, except after prolonged exposure at thermally significant
    levels. Male rats, exposed long-term at about 6 W/kg, showed a slight
    reduction in potential sperm production by the heat-sensitive
    pachytene spermatocytes (Johnson et al., 1984) and were reported to be
    temporarily less fertile (Berman et al., 1980).

        Table 26.  Effects on male fertility
    Exposure conditions           Effect on exposed group          Reference

    2.45 GHz (CW), or direct      Depletion of primary             Saunders &
    heating of lower half of      spermatocytes and spermatids     Kowalczuk
    body, for 30 min              in mice; threshold temperature   (1981);
                                  for depletion 39 °C or SAR of    Kowalczuk et
                                  30 W/kg or greater;              al. (1983)
                                  increased number of abnormal
                                  sperm at higher temperatures

    1.3 GHz (pulsed), 8-10        Depletion of primary             Lebovitz et
    W/kg, for 60 min or more      spermatocytes and spermatids     al. (1987)
                                  in rats; threshold temperature
                                  39-41 °C


    2.45 GHz (CW), up to          No effect on sperm count or      Cairnie &
    20 W/kg, 16 h/day,            number of abnormal sperm in      Harding
    for up to 30 days             conscious mice                   (1981)

    2.45 GHz (CW), 5 W/kg, for    No effect on conscious,          Saunders
    120 h over 8 weeks, then      male mouse fertility,            et al.(1988)
    mice mated over next          pregnancy rates 8 weeks

    2.45 GHz (CW), 5.6 W/kg,      Transient reduction in           Berman et al.
    for 80 h over 4 weeks         conscious, male rat fertility,   (1980)
                                  50% of dams mated 3-9 days
                                  after irradiation of males
                                  showed pregnancies; rectal
                                  temperature 41 °C

    1.3 GHz (pulsed), 6.3 W/kg,   No effect on sperm production,   Lebovitz &
    6 h/day for 9 days            sperm morphology, testes mass,   Johnson
                                  etc. in rats; body temperature   (1983);
                                  rise of 1.5 °C; no effect        Johnson et
                                  on different stages              al. (1984)
                                  of spermatogenesis, except for
                                  a reduction in heat sensitive
                                  pachytene spermatocytes

    1.3 GHz (CW), 9 W/kg, for     No differences in testicular     Lebovitz &
    8 h, rectal temperature       function of conscious rats       Johnson (1987)
    rise 4.5 °C
    (b)  Developmental (teratogenic) effects. Exposure to high levels of
    RF will induce significant rises in maternal body temperature, and
    result in deformities or defects in the offspring, as shown in Table
    27. O'Connor (1980) concluded, from a review of the teratogenic
    effects of exposure to RF, principally in mice and rats, that intense
    exposures that result in significant maternal heating can result in
    reduced fetal mass, specific abnormalities (especially exencephaly),
    and in increased embryo and fetal losses. For rats, most of the
    significant results were based on intense levels of exposure. The most
    commonly reported defects were decreased fetal mass and increased
    embryo and fetal losses.

         RF teratogenesis has also been demonstrated in mice, though
    generally at higher SARs. In one study, it was reported that RF
    exposure at around 4-5 W/kg enhanced the effect of a chemical

         In their review, Lary & Conover (1987) concluded that heat causes
    birth defects and pre-natal mortality, when the temperature of the
    pregnant mother exceeds 40 °C. Exposure that increases the core
    temperature of pregnant dams to 39-41 °C does not usually result in
    gross structural malformations, but may significantly increase the
    incidence of pre-natal mortality, result in lower body weight, cause
    histological or physiological changes, or alter the behaviour of the
    exposed offspring. They suggest that only exposures that have an
    appreciable heating effect are likely to affect the human embryo
    adversely. In contrast, one study described teratological effects in
    rats after exposure to 27.12 MHz at a whole-body SAR of 10-4 W/kg.
    However, these results are difficult to reconcile with those of many
    other studies carried out at the same frequency.
        Table 27.  Teratogenic effects in the MHz-GHz region
    Exposure conditions            Effect on exposed group           Reference

    27.12 MHz (CW), approx.        Embryo and fetal deaths, and      Lary et al.
    11 W/kg, for 20-40 min;        abnormalities at all stages       (1982)
    rectal temperature to 43 °C    of development

    27.12 MHz (CW), 33 kV/m,       Various effects in offspring      Brown-Woodman
    0.8 A/m; mated rats            related to temperature            et al. (1988)
    exposed on day 9 of            increase and duration of
    gestation; temperature         exposure
    increase maintained at
    2.5-5 °C

    27.12 MHz (CW), 1 W/m2,        Decreased post-implantation       Tofani et
    0.1 mW/kg, fetuses exposed     survival, reduced cranial         al. (1986)
    from day 0 to 20 of            ossification in exposed rat
    gestation                      fetuses

    Table 27 (continued)
    Exposure conditions            Effect on exposed group           Reference
    6 GHz (CW), approx.            Slight growth retardation in      Jensh
    7 W/kg, for 8 h/day,           fetuses, no increased deaths      (1984a,b)
    throughout pregnancy           or structural abnormalities

    2.45 GHz (CW), 4 or            Maternal temperature raised       Berman et al.
    6 W/kg, for 100 min/day,       to 40 °C; no abnormalities        (1981);
    from day 6 to 15 of            in fetuses; offspring exposed     Berman &
    gestation                      to higher levels had lower        Carter (1984)
                                   mean body weight

    2.45 GHz (CW), 2-4 W/kg,       No rectal temperature increase;   Jensh et al.
    for 6 h/day throughout         no excess abnormalities in        (1983a,b)
    gestation                      fetuses; no altered performance
                                   in neonatal reflex tests or
                                   adult behaviour, except
                                   increased activity in
                                   exposed offspring

    915 MHz (CW), 3.5 W/kg,        No anatomical defects in          Jensh et al.
    for 6 h/day throughout         fetuses or behavioural            (1982a,b)
    pregnancy                      alterations; maternal temperature
                                   not increased

    100 MHz (CW), 0.4 W/kg,        No teratogenic or embryogenic     Lary et al.
    for 400 min/day, on days       effects in offspring of rats      (1983b)
    6-11 of gestation

    2.45 GHz (CW), 0.4 W/kg        No effects on weight and DNA      Merritt et
    throughout gestation           or RNA content of fetal rat       al. (1984)


    2.45 GHz (CW), 6 or 9 W/kg,    Maternal rectal temperature       Berman et al.
    for 100 min/day, during days   increase 0.4 and 1.6 °C; no       (1982b)
    6-14 of gestation of hamster   effect in low-exposure group;
    fetuses                        increased fetal deaths,
                                   decreased fetal weight, and
                                   decreased skeletal maturity
                                   in high-exposure group


    2.45 GHz (CW), 2.8 or          Mean mass of live fetuses         Berman et al.
    22 W/kg, for 100 min/day,      decreased in high-exposure        (1978)
    throughout gestation           group

    Table 27 (continued)
    Exposure conditions            Effect on exposed group           Reference
    2.45 GHz (CW), 7, 28, or       At 40 W/kg: reduced no.           Nawrot et
    40 W/kg, 8 h/day, for          implantation sites per            al. (1981)
    various times during           litter and fetal weight,
    gestation                      and increased malformations

    2.45 GHz (CW), 16 W/kg,        Lower fetal weight, delayed       Berman et al.
    for 100 min/day during days    skeletal maturation, lower        (1982a, 1984)
    6-17 of gestation              brain weight in exposed fetuses

    2.45 GHz (CW), 4-5 W/kg,       No teratogenic effects in         Chazan et al.
    for 2 h/day and 7 days per     offspring of exposed              (1983)
    week from days 1 to 7, days    animals
    8 to 18, or days 1 to 18 of

    2.45 GHz (CW), 1 or 10         At 4-5 W/kg: reduced fetal body   Marcickiewicz
    W/m2 (equal to 0.5,            mass; exposure combined with      et al. (1986)
    4-5 W/kg) for 2 h/day,         injection of cytosine arabinocide
    from day 1 to 18 of            enhanced incidence of
    gestation                      abnormalities compared with
                                   those on drug alone
        7.3.9  Genetics and mutagenesis

         Since the potential to induce heritable changes would be of
    particular importance for protection standards, many studies designed
    to examine the genetic consequences of exposure have been conducted.
    Studies examining the possible hereditary consequences of RF exposure
    are listed in Table 28, including those on germ cell chromosome
    aberration frequencies and dominant lethal mutation frequencies
    (assessed as the decreased survival of implanted embryos and fetuses).
    Much experimental evidence suggests that acute or long-term RF
    exposures do not result in an increase in chromosome aberration
    frequency, when temperatures are maintained within physiological
    limits. One study reported an increased frequency of cytogenetic
    effects in mice exposed long-term at SARs between 0.05 and 20 W/kg.
    However, this study was not successfully corroborated using a
    different strain of mouse.

        Table 28.  Genetic and mutagenic effects
    Exposure conditions            Effect on exposed group           Reference
    Somatic cells

    2.45 GHz (CW), up to 21 W/kg   No increase in unstable chromo-   Huang et al.
    (in vivo), rectal temperature  some aberrations in Chinese       (1977)
    rose by up to 1.6 0C           hamster blood lymphocytes

    2.45 GHz (CW), 21 W/kg,        No sister chromatid exchanges     McRee et al.
    8 h/day for 28 days            in mouse bone marrow cells        (1981)

    2.375 GHz (CW) and             Partial hepatectomy in rats 5-6   Antipenko &
    2.75 GHz (pulsed).             days after exposure; cytological  Koveshnikova
    0.1, 0.5, 5.0 W/m2             study showed decreased rate of    (1987)
    7 h/day for 45 days            chromosomal aberrations after
                                   0.1 and 0.5 W/m2; increased
                                   after 5.0 W/m2
    Germ cells

    2.45 GHz (CW),                 Increased chromosome ex-          Manikowska -
    0.05-20 W/kg, for 6 h          changes and other cyto-           Czerska et al.
    over 2 weeks                   genetic abnormalities in germ     (1985)
                                   cells exposed as spermatocytes;

    2.45 GHz (CW),                 No chromosome abnormalities       Beechey et al.
    0.05-20 W/kg, for 6 h          in germ cells exposed as stem     (1986)
    over 2 weeks                   cells; rectal temperature in 20
                                   W/kg group rose by up to 3 °C

    1.7 GHz (CW), 25-45 W/kg,      Induction of dominant lethal      Varma &
    for 30 min, or 5-9 W/kg,       mutations in exposed mice;        Traboulay
    for 40 min over 2 weeks        data inclusive                    (1977)

    2.45 GHz (CW), 1.7 kW/m2,      Increased dominant lethality      Goud et al.
    for 70 s                       reduced male fertility            (1982)

    2.45 GHz (CW), 43 W kg,        No change in dominant             Saunders et
    for 30 min                     lethality, but reduced            al. (1983)
                                   pregnancy rate and pre-
                                   implantation survival

    2.45 GHz (CW), 5 W/kg, for     No chromosomal abnormalities;     Saunders et
    120 h over 8 weeks             no change in pregnancy rate       al. (1988)
                                   or dominant lethality

    Table 28 (continued)
    Exposure conditions            Effect on exposed group           Reference
    2.45 GHz (CW) at 50 W/m2       No consistent pattern of          Berman et al.
    (0.9-4.7 W/kg) 4 h/day for     responses, increased fetal        (1980)
    > 90 days                      mortality not related to
    - at 100 W/m2, 5 h/day         decreased live fetuses; no
    for 5 day                      sperm cell mutagenesis
    - at 280 W/m2, 4 h/day, 5
    days/week over 4 weeks
             In general, the data in Table 28 suggest that the only exposures
    that are potentially mutagenic are those at high RF power densities,
    which result in substantial increase in temperature.

    7.3.10  Cancer-related studies

         A summary of cancer-related animal studies is given in Table 29.
    The number and types of studies are limited.

         Exposure to RF levels sufficiently high to induce hyperthermia
    has generally resulted in tumour regression following transplantation
    of tumour cells (Preskorn et al., 1978; Roszkowski et al., 1980). In
    contrast, an increase in tumour progression has been observed in mice
    exposed long-term at lower, possibly thermogenic, SARs (Szmigielski et
    al., 1982). This effect was related to a non-specific stress. The
    authors suggested a transient shift in immune surveillance resulting
    in a lowering of resistance to neoplastic growth, as a likely
    explanation. Exposure at about 1 W/kg did not have any effect on
    melanoma growth in mice (Santini et al., 1988).

         The effects of exposure on spontaneous or chemically-induced
    tumours have also been examined. In contrast to transplantation
    studies, these can test for an effect on the process of
    carcinogenesis. Two early studies (Prausnitz & Suskind, 1962; Skidmore
    & Baum, 1974), relevant to cancer induction, but in which the
    methodology was flawed in relation to an analysis of this end-point,
    are described for completeness. An increased incidence of monocytic
    leukosis (defined as a non-circulating neoplasm of white-blood cells)
    and lymphatic or myeloid leukaemia (defined as a circulating
    "leukosis") was reported in Swiss mice exposed to thermally
    significant levels (half the acute LD50) of 9.27 GHz pulsed RF, for 5
    days per week for 59 days (Prausnitz & Susskind, 1962). However, the
    study suffered several deficiencies: leukosis and leukaemia were
    inadequately defined, infection may well have confounded the results,
    a large proportion of mice died without a cause of death being
    identified, and statistical analysis was absent (Roberts 1983; Kirk

        Table 29.  Cancer-related studies
    Exposure conditions             Effect on exposed group           Reference
    Transplanted tumour cells

    2.45 GHz (CW), 35 W/kg, for     Retarded tumour growth and        Preskorn et
    20 min/day during days 11-      tumour incidence in sarcoma-      al. (1978)
    14 of gestation; offspring      injected offspring of exposed
    injected with sarcoma           pregnant mice; rectal temperature
    cells at 16 days of age         of dams rose over 2 °C; exposed
    exposed for 36 days             mice had increased longevity

    2.45 GHz (CW), 25 W/kg,         Temporary tumour regression       Roszkowski et
    2 h/day for 7 days;             followed by renewed tumour        al. (1980)
    Injection of sarcoma            growth 12 days later, when
    cells in mice 14 days           exposure 14 days after tumour
    after, or just after,           injection; accelerated tumour
    RF exposure                     growth, if exposed before
                                    implantation of tumour;
                                    lung metastases increased

    2.45 GHz (CW), 2-3 W/kg         RF caused increase in             Szmigielski
    or 6-8 W/kg, 2 h/day, for       sarcoma colonies in lungs in      et al. (1982)
    6 days/week; mice exposed       mice injected intravenously
    from 6 weeks of age to          with these cells; chronic via
    12 months of stress             confinement caused similar
                                    increase in lung tumours as
                                    2-3 W/kg, but 6-8 W/kg produced
                                    higher increase in tumours

    2.45 GHz (CW and pulsed)        No difference in mean tumour      Santini et
    10 W/m2, 1.2 W/kg prior         surface area/animal, or in        al. (1988)
    to, and during, B16 melanoma    mean survival time between
    tumour transplantation and      exposed or control mice
    growth; exposed for
    2.5 h/day, 6 times/week for
    15 days, prior to injection of
    melanoma cells, then exposed
    to same schedule until death

    Spontaneous or chemically-induced tumours

    2.45 GHz (CW), 2-3 W/kg         SAR-dependent acceleration of     Szmigielski
    or 6-8 W/kg, 2 h/day, for       mammary tumours in mice           et al. (1982)
    6 days/week, mice exposed       genetically predisposed to these
    from 6 weeks of age to          tumours, and acceleration of skin
    12 months of stress             tumours in mice painted with the
                                    carcinogen 3,4-benzopyrene (BP)

    Table 29 (continued)
    Exposure conditions             Effect on exposed group           Reference
    2.45 GHz (CW), 100 W/m2         Increased development of          Szmigielski
    4-5 W/kg, for 2 h/day, 5-6      chemically-induced hepatomas      et al. (1988)
    days/week for a few months      and sarcomas in mice; survival
                                    of exposed mice decreased;
                                    increased frequency of skin
                                    tumours in mice given
                                    subcarcinogenic dose of BP

    2.45 GHz (10 µs pulses at       Total incidence of neoplasia      Guy et al.
    800 Hz) square wave-            not significantly different       (1985)
    modulated at 8 Hz,              from that in controls; however,
    0.4 W/kg, continuous exposure   increased number of primary
    at 2-27 months of age           malignancies (18) occurred early
    (lifetime study of rats)        in exposed group compared with
                                    controls (5)
             Skidmore & Baum (1974) reported that exposure for 5 days per week
    for 33 weeks to very short pulses (5 ns rise time; 550 ms decay time)
    of high field strength (447 kV/m) pulsed at 5 Hz, resulted in a
    reduced incidence of leukaemia in AKR/J mice (which spontaneously
    develop a high incidence of lymphatic leukaemia between 26 and 52
    weeks of age) compared with controls at the end of the exposure.
    However, the absence of a complete analysis of leukaemia incidence
    (and other causes of death) precludes any conclusion being drawn from
    this study. The authors also reported a zero incidence of mammary
    tumours in 1-year-old female Sprague-Dawley rats that had been exposed
    for 38 weeks; evaluation was probably premature for this end-point,
    the tumours occur spontaneously mainly in older rats. A later study
    (Baum et al., 1976) reported no effects on mammary tumour incidence
    and other lesions in rats exposed for 94 weeks.

         Two studies merit particular attention. The long-term exposure of
    mice at SARs of between 2 and 8 W/kg resulted in an increase in the
    number of sarcoma cell colonies in the lungs (following the injection
    of sarcoma cells), as shown in Fig. 22, and in an SAR-dependent
    increase in the rate of development of spontaneous mammary tumours and
    chemically-induced skin tumours. Repeated microwave exposure, followed
    by a "sub-carcinogenic" dose of carcinogen, resulted in an increased
    number of skin tumours. A study of 100 rats exposed for most of their
    lifetime at about 0.4 W/kg did not show any increased incidence of
    non-neoplastic lesions compared with control animals; longevity was
    very similar in both groups. However, the overall incidence of primary
    malignancy in the exposed group (18) was significantly greater than
    the control value (5), but was reported to be similar to the
    spontaneous incidence given in the literature for the particular
    strain of rat. Under these circumstances, it is difficult to draw any
    firm conclusions.

    FIGURE 22

         Tumour weights were not significantly different in rats implanted
    with mammary adenocarcinoma tissue and either exposed 25 days later to
    2 kHz magnetic fields of up to 2 mT for 1 h a day for 9 days or not
    exposed (Baumann et al., 1989). Handling and restraint stress in
    animals were identified as possible confounders for the detection of
    subtle magnetic field effects.

    7.3.11  Summary and conclusions

         Most of the biological effects of acute exposure to RF fields are
    consistent with responses to induced heating, resulting either in
    rises in tissue or body temperature of about 1 °C or more, or in
    responses for minimizing the total heat load. Most responses in
    different animal species, exposed under various environmental
    conditions, have been reported at SARs above about 1-2 W/kg.

         These animal (particularly primate) data indicate the types of
    response that are likely to occur in humans subject to a sufficient
    heat load. However, direct quantitative extrapolation to humans is
    difficult, given species differences in responses, in general, and in
    thermoregulatory ability particularly.

         The most sensitive animal responses to heat loads are
    thermoregulatory adjustments, such as reduced metabolic heat
    production and vasodilation, with thresholds ranging between about
    0.05 and 5 W/kg, depending on environmental conditions. However, these
    reactions form part of the natural repertoire of thermoregulatory
    responses that serve to maintain normal body temperatures.

         Transient effects seen in exposed animals that are consistent
    with responses to increases in body temperature of 1 °C or more
    (and/or SARs in excess of about 2 W/kg in primates and rats) include
    the reduced performance of learned tasks and increased plasma
    cortico-steroid levels. Other heat-related effects include temporary
    haematopoietic and immune responses, possibly in conjunction with
    elevated corticosteroid levels. The most consistent effects observed
    are reduced levels of circulating lymphocytes and increased levels of
    neutrophils, decreased natural killer cell function, and increased
    macrophage activation; an increase in the primary antibody response of
    B-lymphocytes has also been reported. Cardiovascular changes consonant
    with increased heat load, such as increased heart rate and cardiac
    output, have been observed, together with a reduction in the effects
    of drugs, such as barbiturates, the action of which can be altered by
    changes in circulation and clearance rates.

         Most animal data indicate that implantation and the development
    of the embryo and fetus are unlikely to be affected by exposures that
    increase maternal body temperature by less than 1 °C. Above these
    temperatures, adverse effects, such as losses in implantation, growth
    retardation, and post-natal changes in behaviour, may occur, with more
    severe effects occurring at higher maternal temperatures.

         Most animal data suggest that low RF exposure that does not raise
    body temperatures above the normal physiological range is not
    mutagenic; thus, such exposure will not result in somatic mutation or
    hereditary effects.

         There is much less information describing the effects of
    long-term, low-level exposure. So far, it is not apparent that any
    long-term adverse effects can result from exposures below thermally
    significant levels. The animal data indicate that male fertility is
    unlikely to be affected by long-term exposure at levels insufficient
    to raise body and testis temperatures. Cataracts have not been induced
    in rabbits exposed at 100 W/m2 for 6 months, or in primates exposed
    at 1.5 kW/m2 for 3 months.

         A study of 100 rats, exposed for most of their lifetime at about
    0.4 W/kg, did not show an increased incidence of non-neoplastic
    lesions or total neoplasias compared with control animals; longevity
    was very similar in both groups. There were differences in the overall
    incidence of primary malignancies, but these could not necessarily be
    attributed to the RF exposure. The possibility that exposure to RF
    might influence the process of carcinogenesis is of particular
    concern. So far, there is no definite evidence that RF exposure does
    have an effect, but there is clearly a need for further studies to be
    carried out. Overwhelmingly, the experimental data indicate that RF
    fields are not mutagenic, and so they are unlikely to act as
    initiators of carcinogenesis. In a few studies, evidence has been
    sought of an enhancement of the effect of a known carcinogen. The
    long-term exposure of mice at 2-8 W/kg resulted in an increase in the
    progression of spontaneous mammary tumours and of skin tumours in mice
    the skin of which was tested with a chemical carcinogen. Repeated RF
    exposure followed by a "sub-carcinogenic" dose of carcinogen resulted
    in an increased number of skin tumours; however, this study has been
    reported only briefly, and the authors noted the need for experimental

         In  in vitro studies, enhanced cell transformation rates were
    reported after RF exposure at 4.4 W/kg (alone or combined with
    X-radiation) followed by treatment with a chemical promotor. The
    latter data have not always been consistent between studies. It is
    clear that studies relevant to carcinogenesis need replicating and
    extending further, to reduce uncertainties in this area.

         A substantial body of data exists describing  in vitro
    biological responses to amplitude-modulated RF radiation at SARs too
    low to involve any response to heating. Some studies have reported

    effects after exposure at SARs of less than 0.01 W/kg, occurring
    within modulation frequency "windows" (usually between 1 and 100 Hz)
    and sometimes within power density "windows".

         Changes have been reported in the electroencephalograms of cats
    and rabbits, in calcium ion mobility in the brain tissue  in vitro
    and  in vivo, in lymphocyte cytotoxicity  in vitro, and in the  in
     vitro activity of an enzyme involved in cell growth and division.
    Some of these responses have been difficult to confirm, and their
    physiological or pathological consequences are not clear. However, any
    toxicological investigation should be based on tests carried out at
    appropriate levels of exposure. It is important that these studies be
    confirmed and extended to  in vivo studies and that the health
    implications, if any, for exposed people are determined. Of particular
    importance, would be studies that link extremely low frequency,
    amplitude-modulated RF interactions at the cell surface with changes
    in DNA synthesis or transcription. It is worth noting that this
    interaction implies a "demodulation" of the RF signal at the cell


         Epidemiology can be defined as the study of the occurrence of
    illness; its main goals are to evaluate hypotheses about the causation
    of illness and to relate disease occurrence to the characteristics of
    people and their environment. Epidemiological studies of human
    populations exposed to RF fields are few in number and are generally
    limited in scope. The principal groups studied have been people
    occupationally exposed in the military or in industry. Information
    about worker health status has generally come from medical records,
    questionnaires, and physical and laboratory examinations. Exposure
    data have come from personnel records, questionnaires, environmental
    measurements, and equipment-emission measurements. Determination of
    actual exposure to RF fields and to other risk factors for the same
    outcome is difficult in retrospective human studies.

         Some studies of controlled exposures of volunteers have provided
    valuable information on responses to RF exposure. These studies
    include warming and pain thresholds for RF heating of the skin, RF
    hearing, and RF shocks and burns. Clinical studies of accidental
    overexposures provide information on acute-exposure responses.

    8.1  Laboratory studies

    8.1.1  Cutaneous perception

         Exposure of the human body to RF fields can cause heating that is
    detectable by the temperature-sensitive receptors in the skin. Several
    investigators have determind experimentally the threshold intensities
    that cause sensations of perceptible warmth, pain, and delay in
    response to the stimulus in human subjects, as shown in
    Table 30.

         Adair (1983a) noted that RF exposures to frequencies of 30 GHz
    and above would probably be similar to infrared in their perception
    threshold values. However, over much of the RF spectrum, current
    standards are set at levels that are below those that most would
    consider detectable by sensation. Thus, cutaneous perception may be an
    indicator of exposure only at RF frequencies of the order of several
    gigahertz or more, which have wavelengths that are small in comparison
    with the length of the exposed body, i.e., wavelengths comparable
    with, or smaller than, the thickness of skin. Under these conditions,
    most of the energy is absorbed in the outer tissue layers

        Table 30.  Cutaneous perception in humans
    Exposure conditions           Effects and thresholds           Reference
    3 GHz to inner forearm        Threshold for pain               Cook (1952)
    Area 9.5 cm2 at 31 kW/m2:     20 s latency
    at 8.3 kW/m2:                 180 s latency
    Area 53 cm2 at 5.6 kW/m2:     180 s latency
                                  Pain at skin
                                  temperature of 46 °C

    3 GHz (pulsed) to inner       Latency varied between           Vendrik & Vos
    forearm (area 13 cm2)         less than 0.5 and 3.5 s      (1958)
    3-25 kW/m2

    3 and 10 GHz (pulsed)         Threshold for                    Hendler &
                                  perception:                      Hardy (1960);
    3 GHz, 1 s:                   600 W/m2                         Hendler et al.
    3 GHz, 5 s:                   320 W/m2                         (1963);
    10 GHz, 1 s:                  190 W/m2                         Hendler
    10 GHz, 5 s:                  130 W/m2                         (1968)
                                  Delay in response to
                                  warming 2.4-6.6 s

    2.88 GHz applied to fore-     Delay in response:               Schwan et al.
    head area 38 cm2                                               (1966)
     at 740 W/m2:                 15-73 s
     at 560 W/m2:                 50-180 s

    2.45 GHz (cw), 10 s to        Threshold for                    Justesen et
    forearm, area 100 cm2         perception of warmth             al. (1982)
                                  270 W/m2 (range 150-
                                  440 W/m2); sensation of
                                  warmth persisted for 0.7 s
                                  after exposure ceased

    2.88 GHz to forehead          Reaction time to                 Schwan &
    7 cm diameter                 warming not linearly             Foster (1980)
                                  proportional to reciprocal
                                  of incident power density
        containing thermal sensors. Cutaneous perception depends on the
    frequency of the incident RF field. In the resonance region,
    particularly, internal organs may suffer thermal damage (burns)
    without any sensation of warmth during the exposure.

         The studies that were conducted to determine the thresholds of
    thermal pain and warmth sensations, were on human beings exposed to
    frequencies predominantly in the approximate range of 3-10 GHz. These
    data can be summarized as follows:

    (a)  There is a delay in response or reaction time, from the onset
         of RF exposure to the sensation of warmth, which is variable,
         from fractions of a second to many seconds, depending on the RF
         frequency and power density;

    (b)  Reaction delay to the warming sensation of the RF field does
         not appear to be linearly proportional to the reciprocal of the
         incident power density;

    (c)  The threshold intensity for perception of warming or pain
         from the RF field depends on incident RF frequency, and the area
         and location of the exposed part of the body;

    (d)  The sensation of warmth can persist for a short time (part of
         a second) after termination of exposure to the RF field.

         It has been observed that pain thresholds are about two orders of
    magnitude above the detection threshold, but the value is less
    reliable and thermal damage can be produced at levels judged not
    painful, especially with deeply penetrating microwaves (Justesen,

         At lower frequencies, where the wavelengths are approximately
    equal to, or longer than, the human body, modelling studies have shown
    that much of the energy is absorbed within the body below the
    superficial skin layers. Cutaneous perception of RF energy is not a
    reliable sensory response that protects against potentially harmful
    levels of RF over the broad frequency range of 300 kHz-300 GHz (US
    EPA, 1984).

    8.1.2  Other perception thresholds

         Recently, Meister et al. (1989) reported effects on perception,
    performance, and well-being in eight volunteers, exposed to a 2.45 GHz
    field with power densities of up to 10 W/m2. Changes in visual
    perception thresholds were reported at 5 and 10 W/m2, other effects
    were also found at 10 W/m2. Although the health implication of these
    results seems to be questionable, replication studies should be done
    to validate the findings.

    8.1.3  Auditory effects

         Some people can perceive individual pulses of RF as audible
    clicks, chirping, or buzzing sounds, depending on the pulsing regime
    and intensity of the field. This phenomenon was first investigated by
    Frey (1961). Since that time, there have been many studies on the
    auditory responses of volunteers.

         Other radiation parameters (peak power density, energy density
    per pulse, and pulse width) are important in determining the threshold
    for humans. The phenomenon depends on the energy in a single pulse and
    not on the average power density. For instance, at 2.45 GHz and a

    threshold energy density of 0.4 J/m2 per pulse, an energy absorption
    per pulse of 16 mJ/kg, was calculated (Guy et al., 1975a).

         Most experimental results indicate that the auditory perception
    of RF pulses is due to the induction of thermoelastic waves in the
    head, rather than to direct brain stimulation by the RF. For a more
    extensive review see US EPA (1984) and NCRP (1986).

    8.1.4  Induced-current effects

         Currents can be induced in humans by RF fields in two ways: by
    physical contact with metallic objects charged by RF fields (see
    section 6.5), and by direct exposure to the electric and magnetic
    field components of the RF field (see sections 5.2.1 and 5.2.2).

         Currents induced in the body can be strong enough to exceed the
    stimulation thresholds of certain excitable tissues, such as nerves
    and muscles. At frequencies below about 100 kHz, biological effects
    produced by induced currents can be more important than heating.

         As is explained in section 5, results of experimental animal
    studies and theoretical models can be used to identify frequency
    dependent stimulation thresholds as a function of electric and
    magnetic field strength. These are shown in Fig. 23 and 24,

         Fig. 23 illustrates the unperturbed electric field strength as a
    function of frequency, which induces the indicated current density
    (the dashed, straight lines) in the head or heart region for a person
    exposed with the long axis of the body parallel to the orientation of
    the E-field. Curve A represents the threshold for stimulation of nerve
    or muscle cells and was derived from consideration of various data,
    including threshold values for the stimulation of sensory receptors,
    cardiac stimulation, stimulation of isolated neurons, stimulation
    thresholds for nerve/muscle systems, and induction of membrane

         Fig. 24 represents the sinusoidal magnetic field as a function of
    frequency for inducing current densities to the peripheral regions of
    the head or heart. The curve A is the same as for Fig. 23. Curve B is
    the threshold for diastole stimulation and represents a threshold
    curve for injury (compare also with Fig. 12).

         The data contained in Fig. 23 and 24 represent average values.
    The uncertainties in these data extend over a factor of about 10.

    FIGURE 23

    FIGURE 24

    8.1.5  Thermoregulation

         The need to understand and predict the thermal effects of
    electromagnetic energy deposition arises from several perspectives: in
    occupational and public health it is necessary to determine safe
    limits of environmental exposure to RF fields, in medical therapeutic
    applications there is a need to deposit electromagnetic energy in a
    predetermined quantity in a specific location and volume, and,
    finally, there is an RF energy deposition in diagnostic medical
    applications, such as magnetic resonance imaging.

         In all these instances, there is concern with the effects of
    locally elevated temperatures resulting from the deposition of RF
    energy, and the ability of the thermoregulatory system to dissipate
    the thermal load without unduly stressing the physiological systems

         In "thermally neutral" environments, with the body at rest, the
    total heat production of the human body amounts to about 100 W, and
    this heat production is offset by a heat loss of 100 W with 15-20 W of
    evaporative heat loss from the skin and the respiratory tract; the
    remainder of the heat loss is through radiation, convection, and
    conduction to the surrounding environment. In strenuous exercise,
    and/or in environments with elevated ambient temperatures and water
    vapour pressure, the body temperature tends to increase. Healthy
    individuals can sustain an increase in internal temperature from a
    normal 37.0 °C to 39.0 °C with the latter temperature representing the
    upper safe limit, even for young and healthy individuals. At 39.0 °C,
    sweating at a rate of about one litre per hour is induced, and heart
    rates become considerably elevated. From considerations of metabolism
    and heat exchange, any metabolic heat production in a limited volume
    of tissue does not result in a temperature rise exceeding 0.8 °C above
    deep body temperature.

         In normal, everyday life, thermal loads imposed by resting
    metabolism, the thermal environment, or by muscular activity, vary
    from a minimum of about 1 W/kg to 10 W/kg. Calculations relating
    whole-body SAR to increases in body temperature are, in general,
    supported by the limited results of studies of the responses of
    patients and volunteers exposed to RF fields in magnetic resonance
    imaging systems (Schaefer et al., 1985; Gordon et al., 1986; Kido et
    al., 1987; Shellock & Crues, 1987, 1988; Shellock et al., 1989).

         In these studies, the subjects were at rest and in controlled
    environments. Exposure of healthy volunteers to up to 4 W/kg for 20-30
    minutes resulted in body temperature increases in the range of 0.1-0.5
    °C, confirming predictions derived from models of energy deposition
    and thermoregulatory response. These exposures resulted in minimal
    changes in blood pressure and respiration rate. At the higher SARs,
    subjects felt warm during the procedure and each of them had visible
    signs of sweating on their foreheads, chest, and abdomen.

         Thermal stresses in the form of increased metabolic rates during
    exercise, deposition of RF energy, or exposure to solar radiation,
    tend to result in rises in body temperature and activation of
    thermoregulatory responses, such as sweating and vasodilatation.
    Different individuals have widely varying abilities to tolerate such
    responses, depending on age, physical fitness, clothing, adaptation,
    etc. Thermal stress from RF energy absorption is more severe when it
    is combined with heavy clothing, or a very hot and humid environment.
    The thermal effect of RF energy absorption could be beneficial and
    stress reducing if it occurred in a cold or cool environment.

         Thermal stresses for vulnerable populations, such as infants who
    have an under-developed thermoregulatory system, or the elderly whose
    thermoregulatory systems are no longer fully competent, must be
    limited to less than that of an occupational population, but an
    absolute level is difficult to define.

         Mathematical models of the human thermal system make possible
    reasonably accurate predictions of the steady state and the dynamics
    of both the whole body thermal state, and local tissue temperatures,
    under a variety of internal and external thermal stresses (Stolwijk &
    Hardy, 1966, 1977; Wissler, 1964, 1981).

         The development of models of RF energy deposition was initially
    independent of the development of thermoregulatory models, though
    similar simplifications had to be accepted. The models for human
    thermoregulation and the models for RF energy deposition do not have
    the same priorities or the same capabilities for spatial definition.
    In addition, the level of knowledge of the parameters required for the
    implementation of these models is different for the two types of
    mathematical model. In human thermoregulation models, it is not of
    crucial importance to describe in detail the local blood flow response
    to tissue temperatures above 38 °C. However, in combined models, it is
    very important that this characteristic is adequately incorporated,
    particularly with respect to hyperthermia therapy.

         Models that deal simultaneously with RF energy deposition in the
    human body, and with the effects of the thermal environment on
    thermoregulation and heat transfer in the human body have difficult
    trade-offs between the degree of spatial definition that is pursued,
    the degree of detail in the thermoregulatory response, and the cost of
    computation required to produce and evaluate the predictions from such
    combined models.

    8.1.6  Contact currents

         Persons coming in contact with ungrounded or poorly grounded
    metallic objects in an RF field may experience perception, pain,
    shock, burn, or even more severe reactions. Such phenomena occur for
    sufficiently large objects and intense fields. These interactions are
    described in section 6.5.

    8.2  Epidemiological and clinical comparative studies

         In studies on RF-exposed human populations, epidemiological
    results are frequently based on estimates only of exposure
    characteristics (RF frequency, power density, and exposure duration)
    and some solely on a description of occupation. Despite these
    limitations, they may provide useful information on the possible
    effects of actual RF exposure in humans. In the assessment of RF-field
    effects, comparative, clinical studies of a limited number of exposed
    persons and controls may be useful.

         Studies of health effects from exposure to RF fields have been
    carried out since the 1940s, when man-made sources of RF energy led to
    the increasing exposure of occupational groups and the general
    population. These early studies have been reviewed (WHO, 1981). The
    majority of reports in the literature concern people exposed in
    military or industrial settings. Summaries of studies on the health of
    humans exposed to RF fields are given in Tables 31-33. A wide variety
    of conditions, symptoms, diseases, and clinical measurements have been

    8.2.1  Mortality and morbidity studies

         In the 1960s and 1970s, Soviet and Eastern European literature
    described a collection of symptoms, reported to occur in personnel
    industrially exposed to microwaves. These symptoms, which have been
    variously called the "neurasthenic syndrome", the "chronic
    overexposure syndrome", or "microwave sickness", are based on
    subjective complaints, such as headaches, sleep disturbances,
    weakness, decrease of sexual activity (lessened libido), impotence,
    pains in the chest, and general poorly defined feelings of non-well-
    being (Baranski & Czerski, 1976).
        Table 31.  Morbidity and mortality studies
    Exposure conditions           Effect on exposed group          Reference
    Radar (pulsed),two groups:    No difference in health          Czerski et al.
    (i) <2 (ii) >2 up to          status between 841 adult         (1974b);
    60 W/m2, for 1-10 years       males in groups (i) and (ii)     Siekierzynski
                                  et al. (1974a,b)

    Radar (pulsed), <50 W/m2      No effects in clinical           Djordevic et al.
    (<0.2 W/kg), for 5-10         evaluations in comparisons       (1979)
    years                         between 322 radar workers
                                  and 220 non-radar workers;
                                  however, more neurasthenic
                                  symptoms in exposed group

    Table 31 (continued)
    Exposure conditions           Effect on exposed group          Reference
    0.2-5 GHz (pulsed), approx.   No effect on mortality           Robinette &
    10 W/m2, 0.05 W/kg            in male military personnel       Silverman (1977);
    (max). Occasional exposure    followed for over 20 years,
    to 1 kW/m2                    exposed for 2 years on           Robinette et al.
                                  average                          (1980)
                                  (over 40 000 personnel)

    Males: 2.56-4.1 GHz (CW),     No effect on life span or        Lilienfield et
    0.05 W/m2 (max),              cause of death of 1800           al. (1978)
    0.0002 W/kg (max);            employees and 3000
    Females: 0.6-9.5 GHz          dependents of US Embassy
    (CW),0.018 W/m2 (max),        personnel
    0.0007 W/kg (max), for
    0.5-4 years average

    Long-term microwave           Higher frequency of              Friedman
    exposure of military          microwave exposure               (1981)
    personnel (interviews)        in 14 polycythaemia cases
                                  than in 17 age-matched

    Radar-exposed popula-         Increased cancer mortality       Lester & Moore
    tions near air force bases    compared with population-        (1982); Lester
                                  matched controls.                (1985).
                                  No increase in cancer mor-       Polson & Merritt
                                  tality compared with popu-       (1985)
                                  lation-matched controls

    Children exposed to various   Duration and severity of         Shandala &
    air pollutants and RF         tonsilitis increased             Zvinjatskovsky

    27 MHz shortwave dia-         Association between heart        Hamburger et al.
    thermy (questionnaire to      disease and work with            (1983)
    3004 physiotherapists)        shortwave therapy (number
                                  of treatments/week)

    Work at 27 MHz plastic        Upper limb paraesthesia          Bini et al.
    sealers (70% of measure-      and eye irritation noted         (1986)
    ments at the head and         among 30 exposed workers
    hands >300 V/m)               compared with 11 partially
                                  exposed and 22 unexposed

    Table 31 (continued)
    Exposure conditions           Effect on exposed group          Reference
    Military personnel            Increased risk of cancer         Szmigielski et al.
    exposed to RF/MW fields       morbidity in a retrospective     (1988)
    <2 W/m2 with daily            cohort study of military
    incidental (minutes)          personnel (study group size
    exposures of 2-10 W/m2        not given)
    (some times even
    100-200 W/m2)

    51 male/62 female             Increase rates of paraesthesia   Kolmodin-Hed-
    operators of plastic          in hands, neurasthenia, and      man et al. (1988)
    welding machines (27 MHz,     eye complaints; diminished
    50% of welders exceeded       2-point discrimination ability
    250 W/m2) 23 female controls
    (sewing machine operators)

    Amateur radio operators       Deaths from all causes less      Milham (1985)
                                  than expected from national
                                  rates; increased risk of

    1.3-10 GHz, 0.1 to 10-µs      No differences in                Nilsson et al.
    pulses, RF exposure of        neurological symptoms and        (1989)
    radar mechanics often         findings between 17 exposed
    exceeded 10 W/m2              and 12 controls; increased
                                  protein band in CSF in
                                  the exposed group
             These early studies suffered from various deficiencies and their
    results have not been replicated in later surveys. Some of the results
    could have been attributed to other working conditions (e.g.,
    Djordjevic et al., 1979), and, furthermore, it appears that the
    working environments for exposed and control groups were not similar
    in essential respects. Other factors could also have been operating to
    produce more subjective complaints among the exposed workers, e.g., a
    reporting bias because of enhanced awareness of the possible
    "microwave sickness" syndrome.

         Later studies on mortality and morbidity among US naval
    personnel, occupationally exposed to radars, found no differences
    between exposed and control groups (Robinette & Silverman, 1977;
    Robinette et al., 1980).

         In a study of US embassy personnel, with very low microwave
    exposures, no significant effects were found (Lilienfield et al.,
    1978). Studies on cancer mortality in populations around US Air Force
    bases have given conflicting results, even contradictory findings,
    when evaluating identical study groups (Lester & Moore, 1982; Polson

    & Merritt, 1985; Lester, 1985). However, there are studies indicating
    an increase in cancer in RF field-exposed populations. Friedman (1981)
    reported a limited number of polycythemia cases with histories of
    long-term exposure to microwaves, and, more recently, preliminary
    reports from a retrospective cohort study of Polish military
    personnel, occupationally exposed to RF, indicated an increased risk
    of cancer (Szmigielski et al., 1988). Also a case study on a radar
    mechanic, who developed acute myelogenous leukaemia, has been
    published (Archimbaud et al., 1989).

         Milham (1985), using records of licensed amateur radio operators
    living on the west coast of the USA, derived standardized mortality
    ratios (SMRs) and compared them with the mortility rates for the
    population in the USA. Although the overall mortality rate was lower
    for the radio amateurs, significantly raised SMRs were observed for
    some types of leukaemias. However, it should be noted that around a
    third of the radio amateurs were engaged in electrical/electronics
    occupations. This may have involved exposure to solvents, PCBs, and
    metal fumes. In general, studies on increased cancer risks in certain
    "electrical" occupations (see, e.g., WHO, 1984, 1987) mainly refer to
    exposure to 50/60 Hz magnetic and electric fields with little or no
    contribution of 300 Hz-300 GHz radiation.

         In studies on plastic welding machine operators, with RF exposure
    levels sometimes exceeding existing national standards, upper limb
    paraesthesias have been reported by Bini et al. (1986) and
    Kolmodin-Hedman et al. (1988).

         In a small study on radar mechanics, in which no differences were
    found in neurological symptoms and signs compared with controls,
    changes were reported in a protein band of the cerebral spinal fluid
    (Nilsson et al., 1989). Because this study was small, its significance
    with respect to health is unclear. The clinical observations of
    Nilsson need to be confirmed.

         Also described as part of the early "microwave sickness" syndrome
    (see above) were effects on heart rate including bradycardia as well
    as tachycardia, arterial hypertension (or hypotension), and changes in
    cardiac conduction. With reference to this, the increased risk of
    developing heart diseases found among physiotherapists working with
    shortwave diathermy (Hamburger et al, 1983) calls for further studies.

         The combined effects on children of various pollutants in the
    environment (RF, noise, chemicals etc.) were studied by Shandala &
    Zvinjatskovsky (1988), who found that the duration and severity of
    tonsilitis were increased in the presence of RF.

    8.2.2  Ocular effects

         In health studies on RF field-exposed workers, general eye
    irritation was described (Bini et al., 1986; Kolmodin-Hedman et al.,
    1988). Lens opacities and cataracts have also been noted in some

    studies, as shown in Table 32. In the most extensive study, however
    (Appleton & McCrossan, 1972; Appleton et al., 1975), commented on by
    Frey (1985) and Wike & Martin (1985), no differences were found
    between exposed and unexposed military personnel. Where cases of
    confirmed cataracts have been reported, exposures have exceeded 1

    8.2.3  Effects on reproduction

         Only a limited number of studies, as shown in Table 33, have
    investigated potential reproductive effects in humans exposed to RF in
    the work environment. Sigler et al. (1965) found a higher incidence of
    Downs syndrome in children whose fathers had worked with radars in the
    military. From interviews of the fathers in the Sigler study and
    additional information obtained from military records, Cohen et al.
    (1977) could not confirm the result that the fathers had either an
    excess of radar exposure or a larger proportion were exposed
    personnel. The contradictory results probably reflect the difficulties
    in exposure assessment in retrospective epidemiological studies.
        Table 32.  Lens opacities and cataracts in humans
    Exposure conditions           Effect on exposed group          Reference
    US Army and Air Force         No difference in cataract        Cleary et al.
    veterans, radar               incidence                        (1965)
    personnel, 2644 exposed,
    1956 controls

    Microwave workers,            More lens changes in             Cleary &
    736 exposed, 559              exposed group                    Pasternak (1966)

    Microwave workers,            More lens changes in             Majewska
    60 MHz-10.7 GHz,              exposed group (168 vs 148)       (1968)
    200 exposed, 200

    US military personnel,        No differences in                Appleton &
    91 exposed, 135 controls      incidence of lens                McCrossan
                                  opacities, vacuoles,             (1972)
                                  or subcapsular iridescence

    US military personnel,        Expanded study, same results     Appleton et al.
    1542 exposed, 801                                              (1975); Frey
    controls                                                       (1985); Wike &
                                                                   Martin (1985)

    US military radar             Lens abnormalities same          Odland (1973)
    personnel                     in exposed controls, except
    377 exposed, 320              higher in exposed with pre-
    controls                      existing visual defects

    Table 32 (continued)
    Exposure conditions           Effect on exposed group          Reference
    Two groups of microwave       No difference in lens            Siekierzynski
    workers:                      opacities between the            et al. (1974a,b)
    group 1: <2 W/m2              two groups
    group 2: 2-60 W/m2

    US Air Force and              No difference in                 Shacklett et al.
    civilian                      frequency of opacities,          (1975)
    personnel, 477 exposed,       vacuoles or posterior
    340 controls                  capsular iridescence

    53 radio-linemen              Increased incidence of           Hollows &
    installing and                posterior subcapsular            Douglas (1984)
    maintaining radio, TV,        cataracts
    and repeater towers;
    558 kHz-527 MHz,
    0.8-39.6 kW/m2
        Table 33.  Reproductive effects in humans
    Exposure conditions           Effect on exposed group          Reference
    Work with radar in the        Case-control study of the        Sigler et al.
    military                      fathers of 216 children          (1965)
                                  with Downs syndrome and
                                  216 matched control
                                  fathers: association between
                                  radar exposure and Downs

    Work with radar in the        Extended study from Sigler       Cohen et al.
    military                      et al. (1965) with additional    (1977)
                                  128 cases and 128 controls:
                                  no association between
                                  radar exposure of fathers
                                  and Down's syndrome

    3.6-10 GHz, hundreds to       Decreased sperm number in        Lancranjan
    thousands of mW/m2,           31 males (70% of whom with       et al. (1975)
    0.003-0.04 W/kg               neurasthenia) exposed for
                                  1-17 years (8-year average)
                                  compared with 30 healthy

    Table 33 (continued)
    Exposure conditions           Effect on exposed group          Reference
    Cohort study on pregnancy     Physiotherapists had a better    Kallen et al.
    outcome of 2018 female        than expected pregnancy          (1982)
    physiotherapists giving       outcome; higher use of
    birth to 2043 infants         shortwave units among physio-
                                  therapists giving birth to
                                  malformed or still-born

    305 female RF welders         No differences in pregnancy      Kolmodin-
                                  outcome compared with            Hedman et al.
                                  Swedish birth registers          (1988)

    Case-control study on         17% of "highly" exposed          Larsen et al.
    physiotherapists working      were boys; exposure also         (1991)
    with shortwave diathermy      associated with still-
                                  birth/death within a
                                  year, prematurity, and
                                  low birth weight
             Analysis of semen of 31 technicians with a very low-level
    microwave exposure, revealed a reduced number of sperm compared with
    a control group of 30 persons (Lancranjan et al., 1975). However, 70%
    of the exposed group suffered from neurasthenia, which might wholly or
    partly explain the results.

         In a health study on operators of plastic welding machines
    exposed to RF levels exceeding 250 W/m2 (Kolmodin-Hedman et al.,
    1988), the pregnancy outcome for 305 female plastic welders during
    1974-84 did not show any significant differences with the Swedish
    average concerning malformation or prenatal mortality.

         During the 1980s, two epidemiological studies indicated an
    adverse pregnancy outcome among physiotherapists working with
    shortwave diathermy (Kallen et al., 1982; Larsen et al., 1991). Kallen
    et al. (1982), in Sweden, reported that physiotherapists as a group
    had a slightly lower risk of perinatal deaths and major malformations
    than the Swedish population for the same period. However, the
    physiotherapists who gave birth to a malformed child, or who had a
    perinatal death, had RF exposures (from microwave and shortwave
    diathermy) higher than those recorded for the other physiotherapists.
    In a Danish case-control study on physiotherapists working with
    shortwave diathermy, Larsen et al. (1991) found that only 17% of the
    "highly exposed" newborn infants were boys, and that exposure was
    associated with stillbirth/death within a year, prematurity, and low
    birth weight. The results suggest further study is necessary before
    conclusions can be reached.

    8.2.4  VDU studies

         Concern about the effects of exposure to electromagnetic fields
    and particularly about pregnancy outcome has been expressed with
    regard to the use of VDUs. Work with such equipment may involve job
    stress and ergonomic problems and these can be confounding factors in
    studies of associated pregnancy outcomes. Studies have been reviewed
    by Repacholi (1985), Bergqvist & Knave (1988), and Blackwell & Chang

         Blackwell & Chang (1988) pointed out that, in the USA and the
    United Kingdom, about 10 million VDUs are in use. About 50% of these
    are possibly used by women of childbearing age, and there are some 20
    000 groups of women, in each of which at least 10 women could become
    pregnant in one year. Since the naturally occurring pregnancy failure
    rate is about 15%, there is a chance of about 29 "clusters" each year
    in which more than half the pregnancies end in failure.

         A large number of epidemiological studies have been conducted, in
    order to elucidate whether VDU work during pregnancy increases the
    risks of miscarriage or giving birth to a malformed child. While
    Goldhaber et al. (1988) suggested there was some evidence of increased
    spontaneous abortion rates among VDU operators, most studies have not
    shown this (Bryant & Love, 1989; Goldhaber et al., 1988; McDonald et
    al., 1988; Nielsen et al., 1989; Nurminen & Kurppa, 1988), or
    threatened abortion, changes in placental weight, and maternal blood
    pressure (Nurminen & Kurppa, 1988). Of these studies, just one
    (Schnorr et al., 1991) included the measurement and assessment of the
    emission of ELF and VLF electric and magnetic fields as exposure
    factors. In this study, a cohort of female telephone operators, who
    used VDUs at work, was compared with a cohort of operators who did not
    use VDUs. Exposure was assessed by the number of hours worked per
    week, from company records, and by measuring electric and magnetic
    fields (45-60 Hz and 15 kHz) at the VDU work stations and at the
    workstations without VDTs. Among 2430 women interviewed there were 882
    pregnancies (366 exposed, 516 controls) that met the criteria for
    inclusion in the study. No excess risk of spontaneous abortion was
    found among women who used VDUs during the first trimester of
    pregnancy (OR = 0.93, 95% CL, 0.63-1.38). There was no risk associated
    with the use of VDUs when accounting for multiple pregnancies, early
    and late abortions, and all fetal losses. No dose-response
    relationship was apparent when examining the number of hours at the
    VDU, or the measured electric and magnetic fields.

         The study by McDonald et al. (1988) was designed around all women
    who reported to 11 Montreal hospitals during 1982-84 for childbirths
    or spontaneous abortion. They were interviewed on working conditions
    during their current and previous pregnancies. Apart from an isolated
    increase in renal urinary defects, the study showed no evidence of
    increased malformation. However, the results are not so clear for
    spontaneous abortion, especially among previous abortions. The design
    of this study does, however, tend to exaggerate the odds ratio for VDU

    exposed compared with non-exposed in previous pregnancies (Bergqvist,
    1984; McDonald et al., 1988). By stratification, this systematic error
    has been eliminated, and then the apparent increase in odds among VDU
    exposed was absent (McDonald et al., 1988). A similar, but smaller,
    error is also likely with regard to spontaneous abortion among current

         In a case-control study performed at three Kaiser Permanente
    clinics in Northern California (Goldhaber et al., 1988), there was an
    increase in spontaneous abortion among VDU operators compared with
    referents. However, this significant increase was due to a trend in
    one of the job categories (clerical workers), while a decrease in
    relation to VDU work was reported for another job category (managers,
    professionals). This contrary information from two job categories has
    two ramifications: (1) the summary across job categories is not
    justified; and (2) it makes the interpretation of magnetic fields as
    a cause rather dubious, but does, instead, suggest job-specific
    factors as possible causal factors.

         Experimental studies, while showing a diverse outcome, have, as
    a whole, failed to demonstrate an effect on reproductive processes in
    magnetic field situations resembling those around VDUs.
    Epidemiological studies have failed to show a difference between women
    who worked and those who did not work at a VDU during pregnancy, and
    interest has now turned to possible differences related to work
    situations, e.g., stress, rather than physical emissions from the

    8.2.5  Conclusions

         In summary, the epidemiological and comparative clinical studies
    do not provide clear evidence of detrimental health effects in humans
    from exposure to RF fields. Some occupational groups, such as exposed
    physiotherapists and industrial workers, should be studied further.
    The question of whether RF might act as a carcinogen should be further
    evaluated in epidemiological studies.

         Occupational exposure to RF will be at higher levels than that
    encountered by the general population, and, thus, there is less
    likelihood of health effects in the general population as a whole.

    8.3  Clinical case studies and accidental overexposures

         In a survey of accidental overexposures to RF in the US Air Force
    (Graham, 1985), 26 out of 58 individuals, with exposures exceeding 100
    W/m2, reported that they had felt a warming sensation at the time of
    overexposure. In clinical examinations, no abnormal findings were
    recorded. Symptoms, such as headache, nausea, fatigue, malaise, and
    heart palpitations, were often reported, however. Some high-level
    exposures, e.g., at levels exceeding 5 kW/m2, resulted in anxiety
    reactions so severe that hospitalization and sedation were necessary.
    Similar symptoms were reported in a one-year, clinical, follow-up

    study on two men who were accidentally, acutely irradiated with
    600-900 W/m2 RF fields (Forman et al., 1982). Several months after
    the incidents, hypertension was diagnosed in both patients. Exposures
    to power densities of about 50 W/m2 for one or two hours were not
    found to result in harmful health effects (Hocking et al., 1988).

         In case reports, long-term neuropathies and chronic dysaesthesias
    have been described after excessive microwave exposures from
    malfunctioning microwave-ovens (Ciano et al., 1981; Tintially et al.,
    1983; Fleck, 1983; Dickason & Barutt, 1984; Stein 1985). Also severe
    burns have been reported at work with microwave ovens (Nicholson et
    al., 1987). Similarly, Castillo & Quencer (1988) described the case of
    a pilot who inadvertently stood in front of a functioning microwave
    airfighter radar system for approximately five minutes. At that time
    a moderate sensation of heat was perceived in the head and neck, and
    after some time interstitial oedema and coagulation necrosis developed
    in muscles of the neck. The pilot also noted a loss of recent memory
    and extreme sleepiness.


    9.1  Introduction

         The purpose of reviewing the scientific literature on effects of
    exposure of various biological systems to RF fields is to assess its
    possible impact on human health. Such an assessment is necessary for
    the development of standards and guidelines limiting exposure to RF of
    the general and working populations.

         One of the problems encountered in assessing the possible health
    effects of RF exposure over the whole range of frequencies covered in
    this publication (i.e., 300 Hz-300 GHz) is that most studies have been
    conducted at frequencies particularly in the low GHz region. Little
    information is available from studies of human populations and only
    limited data have been obtained on other biological systems,
    particularly animals exposed to RF at frequencies below 10 MHz and
    above 10 GHz.

         The following categories of effects must be considered for risk
    assessment. The first two of these are sufficiently well understood to
    be used in risk assessment and the development of recommended limits
    of exposure. The third category is reasonably well understood, but
    quantitative data are sparse and any comprehensive recommendations to
    protect workers and the general population have to be based on data at
    other frequencies. The effects noted in the last two categories are
    elaborately described and poorly understood. In view of their
    importance in the possible promotion of cancer or of reproductive
    failures, they must be considered. However, the lack of understanding
    and the total absence of quantitative relationships between these
    effects and either exposures or the outcomes in question makes it
    impossible to derive recommended limits of exposure.

         Points to consider for a health risk assessment of exposure to RF
    fields are:

    (a)  Absorption of RF energy causes tissue heating. This is
         recognized and has been well studied. This effect occurs from the
         absorption of RF fields, especially at the higher end of the
         frequency range (above about 1 MHz). RF heating is not directly
         equivalent to heating by other forms of energy, because of the
         very non-uniform energy deposition that occurs in biological

    (b)  At frequencies below about 100 MHz, currents can be induced in
         humans by physical contact with ungrounded metallic objects (see
         section 6.5). From 300 Hz to approximately 100 kHz, such currents
         may result in the stimulation of electrically excitable tissues
         above the threshold for perception or pain. At frequencies
         between approximately 100 kHz and 100 MHz, contact currents of
         sufficiently high density may cause burns.

    (c)  For frequencies below several hundred kHz, the predominant effect
         is stimulation of excitable tissue resulting from currents
         directly induced in the body by the RF fields. At these lower
         frequencies, thermal interactions occur only at energy levels
         much higher than interactions with excitable tissue.

    (d)  When RF energy is absorbed in the form of pulsed fields, the peak
         power density in the pulse should be considered separately from
         the average. Auditory perception is one example of a pulsed RF
         field effect.

    (e)  When RF fields are amplitude modulated, effects in tissues have
         been noted that do not manifest themselves with unmodulated RF
         fields. Such effects are reported to have a complex dependence on
         intensity and ELF modulation frequency. Too little information is
         available to determine whether such effects occur in humans and,
         thus, this effect cannot be used in a health risk assessment or
         for setting human exposure limits.

    9.2  Thermal effects

         A number of factors in everyday life tend to increase the heat
    load on the human body, such as high ambient temperatures, solar
    radiation, and basal and exercise metabolism. Energy production can
    reach levels of 3-6 W/kg in healthy people. In most individuals, the
    thermoregulatory system can remove heat from the body at these rates
    for extended periods of time. Limited experimental evidence and
    theoretical calculations suggest that the exposure of resting humans
    in moderate environmental conditions at whole body SARs of the order
    of 1-4 W/kg for 30 minutes results in body temperature increases of
    less than 1 °C. In addition, a review of the animal data (see section
    7.3.4) indicates a threshold for behavioural responses in the same 1-4
    W/kg range. Therefore, an occupational RF exposure guideline of 0.4
    W/kg, based on thermal consideration, leaves a considerable margin of
    safety for other limiting conditions, such as high ambient
    temperature, humidity, or physical activity. Higher energy absorption
    rates in extremities and limited body regions, do not appear to cause
    adverse effects, for SAR values below thresholds that are dependent on
    the body part and the volume.

         In infants, the frail elderly, and in individuals taking certain
    drugs, the thermoregulatory capacity may be much reduced and, as a
    result, their tolerance for the combined effects of RF exposure,
    exercise, solar radiation, and high ambient temperature, may be much
    lower. Recognition that this tolerance is lower dictates that
    guidelines for population exposure to RF fields be reduced. A
    whole-body average SAR of 0.08 W/kg offers an additional safety

         Significant overexposures at the higher frequencies that may
    occur in occupational environments may result in very high SARs in
    parts of the body, thus producing local burns. In such cases, the SAR

    is so high that the normal avenues of heat transfer from the exposed
    area are inadequate. The local tissue temperature quickly rises to
    levels that denature proteins. Such burns may occur at depths much
    greater than those usually associated with contact burns.

         Thus, standards should be developed that, at a minimum, limit
    exposure of the healthy and aware (occupational) population, so that
    the whole-body average SAR does not exceed 0.4 W/kg. Additional
    precautions must be exercised for situations that might cause large
    peak values of the SAR, in order to eliminate rapid elevation of local
    temperature by more than 1 °C. This requires that the peak (or local)
    SARs should not exceed about 2 W/100 g in the extremities and 1 W/100
    g in any other part of the body. The eye may need special
    consideration, possibly by averaging over a mass of 10 g (i.e., 100
    mW/10 g).

    9.3  RF contact shocks and burns

         At frequencies below a few hundred kilohertz, the electrical
    stimulation of excitable membranes of nerves and muscle cells is a
    well established phenomenon. These effects exist at very high
    environmental field strengths, unlikely to occur in the general
    environment. On the other hand, current densities sufficient for
    stimulation and other potentially harmful effects can be produced, if
    an individual makes contact with a conductive object energized by the
    electric field component of an RF source.

         For frequencies between 300 Hz and 100 kHz, perception, pain,
    startle, or even inability to let go, may result from physical contact
    with energized objects (see section 8.1.6). The thresholds are
    expressed in terms of the current and are strongly frequency
    dependent. Superficial and deep burns may occur as a result of contact
    with metallic objects exposed to RF fields over a wide frequency
    range. Sufficiently high current densities for contact burns can be
    attained in RF fields that are too low to cause direct heating or
    stimulation. Thresholds depend on the size and shape of the object,
    field frequency, length and type of contact, and other parameters.

         Field exposure guidelines should also contain RF limits to
    eliminate hazards from shocks and burns. In this context, it should be
    kept in mind whether the exposures occur under controlled or
    uncontrolled conditions. Under uncontrolled exposure conditions, it is
    not always possible to limit contact currents for some objects (e.g.,
    vehicles) so that electric field strengths have to be reduced to
    protect the general population. For workers, other measures, such as
    protective clothing or contact avoidance, provide viable alternatives
    for protection.

    9.4  Induced current densities

         At frequencies below approximately 1 MHz, interactions of RF
    fields with biological systems and potential hazards can be considered

    in terms of induced currents and their densities (see section 8.1.4).
    The use of induced current densities, however, is only appropriate for
    the assessment of acute, immediate effects, while it may have some
    limitations for the complete evaluation of long-term effects. The
    waveform of the RF field is an important factor to be considered in
    the response of biological systems. However, peak instantaneous fields
    strengths appear to be important in considering nerve and muscle cell
    stimulation and for perturbing cell functions. Generally, for
    frequencies above 300 Hz, the thresholds for effects increase with
    frequency, up to frequencies where thermal effects dominate. For the
    establishment of derived limits, the distribution of the current
    densities within the body induced from RF fields have to be
    considered. The treatment of this problem is restricted, at present,
    to relatively simplified situations.

    9.5  Pulsed RF fields

         Experimental data suggest that thresholds for the biological
    effects of absorbed energy at frequencies above hundreds of megahertz,
    when in the form of short duration pulses (approx. 1-10 µs), are lower
    than those for continuous fields at the same average energy level and
    the same SAR. This indicates that the peak value of energy transfer to
    the biological object can be an important determinant of the
    biological effect. A well-investigated effect is the perception of
    pulsed fields, such as from radar, as an audible sound described as a
    click, chirp, or knocking sensation (see section 8.1.3).

         Pulsed RF exposure effects observed in animals are suppression of
    a startle response, stunning, ocular effects, and alterations in
    responses to certain drugs. Thresholds in terms of the energy density
    per pulse or the peak electric field strength for a given pulse
    duration are known for these effects only at a limited number of
    frequencies. Suppression of startle response was observed for pulse
    durations of up to a few seconds. Shorter pulses with the same or
    greater energy had a slightly enhanced effect on startle.

         Since a single pulse, or a series of short pulses, of RF of very
    high peak power density, but very low average power density, can
    produce potentially harmful biological effects, it is necessary to
    limit the maximum energy density per pulse. The available scientific
    evidence is incomplete, and, therefore, the formulation of exposure
    limits for pulsed fields presents difficulties.

    9.6  RF fields amplitude modulated at ELF frequencies

         Effects have been reported in  in vitro systems and animals
    exposed to RF fields of low intensities amplitude modulated at ELF.
    Some of the same or similar effects have also been observed as a
    result of exposure to ELF and VF fields. The effects usually exhibit
    "window" characteristics, i.e., the effects occur only within
    relatively narrow ranges, in both the modulation frequency and field
    intensity. Even though the intensities of the fields in tissue at

    which these effects occur are below the broadband thermal noise, there
    are hypotheses that might account for such apparently aberrant
    behaviour. The biological significance and possible adverse health
    impact, if any, of the reported effects cannot be determined at this

    9.7  RF effects on tumour induction and progression

         There have been isolated reports that, in certain cell lines and
    in intact animals, RF exposures have been associated with increased
    growth rates of cells and tumours and with increases in the incidence
    of neoplastic transformations. Very few epidemiological studies have
    been reported. The available evidence does not confirm that RF
    exposure results in the induction of cancer, or causes existing
    cancers to progress more rapidly. Because of incompleteness and
    inconsistencies, the available scientific evidence is an entirely
    inadequate basis for recommendations of health protection guidelines. 


    10.1  General considerations

         The development of protection standards for any environmental
    agent is a difficult and complex task. Setting exposure limits
    requires an in-depth evaluation of the established scientific
    literature, since to base standards on preliminary data or unproven
    hypotheses means that the limit values may be either unprotective or
    unduly restrictive. Using established scientific data allows exposure
    limits to be determined with a higher degree of confidence about their
    level of protection.

         Certain criteria must be met, if claims of positive effects or
    negative data are to be accepted within the body of scientifically
    established effects (Michaelson, 1983; Repacholi, 1990):

    (a)  Experimental techniques, methods, and conditions should be as
         completely described and objective as possible.
    (b)  All data analyses should be fully and completely objective, no
         relevant data should be deleted from consideration, and uniform
         analytical methods should be used.
    (c)  Results should demonstrate an effect of the relevant variable at
         a high level of statistical significance using appropriate tests.
         The effects of interest should ordinarily be shown by different
         test organisms and the responses found be consistent.
    (d)  Results should be quantifiable and susceptible to confirmation by
         independent researchers. Preferably, the studies should be
         repeated and the data confirmed independently; or the claimed
         effects should be consistent with results of similar studies,
         where the biological systems involved were comparable.

         From the body of established literature, a distinction must be
    made between  in vitro and  in vivo studies.  In vitro studies are
    conducted to elucidate the mechanisms of interaction or to identify
    biological effects or exposure parameters that need to be further
    investigated to determine if they occur  in vivo. Standard-setting
    organizations can place only limited value on the results of  in vitro

         An important part of the rationale for any exposure standard is
    the definition of the population to be protected. Occupational health
    standards are aimed at protecting healthy adults, exposed as a
    necessary part of their work, who are aware of the occupational risk
    and who are likely to be subject to medical surveillance. General
    population standards must be based on broader considerations,
    including widely different health status, special sensitivities,
    possible effects on the course of various diseases, as well as
    limitations in adaptation to environmental conditions and responses to
    any kind of stress. Exposure limits for the general population must
    include an adequate additional safety factor, also taking into account
    the possibility of a 24-h exposure compared with 8-h occupational

    exposure (or whatever the duration of the workday). Additionally, the
    RF fields in the environment can be complex and may be affected by
    reflections from buildings.

         A distinction should be made between exposure limits and
    equipment emission standards. The latter are based on safe operational
    considerations, and should not allow exposure above the adopted
    exposure limits.

    Over the past decade, major advances in the study of RF fields have
    come from the development of dosimetry as reviewed in section 5.
    Methods of intercomparing the results of animal studies and relating
    them to the human situation, have been developed to facilitate
    standard-making. With increasing knowledge of RF dosimetry, standards
    are becoming more specific.

    10.2  Present trends

         Many countries have now established health protection standards
    or guidelines. There have been a number of in-depth reviews of current
    RF standards (Czerski, 1985; Sliney, 1988; Grandolfo & Mild, 1989;
    Repacholi, 1990; Szmigielski & Obara, 1989). Most of the early
    standards addressed the microwave region only (300 MHz-300 GHz),
    because of the introduction and proliferation of radars,
    telecommunications, and radio and TV broadcasting. Later standards
    recognised the vastly expanded use of the electromagnetic spectrum,
    especially at lower frequencies, where concerns were raised about RF
    exposures from induction heaters, heat sealers, and other industrial

         RF exposure standards development is continuing, at present, and
    with the availability of detailed reviews elsewhere, standards in
    various countries and their rationales are not discussed here.

         The maximum RF exposure levels permitted in some standards differ
    by one to two orders of magnitude (factors between 20 and 100). It may
    be speculated that these differences result from: (a) the physical and
    biological effects data selected as the basis for the standards, (b)
    the interpretation of these data, (c) the different purposes to be
    served by the standards, (d) the compromises made between levels of
    risk and degrees of conservatism, and (e) the influence of preceding
    standards in each particular nation and in neighbouring areas having
    allied socio-political outlooks. In recent years, an increasing number
    of countries have adopted standards with limits identical, or very
    close, to those of IRPA.

    10.3  Recommendations by the IRPA

         A joint WHO/IRPA Task Group on Radiofrequency and Microwaves
    reviewed existing scientific literature (WHO, 1981). An evaluation of
    the health risks of exposure to electromagnetic fields was made and
    the rationale for the development of exposure limits was considered.

    The Task Group suggested that RF exposure to power densities in the
    range 1-10 W/m2 were acceptable for occupational exposure throughout
    a complete working day and that higher exposures might be acceptable
    for some frequency ranges and occasional exposure. For the general
    population, it was suggested that lower, unspecified, exposure levels
    were appropriate.

         In 1984, IRPA issued recommendations based on the WHO publication
    (WHO, 1981). These recommendations were more specific and provided
    guidance on limits of exposure to electromagnetic fields in the
    frequency range from 100 kHz to 300 GHz. The basic limits of exposure
    formulated for the frequency region of 10 MHz and above were expressed
    in terms of the specific absorption rate. In the frequency region
    below 10 MHz, basic limits were expressed in terms of the electric and
    magnetic field strengths.

         The IRPA revision (1988a) of its 1984 guideline, shown in Tables
    34 and 35, reaffirmed that research data, obtained over the past
    years, did not alter the threshold whole-body exposure for health
    effects on which the basic limit was derived: i.e., occupational
    whole-body exposure to RF fields should not exceed 0.4 W/kg. The
    revision was essentially a "fine tuning". Although the whole body
    average SAR might not exceed 0.4 W/kg, several reports indicated that,
    under certain conditions, local peak SARs in the extremities
    (particularly wrists and ankles) could exceed the 0.4 W/kg value by a
    factor of up to 300, at certain frequencies. Because of this, an
    additional recommendation was introduced to limit the body-to-ground
    current to 200 mA. It was also found that there was no adequate basis
    for identifying SAR limits as averaged over any gram of tissue. IRPA
    therefore recommended that the local SAR should not exceed 2W/100g in
    the extremities (hands, wrists, ankles, and feet) and 1 W/100g in any
    other part of the body.

         Occupational exposure to frequencies up to 10 MHz should not
    exceed the levels of unperturbed electric and magnetic field strengths
    (rms), given in Table 34, when the squares of the electric and
    magnetic field strengths are averaged over any 6-min period during the
    working day, provided that the body-to-ground current does not exceed
    200 mA, and the hazard for RF burns is eliminated. In general, RF
    burns will not occur if the current at the point of contact does not
    exceed 50 mA.

        Table 34.  IRPA occupational exposure limits for RF fieldsa
    Frequency      Unperturbed     Unperturbed     Equivalent plane-wave
    range          rms electric    rms magnetic    power density
                   field strength  field strength

    (MHz)          (V/m)b          (A/m)b          (W/m2)b       (mW/cm2)b
    0.1-1          614             1.6/f           -         -

    >1-10          614/f           1.6/f           -         -

    >10-400        61              0.16            10        1

    >400-2000      3f0.5           0.008f0.5       f/40      f/400

    >2000-300 000  137             0.36            50        5

    a From: IRPA (1988a).
    b f = frequency in MHz.

    Note: Hazards of RF burns should be eliminated by limiting currents
    from contact with metal objects. In most situations, this may be
    achieved by reducing the E values from 614 to 194 V/m in the range
    from 0.1 to 1 MHz and from 614/f to 194/f0.5 in the range from >1
    to 10 MHz.
         The limits of occupational exposure given in Table 34 for the
    frequencies between 10 MHz and 300 GHz are the working limits derived
    from the SAR value of 0.4 W/kg. They apply to whole-body exposure from
    one or more sources, averaged over any 6-min period during the working

         Exposure of the general population at frequencies up to 10 MHz
    should not exceed the levels of unperturbed electric and magnetic
    field strengths (rms) given in Table 35, provided that any hazard from
    RF burns is eliminated.

        Table 35.  IRPA general population exposure limits for RF fieldsa
    Frequency      Unperturbed     Unperturbed     Equivalent plane-wave
    range          rms electric    rms magnetic    power density
                   field strength  field strength

    (MHz)          (V/m)b          (A/m)b          (W/m2)b       (mW/cm2)b

    0.1-1          87              0.23/f0.5       -         -

    >1-10          87/f0.5         0.23/f0.5       -         -

    >10-400        27.5            0.073           2         0.2

    >400-2000      1.375f0.5       0.0037f0.5      f/200     f/2000

    >2000-300 000  61              0.61            10        1

    a From: IRPA (1988a).
    b f = frequency in MHz.
         For RF-field exposure of the general population at frequencies
    above 10 MHz, a SAR of 0.08 W/kg should not be exceeded when averaged
    over any 6 min and over the whole body. The limits of RF exposure of
    the general population given in Table 35 for the frequencies between
    10 MHz and 300 GHz, are derived from the SAR value of 0.08 W/kg. These
    limits apply to whole-body exposure from either continuous or
    modulated electromagnetic fields from one or more sources, averaged
    over any 6-min period during the 24-h day.

         Although very little information is available at present on the
    relation of biological effects with pulsed fields, a conservative
    approach is to limit pulsed electric and magnetic field strengths, as
    averaged over the pulse width, to 32 times the appropriate values
    given in Tables 34 and 35 for workers and the public; or to limit the
    equivalent plane-wave power density, as averaged over the pulse width,
    to 1000 times the corresponding values in Tables 34 and 35. In
    addition, the exposure as averaged over any 6 min should not exceed
    the values indicated in these tables.

    10.4  Concluding remarks

         Various approaches have produced different philosophies of
    protection guidelines and, thus, different exposure limits. It is
    apparent that, in the light of the continuous advancement of
    scientific results, the differences are decreasing and the revisions
    of existing standards or the setting of new ones reflect, at least,
    the tendency to merge to a common area.

         The international cooperation in the development of more uniform
    standards should be encouraged, because the lack of international
    agreement on the protection standards to be used for non-ionizing
    radiation constitutes a major drawback for the development of safety
    regulations in countries where they do not yet exist (Duchêne &
    Komarov, 1984). Efforts, outlined above, to achieve international
    cooperation in the field of non-ionizing radiation together with
    progress in knowledge on the biological effects will, hopefully, allow
    protection against non-ionizing electromagnetic fields to develop in
    a climate of international agreement.


         In situations where recommended limits can be exceeded,
    protective measures need to cover at least three types of potential

    -    exposure to RF electric and magnetic fields;
    -    contact with ungrounded or poorly grounded metallic objects; and
    -    interference with implantable and other medical devices.

         A programme of measurement surveys, inspections and education on
    worker safety, is necessary for an effective protection programme.
    Protective measures can be broadly divided into three categories:
    engineering controls, administrative controls, and personal

    11.1  Engineering measures

         Engineering controls for limiting human exposure to RF fields
    include design, siting, and installation of generating equipment.
    These depend on the purpose of the equipment and its operational
    characteristics. While strong fields around antennas of deliberate
    radiators, such as broadcast transmitters or radars, are unavoidable,
    appropriate design of the generating equipment can ensure negligibly
    weak fields around cabinets housing generators and other electronic
    circuits, and around transmission lines, such as cables and
    waveguides. The limitation of leakage fields at the design and
    manufacturing stages is more effective and less costly than later
    remedies, such as additional shielding, barriers, etc. At the
    frequency bands allocated for telecommunication, leakage (stray)
    fields are frequently at such low levels that they are an
    electromagnetic interference (EMI) problem rather than a health

         However, at frequencies allocated for industrial, scientific, and
    medical (ISM) uses, human exposure to strong stray fields is more
    likely to occur, as exemplified by RF industrial heaters (West et al.,
    1980; Stuchly et al., 1980; Eriksson & Mild, 1985; Joyner & Bangay,

         The siting and installation of deliberate transmitters must take
    into account exposure standards, as well as other technical
    considerations. It is important that an assessment of RF fields around
    various antennas is made and particularly, in the near-field, is
    verified by measurements. In siting deliberate radiators and
    evaluating exposure fields, the existence of multiple RF sources has
    to be taken into account where applicable. Often, broadcasting and
    other communication or navigation transmitters are located on the same
    tower. Furthermore, metal structures can cause reflections, and, thus,
    produce local enhancement of the fields. However, depending on the
    shape and location of the structure, it may also reduce the field. The
    reduction usually occurs for fields of frequencies below approximately

    10 MHz. If after the erection of a radio-transmitting structure, a
    building is also to be erected, then it is recommended that planning
    authorities seek guidance as to whether the new building could reflect
    fields in such a way that exposure limits could be exceeded. This
    would entail:

    (a) obtaining assurances from the broadcasters that the field
    intensities at the new site will not exceed relevant exposure limits,

    (b) seeking assurances from the broadcasters and the builders that the
    new building will not adversely affect broadcast coverage or
    significantly increase fields in the vicinity, due to reflections,
    such that the new levels exceed exposure limits.

         Engineering controls against excessive contact currents include
    the grounding of metal fences and other permanently located metal
    objects, and the installation of special grounding straps on mobile
    metal objects. Special techniques have to be used to ensure the
    effective grounding of fences and other objects. Furthermore, the
    contact currents should be measured after the grounding of the object.

     RF hot spot - a special case

         Tell (1990) conducted measurements and calculations directed to
    applications in the VHF and UHF broadcasting bands, but the concepts
    are also applicable to assessing RF hot spots near AM radio stations.
    He summarized the problem of RF hot spots as shown below.

         An RF hot spot may be defined as a point or small area in which
    the local values of electric and/or magnetic field strengths are
    significantly elevated above the typical ambient field levels and
    often are confined near the surface of a conductive object. RF hot
    spots usually complicate the process of evaluating compliance with
    exposure standards, because it is often only at the small area of the
    hot spots that fields exceed the exposure limits.

         RF hot spots may be produced by an intersection of narrow beams
    of RF energy (directional antennas), by the reflection of fields from
    conductive surfaces (standing waves), or by induced currents flowing
    in conductive objects exposed to ambient RF fields (re-radiation). RF
    hot spots are characterized by very rapid spatial variation of the
    fields and, typically, result in partial body exposures of individuals
    near the hot spots. Uniform exposure of the body is essentially
    impossible because of the high spatial gradient of the fields
    associated with RF hot spots.

         Several conclusions relevant to the exposure limit compliance
    issue have been drawn from the results and experience of this

    (a)  In the RF hot-spot situation, involving re-radiating objects, the
         high, localized fields at the hot spot do not generally have the
         capacity to deliver whole-body SARs to exposed individuals in
         excess of exposure guidelines, where SARs are limited to 0.08
         W/kg, regardless of the enhanced field magnitude. When the
         ambient RF field strengths are already at, or above, the exposure
         limits, the partial body exposure that accompanies proximity of
         the body to the object will generally increase the whole-body SAR
         only slightly.

    (b)  The high-intensity, electric and magnetic fields accompanying RF
         hot spots are not good indicators of whole-body or spatial peak
         SARs in the body, because of the high variability in coupling
         between the body of an exposed person and the hot-spot source.

    (c)  A measurement of the contact current that flows between the
         exposed person and a re-radiating object provides a meaningful
         alternative to field measurements and makes possible the
         evaluation of the peak SAR that may exist in a person touching
         the hot-spot source.

    (d)  For most practical exposure situations, when hand contact is made
         with a RF source, the greatest RF current will flow in the body,
         resulting in the worst-case situation for peak SAR. The contact
         case will result in significantly greater local SARs than for the
         non-contact condition and should be assumed to be the exposure of
         possible concern. This maximum SAR will be in the wrist, the
         anatomical structure with the smallest cross-sectional area
         through which the contact current can flow.

    (e)  Determining the wrist SAR for contact conditions requires a
         measurement of the contact current, knowledge of the conductivity
         of the tissues, and knowledge of the effective, conductive,
         cross-sectional area.

    (f)  To determine whether a particular RF source meets absorption
         criteria would be difficult and could be done only by a properly
         qualified laboratory or by an appropriate scientific body for a
         general class of equipment. In no case could a routine field
         survey determine conformance with the SAR criteria. The
         dosimetric procedures required for accurate SAR assessments
         remain complex and are relegated, for many cases, to the
         laboratory setting.

    (g)  Complex exposure environments, such as the interior of antenna
         towers, that present highly localized RF fields on climbing
         structures (e.g., ladders) are candidate locations where contact
         current measurements may prove effective in evaluating compliance
         with the exposure standards.

    (h)  Contact current measurements appear the only practical avenue of
         evaluating RF hot spots found in public environments, where

         ambient field levels are usually well within the standards, but
         local fields are apparently excessive.

    (i)  Maximum contact currents are associated with the points on a
         conducting object that generally exhibit the greatest surface
         electric field strengths. Apparently this is because such points
         have relatively low impedance and current is transferred when
         contacted by the relatively low impedance of the human body.

    11.2  Administrative controls

         Administrative controls that can be used to reduce or prevent
    exposure to RF fields are:

    -    access restriction, e.g., barrier fences, locked doors;
    -    occupancy restriction (only to authorized personnel);
    -    occupancy duration restriction (applicable only to workers);
    -    warning signs, and visible and audible alarms.

         Protective measures should be applied also against ancillary
    hazards such as the ignition of flammable gases and detonators or
    blasting caps. Specific guidance on how to deal with these problems is
    given elsewhere (Hall & Burstow, 1980; ANSI, 1985).

    11.3  Personal protection

         Protective clothing, such as conductive suits, gloves, and safety
    shoes, can be used. However, very few are commercially available and
    they are useful for RF shielding only over a specific frequency range.
    The results of testing a few microwave suits have been published
    recently (Guy et al., 1987; Joyner et al., 1989). Such suits should
    not be used indiscriminantly. Their use should be confined to ensuring
    compliance with exposure standards, when engineering and
    administrative controls are insufficient to do so (Joyner et al.,
    1989). Safety shoes have been proposed to reduce high local SARs for
    people on the ground plane (Kanai et al., 1984). Safety glasses have
    also been proposed for RF protection, but there is no convincing
    evidence that any of them are effective. On the contrary, they may act
    as receiving antennas and locally enhance the field.

    11.4  Medical surveillance

         Medical surveillance of workers should only be instituted if, in
    the normal course of their work, they could be exposed to RF-field
    intensities that would significantly exceed the general population
    limits. Other than a pre-employment general medical examination to
    determine baseline health status, a medical surveillance programme
    would serve little purpose, unless workers could reasonably be exposed
    to RF levels that approach or exceed occupational limits.

    Medical surveillance of RF workers involves:

    (a)  The assessment of the health status of the worker before
         commencing work (pre-employment assessment), during work, if
         overexposures occur, and on termination of work involving RF

    (b)  The detection and early treatment of signs of any adverse health
         effects that might be due to RF exposure.

    (c)  The maintenance of precise and adequate medical records for
         future epidemiological studies. The nature of the work and the
         physical parameters of RF exposure (field strengths, exposure
         durations, etc.) for each worker should be documented very

         In many countries, the initial and periodic medical examinations
    of workers are a legal requirement; in others, industries and
    governmental agencies may require pre-employment and periodic
    examinations. Contraindications to employment involving RF exposure
    should be identified by national authorities.


         When RF exposure exceeding occupational limits occurs, depending
    on the circumstances, a medical examination may be required. It should
    be noted that no unique syndrome for RF exposure has been identified
    requiring highly specialized treatment. Treatment can be expected to
    be symptomatic. From very high local exposures to RF of frequencies in
    the GHz range, deep burns and local tissue necrosis may be observed
    with a long-term and severe evolution. Very strong fields in the kHz
    and low MHz range could result in symptoms due to involuntary muscle
    contractions or stimulation of nervous tissue.

         When RF over-exposure exceeds occupational limits, the following
    is suggested (Hocking & Joyner 1988):

    (a)  The circumstances causing the over-exposure should be determined
         and corrected.

    (b)  An investigation should determine the extent of over-exposure of
         the worker(s).

    (c)  A medical examination should be conducted using data on the
         over-exposure to direct the type of clinical examination.

    11.5  Interference with medical devices and safety equipment

         The susceptibility of electronic devices, particularly emergency
    equipment, to interference from electromagnetic fields must be
    evaluated in hospitals, clinics, and industry. Certain devices are
    subject to interference at some frequencies at electric field

    strengths below those permitted in many standards (Maskell, 1985).
    Shielding of the devices or hospital rooms is a practical solution to
    the problem.

         A separate concern relates to electromagnetic interference with
    implantable medical devices and, most prominently, cardiac pacemakers.
    Improvements in pacemaker design have largely eliminated their
    susceptibility, however, in some instances, interference may still
    occur (Irnich, 1984; Sager, 1987). Cardiac pacemaker wearers need to
    be informed by their physician about its susceptibility to
    electromagnetic interference. RF workers who have implanted medical
    devices should be evaluated prior to commencing (or resuming) work
    (Hocking et al., 1991).


         Wherever possible, this glossary gives terms and definitions
    standardized by the International Electrotechnical Commission in the
    International Electrotechnical Vocabulary (IEV) or by the
    International Organization for Standardization (ISO). In such cases,
    the IEV number, or the number of the ISO standard in which the
    definition appears, is given in parentheses. This glossary was
    compiled from WHO (1981) and US EPA (1984).

     absorption. In radio wave propagation, attenuation of a radio wave
    due to its energy being dissipated, i.e., converted into another form,
    such as heat (IEV 60-20-105).

     absorption cross-section effective area. Of an [antenna], oriented
    for maximum power absorption unless otherwise stated, an area
    determined by dividing the maximum power absorbed from a plane wave by
    the incident power flux density, the load being matched to the
    [antenna] (IEV 60-32-035).

     antenna. The part of a radio system that is designed to radiate
    electromagnetic waves into free space (or to receive them). This does
    not include the transmission lines or waveguide to the radiator (IEV

     antenna, dipole. See dipole.

     antenna directivity. See directivity.

     antenna gain. See power gain of an antenna.

     antenna, horn. See horn.

     antenna isotropic. See isotropic radiator.

     antenna pattern. See radiation pattern.

     antenna regions. The distinction between electromagnetic fields far
    from, and those near to, the antenna. The regions are usually
    classified into three zones; near (static) zone, intermediate
    (induction) zone and far zone, located by drawing spheres of different
    radii around the antenna. The radii are approximately r < lambda for
    the near zone, r approx.= lamda for the intermediate zone, and r >
    lamda for the far zone. Note that lamda is the wavelength of the
    electromagnetic field produced by the antenna. In the far zone, field
    components (E and H) lie transverse to the direction of the
    propagation, and the shape of the field pattern is independent of the
    radius at which it is taken. In the near, and intermediate, zones, the
    field patterns are quite complicated, and the shape is, in general, a
    function of the radius and angular position (azimuth and elevation) in
    front of the antenna.

     antenna scanning. See scanning.

     attenuation. The progressive diminution in space of certain
    quantities characteristic of a propagation phenomenon (IEV 05-03-115).

     athermal effect (nonthermal effect). Any effect of electromagnetic
    energy on a body that is not a heat-related effect.

     blood-brain barrier. A functional concept to explain the observation
    that many substances transported by blood readily enter other tissues,
    but do not enter the brain. The barrier functions as if it were a
    continuous membrane lining the brain vasculature.

     calcium efflux. The release of calcium ions from a sample into a
    surrounding solution.

     circularly polarized. If the electric field is viewed as a point in
    space, the locus of the end point of the vector will rotate and trace
    out an ellipse, once each cycle.

     conductance. The reciprocal of resistance (IEV 05-20-170).  Symbol:
     G. Unit: siemens (S).

     conductivity. The scalar or matrix quantity whose product by the
    electric field strength is the conduction current density (IEV
    121-02-1). It is the reciprocal of resistivity.

     continuous wave. A wave whose successive oscillations are, under
    steady-state conditions, identical.

     current density. A vector of which the integral over a given surface
    is equal to the current flowing through the surface. The mean density
    in a linear conductor is equal to the current divided by the
    cross-sectional area of the conductor (IEV 05-20-045.

     cycle. The complete range of states or values through which a
    phenomenon or periodic function passes before repeating itself
    identically (IEV 05-02-050).

     depth of penetration. For a plane wave electromagnetic field,
    incident on the boundary of a good conductor, the depth of penetration
    of the wave is the depth at which the field strength of the wave has
    been reduced to 1/e, or approximately 37% of its original value.

     dielectric constant. See permittivity.

     dielectric material. A class of materials that act as electric
    insulators. For this class, the conductivity is presumed to be zero,
    or very small. The positive and negative charges in dielectrics are
    tightly bound together so that there is no actual transport of charge
    under the influence of a field. Such material alters electromagnetic

    fields because of induced charges formed by the interaction of the
    dielectric with the incident field.

     dipole. A centre-fed open antenna excited in such a way that the
    standing wave of current is symmetrical about the mid point of the
    antenna (IEV 60-34-005).

     directivity. That property of an antenna by virtue of which it
    radiates more strongly in some directions than in others (IEV

     dosimetry. The measurement or the determination by calculations of
    the internal electric field strength or induced current density, or of
    the specific absorption (SA) or specific absorption rate (SAR)
    distributions, in humans or animals exposed to electromagnetic fields
    and waves.

     duty factor. The ratio of (1) the sum of pulse durations to (2) a
    stated averaging time. For repetitive phenomena, the averaging time is
    the pulse repetition period (IEV 531-18-15).

     duty ratio. The ratio, for a given time interval, of the on-load
    duration to the total time (IEV 151-4-13).

     effective radiated power in a given direction. The power supplied to
    the antenna multiplied by the gain of the antenna in that direction
    relative to a half-wave dipole (IEV 60-32-095).

     electric field strength. The force on a stationary unit positive
    charge at a point in an electric field. This quantity may be measured
    in volts per metre (V/m).

     electromagnetic energy. The energy stored in an electromagnetic
    field (IEV 121-01-39).

     electromagnetic wave. A wave characterized by variation of the
    electric and magnetic fields (IEV 121-01-38).

     exposure, intermittent. This term refers to alternating periods of
    exposure and absence of exposure varying from a few seconds to several
    hours. If exposure lasting a few minutes to a few hours alternates
    with periods of absence of exposure lasting 18-24 hours (exposure
    repeated on successive days), "repeated exposure" might be a more
    appropriate term.

     exposure, long-term. This term indicates exposure during a major
    part of the lifetime of the biological system involved; it may,
    therefore, vary from a few weeks to many years in duration.

     far-field or far-zone. See radiation zone and antenna regions.

     field strength. In radio wave propagation, the magnitude of a
    component of specified polarization of the electric or magnetic field.
    The term normally refers to the root-mean-square value of the electric
    field (IEV 60-20-070).

     Fraunhofer region. Of a transmitting [antenna] system, the region
    which is sufficiently remote from the [antenna] system for the
    wavelets arriving from the various parts of the system to be
    considered to follow parallel paths (IEV 60-32-60).

     free space. An ideal, perfectly homogeneous medium possessing a
    relative dielectric constant of unity, in which there is nothing to
    reflect, refract, or absorb energy. A perfect vacuum possesses these

     Fresnel region. Of a transmitting [antenna] system, the region near
    the [antenna] system where the wavelets arriving from the various
    parts of the system cannot be considered to follow parallel paths (IEV

     frequency. The number of sinusoidal cycles made by electromagnetic
    waves in one second; usually expressed in units of hertz.

     gain. The increase in power between two points 1 and 2 at which the
    power is respectively P1 and P2, expressed by the ratio P2/P1
    in transmission units (IEV 55-05-185).

     gigahertz (GHz). One billion (1 000 000 000) hertz.

     hertz (Hz). One cycle per second.

     horn. An elementary [antenna] consisting of a waveguide in which one
    or more transverse dimensions increase towards the open end (IEV

     hyperthermia. The condition of a temperature-regulating animal when
    the core temperature is more than one standard deviation above the
    mean core temperature of the species in resting conditions in a
    thermoneutral environment.

     hypothermia. The condition of a temperature-regulating animal when
    the core temperature is more than one standard deviation below the
    mean core temperature of the species in resting conditions in a
    thermoneutral environment.

     impedance, wave (at a given frequency). The ratio of the complex
    number (vector) representing the transverse electric field at a point,
    to that representing the transverse magnetic field at that point. The
    sign is so chosen that the real part is positive (IEV 62-05-095).

     induction zone; near zone. The region surrounding a transmitting
    antenna in which there is a significant pulsation of energy to and fro

    between the antenna and the medium. Note: The magnetic field strength
    (multiplied by the impedance of space) and the electric field strength
    are unequal and, at distances less than one tenth of a wavelength from
    an antenna, vary inversely as the square or cube of the distance, if
    the antenna is small compared with this distance (IEV 60-32-055).

     irradiation, partial body. Exposure of only part of the body to
    incident electromagnetic energy.

     irradiation, whole body. Exposure of the entire body to incident
    electromagnetic energy.

     isotropic. Having the same properties in all directions.

     isotropic radiator. An [antenna] which radiates uniformly in all
    directions. This is a hypothetical concept used as a standard in
    connection with the gain function (IEV 60-32-110).

     kilohertz (kHz). One thousand (1000) hertz.

     magnetic field strength. An axial vector quantity which, together
    with magnetic induction, specifies a magnetic field at any point in
    space. It can be detected by a small magnetized needle, freely
    suspended, which sets itself in the direction of the field. The free
    suspension of the magnetized needle assumes,however, that the medium
    is fluid or that a small gap is provided of such a shape and in such
    a direction that free movement is possible. As long as the induction
    is solenoidal, the magnetic field is irrotational outside the spaces
    in which the current density is not zero, so that it derives a
    potential (non-uniform) therefrom. On the other hand, in the interior
    of currents, its curl, in the rationalised system, is equal to the
    vector current density, including the displacement current. The
    direction of the field is represented at every point by the axis of a
    small elongated solenoid, its intensity and direction being such that
    it counterbalances all magnetic effects in its interior, whilst the
    field intensity is equal to the linear current density of the solenoid
    (IEV 05-25-020).  Symbol: H.  Unit: ampere per metre (A/m).

     megahertz (MHz). One million (1 000 000) hertz.

     metabolic rate. See resting metabolic rate.

     metastable. A state that is not stable, but will exist for a long
    period of time.

     microwaves. Electromagnetic waves of sufficiently short wavelength
    that practical use can be made of waveguide and associated cavity
    techniques in their transmission and reception (IEV 60-02-025). Note:
    the term is taken to signify waves having a frequency range of 300
    MHz-300 GHz.

     modulation. The process of varying the amplitude, frequency, or
    phase of an RF carrier wave.

     near-field. See induction zone.

     non-ionizing radiation (NIR). Non-ionizing electromagnetic radiation
    incorporates all radiations and fields of the electromagnetic spectrum
    that do not normally have enough energy to produce ionization in
    matter. NIRs have an energy per photon less than about 12 eV,
    wavelengths longer than 100 nm, and frequencies lower than 300 THz.

     permeability. The scalar or matrix quantity whose product by the
    magnetic field strength is the magnetic flux density.  Note: For
    isotropic media, the permeability is a scalar; for anisotropic media,
    a matrix (IEV 121-01-37).  Synonym: absolute permeability. If the
    permeability of a material or medium is divided by the permeability of
    vacuum (magnetic constant) m, the result is termed relative
    permeability.  Symbol: µ.  Unit: henry per metre (H/m).

     permittivity; dielectric constant. A constant giving the influence
    of an isotropic medium on the forces of attraction or repulsion
    between electrified bodies (IEV 05-15-120).  Symbol: epsilon.  Unit:
    farad per metre (F/m).

     permittivity; relative. The ratio of the permitivity of a dielectric
    to that of a vacuum (IEV 05-15-140). Symbol: epsilonr.

     phase. Of a periodic phenomenon, the fraction of a period through
    which the time has advanced relative to an arbitrary time origin.

     plane wave. An electromagnetic wave in which the electric and
    magnetic field vectors lie in a plane perpendicular to the direction
    of wave propagation.

     polarization. A vector quantity representing the state of dielectric
    polarization of a medium, and defined at each point of the medium by
    the dipole moment of the volume element surrounding that point,
    divided by the volume of that element (IEV 05-15-115).

     polarization, plane of. In a linearly polarized wave, the fixed
    plane parallel to the direction of polarization and the direction of
    propagation.  Note: In optics the plane of polarization is normal to
    the plane defined above (IEV 60-20-010).

     power flux density. In radio wave propagation, the power crossing
    unit area normal to the direction of wave propagation (IEV 60-20-075).
     Symbol: W.  Unit: watts per square metre (W/m2).

     power (surface) density. Radiant power incident on a small sphere,
    divided by the cross-sectional area of that sphere.

     power gain of an antenna (in a given direction). The ratio, usually
    expressed in decibels, of the power that would have to be supplied to
    a reference antenna to the power supplied to the antenna being
    considered, so that they produce the same field strength at the same
    distance in the same direction; unless otherwise specified, the gain
    is for the direction of maximum radiation; in each case the reference
    antenna and its direction of radiation must be specified. For example:
    half-wave loss-free dipole (the specified direction being in the
    equatorial plane), an isotropic radiator in space (IEV 60-32-115).
     Symbol: G.  Unit: decibel (dB).

     Poynting vector. A vector, the flux of which through any surface
    represents the instantaneous electromagnetic power transmitted through
    this surface (IEV 05-03-85).  Synonym: power flux density.

     pulse amplitude. The peak value of a pulse (IEV 55-35-100).

     pulse duration. The interval of time between the first and last
    instant at which the instantaneous value of a pulse (or of its
    envelope if a carrier frequency pulse is concerned) reaches a
    specified fraction of the peak amplitude (IEV 55-35-105).

     pulse output power. The ratio of (1) the average output power to (2)
    the pulse duty factor (IEV 531-41-14).

     pulse repetition rate. The averge number of pulses in unit time
    during a specified period (IEV 55-35-125).

     radar. The use of radiowaves, reflected or automatically
    retransmitted, to gain information concerning a distant object. The
    measurement of range is usually included (IEV 60-72-005).

     radiation field. That part of the field of an [antenna] which is
    associated with an outward flow of energy (IEV 60-32-040).

     radiation pattern; radiation diagram; directivity pattern. A diagram
    relating power flux density (or field strength) to direction relative
    to the [antenna] at a constant large distance from the [antenna].
     Note: Such diagrams usually refer to planes or the surface of a cone
    containing the [antenna] and are usually normalized to the maximum
    value of the power flux density or field strength (IEV 60-32-135).

     radiation zone. The region sufficiently remote from a transmitting
    antenna for the energy in the wave to be considered as outward
    flowing.  Note: In free space, the magnetic field strength
    (multiplied by the impedance of space) and the electric field strength
    are equal in this region and, beyond the Fresnel region, vary
    inversely with distance from the antenna. The inner boundary of the
    radiation zone can be taken as one wavelength from the antenna if the
    antenna is small compared with the distance (IEV 60-32-050).

     radiofrequency (RF). Any frequency at which electromagnetic
    radiation is useful for telecommunication (IEV 55-05-060).  Note: in
    this publication RF refers to the frequency range 300 Hz-300 GHz.

     reflected wave. A wave, produced by an incident wave, which returns
    in the opposite direction to the incident wave after reflection at the
    point of transition (IEV 25-50-065).

     resonance. The change in amplitude as the frequency of the wave
    approaches or coincides with a natural frequency of the medium. The
    whole-body absorption of electromagnetic waves presents its highest
    value, i.e., the resonance, for frequencies (in MHz) corresponding
    approximately to 114/L, where L is the height of the individual in

     resting metabolic rate (RMR). The metabolic rate of an animal that
    is resting in a thermoneutral environment, but not in the
    postabsorptive state. The relationship of RMR (W/kg) to body mass, M
    (kg), is RMR = 3.86M-0.24 Basal metabolic rate (BMR) is the rate of
    energy production of an animal in a rested, awake, fasting, and
    thermoneutral state.

     root mean square (RMS). Certain electrical effects are proportional
    to the square root of the mean value of the square of a periodic
    function (over one period). This value is known as the effective value
    or the root-mean-square (RMS) value, since it is derived by first
    squaring the function, determining the mean value of this squared
    value, and extracting the square root of the mean value to determine
    the end result.

     scanning. Of a radar [antenna], systematic variation of the beam
    direction for search or angle tracking (IEV 60-72-095). The term is
    also applied to periodic motion of a radiocommunication antenna.

     scattering. The process by which the propagation of electromagnetic
    waves is modified by one or more discontinuities in the medium which
    have lengths of the order of the wave length (IEV 60-20-120); a
    process in which a change in direction or energy of an incident
    particle or incident radiation is caused by a collision with a
    particle or a system of particles (ISO 921). The extent to which the
    intensity of radiation is decreased in this manner is measured in
    terms of the  attenuation coefficient (scattering).

     shield. A mechanical barrier or enclosure provided for protection
    (IEV 151-01-18). The term is modified in accordance with the type of
    protection afforded; e.g., a magnetic shield is a shield designed to
    afford protection against magnetic fields.

     specific absorption (SA). The energy absorbed per unit mass of
    biological tissue, expressed in joules per kilogram (J/kg). SA is
    defined as the quotient of the incremental energy absorbed by, or
    dissipated in, an incremental mass contained in a volume element of a

    given density. SA is the time integral of specific absorption rate

     specific absorption rate (SAR). The rate at which energy is absorbed
    in body tissues, in watts per kilogram (W/kg). SAR is defined as the
    time derivative of the incremental energy absorbed by, or dissipated
    in, an incremental mass contained in a volume element of a given
    density. SAR is the dosimetric measure that has been widely adopted at
    frequencies above about 100 kHz.

     temperature regulation. The maintenance of the temperature or
    temperatures of a body within a restricted range, under conditions
    involving variable, internal and/or external heat loads. Biologically,
    the existence of some degree of body temperature regulation by
    autonomic or behavioural means.

     temperature regulation, autonomic. The regulation of body
    temperature by autonomic (i.e., involuntary) responses to heat and
    cold, which modify the rates of heat production and heat loss (i.e.,
    by sweating, thermal tachypnea, shivering, and variations in
    peripheral vasomotor tone and basal metabolism).

     temperature regulation, behavioural. The regulation of body
    temperature by complex patterns of responses of the skeletal
    musculature to heat and cold, which modify the rates of heat
    production and/or heat loss (e.g., by exercise, change in body
    conformation, and in the thermal insulation of bedding and, in humans,
    of clothing, and by the selection of an environment that reduces
    thermal stress).

     thermal effect. In the biological tissue or system, an effect that
    is related to heating of the tissue through the application of
    electromagnetic fields, and that can occur through other forms of

     thermogenic levels. Power densities of RF that produce a measurable
    temperature increase in the exposed object.

     thermoneutral zone. The range of ambient temperature within which
    metabolic rate is at a minimum, and within which temperature
    regulation is achieved by nonevaporative physical processes alone.

     thermoregulation. See temperature regulation.

     wave. A modification of the physical state of a medium which is
    propagated as a result of a local disturbance (IEV 05-03-005).

     waveguide. A system for the transmission of electromagnetic energy
    by a wave not of TEM type. It may, for example, consist of a metal
    tube, a dielectric rod or tube, or a single wire (IEV 62-10-005).

     wavelength. The distance between two successive points of a periodic
    wave in the direction of propagation, in which the oscillation has the
    same phase (IEV 05-03-030).  Symbol: lambda.  Unit: metre (m).

     wave, plane. A wave such that the corresponding physical quantities
    are uniform in any plane perpendicular to a fixed direction (IEV

     wave, transmitted. A wave (or waves) produced by an incident wave
    which continue(s) beyond the transition point (IEV 25-50-060).

     wave, transverse. A wave characterised by a vector at right angles
    to the direction of propagation (IEV 05-03-070).

     whole-body exposure. Pertains to the case in which the entire body
    is exposed to the incident electromagnetic energy or the case in which
    the cross section (physical area) of the body is smaller than the
    cross section of the incident radiation beam.


    ADAIR, E.R. (1983a) Sensation, subtleties, and standards: synopsis of
    a panel discussion. In: Adair, E.R., ed. Microwaves and
    thermoregulation. New York, Academic Press, pp. 231-238.

    ADAIR, E.R. (1983b) Initiation of thermoregulatory sweating by
    whole-body 2450 MHz microwave exposure. Fed. Proc., 42: 2658

    ADAIR, E.R. (1988) Microwave challenges to the thermoregulatory
    system. In: O'Connor, M.E. & Lovely, R.H., ed. Electromagnetic fields
    and neurobehavioral function, New York, Alan R. Liss Inc., pp.

    ADAIR, E.R. & ADAMS, B.W. (1980a) Microwaves induce peripheral
    vasodilation in squirrel monkey. Science, 207: 1381-1383.

    ADAIR, E.R. & ADAMS, B.W. (1980b) Microwaves modify thermoregulatory
    behaviour in squirrel monkey. Bioelectromagnetics, 1: 1-20.

    ADAIR, E.R. & ADAMS, B.W. (1982) Adjustments in metabolic heat
    production by squirrel monkeys exposed to microwaves. J. appl.
    Physiol.: Respirat. Environ. Exercise Physiol., 52: 1049-1058.

    ADAIR, E.R. & ADAMS, B.W. (1988) Microwave exposure at resonant
    frequency alters behavioral thermoregulation. In: Abstracts, 10th
    Annual Meeting of the Bioelectromagnetics Society, June 1988,
    Stamford, Connecticut, p. 45.

    ADEY, W.R. (1981) Tissue interactions with non-ionizing
    electromagnetic fields. Physiol. Rev., 61: 435.

    ADEY, W.R. (1983) Some fundamental aspects of biological effects of
    extremely low frequency (ELF). In: Grandolfo, M., Michaelson, S.M., &
    Rindi, A., ed. Biological effects and dosimetry of non-ionizing
    radiation. New York, London, Plenum Press, pp. 561-580.

    ADEY, W.R. (1988) Cell membranes: the electromagnetic environment and
    cancer promotion. Neurochem. Res., 13: 671.

    ADEY, W.R. (1989) The extracellular space and energetic hierarchies in
    electrochemical signalling between cells. In: Allen, M.J., Cleary,
    S.F., & Hawkridge, F.M., ed. Charge and field effects in biosystems-2.
    New York, Plenum Publishing Corporation, p.263.

    ADEY, W.R. (1990) Nonlinear electrodynamics in cell membrane
    transductive coupling. In: Membrane transport and information storage.
    New York, Alan Liss, Inc., pp. 1-27.

    ADEY, W.R., BAWIN, S.M., & LAWRENCE, A.F. (1982) Effects of weak
    amplitude-modulated microwave fields on calcium efflux from awake cat
    cerebral cortex. Bioelectromagnetics, 3: 295-307.

    [Primary mechanisms of action of radiofrequency radiation.] In: Akoev,
    I.G., ed. [Biological effects of electromagnetic fields. Problems of
    their use and safety.] Pushchino USSR Academy of Sciences (in

    ALBERT, E.N. (1977) Light and electron microscopic observations on the
    blood-brain barrier after microwave irradiation. In: Hazzard, D.G.,
    ed. Symposium on Biological Effects and Measurement of Radio
    Frequency/Microwaves, Rockville, Maryland, US Department of Health,
    Education and Welfare, pp. 294-304 (HEW Publication (FDA) 8026).

    ALBERT, E.N., SLABY, F., ROCHE, J., & LOFTUN, J. (1987) Effect of
    amplitude modulated 147 MHz radiofrequency radiation on calcium ion
    efflux from avian brain tissue. Radiat. Res., 109:19-27.

    ALLEN, S.G., BLACKWELL, R.P., & UNSWORTH, C. (1986) Field intensity
    measurements, body currents, specific absorption rates and their
    relevance to operators of dielectric PVC welding machines. In:
    Proceedings of BNCE Conference on Heating and Processing 1-3000 MHz,
    Cambridge, St John's College.

    ALLEN, S.G., BLACKWELL, R.P., UNSWORTH, C., & DENNIS, J.A. (1988) The
    measurement of body currents induced by radiofrequency fields. In: 7th
    International Congress of IRPA, Radiation Protection Practice, Vol.
    II, p. 607.

    ALLIS, J.W. & SINHA, B.L. (1981) Fluorescence depolarisation of red
    cell membrane fluidity. The effect of exposure to 1.0 GHz microwave
    radiation. Bioelectromagnetics, 2: 13.

    ALLIS, J.W. & SINHA-ROBINSON, B.L. (1987) Temperature-specific
    inhibition of human red cell Na+/K+ ATPase by 2450-MHz microwave
    radiation. Bioelectromagnetics, 8: 203-212.

    VANNI, R. (1988) Analysis of electric and magnetic fields leaking from
    induction heaters. Bioelectromagnetics, 9: 373-379.

    ANSI (1981) American National Standards Institute recommended practice
    for the measurement of hazardous electromagnetic fields - RF and
    microwave. New York, Institute of Electrical and Electronics
    Engineers, (ANSI Committee C95.5-1981).

    ANSI (1985) Safe distances from radiofrequency transmitting antennas
    for electric blasting operations. New York, Institute of Electrical
    and Electronics Engineers (ANSI C95.5-1985).

    ANSI (1990) American National Standard safety level with respect to
    human exposure to radiofrequency electromagnetic fields, 3kHz to 300
    GHz. New York, Institute of Electrical and Electronics Engineers (ANSI

    ANTIPENKO, E.N. & KOVESHNIKOVA, I.V. (1987) [Cytogenetic effects of
    microwaves of non-thermal intensity in mammals.] Dok. Akad. Nauk USSR,
    296(3): 724-726 (in Russian).

    APPLETON, B. & McCROSSAN, G.C. (1972) Microwave lens effects in
    humans. Arch. Ophthal., 88: 259-262.

    APPLETON, B., HIRSCH, S.E., & BROWN, P.V.K. (1975) Investigation of
    single-exposure microwave ocular effects at 3000 MHz. Ann. N.Y. Acad.
    Sci., 247: 125-134.

    A., MARINE, C., & MAURO, F. (1985) Tumour response to heat and
    radiation: prognostic variables in the treatment of neck node
    metastases from head and neck cancer. Int. J. Hypertherm., 1: 207-217.

    ARCHIMBAUD, E., CHARRIN, C., GUYOTAT, D., & VIALA, J.J. (1989) Acute
    myelogenous leukaemia following exposure to microwaves. Br. J.
    Haematol., 73(2): 272-273.

    BALCER-KUBICZEK, E.K. & HARRISON, G.H. (1985) Evidence for microwave
    carcinogenesis  in-vitro. Carcinogenesis, 6: 859-864.

    BALCER-KUBICZEK, E.K. & HARRISON, G.H. (1989) Induction of neoplastic
    transformation in C3H/10T+ cells by 2.45 GHz microwaves and phorbol
    ester. Radiat. Res., 117: 531-537.

    BARANSKI, S. & EDELWEJN, Z. (1974) Pharmacologic analysis of microwave
    effects on the central nervous system in experimental animals. In:
    Czerski, P., Ostrowski, K., Shore, M.L., Silverman, Ch., Suess, M.J.,
    & Waldeskog, B., ed. Biological effects and health hazards of
    microwave radiation. Warsaw, Polish Medical Publishers, pp. 119-127.

    BARANSKI, S. & EDELWEJN, Z. (1975) Experimental morphologic and
    electroencephalographic studies of microwave effects on the nervous
    system. Ann. N.Y. Acad. Sci., 247: 109-116.

    BARANSKI, S. & CZERSKI, P. (1976) Biological effects of microwaves.
    Stroudsburg, Pennyslvania, Dowden, Hutchinson, and Ross, 234 pp.

    BARANSKI, S, CZERSKI, P, & SZMIGIELSKI, S. (1971) The influence of
    microwaves on the mitosis  in vivo and  in vitro. Postepy Fiz.
    Medcznej, 6: 93-97.

    J.L. (1976) Biological measurements in rodents exposed continuously
    throughout their adult life to pulsed electromagnetic radiation.
    Health Phys., 30: 161.

    BAUMANN, S., COOPER, R., BERMAN, E., HOUSE, D., & JOINES, D. (1989)
    Lack of effects from 2000 Hz magnetic fields on mammary adenocarcinoma
    and reproductive hormones in rats. Bioelectromagnetics, 10 : 329-333.

    BAWIN, S.M., GAVALAS-MEDICI, R.J., & ADEY, W.R. (1973) Effects of
    modulated very high frequency fields on specific brain rhythms in
    cats. Brain Res., 58: 365-384.

    BAWIN, S.M., GAVALAS-MEDICI, R.J., & ADEY, W.R. (1974) Reinforcement
    of transient brain rhythms by amplitude-modulated VHF fields. In:
    Llaurado, J.G., Sances, A, & Battocletti, J.H., ed. Biological and
    clinical effects of low frequency magnetic and electric fields.
    Springfield, Charles C. Thomas, pp. 172-186.

    BAWIN, S.M., KACZMAREK, L.K., & ADEY, W.R. (1975) Effects of modulated
    VHF fields on the central nervous system. Ann. N.Y. Acad. Sci., 247:

    A.G. (1986) Cytogenetic effects of microwave irradiation on male germ
    cells of the mouse. Int. J. radiat. Biol., 50: 909-918.

    BERGQVIST, U. (1984) Video display terminals and health. Scand J. Work
    Environ. Health, 10(Suppl. 2): 1-87.

    BERGQVIST, U. & KNAVE, B.G. (1988) VDT work - An occupational health
    hazard? In: Repacholi, M.H., ed. Non-ionizing radiations: physical
    characteristics, biological effects and health hazard assessment.
    London, IRPA Publications, pp. 395-409.

    BERMAN, E. & CARTER, H.B. (1984) Decreased body weight in fetal rats
    after irradiation with 2450-MHz (CW) microwaves. Health Phys., 46:

    BERMAN, E., KINN, J.B., & CARTER, H.B. (1978) Observations of mouse
    fetuses after irradiation with 2.45 GHz microwaves. Health Phys., 35:

    BERMAN, E., CARTER, H.B., & HOUSE, D. (1980) Tests for mutagenesis and
    reproduction in male rats exposed to 2450 MHz (CW) microwaves.
    Bioelectromagnetics, 1: 65-76.

    BERMAN, E., CARTER, H.B., & HOUSE, D. (1981) Observations of rat
    fetuses after irradiation with 2450 MHz (CW) microwaves. J. microwave
    Power, 16: 9-13.

    BERMAN, E., CARTER, H.B., & HOUSE, D. (1982a) Reduced weight in mice
    offspring after  in utero exposure to 2450 MHz (CW) microwaves.
    Bioelectromagnetics, 3: 285-291.

    BERMAN, E., CARTER, H.B., & HOUSE, D. (1982b) Observations of Syrian
    hamster fetuses after exposure to 2450 MHz microwaves. J. microwave
    Power, 17: 107-112.

    BERMAN, E., CARTER, H.B., & HOUSE, D. (1984) Growth and development of
    mice offspring after irradiation  in utero with 2450 MHz microwaves.
    Teratology, 30: 402.

    BERNARDI, P., MURA, A., & VEGNI, L. (1981) Field measurements in
    proximity to medium frequency high power broadcast stations. IEEE
    First Mediterranean Electrotechnical Conference, Tel Aviv (Paper

    BERNHARDT, J.H. (1979) The direct influence of electromagnetic fields
    on nerve- and muscle cells of man within the frequency range of 1 Hz
    to 30 MHz. Radiat. environ. Biophys., 16: 309-323.

    BERNHARDT, J.H. (1985) Evaluation of human exposure to low frequency
    fields. In: The impact of proposed radiofrequency radiation standards
    on military operations. Neuilly sur Seine, France, NATO AGARD, pp.
    8.1-8.18 (AGARD lecture series No 138).

    BERNHARDT, J.H. (1986) Assessment of experimentally observed
    bioeffects in view of their clinical relevance and the exposure at
    work places. In: Bernhardt, J.H., ed. Biological effects of static and
    extremely low frequency magnetic fields. Proceedings of Symposium,
    Neuherberg, May 1985, Munich, MMV Medizin Verlag, pp. 157-168 (BGA
    Schriften 3/86).

    BERNHARDT, J.H. (1988) The establishment of frequency dependent limits
    for electric and magnetic fields and evaluation of indirect effects.
    Radiat. environ. Biophys., 27: 1-27.

    BERNHARDT, J.H. & PAULY, H. (1973) On the generation of potential
    differences across the membranes of ellipsoidal cells in an
    alternating electrical field. Biophysik, 10: 89-98.

    BICKMORE, R.W. & HANSEN, R.C. (1959) Antenna power densities in the
    fresnel region, Proc. IRE, 47: 2119-2120.

    BINI, M.G., IGNESTI, A., MILLANTA, L., RUBINO, N., & VANNI, R. (1980)
    A comparative analysis of the various potentially polluting RF
    sources. Alta Frequenza, XLIX: 76-84.

    N., & VANNI, R. (1986) Exposure of workers to intense RF electric
    fields that leak from plastic sealers. J. microwave Power, 21: 33-40.

    M.M. (1975) Microwave and infra-red effects on heart rate, respiration
    rate and subcutaneous temperature of the rabbit. J. microwave Power,
    10: 3-18.

    D.C., & HOUSE, D.E. (1979) Induction of calcium-ion efflux from brain
    tissue by radio-frequency radiation: Effects of modulation frequency
    and field strength. Radio Sci., 14(6S): 93-98.

    & FAULK, J.M. (1980a) Induction of calcium-ion efflux from brain
    tissue by radiofrequency radiation: Effect of sample number and
    modulation frequency on the power-density window. Bioelectromagnetics,
    1: 35-43.

    D.E. (1980b) Calcium-ion efflux from brain tissue: Power-density vs
    internal field-intensity dependencies at 50 MHz RF radiation.
    Bioelectromagnetics, 1: 277-283.

    W.T. (1985) A role for the magnetic field in the radiation-induces
    efflux of calcium ions from brain tissue,  in vitro.
    Bioelectromagnetics, 6: 327-337.

    R.J. (1988) Effect of ambient levels of power-line-frequency electric
    fields on a developing vertebrate. Bioelectromagnetics, 9(2): 129-140.

    BLACKMAN, C.F., KINNEY, L.S., HOUSE, D.E., & JOINES, W.T. (1989)
    Multiple power-density windows and their possible origin.
    Bioelectromagnetics, 10: 115-128.

    BLACKMAN, C.F., BENANE, S.G., HOUSE, D.E., & ELLIOTT, D.J. (1990)
    Importance of alignment between local DC magnetic field and an
    oscillating magnetic field in responses of brain tissue  in vitro and
     in vivo. Bioelectromagnetics, 11: 159-167.

    BLACKMAN, C.F., BENANE, S.G., HOUSE, D.E. (1991) The influence of
    temperature during electric- and magnetic-field-induced alteration of
    calcium-ion release from  in vitro brain tissue. Bioelectromagnetics,
    12: 173-182.

    BLACKWELL, R.P. (1980) Effects of microwave exposure on anaesthesia in
    the mouse. In: Proceedings of the International Symposium on
    Electromagnetic Waves and Biology, Jouy en Josas, June-July 1980.
    Paris, URSI, CNFRS, pp. 71-73.

    BLACKWELL, R.P. (1990) The personal current meter - A novel ankle
    device for the measurement of RF body current in a mobile subject. J.
    radiol. Prot., 10: 109-114.

    BLACKWELL, R. & CHANG, A. (1988) Video display terminals and
    pregnancy. A review. Br. J. Obstet. Gynaecol., 95: 446-453.

    BLACKWELL, R.P. & SAUNDERS, R.D. (1986) The effects of low-level
    radiofrequency and microwave radiation on brain tissue and animal
    behaviour. Int. J. radiat. Biol., 50: 761-787.

    BONKOWSKI, J. & MAKIEWICZ I. (1986) Very high& frequency
    electromagnetic energy - a hazard to medical personnel. Ochr. Prac.,
    40: 4-6.

    (1985) Estimating radiofrequency deposition in body NMR imaging. Magn.
    Res. Med., 2: 336-349.

    VEYRET, B. (1987) Effects of superimposed pulsed microwave and
    magnetic fields on the immune system of mice. In: Abstracts, 9th
    Annual Meeting of the Bioelectromagnetics Society, June 1987,
    Portland, Oregon, p. 75.

    BRH (1981) An evaluation of radiation emissions from video display
    terminals, Rockville, Maryland, US Department of Health and Human
    Services, Bureau of Radiological Health, FDA (Publication No. FDA

    (1988) Teratogenic effects of exposure to radiofrequency (27.12 MHz)
    from a shortwave diathermy unit. Ind. Health, 26(1): 1-10.

    BRYANT, H.E. & LOVE, E.S. (1989) Video display terminal use and
    spontaneous abortion risk. Int. J. Epidemiol., 18: 132-138.

    BUDINGER, T.F. (1988) Safety of NMR  in vivo imaging and
    spectroscopy. In: Budinger, T.F. & Margulis, A.R., ed. Medical
    magnetic resonance: a primer-1988. Berkeley, Society of Magnetic
    Resonance in Medicine, Inc., pp. 327-343.

    BYUS, C.V., LUNDAK, R.L., FLETCHER, R.M., & ADEY, W.R. (1984)
    Alterations in protein kinase activity following exposure of cultured
    human lymphocytes to modulated microwave fields. Bioelectromagnetics,
    5: 341-351.

    BYUS, C.V., KARTUN, K., PIEPER, S., & ADEY, W.R. (1988) Increased
    ornithine decarboxylase activity in cultured cells exposed to low
    energy modulated microwave fields and phorbol ester tumor promoters.
    Cancer Res., 48: 4222-4226.

    CAIRNIE, A.B. & HARDING, R.K. (1981) Cytological studies in mouse
    testis irradiated with 2.45 GHz continuous-wave microwaves. Radiat.
    Res., 87: 100-108.

    CARPENTER, R.L. (1979) Ocular effects of microwave radiation. Bull.
    N.Y. Acad. Med., 55: 1048-1057.

    CARPENTER, R.L. & VAN UMMERSON, C.A. (1968) The action of microwave
    power on the eye. J. microwave Power, 3: 3-19.

    CARPENTER, R.L., BIDDLE, D.K., & VAN UMMERSON, C.A.(1960a) Opacities
    in the lens of the eye experimentally induced by exposure to microwave
    radiation. IRE Trans. med. Electronics, ME-7: 152-157.

    CARPENTER, R.L., BIDDLE, D.K., & VAN UMMERSON, C.A. (1960b) Biological
    effects of microwave radiation with particular reference to the eye.
    In: Proceedings of the Third International Conference on Medical
    Electronics, London, International Federation for Medical Electronics,
    pp. 401-408.

    CARPENTER, R.L., FERRI, E.S., & HAGAN, G.L. (1974) Assessing
    microwaves as a hazard to the eye - Progress and problems, pp.
    178-185. In: Czerski, P., Ostrowski, K., Silverman, C., Shore, M.L.,
    Suess, M.J., & Waldeskog, B., ed. Biologic effects and health hazards
    of microwave radiation. Warsaw, Polish Medical Publishers.

    CASTILLO, M. & QUENCER R.M. (1988) Sublethal exposure to microwave
    radar. J. Am. Med. Soc., 259 (3): 355.

    CHATTERJEE, I., WU, D., & GANDHI, O.P. (1986) Human body impedance and
    threshold currents for perception and pain for contact hazard analysis
    in the VLF-MF Band. IEEE Trans. biomed. Eng., 33: 486-494.

    & SZMIGIELSKI, S. (1983) Effects of microwave exposure  in utero on
    embryonal, fetal and postnatal development of mice. Biol. Neonate, 44:

    CHIABRERA, A., GRATTAROLA, M., & VIVIANI, R. (1984) Interaction
    between electromagnetic fields and cells: microelectrophoretic effect
    on ligand and surface receptors. Bioelectromagnetics, 5: 173-191.

    CHOU, C.-K. & GUY, A.W. (1973) Effect of 2450 MHz microwave fields on
    peripheral nerves. In: Digest of technical papers, IEEE International
    Microwave Symposium, Boulder, Colorado, June 1973, pp. 318-320.

    CHOU, C.-K., YEE, K.-C., & GUY, A.W. (1980) Microwave radiation and
    heart-beat rate of rabbits. J. microwave Power, 15: 87-93.

    CHOU, C.-K., YEE, K.-C., & GUY, A.W. (1985) Auditory response in rats
    exposed to 2.450 MHz electromagnetic fields in a circularly polarized
    waveguide. Bioelectromagnetics, 6: 323-326.

    CIANO, M. J., BURLIN, R., PARDIO, R., MILLS, R. L., & HENTZ, V. R.
    (1981) High frequency electromagnetic radiation injury to the upper
    extremity: local and systemic effects. A. plast. Surg., 7 (2):

    CLAPMAN, R.M. & CAIN, C.A. (1975) Absence of heart-rate effects in
    isolated frog heart irradiated with pulse modulated microwave energy.
    J. microwave Power, 10: 412-419.

    CLEARY, S.F. (1989) Biological effects of radiofrequency radiation: An
    overview. In: Franceschetti, G. Gandhi, O.P., & Grandolfo, M., ed.
    Electromagnetic biointeraction. Mechanisms, safety standards
    protection guides. New York, London, Plenum Press, pp.59-79.

    CLEARY, S.F. & PASTERNACK, B.S. (1966) Lenticular changes in microwave
    workers: A statistical study. Arch. environ. Health, 12: 23-29.

    CLEARY, S.F. & WANGEMANN, R.T. (1976) Effect of microwave radiation on
    pentobarbital-induced sleeping time. In: Johnson, C.C. & Shore, M.L.,
    ed. Biological effects of electromagnetic fields. Selected papers of
    the USNC/URSI Annual Meeting, Boulder, Colorado, October, 1975.
    Rockville, Maryland, US Department of Health, Education, and Welfare,
    Vol.1, pp. 311-323 (HEW Publication (FDA) 77-8010).

    CLEARY, S.F., PASTERNACK, B.S., & BEEBE, G.W. (1965) Cataract
    incidence in radar workers. Arch. environ. Health, 11: 179-182.

    CLEARY, S.F., GARBER, F., & LIU, L.M. (1982) Effects of X-band
    microwave exposure on rabbit erythrocytes. Bioelectromagnetics, 3:

    COHEN, B.H., LILIENFILED, A.M., KRAMER, A.M., & HYMAN, L.C.C. (1977)
    Parental factors in Down's Syndrome: Results of the second Baltimore
    case control study. In: Hook, E.B. & Porter, I.H., ed. Population
    cytogenetics - Studies in humans. New York, Academic Press, pp.

    (1980) Measurement of electric- and magnetic-field strengths from
    industrial radiofrequency (6-38 MHz). plastic sealers. Proc. IEEE, 68:

    CONOVER, D.L., MURRAY, W.E., LANG, J.M., & JOHNSON, P.H. (1986)
    Magnetic field measurements near RF industrial heaters.
    Bioelectromagnetics, 7: 83-90.

    COOK, H.F. (1952) The pain threshold for microwave and infra-red
    radiations. J. Physiol., 118: 1-11.

    COURTNEY, K.R., LIN, J.C., GUY, A.W., & CHOU, C.K. (1975) Microwave
    effect on rabbit superior cervical ganglion. IEEE Trans. microwave
    Theory Tech., MTT-23: 809-813.

    CZERSKI, P. (1985) Radiofrequency radiation exposure limits in Eastern
    Europe. J. microwave Power, 20: 233.

    CZERSKI, P., PAPROCKA-STONKA, E., & STOLANSKA, A. (1974a) Microwave
    irradiation and the circadian rhythm of bone cell mitoses. J.
    microwave Power, 9: 31-37.

    CZERSKI, P., SIERKIERZYNSKI, M., & GIDYNSKI, A. (1974b) Health
    surveillance of personnel occupationally exposed to microwaves. I.
    Theoretical considerations and practical aspects. Aerospace Med., 45:

    DALZIEL, C.F. (1954a) The threshold of perception currents. IEEE Trans
    Power Apparatus Syst., 73: 990-996.

    DALZIEL, C.F. (1954b) The threshold of perception currents. Elec. Eng.
    73: 625-630.

    D'ANDREA, J.A., GANDHI, O.P., & KESNER, R.P. (1976) Behavioral effects
    of resonant electromagnetic power absorption in rats. In: Johnson,
    C.C. & Shore, M.L., ed. Biological effects of electromagnetic waves.
    Rockville, Maryland, US Department of Health, Education, and Welfare,
    FDA, Vol. I, pp. 257-273 (HEW Publication (FDA) 77-8010).

    D'ANDREA, J.A., GANDHI, O.P., & LORDS, J.L. (1977) Behavioral and
    thermal effects of microwave radiation at resonant and nonresonant
    wavelengths. Radio. Sci., 12: 251-256.

    C.C., & ASTLE, L. (1979) Physiological and behavioral effects of
    chronic exposure to 2450 MHz microwaves. J. microwave Power, 14:

    STENSAAS, L.J., & SCHOENBERG, A.A. (1980) Physiological and behavioral
    effects of prolonged exposure to 915 MHz microwaves. J. microwave
    Power, 15: 123-135.

    & NEILSON, H.C. (1986a) Behavioral and physiological effects of
    chronic 2450 MHz microwave irradiation of the rat at 0.5 mW/cmi.
    Bioelectromagnetics, 7: 45-56.

    S., & GANDHI, O.P. (1986b) Intermittent exposure of rats to 2450 MHz
    microwaves at 2.5 mW/cm2: Behavioral and physiological

    DELGADO, J.M.R., LEAL, J., MONTEAGUDO, J.L., & GRACIA, M.G. (1982)
    Embryological changes induced by weak, extremely low frequency
    electromagnetic fields. J. Anat., 134: 533.
    effects. Bioelectromagnetics, 7: 315-328.

    DE LORGE, J.O. (1976) The effects of microwave radiation on behaviour
    and temperature in Rhesus monkeys. In: Johnson, C.C. & Shore, M.L.,
    ed. Biological effects of electromagnetic waves. Selected papers of
    the USNC/URSI Annual Meeting, Boulder, Colorado, October, 1975.
    Rockville, Maryland, US Department of Health, Education, and Welfare,
    Vol.1, pp. 168-174 (HEW Publication (FDA) 77-8010).

    DE LORGE, J.O. (1979) Operant behaviour and rectal temperature of
    squirrel monkeys during 2.45-GHz microwave irradiation. Radio Sci.,
    14: 217-225.

    DE LORGE, J.O. (1984) Operant behaviour and colonic temperature of
     Macaca mulatta exposed to radio frequency fields at above resonant
    frequencies. Bioelectromagnetics, 5: 232-246.

    DE LORGE, J.O. & EZELL, C.S. (1980) Observing responses of rats
    exposed to 1.28-and 5.62-GHz microwaves. Bioelectromagnetics, 1:

    DELPIZZO, V. & JOYNER, K.J. (1987) On the safe use of microwave and
    shortwave diathermy units. Austral. J. Physiother., 33: 152-161.

    DENO, D.W. (1974) Calculating electrostatic effects of overhead
    transmission lines. IEEE Trans. Power Appl. Syst., PAS-93: 1458-1471.

    DENO, D.W. (1977) Current induced in the human body by high-voltage
    transmission line electric field-measurement and calculation of
    distribution and dose. IEEE Trans. Power Appar. Syst., PAS - 96:

    DEWITT, J.R., D'ANDREA, J.A., EMMERSON, R.Y., & GANDHI, O.P. (1987)
    Behavioral effects of chronic exposure to 0.5 mW/cm2 of 2,450 MHz
    microwaves. Bioelectromagnetics, 8: 149-157.

    DICKASON, W.L. & BARUTT, J.P. (1984) Investigation of an acute
    micro-wave-oven hand injury. J. hand Surg. [Am]., 9A (1): 132-135.

    DIMBYLOW, P.J. (1987) Finite difference calculations of current
    densities in a homogeneous model of a man exposed to extremely low
    frequency electric fields. Bioelectromagnetics, 8: 355-375.

    DIMBYLOW, P.J. (1988) The calculation of induced and absorbed power in
    a realistic, heterogeneous model of the lower leg for applied electric
    fields from 60 Hz to 30 MHz. Phys. Med. Biol., 33(12): 1453-1468.

    DJORDJEVIC, Z. & KOLAK, A. (1973) Change in the peripheral blood of
    the rat exposed to microwave radiation (2400 MHz) in conditions of
    chronic exposure. Aerosp. Med., 44: 1051-1054.

    DJORDJEVIC, Z., LAZAREVIC, N., & DJOKOVIC, V. (1977) Studies on the
    haematologic effects of long-term, low-dose microwave exposure. Aviat.
    space environ. Med., 48: 516-518.

    (1979) A study of the health status of radar workers. Aviat. space
    environ. Med., 50: 396-398.

    DUCHENE, A. & KOMAROV, E. (1984) International Programmes and
    Management of Non-ionizing Radiation Protection, Proceedings of the
    IRPA 6th International Congress, Berlin. Cologne, TUV Rheinland, Vol.
    3, pp. 1307-1310.

    [Methodical approaches to hygienic evaluation of radiolocation
    devices.] Gig. i Sanit., 8: 42-44 (in Russian).

    DUMANSKY, YU.D., KARACHEV, I., & IVANOV, D. (1985a) [Questions of
    hygienic standard - setting of electromagnetic energy (EME).] Gig. i
    Sanit., 3: 39-42 (in Russian).

    (1985b) [Methods of sanitary defence zone construction and
    construction limiting zone in radiolocation device location. In: Means
    and methods of diminishing the adverse action of aviation upon the
    environment under aviatransport processes.] Kiev, KIIGA, pp. 79-85 (in

    DUMANSKY, YU., IVANOV, D., & KARACHEV, I. (1986) [Evaluation of
    electromagnetic situation in dwelling space and indoors.] Gig. i
    Sanit., 3: 80-81 (in Russian).

    DUMANSKY, YU., IVANOV, D., & NIKITINA, N.G. (1988) [Definition of
    sanitary-defence zone and control for bichanel meteorologic
    radiolocators.] Gig. i sanit., 5: 31-33 (in Russian).

    DURNEY, C.H. (1980) Electromagnetic dosimetry for models of humans and
    animals: a review of theoretical and numerical techniques, Proc. IEEE,
    68: 33-40.

    M.F., LORDS, J.L., RYSER, D.K., ALLEN, S.J., & MITCHELL, J.C. (1978)
    Radiofrequency radiation dosimetry handbook, 2nd ed. Texas, Brooks Air
    Force Base, USAF School of Aerospace Medicine (Report SAM-TR-78-22).

    DURNEY, C.H., MASSOUDI, H., & ISKANDER, M.F. (1986) Radiofrequency
    radiation dosimetry handbook, 4th ed. Texas, Brooks Air Force Base,
    USAF School of Aerospace Medicine, pp. 286 (Report SAM-TR-85-73).

    Microwave radiation-induced calcium ion efflux from human
    neuroblastoma cells in culture. Bioelectromagnetics, 5: 71-78.

    DUTTA, S.K., GHOSH, B., & BLACKMAN, C.F. (1989) Radiofrequency
    radiation-induced calcium efflux enhancement from human and other
    neuroblastoma cells in culture. Biolectromagnetics, 10: 197-202.

    EDWARDS, G.S., DAVIS, C.C., SAFFER, J.D., & SWICORD, M.L. (1984)
    Resonant microwave absorption of selected DNA molecules. Phys. Rev.
    Lett., 53: 1284-1287.

    EDWARDS, G.S., DAVIS, C.C., SAFFER, J.D., & SWICORD, M.L. (1985)
    Microwave field driven acoustic modes in DNA. Biophys. J., 47:

    EHD (1980) Canada-wide survey of non-ionizing radiation emitting
    medical devices. Part I. Short-wave and microwave devices. Ottawa,
    Canada, Environmental Health Directorate, Health and Welfare Canada
    (Publication 80-EHD-52).

    ELDER, J.A. & CAHILL, D.F., ed. (1984) Biological effects of
    radiofrequency radiation, Research Triangle Park, NC, US Environmental
    Protection Agency (EPA-600/8-83-026).

    ELLIOTT, G., GIES, P., JOYNER, K.H., & ROY, C.R. (1986)
    Electromagnetic radiation emissions from video display terminals
    (VDTs). Clin. exp. Optom., 69: 53-61.

    EMERY, A.F., SHORT, R.E., GUY, A.W., & KRANING, K.K. (1976) The
    numerical thermal simulation of the human body when undergoing
    exercise or nonionizing electromagnetic irradiation. Trans. Am. Soc.
    Mech. Eng., pp. 284-291.

    EPRI (1979) Biological effects of high-voltage electric fields: An
    update. Vol.1 and 2. Final report prepared by IIT Research Institute,
    Chicago, Illinois. Palo Alto, California, Electric Power Research
    Institute (EPRI EA-1123).

    EPSTEIN, B.R. & FOSTER, K.R. (1983) Anisotropy in the dielectric
    properties of skeletal muscle. Med. Biol. Eng. Comput., 21: 25-55.

    ERIKSSON, A. & MILD, K. H. (1985) Radiofrequency electromagnetic
    leakage fields from plastic welding machines. Measurements and
    reducing measures. J. microwave Power, 20: 95-107.

    FERRI, E.S. & HAGAN, G.J. (1976) Chronic low-level exposure of rabbits
    to microwaves. In: Johnson, C.C. & Shore, M.L., ed. Biological effects
    of electromagnetic waves. Selected papers of the USNC/URSI Annual
    Meeting, Boulder, Colorado, October 1975. Rockville, Maryland, US
    Department of Health, Education, and Welfare, Vol.1, pp. 129-142 (HEW
    Publication (FDA) 77-8010).

    FISHER, P.D., POZNANSKI, M.J., & VOSS, W.A.G. (1982) Effect of
    microwave radiation 2450 MHz on the active and passive components of
    efflux from human erythrocytes. Radiat. Res., 92: 441-422.

    FLECK, H. (1983) Microwave oven burn. Bull. N. Y. Acad. Med., 59(3):

    FORMAN, S. A., HOLMES, C.K. McMANAMON, T.V., & WEDDING, W.R. (1982)
    Psychological symptoms and intermittent hypertension following acute
    microwave exposure. J. occup. Med., 24(11): 932-934.

    FOSTER, K.R. & SCHWAN, H.P. (1986) Dielectric properties of tissues.
    In: Polk, C. & Postow, E., ed. CRC handbook of biological effects of
    electromagnetic fields. Boca Raton, Florida, CRC Press, pp. 27-96.

    FOSTER, K.R. & SCHWAN, H.P. (1989) Dielectric properties of tissues
    and biological materials. Crit. Rev. biomed. Eng., 17(1): 25-104.

    Microwave dielectric absorption of DNA in aqueous solution.
    Biopolymers, 23: 593-599.

    FOSTER, K.R., EPSTEIN, B.R., & GEALT, M.A. (1987) "Resonances" in the
    dielectric absorption of DNA? Biophys. J., 52: 421-425.

    FRANCESCHETTI, G., GANDHI, O.P., & GRANDOLFO, M., ed. (1989)
    Electromagnetic biointeraction. mechanisms, safety standards,
    protection guides. New York, London, Plenum Press.

    FREY, A. H. (1985) Data analysis reveals significant microwave-induced
    eye damage in humans. J. microwave Power electromag. Energy, 20(1):

    FREY, A.H. & FELD, S.R. (1975) Avoidance by rats of illumination with
    low power non-ionizing electromagnetic energy. J. comp. Physiol.
    Psychol., 89: 183-188.

    FREY, A.H. & MESSENGER, R. (1973) Human perception of illumination
    with pulsed ultra-high-frequency electromagnetic radiation. Science,
    181: 356-358.

    FREY, A.H., FELD, S.R., & FREY, B., (1975) Neutral function and
    behaviour: Defining the relationship. Ann. N. Y. Acad. Sci., 247:

    FREY, A.M. (1961) Auditory system response to radiofrequency energy.
    Aerospace Med., 32: 1140-1142.

    FRIEDMAN, H. L. (1981) Are chronic exposure to microwaves and
    polycythemia associated [letter]. New England J. Med., 304(6):

    FROHLICH, H. (1968) Long-range coherence and energy storage in
    biological systems. Int. J. quant. Chem., 2: 641-649.

    FROHLICH, H. (1977) Possibilities of long-and short-range electric
    interactions with biological systems. Neurosci. Res. prog. Bull., 15:

    (1987) Repetition of a study of the effect of pulsed magnetic fields
    on the development of fetuses in mice. English language version of
    concluding report, June 1987. Sweden, National Institute of Radiation
    Protection, pp. 86 (SSI Project 346).

    NORELAND, E. (1987) Microwave absorption in aqueous solutions of DNA.
    Nature (Lond.), 328(9): 145-146.

    GAGE, M.I. (1979a) Behaviour in rats after exposures to various power
    densities of 2450 MHz microwaves. Neurobehav. Toxicol., 1: 137-143.

    GAGE, M.I. (1979b) Microwave irradiation and ambient temperature
    interact to alter rat behaviour following overnight exposure. J.
    microwave Power, 14: 389-398.

    GALVIN, M.J., ORTNER, M.J., & McREE, D.I. (1982) Studies on acute  in
     vivo exposure of rats to 2450-MHz microwave radiation. III.
    Biochemical and haematologic effects. Radiat. Res., 90: 558-563.

    GANDHI, O.P. & RIAZI, A. (1986) Absorption of millimetre waves by
    human beings and its biological implications. IEEE Trans. microwave
    Theory Tech., 34: 228-235.

    GANDHI, O.P., DEFORD, J.F., & KANAI, H. (1984) Impedance method for
    calculation of power deposition patterns in magnetically induced
    hyperthermia. IEEE Trans. biomed. Eng., 31: 644-651.

    (1985a) Very low frequency (VLF) hazard study. Texas, Brooks Air Force
    Base, USAF School of Aerospace Medicine (Report USAFSAM-TR-84).

    GANDHI, O.P., CHATTERJEE, I., WU, D., & GU, Y.G. (1985b) Likelihood of
    high rates of energy deposition in the human legs at the ANSI
    recommended 3-30 MHz RF safety levels. Proc. IEEE, 73: 1145-1147.

    GANDHI, O.P., CHEN, J.Y., & RIAZI, A. (1986) Currents induced in human
    beings for plane-wave exposure conditions 0-50 MHz and for RF sealers.
    IEEE Trans. biomed. Eng., 33: 757-767.

    GOLDHABER, M.K., POLEN, M.R., & HIATT, R.A. (1988) The risk of
    miscarriage and birth defects among women who use visual display
    terminals during pregnancy. Am. J. ind. Med. 13: 695-706.

    GOLDSTEIN, L. & SISKO, Z. (1974) A quantitative
    electroencephalographic study of the acute effects of X-band
    microwaves in rabbits. In: Czerski, P., Ostrowski, K., Shore, M.L.,
    Silverman, Ch., Suess, M.J., & Waldeskog, B., ed. Biological effects
    and health hazards of microwave radiation. Warsaw, Polish Medical
    Publishers, pp. 128-133.

    GORDON, C.J. (1983) Behavioral and autonomic thermoregulation in mice
    exposed to microwave radiation. J. appl. Physiol.: Respirat. Environ.
    Exercise Physiol., 55: 1242.

    GORDON, C.J. (1987) Normalizing the thermal effects of radiofrequency
    radiation: body mass versus total body surface area.
    Bioelectromagnetics, 8: 111-118.

    Thermoregulatory effects of magnetic resonance (MR) imaging. Fed.
    Proc., 45: 1017.

    GORDON, Z.A. (1974) [Biological effects of extremely high frequency
    electromagnetic fields.] Moscow, Medicina (in Russian).

    GOUD, G.N., USHA RANI, M.U., REDDY, P.P., REDDI, O.S., RAO, M.S., &
    SAXENA, V.K. (1982) Genetic effects of microwave radiation in mice.
    Mutat. Res., 103: 39-42.

    GRAHAM, R.B. (1985) The medical results of human exposures to
    radiofrequency radiation. In: The impact of proposed radio frequency
    radiation standards on military operations. Neuilly-sur-Seine, France,
    Advisory Group for Aerospace Research and Development (AGARD), pp.
    6-1-6-8 (Lecture Series No. 138).

    GRANDOLFO, M. & MILD, K. H. (1989) Worldwide public and occupational
    radiofrequency and microwave protection guides. In: Franceschetti, G.,
    Gandhi, O.P., & Grandolfo M., ed. Electromagnetic biointeraction
    mechanisms, safety standards, protection guides. New York, London,
    Plenum Press, pp. 99-134.

    GRANDOLFO, M. & VECCHIA, P. (1988) Physical aspects of radiofrequency
    electromagnetic field interactions. In: Repacholi, M.H., ed.
    Non-ionizing radiations: physical characteristics, biological effects
    and health hazard assessment. London, IRPA Publications, pp. 173-196.

    Occupational exposure to radiofrequency and microwave electromagnetic
    fields. G. Ital. Med. Lav., 4: 49-53.

    GRANDOLFO, M., MICHAELSON, S.M., & RINDI, A., ed. (1983) Biological
    effects and dosimetry of nonionizing radiation: radiofrequency and
    microwave energies. New York, London, Plenum Press, p. 669.

    GRANDOLFO, M., VECCHIA, P., & GANDHI O.P. (1990) Magnetic resonance
    imaging calculation of radiofrequency power deposition in the human
    torso model. Bioelectromagnetics, 11: 117-128.

    GRUNDLER, W. & KEILMANN, F. (1983) Sharp resonances in yeast growth
    prove nonthermal sensitivity to microwaves. Phys. Rev. Lett. 51(13):

    GRUNDLER, W. & KEILMANN, F. (1989) Resonant microwave effect on
    locally fixed yeast microcolonies. Z. Naturforsch. (C), 44(9-10):

    GUY, A.W. (1985) Hazards of VLF electromagnetic fields. In: The impact
    of proposed radiofrequency radiation standards on military operations.
    Neuilly-sur-Seine, France, Advisory Group for Aerospace Research and
    Development (AGARD), pp. 9.1-9.20 (Lecture Series No. 138).

    GUY, A.W. (1987) Dosimetry associated with exposure to nonionizing
    radiation: very low frequency to microwaves. Health Phys., 53:

    GUY, A.W. & CHOU, C.K. (1982) Hazard analysis: Very low frequency
    through medium frequency range, Texas, Brooks Air Force Base, USAF
    School of Aerospace Medicine, Aerospace Medical Division (Report
    USAFSAM 33615-78-D-0617).

    GUY, A.W., CHOU, C.K., LIN, J.C., & CHRISTENSEN, D. (1975a)
    Microwave-induced effects in mammalian auditory systems and physical
    materials. Ann. N.Y. Acad. Sci., 247: 194-218.

    GUY, A.W., LIN, J.C., KRAMAR, P.O., & EMERY, A.F. (1975b) Effect of
    2450 MHz radiation on the rabbit eye. IEEE Trans. microwave Theory
    Tech., MTT-23: 492-498.

    GUY, A.W., KRAMAR, P.O., HARRIS, C.A., & CHOU, C.K. (1980) Long-term
    2450 MHz CW microwave irradiation of rabbits: Methodology and
    evaluation of ocular and physiologic effects. J. microwave Power, 15:

    GUY, A.W., DAVIDOW, S., YUANG, G.Y., & CHOU, C.K. (1982) Determination
    of electric current distributions in animals and humans exposed to a
    uniform 60-Hz high-intensity electric field. Bioelectromagnetics, 3:

    GUY, A.W., CHOU, C.K., & NEUHAUS, B. (1984) Average SAR and SAR
    distribution in man exposed to 450 MHz radiofrequency radiation. IEEE
    Trans. microwave Theory Tech., MTT-32: 752-762.

    GUY, A.W., CHOU, C-K, KUNZ, L.L., CROWLEY, J., & KRUPP, J. (1985)
    Effects of long-term low-level radiofrequency radiation exposure on
    rats. Volume 9. Summary. Texas, Brooks Air Force Base, USAF School of
    Aerospace Medicine (USFSAM-TR-85-11).

    GUY, A.W., CHOU, C.K., McDOUGALL, J.A., & SORENSEN, C. (1987)
    Measurement of shielding effectiveness of microwave-protective suits.
    IEEE Trans. microwave Theory Tech., 35: 984-993.

    HAGMANN, M.J., LEVIN, R.L., & TURNER, P.F. (1985) A comparison of the
    annular phased array to helical coil applicators for limb and torso
    hyperthermia. IEEE Trans., BME-32: 916-927.

    HALL, A. & BURSTOW, D.J. (1980) Risk of ignition of flammable gases
    and vapours by radio transmission. Electrotechnology, Jan: 12-15.

    HALLE, B. (1988) On the cyclotron resonance mechanism for magnetic
    field effects on transmembrane ion conductivity. Bioelectromagnetics,
    9(4): 381-385.

    HAMRICK, P.E. & FOX, S.S. (1977) Rat lymphocytes in cell culture
    exposed to 2450 MHz (CW) microwave radiation. J. microwave Power, 12:

    HAMRICK, P.E. & ZINKL, J.G. (1975) Exposure of rabbit erythrocytes to
    microwave irradiation. Radiat. Res., 62: 164.

    HAMBURGER, S., LOGUE, J.N., & STERNTHAL, P.M. (1983) Occupational
    exposure to non-ionizing radiation and an association with heart
    disease: an exploratory study. J. chronic Dis., 36: 791-802.

    HANKIN, N.N. (1974) An evaluation of selected satellite communications
    systems as sources of environmental microwave radiation. Silver
    Springs, Maryland, US Environmental Protection Agency (Report

    HARVEY, S.M. (1984) Electric-field exposure of persons using video
    display units. Bioelectromagnetics, 5: 1-12.

    HENDLER, E. (1968) Cutaneous receptor response to microwave
    irradiation. In: Hardy, J.D., ed. Thermal problems in aerospace
    medicine. Maidenhead, England, Technivision Services, pp. 149-161.

    HENDLER, E. & HARDY, J.D. (1960) Infrared and microwave effects on
    skin heating and temperature sensation. IRE Trans med. Electron.,
    Me-7: 143-152.

    HENDLER, E., HARDY, J.D., & MURGATROYD, D. (1963) Skin heating and
    temperature sensation produced by infra-red and microwave irradiation.
    In: Herzfeld, C.M., ed. Temperature: Its measurement and control in
    science and industry. Part 3. Biology and medicine. New York,
    Reinhold, pp. 211-230.

    HILL, D.A. (1984a) The effect of frequency and grounding on whole-body
    absorption of human in E-polarized radiofrequency fields.
    Bioelectromagnetics, 5: 131-146.

    HILL, D.A. (1984b) Effect of separation from ground on human
    whole-body RF absorption rates. IEEE Trans. microwave Theory Tech.,
    MTT-32: 772-778.

    HILL, D.A. (1984c) Application of human whole-body RF absorption
    measurements to RFR safety standards. In: Mitchell, J.C., ed.
    Proceedings of Radiofrequency Radiation Bioeffects. Texas, Brooks Air
    Force Base, USAF School of Aerospace Medicine, 5301 pp.

    HILL, D.A. & WALSH, J.A. (1985) Radiofrequency current through the
    feet of a grounded man. IEEE Trans. Electromag. Compat., EMC-27:

    HO, H.S. & EDWARDS, W.P. (1977) Oxygen-consumption rate of mice under
    differing dose rates of microwave radiation, Radio Sci., 12 (Suppl.):

    HOCKING, B. (1984) Microwave cataract in radiolinemen and controls
    [letter]. Lancet, 2(8405): 760.

    HOCKING, B & JOYNER, K. (1988) Health aspects of RFR accidents. III.
    A protocol for assessment of health effects in RFR accidents. J.
    microwave Power electromag. Energy, 23(2): 75-80.

    HOCKING, B., JOYNER, K., & FLEMING, R. (1988) Health aspects of RFR
    accidents. Part I. Assessment of health after a radiofrequency
    radiation accident. J. microwave Power electromag. Energy, 23(2):

    HOCKING B., JOYNER, K.H., & FLEMING, A.J.J. (1991) Implanted medical
    devices in workers exposed to radiofrequency radiation. Scan. J. Work
    Environ. Health, 17: 1-6.

    HOLLOWS, F.C. & DOUGLAS, J.B. (1984) Microwave cataract in
    radiolinemen and controls. Lancet, 2(8399): 406-407.

    HUANG, A.T-F & MOLD, N.G. (1980) Immunologic and haematopoietic
    alterations by 2,450-MHz electromagnetic radiation.
    Bioelectromagnetics, 1: 77-87.

    HUANG, A.T., ENGLE, M.E., ELDER, J.A., KINN, J.B., & WARD, T.R. (1977)
    The effect of microwave radiation (2450 MHz) on the morphology and
    chromosomes of lymphocytes. Radio Sci., 12: 173-177.

    HUNT, E.L., KING, N.W., & PHILLIPS, R.D. (1975) Behavioral effects of
    pulsed microwave radiation. Ann. N.Y. Acad. Sci., 247: 440-453.

    IEC PUBLICATION 479-1 (1984) Effects of current passing through the
    human body. Part 1: General aspects, Chapter 1: Electrical impedance
    of the human body, Chapter 2: Effects of alternating current in the
    range of 15 Hz to 100 Hz, Chapter 3: Effects of direct current.

    Geneva, Bureau Central de la Commission Electrotechnique

    IEC PUBLICATIONS 479 (1987) Effects of current passing through the
    human body, Part 2, Chapter 4: Effects of alternating current with
    frequencies above 100 Hz. Geneva, Bureau Central de la Commission
    Electrotechnique Internationale.

    IEEE Committee Report (1978) Electric and magnetic field coupling from
    high voltage power transmission lines - Classification of short-term
    effects on people. New York, IEEE.

    ILO (In press) Video display units - radiation protection guidance.
    Geneva, International Labour Office.

    IRNICH, W. (1984) Interference in pacemakers. Pace, 7: 1021-1048.

    IRPA (1984) Interim guidelines on limits of exposure to radiofrequency
    electromagnetic fields in the frequency range from 100 kHz to 300 GHz.
    Health Phys., 46: 975-984.

    IRPA (1988a) Guidelines on limits of exposure to radiofrequency
    electromagnetic fields in the frequency range from 100 kHz to 300 GHz.
    Health Phys., 54: 115-123.

    IRPA (1988b) Alleged radiation risks form visual display units. Health
    Phys., 54: 231-232.

    IRPA (1991) Protection of patients undergoing a magnetic resonance
    examination. Health Phys., 61(6): 923-928.

    ITU (1981) Radio regulations. Geneva, General Secretariat of the
    International Telecommunication Union.

    JENSH, R.P. (1984a) Studies of the teratogenic potential of exposure
    of rats to 600 MHz microwave radiation. I. Morphologic analysis at
    term. Radiat. Res., 97: 272-281.

    JENSH, R.P. (1984b) Studies of the teratogenic potential of exposure
    of rats to 600 MHz microwave radiation. II. Postnatal
    psychophysiologic evaluations. Radiat. Res., 97: 282-301.

    JENSH, R.P., VOGEL, W.H., & BRENT, R.L. (1982a) Postnatal functional
    analysis of prenatal exposure of rats to 915 MHz microwave radiation.
    J. Am. Coll. Toxicol., 1: 73-90.

    JENSH, R.P., WEINBERG, I., & BRENT, R.L. (1982b) Teratologic studies
    of prenatal exposure of rats to 915 MHz microwave radiation. Radiat.
    Res. 92: 160-171.

    JENSH, R.P., VOGEL, W.H., & BRENT, R.L. (1983a) An evaluation of the
    teratogenic potential of protracted exposure of pregnant rats to 2450

    MHz microwave radiation. I. Morphologic analysis at term. J. Toxicol.
    environ. Health, 11: 23-35.

    JENSH, R.P., VOGEL, W.H., & BRENT, R.L. (1983b) An evaluation of the
    teratogenic potential of protracted exposure of pregnant rats to 2450
    MHz microwave radiation. II. Postnatal psychophysiologic analysis. J.
    Toxicol. environ. Health, 11: 37-59.

    JOHNSON, C.C. & GUY, A.W. (1972) Nonionizing electromagnetic wave
    effects in biological materials and systems. Proc. IEEE, 60: 692-718.

    JOHNSON, L., LEBOVITZ, R.M., & SAMSON, W.K. (1984) Germ cell
    degeneration in normal and microwave-irradiated rats: Potential sperm
    production rates at different developmental steps in spermatogenesis.
    Anat. Rec., 209: 501-507.

    JOHNSON, R.B, MYERS, D.E., GUY, A.W., & LOVELY, R.H. (1977)
    Discriminative control of appetitative behaviour by pulsed microwave
    radiation in rats. In: Johnson, C.C. & Shore, M.L., ed. Biological
    effects of electromagnetic waves. Selected papers of the USNC/URSI
    Annual Meeting, Boulder, Colorado, October 1975. Rockville, Maryland,
    US Department of Health, Education, and Welfare, Vol. 1, pp.238-247
    (HEW Publication (FDA) 77-8010).

    KUNZ, L.L., & GUY, A.W. (1983) Effects of long-term low-level
    radiofrequency radiation exposure on rats. Volume 4. Open-field
    behaviour and corticosterone. Brooks Air Force Base, Texas, USAF
    School of Aerospace Medicine (USAFSAM-TR-83-42).

    JORDAN, E.C. & BALMAIN, K.G. (1968) Electromagnetic waves and
    radiating system. New Jersey, Prentice Hall, pp. 317-338.

    JOYNER, K.H. (1988) Measurement of electromagnetic radiation below 100
    GHz. In: Repacholi, M.H., ed. Non-ionizing radiations. Physical
    characteristics biological effects and health hazard assessment.
    Proceedings of the International Non-ionizing Radiation Workshop,
    Melbourne, 5-9 April 1988, pp. 373-393.

    JOYNER, K.H. & BANGAY, M.J. (1986a) Exposure survey of civilian
    airport radar workers in Australia. J. microwave Power, 21: 209-219.

    JOYNER, K.H. & BANGAY, M.J. (1986b) Exposure survey of operators of
    radiofrequency dielectric heaters in Australia. Health Phys., 50:

    JOYNER, K.H., COPELAND, P.R., & MACFARLANE, I.P. (1989) An evaluation
    of a radiofrequency protective suit and electrically conductive
    fabrics. IEEE Trans. EMC, 31(2): 129-137.

    JUSTESEN, D.R. (1988) Microwave and infrared radiations as sensory,
    motivational and reinforcing stimuli. In: O'Connor, M.E. & Lovely, R.
    H., ed. Electromagnetic fields and neurobehavioral function. New York,
    Alan R. Liss Inc., pp. 235-264.

    A comparative study of human sensory thresholds: 2450 MHz microwaves
    vs far-infra-red radiation. Bioelectromagnetics, 3: 117-125.

    JUUTILAINEN, J. & SAALI, K. (1986) Development of chick embryos in 1
    Hz to 100 kHz magnetic fields. Radiat. environ. Biophys., 25: 135.

    KACZMAREK, L.K. & ADEY, W.R. (1973) The efflux of 45CA2+ and
    O3HE-gamma-aminobutyric acid from cat cerebral cortex. Brain Res., 63:

    KALLEN, B., MALMQUIST, G., & MORITZ, U. (1982) Delivery outcome among
    physiotherapists in Sweden: Is non-ionizing radiation a fetal hazard?
    Arch. environ. Health, 37: 81-85.

    KANAI, H., CHATTERJEE, I., & GANDHI, O.P. (1984) Human body impedance
    for electromagnetic hazard analysis in the VLF to MF band. IEEE Trans.
    microwave Theory Tech., 32: 763-771.

    KARACHEV, I. & BITKIN, S. (1985) [Hygienic estimation of EMF tension
    in the locations of TV stations.] Gig. naselyon. mest, Kiev, 24: 49-52
    (in Russian).

    KAUNE, W.T. & FORSYTHE, W.C. (1985) Current densities measured in
    human models exposed to 60 Hz electric fields. Bioelectromagnetics, 6:

    KAUNE, W.T. & PHILLIPS, R.D. (1980) Comparison of the coupling of
    grounded humans, swine and rats to vertical 60 Hz electric fields.
    Bioelectromagnetics, 1: 117-129.

    (1987) Physiologic changes during high field strength MR imaging. Am.
    J. Neuroradiol., 8, 263-2666.

    KING, N.W., JUSTESEN, D.R., & CLARKE, R.L. (1971) Behavioral
    sensitivity to microwave irradiation. Science, 172: 398-401.

    KIRK, W.P. (1984) Life span and carcinogenesis. In: Elder, J.A. &
    Cahill, D.F., ed. Biological effects of radiofrequency radiation.
    Research Triangle Park, North Carolina, Health Effect Research
    Laboratory, US Environmental Protection Agency, pp. 5-106-5-111

    ERIKSSON, A. (1988) Health problems among operators of plastic welding

    machines and exposure to radiofrequency electromagnetic fields. Ind.
    Arch. occup. environ. Health, 60(4): 243-247.

    KOWALCZUK, C.I., SAUNDERS, R.D., & STAPLETON, H.R. (1983) Sperm count
    and sperm abnormality in male mice after exposure to 2.45 GHz
    microwave radiation. Mutat. Res., 122: 155-161.

    KRAMAR, P., HARRIS, C., EMERY, A.F., & GUY, A.W. (1978) Acute
    microwave irradiation and cataract formation in rabbits and monkeys.
    J. microwave Power, 13: 239-249.

    ADAMSKI, D. (1984) Specific absorption rate distribution in a
    full-scale model of man at 350 MHz. IEEE Trans. microwave Theory
    Tech., MTT-32: 779-782.

    G.R. (1985) Effects of 2.45 GHz microwaves on primate corneal
    endothelium. Bioelectromagnetics, 6: 177-188.

    KUES, H.A., McLEOD, D.S., D'ANNA, S.A., LUTTY, G.A., & MONOHAN, J.C.
    (1988) Histological evaluation of microwave-induced vascular leakage
    in the iris. In: The Tenth Annual Bioelectromagnetics Society Meeting
    Abstracts, June 1988. Stamford, Connecticut, p. 49.

    Effect of high-frequency current on nerve and muscle tissue. IEEE
    Trans. biomed. Eng., 32: 82-86.

    LAI, H., HORITA, A., & GUY, A.W. (1988) Acute low-level microwave
    exposure and central cholinergic activity: studies of irradiation
    parameters. Bioelectromagnetics, 9: 355-362.

    LAI, H., CARINO, M.A., HORITA, A., & GUY, A.W. (1989) Low-level
    microwave irradiation and central cholinergic activity: A
    dose-response study. Bioelectromagnetics, 10: 203-208.

    LAI, H., CARINO, M., HORITA, A., & GUY, A.W. (1990) Effects of acute
    and repeated microwave exposures on benzodiazepine receptors in the
    brain of the rat. In: Abstracts, 12th Annual Meeting of the
    Bioelectromagnetics Society, June 1990, San Antonio, Texas, p. 41.

    H.I. (1975) Gonadic function in workmen with long-term exposure to
    microwaves. Health Phys., 29: 381-383.

    LARSEN, A.I., OLSEN, J., & SVANE, O. (1991) Gender-specific
    reproductive outcome and exposure to high-frequency electromagnetic
    radiation among physiotherapists. Scand. J. Work Environ. Health, 17:

    LARY, J.M., CONOVER, D.L., FOLEY, E.D., & HANSER, P.L. (1982)
    Teratogenic effects of 27.12 MHz radiofrequency radiation in rats.
    Teratology, 26: 299-309.

    LARY, J.M., CONOVER, D.L., JOHNSON, P.H., & BURG, J.R. (1983a)
    Teratogenicity of 27.12 MHz radiation in rats is related to duration
    of hyperthermic exposure. Bioelectromagnetics, 4: 249-255.

    LARY, J.M., CONOVER, D.L., & JOHNSON, P.H. (1983b) Absence of
    embryotoxic effects from low-level (non-thermal) exposure of rats to
    100 MHz radiofrequency radiation. Scand. J. Work Environ. Health, 9:

    LARY, J.M. & CONOVER, D.L. (1987) Teratogenic effects of
    radiofrequency radiation. IEEE Eng. Med. Biol. Mag., March: 42-46.

    LEBOVITZ, R.M. & JOHNSON, L. (1983) Testicular function of rats
    following exposure to microwave radiation. Bioelectromagnetics, 4:

    LEBOVITZ, R.M. & JOHNSON, L. (1987) Acute, whole body microwave
    exposure and testicular function of rats. Bioelectromagnetics, 8:

    LEDNEV, V.D. (1990) Possible mechanism for influence of weak magnetic
    fields on biosystems. Presented at the 12th Annual Meeting of
    Bioelectromagnetic Society, San Antonio, Texas, June.

    LEE, Q.P., GUY, A.W., LAI, H., & HORITA, A. (1987) The effects of
    modulated radiofrequency radiation on the calcium efflux from the
    chick brains  in vitro. In: Ninth Annual Meeting of the
    Bioelectromagnetics Society, Portland, Oregon, 21-25 June 1987.
    Gaithersburg, Maryland, BEMS (Abstract D1).

    LESTER, J.R. (1985) Reply to "Cancer mortality and Air Force bases: A
    reevaluation." J. Bioelec., 4: 129-131.

    LESTER, J.R. & MOORE, D.F. (1982) Cancer mortality and Air Force
    bases. J. Bioelec., 1:77-82.

    LIBOFF, A.R. (1985) Cyclotron resonance in membrane transport. In:
    Chiabrera, A., Nicolini, C., & Schwan, H.P., ed. Interactions between
    electromagnetic fields and cells. New York, London, Plenum Press, pp.

    LIBURDY, R.P. (1977) Effects of radio-frequency radiation on
    inflammation. Radio Sci., 12: 179-183.

    LIBURDY, R.P. (1979) Radiofrequency radiation alters the immune
    system: Modification of T - and B-lymphocyte levels and cell-mediated
    immunocompetence by hyperthermic radiation. Radiat. Res., 77: 34-46.

    LIBURDY, R.P. (1980) Radiofrequency radiation alters the immune
    system. II. Modulation of  in vivo lymphocyte circulation. Radiat.
    Res., 83: 63-73.

    LIBURDY, R.P. & MAGIN, R.L. (1985) Microwave-stimulated drug release
    from liposomes. Radiat. Res., 103: 266-275.

    LIBURDY, R.P. & PENN, A. (1984) Microwave bioeffects in the
    erythrocyte are temperature and pO2 dependent: Cation permeability
    and protein shedding occur at the membrane phase transition.
    Bioelectromagnetics, 5: 283-291.

    LIBURDY, R.P. & VANEK, Jr, P.F. (1987) Microwaves and the cell
    membrane. III. Protein shedding is oxygen and temperature dependent:
    Evidence for cation bridge involvement. Radiat. Res., 109: 382.

    LIDDLE, C.G. & BLACKMAN, C.F. (1984) Endocrine, physiological and
    biochemical effects. In: Elder, J.A. & Cahill, D.F., ed. Biological
    effects of radiofrequency radiation. Research Triangle Park, North
    Carolina, Health Effect Research Laboratory, US Environmental
    Protection Agency, pp. 5-79-5-93 (EPA-600/8-83-026F).

    M., & LEWTER, O.H. (1980) Alteration of circulating antibody response
    of mice exposed to 9-GHz pulsed microwaves. Bioelectromagnetics, l:

    (1986) Circulating antibody response of mice to 9-GHz pulsed microwave
    radiation. Bioelectromagnetics, 7(1): 91-94.

    CAUTHEN, G.M. (1978) Foreign service health status study - evaluation
    of health status of foreign service and other employees from selected
    eastern European posts. Final report. Washington, DC, Department of
    State, pp. 436 (Contract No. 6025-619073) (NTIS PB-288163).

    LIN, J.C. (1978) Microwave auditory effects and applications,
    Springfield, Illinois, Charles C. Thomas.

    & FRACASSA, M. (1979) Microwave effects on granulocytes and macrophage
    precursor cells in mice  in vitro. Radiat. Res., 80: 292-302.

    LIN, J.C., SU, J.L., & WAN, Y. (1988) Microwave-induced thermoelastic
    pressure wave propagated in the cat brain. Bioelectromagnetics, 9(2):

    LIN-LIU, S. & ADEY, W.R. (1982) Low frequency amplitude modulated
    microwave fields change calcium efflux rates from synaptosomes.
    Bioelectromagnetics, 3: 309-322.

    LIU, L.M., NICKLESS, F.G., & CLEARY, S.F. (1979) Effects of microwave
    radiation on erythrocyte membranes. Radio Sci., 14: 109.

    LLOYD, D.C., SAUNDERS, R.D., FINNON, P., & KOWALCZUK, C.I. (1984) No
    clastogenic effect from  in vitro microwave irradiation of GO human
    lymphocytes. Int. J. radiat. Biol., 46: 135-141.

    Absence of chromosomal damage in human lymphocytes exposed to
    microwave radiation with hyperthermia. Bioelectromagnetics, 7:

    LOTZ, W.G. (1983) Influence of the circadian rhythm on body
    temperature on the physiological response to microwaves: Day vs night
    exposures. In: Adair, E.R., ed. Microwaves and thermoregulation. New
    York, Academic Press, pp. 445-460.

    LOTZ, W.G. (1985) Hyperthermia in radiofrequency-exposed Rhesus
    monkeys: A comparison of frequency and orientation effects. Radiat.
    Res., 102: 59-70.

    LOTZ, W.G. & MICHAELSON, S.M. (1978) Temperature and corticosterone
    relationships in microwave-exposed rats. J. appl. Physiol.: Respirat.
    environ. Exercise Physiol., 44: 438-445.

    LOTZ, W.G. & MICHAELSON, S.M. (1979) Effects of hypophysectomy and
    dexamethasone on rat adrenal response to microwaves. J. appl.
    Physiol.: Respirat. environ. Exercise Physiol., 47: 1284-1288.

    LOTZ, W.G. & PODGORSKI, R.P. (1982) Temperature and adrenocortical
    responses in Rhesus monkeys exposed to microwaves. J. appl. Physiol.:
    Respirat. environ. Exercise Physiol., 53: 1565-1571.

    LOTZ, W.G. & SAXTON, J.L. (1987) Metabolic and vasomotor responses of
    Rhesus monkeys exposed to 225 MHz radiofrequency energy.
    Bioelectromagnetics, 8: 73-89.

    LOTZ, W.G. & SAXTON, J.L. (1988) Thermoregulatory responses in the
    rhesus monkey during exposure at a frequency (255 MHz) near whole body
    resonance. In: O'Connor, M.E. & Lovely, R.H., ed. Electromagnetic
    fields and neurobehavioral function. New York, Alan R. Liss Inc., pp.

    LOVELY, R.H., MYERS, D.E., & GUY, A.W. (1977) Irradiation of rats by
    918 MHz microwaves at 2.5 mW/cm2: Delineating the dose-response
    relationship. Radio Sci., 12: 139-146.

    LOVELY, R.H., MIZUMORI, S.J.Y., JOHNSON, R.B., & GUY, A.W. (1983)
    Subtle consequences of exposure to weak microwave fields: Are there
    nonthermal effects? In: Adair, E.R., ed. Microwaves and
    thermoregulation. New York, Academic Press, pp. 401-429.

    [Methodological problems and prospectives of the control of high
    quality of surface (low depth) electromagnetic field hyperthermia:
    Situation in Italy with respect to that in Europe and
    internationally.] In: [Quality control and optimization in the use of
    radiation in medicine. Proceedings of Congress, Brescia, Italy.] pp.
    103-112 (in Italian).

    (1977) Thermal and endocrinological effects of protracted irradiation
    of rats by 2450 MHz microwaves. Radio Sci., 12(S): 147-156.

    LU, S-T., LOTZ, W.G., & MICHAELSON, S.M. (1980a) Advances in
    microwave-induced neuroendocrine effects: The concept of stress. Proc.
    IEEE, 68: 73-77.

    LU, S-T., LOTZ, W.G., & MICHAELSON, S.M. (1980b) Delineating acute
    neuroendocrine responses in microwave-exposed rats. J. appl. Physiol.:
    Respirat. environ. Exercise Physiol., 48: 927-932.

    LU, S-T, LEBDA, N., PETTIT, S., & MICHAELSON, S.M. (1981)
    Microwave-induced temperature, corticosterone, and thyrotropin
    interrelationships. J. appl. Physiol.: Respirat. environ. Exercise
    Physiol., 50: 399-405.

    LYLE, D.B., SCHECHTER, P., ADEY, W.R., & LUNDAK, R.L. (1983)
    Suppression of T-lymphocyte cytotoxicity following exposure to
    sinusoidally amplitude-modulated fields. Bioelectromagnetics, 4:

    MAGIN, R.L., LU, S-T., & MICHAELSON, S.M. (1977a) Microwave heating
    effect on the dog thyroid gland. IEEE Trans. biomed. Eng., BME-24:

    MAGIN, R.L., LU, S-T., & MICHAELSON, S.M. (1977b) Stimulation of dog
    thyroid by local application of high intensity microwaves. Am. J.
    Physiol., 233: E363-E368.

    MAJEWSKA, K. (1968) Investigations on the effect of microwaves on the
    eye. Pol. med. J., 7: 989-994.

    MALE, J.C. & EDMONDS, D. T. (1990) Ion vibrational procession, a model
    for biological interactions with ELF magnetic fields. Presented at the
    12th Annual Meeting of Biolectromagnetic Society, San Antonio, Texas,

    YERETELNIK, Y.V. (1987) Does DNA absorb microwave energy? Biopolymers,
    26: 1965-1970.

    SZABO, L.D. (1990) Effect of 2.45 GHz microwave irradiation on the

    viability and metastatic ability of P388 lymphoid tumour cells. In:
    Riklis, E., ed. Frontiers of radiation biology. VCH, Germany.

    MANIKOWSKA-CZERSKA, E., CZERSKI, P., & LEACH, W.M. (1985) Effects of
    2.45 GHz microwaves on meiotic chromosomes of male CBA/CAY mice. J.
    Hered., 76: 71-73.

    N., LUCZAK, M., & SZMIGIELSKI, S. (1986) Microwave radiation enhances
    teratogenic effect of cytosine arabinoside in mice. Biol. Neonate, 50:

    MASKELL, S.J. (1985) RF susceptibility of an EEG and consideration for
    attenuating RFI in hospitals. IEEE Trans. Ind. Appl., 21: 876-881.

    MAYERS, C.P. & HABERSHAW, J.A. (1973) Depression of phagocytosis: A
    non-thermal effect of microwave radiation as a potential hazard to
    health. Int. J. radiat. Biol., 24: 449-461.

    HOLLAND, M.G., & GORDON, R. (1979) Absence of ocular pathology after
    repeated exposure of unanaesthetised monkeys to 9.3-GHz microwaves. J.
    microwave Power, 14: 41-44.

    A.D., & ROBERTS, D. (1988) Work with visual display units in
    pregnancy. Br. J. ind. Med., 45: 509-515.

    McLEOD, B.R. & LIBOFF, A.R. (1986) Dynamic characteristics of membrane
    ions in multifold configurations of low-frequency electromagnetic
    radiation. Bioelectromagnetics, 7: 177-189.

    McREE, D.I. & WACHTEL, H. (1980) The effects of microwave radiation on
    the vitality of isolated frog sciatic nerves. Radiat. Res., 82:

    McREE, D.I. & WACHTEL, H. (1982) Pulse microwave effects on nerve
    vitality. Radiat. Res., 91: 212-218.

    McREE, D.I., FAITH, R., McCONNELL, E.E., & GUY, A.W. (1980) Long-term
    2450-MHz CW microwave irradiation of rabbits: Evaluation of
    haematological and immunological effects. J. microwave Power, 15:

    McREE, D.I., MACNICHOLS, G., & LIVINGSTON, G.K. (1981) Incidence of
    sister chromatid exchange in bone marrow cells of the mouse following
    microwave exposure. Radiat. Res., 85: 340-348.

    McREE, D.I., GALVIN, M.J., & MITCHELL, C.L. (1988) Microwave effects
    on the cardiovascular system: A model for studying the responsivity of
    the automatic nervous system to microwaves. In: O'Connor, M.E. &
    Lovely, R.H., ed. Electromagnetic fields and neurobehavioral function:

    Progress in clinical and biological research. New York, Alan R. Liss
    Inc., Vol. 257, pp. 153-177.

    MEISTER, A., EGGERT, S., RICHTER, J., & RUPPE, I. (1989) [The effect
    of a high frequency electromagnetic field (2.45 GHz) on the perception
    process, mental performance and mental condition.] Z. gesamte Hyg.,
    Berlin, 35(4): 203-205.

    MERRITT, J.H., SHELTON, W.W., & CHAMNESS, A.F. (1982) Attempts to
    alter Ca-452+ binding to brain tissue with pulse-modulated microwave
    energy. Bioelectromagnetics, 3: 457-478.

    MERRITT, J.H., HARDY, K.A., & CHAMNESS, A.F. (1984)  In utero
    exposure to microwave radiation and rat brain development.
    Bioelectromagnetics, 5: 315-322.

    METAXAS, A.C. & MEREDITH, R.J. (1983) Industrial microwave heating.
    Exeter, Peter Peregrinus Ltd, pp. 281-282.

    MICHAELSON, S.M. (1983) Microwave/radiofrequency protection guide and
    standards. In: Grandolfo, M., Michaelson, S., & Rindi, A., ed.
    Biological effects and dosimetry of non-ionizing radiation:
    radiofrequency and microwave energies. New York, London, Plenum Press.

    (1975) Biochemical and neuroendocrine aspects of exposure to
    microwaves. Ann. N.Y. Acad. Sci, 247: 21-45.

    MIKOLAJCZYK, H. (1976) Microwave-induced shifts of gonadotropic
    activity in anterior pituitary gland of rats. In: Johnson, C.C. &
    Shore, M.L., ed. Biological effects of electromagnetic waves. Selected
    papers of the USNC/URSI Annual Meeting, Boulder, Colorado, October
    1975. Rockville, Maryland, US Department of Health, Education and
    Welfare, Vol. 1, pp. 377-383 (HEW Publication (FDA) 77-8010).

    MILD, K.H. & LOVSTRAND, K.G. (1990) Environmental and professionally
    encountered electromagnetic fields. In: Gandi, O.P., ed. Biological
    effects and medical applications of electromagnetic fields. Engelwood
    Cliffs, New Jersey, Prentice Hall, Inc.

    MILHAM, S. (1985) Silent Keys: leukaemia mortality in amateur radio
    operators. Lancet, i: 8120.

    MITCHELL, C.L., McREE, D.I., PETERSON, J., & TILSON, H.A. (1988) Some
    behavioral effects of short-term exposure of rats to 2.45 GHz
    microwave radiation. Bioelectromagnetics, 9: 259-268.

    MOE, K.E., LOVELY, R.H., MYERS, D.E., & GUY, A.W. (1976) Physiological
    and behavioral effects of chronic low level microwave radiation in
    rats. In: Johnson, C. C. & Shore, M.L., ed. Biological effects of
    electromagnetic waves. Selected papers of the USNC/URSI Annual
    Meeting, Boulder, Colorado, October 1975. Rockville, Maryland, US

    Department of Health, Education, and Welfare, Vol. 1, pp. 248-256 (HEW
    Publication (FDA) 77-8010).

    MONAHAN, J.C., KUES, H.A., McLEOD, D.S., D'ANNA, S.A., & LUTTY, G.A.
    (1988) Lowering of microwave exposure threshold for induction of
    primate ocular effects by timolol maleate. Abstract. Tenth Annual
    Meeting, Bioelectromagnetic Society, Stamford, Connecticut, 19-23 June

    SATHIASEELAN, V. (1989) Physical predictors of adequate hyperthermia
    with the annular phased array. Int. J. Hyperther., 5: 749-755.

    NAWROT, P.S., McREE, D.I., & STAPLES, R.E. (1981) Effects of 2.45 GHz
    microwave radiation on embryofetal development in mice. Teratology,
    24: 303-314.

    NCRP (1981) Radiofrequency electromagnetic fields: properties,
    quantities and units, biophysical interaction, and measurements.
    Washington, DC, National Council on Radiation Protection and
    Measurements, 134 pp. (NCRP Report No. 67).

    NCRP (1986) Biological effects and exposure criteria for
    radiofrequency electromagnetic fields. Bethesda, Maryland, National
    Council on Radiation Protection and Measurements, 382 pp. (NCRP Report
    No. 86).

    NICHOLSON, C.P., GROTTING, J.C., & DIMICK, A.R., (1987) Acute
    microwave injury to the hand. J. hand Surg. (Am.), 12(3): 446-449.

    L.T. (1989) [The effect of VDT work on the course of pregnancy.]
    Report of the Department of Social Medicine, Aarhus, Denmark,
    University of Aarhus.

    OLANDERS, S., & PERSSON, L.I. (1989) Microwave effects on the central
    nervous system - a study of radar mechanics. Health Phys., 56(5):

    (1989) [Effect of low frequency magnetic fields at a chromosomal level
    in human amniotic cells.] Solna, Sweden, National Institute of
    Occupational Health, p. 25 (in Swedish).

    NURMINEN, T. & KURPPA, K. (1988) Office employment, work with video
    display terminals, and the course of pregnancy. Scand. J. Work
    Environ. Health, 14: 293-298.

    O'CONNOR, M.E. (1980) Mammalian teratogenesis and radio-frequency
    fields. Proc. IEEE, 68: 56-60.

    ODLAND, L.T. (1973) Radiofrequency energy: A hazard to workers? Ind.
    Med. Surg., 42: 23-26.

    J.R. (1980) The increased passive efflux of sodium and rubidium from
    rabbit erythrocytes by microwave radiation. Radiat. Res., 82: 244-256.

    OLSEN, R.G. (1982) Far-field dosimetric measurements in a full-sized
    man model at 2.0 GHz. Bioelectromagnetics, 3: 433-441.

    OLSEN, R.G. & GRINER, T.A. (1982) Electromagnetic dosimetry in a
    sitting rhesus model at 225 MHz. Bioelectromagnetics, 3: 385-389.

    ONORM (1986) [Microwave and radiofrequency electromagnetic fields;
    definitions, limits of exposure, measurements.] Vienna,
    Osterreichisches Normungsinstitut (Onorm S1120) (in German).

    OSCAR, K.J. & HAWKINS, T.D. (1977) Microwave alteration of the
    blood-brain barrier system of rats. Brain Res., 126: 281-293.

    OSEPCHUK, J.M. (1979) A review of microwave oven safety. Microwave J.,
    22: 25-37.

    PARKER, L.N. (1973) Thyroid suppression and adrenomedullary activation
    by low-intensity microwave radiation. Am. J. Physiol., 224: 1388-1390.

    PENNES, H. H. (1948) Analysis of tissue and arterial blood
    temperatures in the resting human forearm. J. appl. Physiol., 1:

    & RUBIN, P. (1991) Randomized phase - III. Study comparing irradiation
    and hyperthermia with irradiation alone in superficial measurable
    tumours: final report by the Radiation Therapy Oncology Group. Am. J.
    clin. Oncol. Cancer Clin. Trials (USA) 14(2): 133-141.

    ASTRAHAN, M. (1989) Regional hyperthermia for advanced tumours: a
    clinical study of 353 patients. Int. J. Radiat. Oncol. Biol. Phys.,
    16: 601-607.

    PHILLIPS, R.D., HUNT, E.L., CASTRO, R.D., & KING, N.W. (1975)
    Thermoregulatory, metabolic and cardiovascular responses of rats to
    microwaves. J. appl. Physiol., 38: 630-635.

    POLK, C. & POSTOW, E., ed. (1986) CRC handbook of biological effects
    of electromagnetic fields. Boca Raton, Florida, CRC Press.

    POLSON, P. & MERRITT, J.H. (1985) Cancer mortality and Air Force
    bases: A reevaluation. J. Bioelec., 4: 121-127.

    DROST, D.J., & LEE, T.Y. (1990) Magnetic resonance imaging increases
    the brain space of 153 gadolinium diethylene triaminopentascetic acid
    in rats. In: Abstracts, 12th Annual Meeting of the Bioelectromagnetic
    Society, June 1990, San Antonio, Texas, p. 46.

    PRAUSNITZ, S. & SUSSKIND, C. (1962) Effects of chronic microwave
    irradiation on mice. IRE Trans. Biomed. Electron., 9: 104-108.

    PRESKORN, S.H., EDWARDS, W.D., & JUSTESEN, D.R. (1978) Retarded tumor
    growth and greater longevity in mice after fetal irradiation by 2450
    MHz microwaves. J. Surg. Oncol., 10: 483-492.

    PRINCE, J. E., MORI, L.H., FRAZER, J.W., & MITCHELL, J.C. (1972)
    Cytologic aspect of RF radiation in the monkey. Aerosp. Med., 43:

    J.E. (1983) Haematologic and immunologic effects of pulsed microwaves
    in mice. Bioelectromagnetics, 4: 383-396.

    RAMA RAO, G., CAIN, C.A., LOCKWOOD, J., & TOMPKINS, W.A.F. (1983)
    Effects of microwave exposure on the hamster immune system. II.
    Peritoneal macrophage function. Bioelectromagnetics, 4: 141-155.

    RAMA RAO, G., CAIN, C.A., & TOMPKINS, W.A.F. (1985) Effects of
    microwave exposure on the hamster immune system. IV. Spleen cell IgM
    haemolytic plaque formation. Bioelectromagnetics, 6: 41-52.

    REILLY, J.P. (1988) Electrical models for neural excitation studies.
    Johns Hopkins University, Applied Physics Laboratory, Tech. Digest, 9:

    REPACHOLI, M.H. (1983a) Sources and applications of radiofrequency and
    microwave energy. In: Grandolfo, M., Michaelson, S.M., & Rindi, R.,
    ed. Biological effects and dosimetry of nonionizing radiation:
    radiofrequency and microwave energies. New York, London, Plenum Press,
    pp. 19-41.

    REPACHOLI, M.H. (1983b) Development of standards - Assessment of
    health hazards and other factors. In: Grandolfo, M., Michaelson, S.M.,
    & Rindi, A., ed. Biological effects and dosimetry of nonionizing
    radiation: radiofrequency and microwave energies. New York, London,
    Plenum Press, pp. 611-625.

    REPACHOLI, M.H. (1985) Video display terminals - should operators be
    concerned? Austral. phys. engin. Sci. Med., 8(2): 51-61.

    REPACHOLI, M.H., ed. (1988) Non-ionizing radiations: physical
    characteristics, biological effects and health hazard assessment.
    London, IRPA Publications, 464 pp.

    REPACHOLI, M.H. (1990) Radiofrequency field exposure standards:
    Current limits and the relevant bioeffects data. In: Gandhi, O.P., ed.
    Biological effects and medical applications of electromagnetic fields.
    Englewood Cliffs, New Jersey, Prentice Hall, pp. 9-27.

    (1988) Further studies of the microwave absorption characteristics of
    different forms of DNA in solution. (Abstract). 10th Annual Meeting of
    Bioelectromagnetics Society, Stamford, Connecticut, p. 17.

    WOLTHUIS, O.L. (1975) Preliminary investigations of the effects of
    low-level microwave radiation on spontaneous motor activity in rats.
    Ann. N.Y. Acad. Sci., 247: 417-424.

    ROBERTS, N.J., Jr (1979) Temperature and host defence. Microbiol.
    Rev., 43: 241-259.

    ROBERTS, N.J., Jr (1983) Radiofrequency and microwave effects on
    immunological and haematopoietic systems. In: Grandolfo, M.,
    Michaelson, S.M., & Rindi, A., ed. Biological effects and dosimetry of
    nonionizing radiation, radiofrequency and microwave energies. New
    York, London, Plenum Press, pp. 429-459.

    ROBERTS, N.J., Jr, LU, S.T., & MICHAELSON, S.M. (1983) Human leukocyte
    functions and the US safety standard for exposure to radio-frequency
    radiation. Science, 220: 318-320.

    ROBERTS, N.J., Jr, MICHAELSON, S.M., & LU, S.T. (1984) Exposure of
    human mononuclear leukocytes to microwave energy pulse modulated at 16
    or 60 Hz. IEEE Trans. microwave Theory Tech., MTT-32: 803-807.

    ROBERTS, N.J., Jr, MICHAELSON, S.M., & LU, S.T. (1986) The biological
    effects of radiofrequency radiation: A critical review and
    recommendations. Int. J. radiat. Biol., 50: 379-420.

    ROBINETTE, C.D. & SILVERMAN, C. (1977) Causes of death following
    occupational exposure to microwave radiation (radar) 1950-1974. In:
    Hazzard, D.G., ed. Symposium on the Biological Effects and Measurement
    of Radiofrequency/Microwaves. Washington, DC, Department of Health,
    Education, and Welfare (HEW Publication No (FDA) 77-8026).

    ROBINETTE, C.D., SILVERMAN, C., & JABLON, S. (1980) Effects upon
    health of occupational exposure to microwave radiation (radar). Am. J.
    Epidemiol., 112: 39-53.

    ROGERS, S.J. (1981) Radiofrequency burn hazards in the MF/HF band.
    (Aeromedical Review 3-81), pp. 76-89. In: Proceedings of a Workshop on
    the Protection of Personnel Against Radiofrequency Electromagnetic
    Radiation, Texas, Brooks Air Force Base, USAF/SAM Aerospace Medical

    W.Z., & ZARET, M.M. (1976) Effects of 35 and 107 GHz CW microwaves on
    the rabbit eye. In: Johnson, C.C. & Shore, M.L., ed. Biological
    effects of electromagnetic waves. Selected Papers of the USNC/URSI
    Annual Meeting, Boulder, Colorado, October 1975. Rockville, Maryland,
    US Department of Health, Education, and Welfare, Vol. 1, pp. 110-128
    (HEW Publication (FDA) 77-8010).

    PERSSON, B.R.R., ROOS, M.S., de MARINCOR, O.J., & BRENNAN, K.M. (1990)
    Possibility that the blood-bone barrier (BBB) of the rat to albumin is
    not significantly altered by nuclear magnetic resonance imaging
    (NMRI)fields. In: Abstracts, 12th Annual Meeting of the
    Bioelectromagnetics Society, June, 1990, San Antonio, Texas. p. 46.

    SZMIGIELSKI, S. (1980) Does whole-body hyperthermia therapy involve
    participation of the immune system? Int. J. Cancer, 25: 289-292.

    ROTKOVSKA, D., VACEK, A., & BARTONICKOVA, A. (1987) Effects of
    microwaves on the colony-forming ability of haemopoietic stem cells in
    mice. Acta oncol., 26: 233-236.

    ROZZELL, T.C. (1985) West Germany EMF exposure standard (BEMS
    Newsletter, 55).

    RUGGERA, P.S. (1980) Measurements of emission levels during microwave
    and short wave diathermy treatments. Rockville, Maryland, US
    Department of Health and Human Services, FDA (Publication No. FDA

    SAA (1988) Radio-frequency radiation - principles and methods of
    measurement. Sydney, Standards Association of Australia.

    SAGER, D.P. (1987) Current facts on pacemaker electromagnetic
    interference and their application to clinical care. Heart Lung, 16:

    SANDSTROM, M., HANSSON-MILD, K., & LOVTRUP, S. (1987) Effects of weak
    pulsed magnetic fields on chick embryogenesis. In: Knave, B. &
    Wideback, P.G., ed. Work with display units 86. Amsterdam, Elsevier,
    p. 135.

    SANTINI, R., HOSNI, M., DESCHAUX, P., & PACKECO, H. (1988) B16
    melanoma development in black mice exposed to low-level microwave
    radiation. Bioelectromagnetics, 9(1): 105-107.

    SANZA, J.N. & DE LORGE, J. (1977) Fixed interval behaviour of rats
    exposed to microwaves at low power densities. Radio Sci., 12: 273-277.

    SAUNDERS, R.D., & KOWALCZUK, C.I. (1981) Effects of 2.45 GHz microwave
    radiation and heat on mouse spermatogenic epithelium. Int. J. radiat.
    Biol., 40: 623-632.

    SAUNDERS, R.D., DARBY, S.C., & KOWALCZUK, C.I. (1983) Dominant lethal
    studies in male mice after exposure to 2.45 GHz microwave radiation.
    Mutat. Res., 117: 345-356.

    Studies of the induction of dominant lethals and translocations in
    male mice after chronic exposure to microwave radiation. Int. J.
    radiat. Biol., 53: 983-992.

    biological effects of non-ionizing electromagnetic fields and
    radiation: III. Radiofrequency and microwave radiation. Oxfordshire,
    England, National Radiological Protection Board (NRPB R 240).

    SAVIN, B.M. (1986) Safety regulations for non-ionizing radiation. In:
    Hygienic standardization of NIR. Moscow, Medicina, pp. 115-146.

    LOBED, E.K. (1983) [Novelties in safety standards of EM radiation of
    the microwave range.] Gig. Truda, 3: 1 (in Russian).

    (1985) Thermal effects of magnetic resonance imaging (MRI). In:
    Abstracts, Meeting of the Society of Magnetic Resonance in Medicine,
    Vol. 2, pp. 925-926, Berkeley, California, Society of Magnetic
    Resonance in Medicine.

    SCHLAGEL, C.J. & AHMED, A. (1982) Evidence for genetic control of
    microwave-induced augmentation of complement receptor-bearing B
    lymphocytes. J. Immunol., 129(4): 1530-1533.

    J.N. (1980) Biological effects of microwave exposure. II Studies on
    the mechanisms controlling susceptibility to microwave-induced
    increases in complement receptor-positive spleen cells.
    Bioelectromagnetics, 1: 405-414.

    G.M., MURRAY, W.E., CONOVER, D.L., & HALPERIN, W.E. (1991) Video
    display terminals and the risk of spontaneous abortion. New England J.
    Med., 324: 727-733.

    SCHOLL, D.J. & ALLEN, S.J., (1979) Skilled visual-motor performance by
    monkeys in a 1.2-GHz microwave field. Radio Sci., 12: 247-252.

    SCHROT, J., THOMAS, J.R., & BANVARD, R.A. (1980) Modification of the
    repeated acquisition of response sequences in rats by low-level
    microwave exposure. Bioelectromagnetics, 1: 89-99.

    SCHWAN, H.P. (1984) Frequency selective propagation of extracellular
    electrical stimuli to intracellular compartments. In: Adey, W.R. &
    Lawrence, A.F., ed. Nonlinear electrodynamics in biological systems.
    New York, London, Plenum Press, pp. 327-338.

    SCHWAN, H.P. (1985) Biophysical principles of interactions and forces.
    In: Grandolfo, M., Michaelson, S.M., & Rindi, A., ed. Biological
    effects and dosimetry of static and ELF electromagnetic fields. New
    York, London, Plenum Press, p. 243-271.

    SCHWAN, H.P. & FOSTER, K.R. (1980) RF field interactions with
    biological systems: Electrical properties and biophysical mechanisms.
    Proc. IEEE, 68: 104-113.

    SCHWAN, H.P., ANNE, A., & SHER, L. (1966) Heating in living tissues.
    Philadelphia, US Naval Air Engineering Center (NAEC-ACEL-534).

    SCHWARTZ, J.L., HOUSE, D.E., & MEALING, S.A.R. (1990) Exposure of frog
    hearts to CW or amplitude-modulated VHF fields: selective efflux of
    calcium ions at 16 Hz. Bioelectromagnetics, 11: 349-358.

    SCOTT, A.C. (1985) Soliton oscillations in DNA. Phys. Rev. A., 31:

    SCOTT, R.S., CLAY, L., STOREY, K.V., & JOHNSON, R.J. (1985) Transient
    microwave induced neurosensory reactions during superficial
    hyperthermia treatment. Int. J. radiat. Oncol. Biol. Phys., 11(3):

    SEAMAN, R.L. (1977) Effects of microwave radiation on Aplysian
    ganglion cells. In: Adey, W.R. & Bawin, S.M., ed. Brain interactions
    with weak electric and magnetic fields. pp. 45-48 (Neurosciences
    Research Programme Bulletin, 15(1)).

    SERVANTIE, A.M. & ETIENNE, J. (1975) Synchronization of cortical
    neurons by a pulsed microwave field as evidenced by spectral analysis
    of electrocorticograms from the white rat. Ann. N.Y. Acad. Sci., 247:

    DREYFUS, P., & ESCOUBET, P. (1974) Pharmacologic effects of a pulsed
    microwave field. In: Czerski, P., Ostrowski, K., Shore, M.L.,
    Silverman, Ch., Suess, M.J., & Waldeskog, B., ed. Biological effects
    and health hazards of microwave radiation. Warsaw, Polish Medical
    Publishers, pp. 119-127.

    SHACKLETT, D.E., TREDICI, T.J., & EPSTEIN, D.L. (1975) Evaluation of
    possible microwave-induced lens changes in the Unites States Air
    Force. Aviat. space environ. Med., 46: 1403-1406.

    SHANDALA, M. & ZVINYATSKOVSKY, YA. (1988) [Environment and health of
    the population.] Kiev, Zdorovja, p. 150 (in Russian).

    SHANDALA, M., DUMANSKY, YU., & SERDYIUK, A. (1983) [Environmental
    electromagnetic factors and questions of their regulations.] In:
    [Experimental and practical problems in the biology of electromagnetic
    radiation.] Pushchino, Sbornik nauchnykh, pp. 113-122 (in Russian).

    SHANDALA, M.G. & VIROGNODOV, G.I. (1990) Non-ionizing microwave
    radiation as autoimmune indicator. In: Abstracts, 12th Annual Meeting
    of the Bioelectromagnetics Society, June 1990, San Antonio, Texas, p.

    SHANDALA, M.G., RUDNEV, M.I., & NAVAKATIAN, M.A. (1977) Patterns of
    change in behavioral reactions to low power densities of microwaves
    (Abstract). International Symposium on the Biological Effects of
    Electromagnetic Waves (URSI), Airlie, Virginia, p. 88.

    SHANDALA, M.S. & VINOGRADOV, G.I. (1982) [Autoallergic effects of
    electromagnetic energy (EHF) and their influence on the fetus and
    offspring.] Vestn. Akad. Med. USSR, 10: 13-16 (in Russian).

    SHELLOCK, F.G. & CRUES, J.V. (1987) Temperature, heart rate and blood
    pressure changes associated with clinical MR imaging at 1.5 T.
    Radiology, 163: 259-262.

    SHELLOCK, F. G. & CRUES, J.V. (1988) Temperature changes caused by MR
    imaging of the brain with a head coil. Am. J. Neuroradiol. 9: 287-291.

    SHELLOCK, F.G., SHAEFER, D.J., & CRUES, J.V. (1989) Alterations in
    body and skin temperatures caused by MR imaging: is the recommended
    exposure for radiofrequency radiation too conservative? Br. J.
    Radiol., 61: 904.

    SHELTON, W.W. & MERRITT, J.H. (1981)  In vitro study of microwave
    effects on calcium efflux in rat brain tissue. Bioelectromagnetics, 2:

    SHEPPARD, A.R., BAWIN, S.M., & ADEY, W.R. (1979) Models of long-range
    order in cerebral macromolecules: Effects of sub-ELF and of modulated
    VHF and UHF fields. Radio Sci., 14(S): 141-145.

    SHEPPARD, A.R., FRENCH, E., & ADEY, W.R. (1980) Extracellular
    alternating currents change firing rate in Aplysia pacemaker neurons.
    Soc. Neurosci. Abstr., 6: 197.

    SIEKIERZYNSKI, M. (1972) The influence of microwave radiation on iron
    metabolism in rabbits. Med. Lotnic., 39: 53-77.

    CZARNECKI, C., DZIUK, E., & JEDRZEJCZAK, W. (1974a) Health
    surveillance of personnel occupationally exposed to microwaves. II.
    Functional disturbances. Aerospace Med. 45: 1143-1145.

    C., DZIUK, E., & JEDRZEJCZAK, W. (1974b) Health surveillance of
    personnel occupationally exposed to microwaves III. Lens translucency.
    Aerospace Med., 45: 1146-1148.

    Radiation exposure in parents of children with mongolism (Down's
    Syndrome). Bull. J. Hopkins Hosp., 117: 374-399.

    A.A. (1986) Pulsed electromagnetic fields and normal chick
    development. J. Bioelec., 5: 25.

    SKIDMORE, W.D. & BAUM, S.J. (1974) Biological effects in rodents
    exposed to 108 pulses of electromagnetic radiation. Health Phys.,
    26: 391.

    SLINEY, D.H. (1988) Current RF safety standards. In: Repacholi, M.H.,
    ed. Non-ionizing radiations: physical characteristics, biological
    effects and health hazard assessment. London, IRPA Publications, pp.

    SMIALOWICZ, R.J. (1976) The effect of microwaves (2450 MHz) on
    lymphocyte blast transformation  in vitro. In: Johnson, C.C. & Shore,
    M.L., ed. Biological effects of electromagnetic waves. Selected papers
    of the USNC/URSI Annual Meeting, Boulder, Colorado, October 1975.
    Rockville, Maryland, US Department of Health, Education and Welfare,
    Vol.1, pp. 472-483 (HEW Publication (FDA) 77-8010).

    SMIALOWICZ, R.J. (1984) Haematologic and immunologic effects. In:
    Elder, J.A. & Cahill, D.F., ed. Biological effects of radiofrequency
    radiation. Research Triangle Park, North Carolina, Health Effect
    Research Laboratory, US Environmental Protection Agency, pp. 5-13-5-28

    KINN, J.B. (1979a) Evaluation of lymphocyte function in mice exposed
    to 2450 MHz (CW) microwaves. In: Stuchly, S.S., ed. Electromagnetic
    fields in biological systems. Edmonton, Canada, International
    Microwave Power Institute, pp. 122-152.

    SMIALOWICZ, R.J., KINN, J.B., & ELDER, J.A. (1979b) Perinatal exposure
    of rats to 2450 MHz CW microwave radiation: Effects on lymphocytes.
    Radio Sci., 14: 147-153.

    & REHNBERG, B.F. (1981a) Biological effects of long-term exposure of
    rats to 970 MHz radiofrequency radiation. Bioelectromagnetics, 2:

    LIDDLE, C.G., REITER, L.W., & WEIL, C.M. (1981b) Chronic exposure of

    rats to 100-MHz (CW) radiofrequency radiation: Assessment of
    biological effects. Radiat. Res., 86: 488-505.

    SMIALOWICZ, R.J., BRUGNOLOTTI, P.L., & RIDDLE, M.M. (1981c) Complement
    receptor positive spleen cells in microwave (2450 MHz) irradiated
    mice. J. microwave Power, 16: 73-77.

    SMIALOWICZ, R.J., WEIL, C.M., KINN, J.B., & ELDER, J.A. (1982)
    Exposure of rats to 425-MHz (CW) radiofrequency radiation: Effects on
    lymphocytes. J. microwave Power, 17: 211-221.

    R.W., & TOWE, D.G. (1983) Microwaves (2,450 MHz) suppress murine
    natural killer cell activity. Bioelectromagnetics, 4: 371-381.

    SPALDING, J.F., FREYMAN, R.W., & HOLLAND, L.M. (1971) Effects of 800
    MHz electromagnetic radiation on body weight, activity, haematopoiesis
    and life span in mice. Health Phys., 20: 421.

    SPIEGEL, R.J. (1976) ELF coupling to spherical models of man and
    animals. IEEE Trans. biomed. Eng., 23: 387-391.

    SPIEGEL, R.J. (1981) Numerical determination of induced currents in
    humans and baboons exposed to 60 Hz electric fields. IEEE Trans. EMC,
    23: 382-390.

    SPIEGEL, R.J. (1982) The thermal response of a human in the near-zone
    of a resonant thin-wire antenna. IEEE Trans. microwave Theory Tech.,
    30: 177-184.

    SPIEGEL, R.J., DEFFENBAUGH, D.M., & MANN, J.E. (1980) A thermal model
    of the human body exposed to an electromagnetic field.
    Bioelectromagnetics, 1: 253-270.

    STEIN, J. M. (1985) Hand exposure to microwaves [letter]. Ann. emerg.
    Med., 14 (3): 278-279.

    Microwaves: Effects on thermoregulatory behaviour in rats. Science,
    206: 1198-1201.

    STOLWIJK, J.A.J., & HARDY, J.D. (1966) Temperature regulation in man
    - A theoretical study. Pflugers Archiv., 291: 129-162.

    STOLWIJK, J.A.J. & HARDY, J.D. (1977) Control of body temperature. In:
    Lee, D.H.K., ed. Handbook of physiology - Reactions to environmental
    agents. Baltimore, Williams and Wilkins, Chapter 4.

    D.L. (1981) Radiofrequency hyperthermia of advanced human sarcomas. J.
    surg. Oncol., 17: 94-98.

    STRUZAK, R.G. (1982) Terrestrial electromagnetic environment. In:
    Rotkiewicz, W., ed. Electromagnetic compatibility in radio
    engineering. Amsterdam, Elsevier Science Publishers, and Warsaw,
    Widawnictwa komunikacji i Lacznosci, pp. 3-56.

    STRUZAK, R.G. (1985) Vestigial radiation from industrial, scientific,
    and medical radiofrequency equipment. In: Kikuchi, H., ed. Nonlinear
    and environmental electromagnetics. Amsterdam, Elsevier Science
    Publishers, pp. 223-252.

    STUCHLY, M.A. (1977) Potentially hazardous microwave radiation
    sources: a review. J. microwave Power, 12: 370-381.

    STUCHLY, M.A. (1983) Fundamentals of the interactions of
    radiofrequency and microwave energies with health. In: Grandolfo, M.,
    Michaelson, S. M., & Rindi, A., ed. Biological effects and dosimetry
    of nonionizing radiation: radiofrequency and microwave energies. New
    York, London, Plenum Press, pp. 75-93.

    STUCHLY, M.A. (1986) Human exposure to static and time-varying
    magnetic fields. Health Phys., 51: 215-225.

    STUCHLY, M.A. & LECUYER, D.W. (1985) Induction heating and operator
    exposure to electromagnetic fields. Health Phys., 49: 693-700.

    STUCHLY, M.A. & LECUYER, D.W. (1987) Electromagnetic fields around
    induction heating stoves. J. microwave Power, 22: 63-69.

    STUCHLY, M.A. & LECUYER, D.W. (1989) Exposure to electromagnetic
    fields in arc welding. Health Phys., 56: 297-302.

    STUCHLY, M. A. & MILD, K. H. (1987) Environmental and occupational
    exposure to electromagnetic fields. IEEE Eng. Med. Biol. Mag., 6:

    STUCHLY, M.A. & STUCHLY, S.S. (1986) Experimental radio and microwave
    dosimetry. In: Polk, C. & Postow, E., ed. Handbook of biological
    effects of electromagnetic fields. Boca Raton, Florida, CRC Press, pp.

    STUCHLY, M.A. & STUCHLY, S.S. (1987) Measurements of electromagnetic
    fields in biomedical applications. CRC crit. Rev. biomed. Eng., 14:

    STUCHLY, M.A. & STUCHLY, S.S. (1990) Electrical properties of
    biological substances. In: Gandhi, O.P., ed. Biological effects and
    medical applications of electromagnetic fields, Englewood Cliffs, New
    Jersey, Prentice Hall Inc., pp. 75-112.

    STUCHLY, M.A., REPACHOLI, M.H., LECUYER, D.W., & MANN, R. (1980)
    Radiation survey of dielectric (RF) heaters in Canada. J. microwave
    Power, 15: 113-121.

    STUCHLY, M.A., REPACHOLI, M.H., LECUYER, D.W., & MANN, R.D. (1982)
    Exposure to the operator and patient during short wave diathermy
    treatments. Health Phys., 42: 341-366.

    STUCHLY, M.A., REPACHOLI, M.H., & LECUYER, D.W. (1983a) Operator
    exposure to radiofrequency fields near a hyperthermia device. Health
    Phys., 45: 101-107.

    STUCHLY, M.A., REPACHOLI, M.H., LECUYER, D.W., & MANN, R.D. (1983b)
    Radiofrequency emissions from video display terminals. Health Phys.,
    45: 772-775.

    STUCHLY, M.A., KRASZEWSKI, A., & STUCHLY, S.S. (1985) Exposure of
    human body models in the near- and far-field. A comparison. IEEE
    Trans. Biomed. Eng., BME-32: 609-616.

    Exposure of man in the near-field of a resonant dipole: comparison
    between theory and measurements. IEEE Trans. microwave Theory Tech.,
    MTT-34: 26-30.

    SPIEGEL, R.J. (1987) Energy deposition in a heterogeneous model of
    man: near-field exposures. IEEE Trans. Biomed. Eng., BME-34: 944-950.

    LECUYER, D.W., TAN, K., & WONG, J. (1988) Teratological assessment of
    exposure to time-varying magnetic field. Teratology, 38: 461.

    ADAMSKI, D. (1985) Energy deposition in a model of man in the
    near-field. Bioelectromagnetics, 6: 115-129.

    Energy deposition in a model of man; frequency effects. IEEE Trans.
    biomed. Eng., BME-33: 702-711.

    SPIEGEL, R.J. (1987) RF energy deposition in a heterogeneous model of
    man: far-field exposures. IEEE Trans. biomed. Eng., BME-34: 951-957.

    SUESS, M.J. & BENWELL-MORISON, D.A., ed. (1989) Non-ionizing radiation
    protection, 2nd ed. Copenhagen, World Health Organization Regional
    Office for Europe, 346 pp. (European Series No. 25).

    SULTAN, M.F., CAIN, C.A., & TOMPKINS, W.A.F. (1983a) Effects of
    microwaves and hyperthermia on capping of antigen-antibody complexes
    on the surface of normal mouse B lymphocytes. Bioelectromagnetics, 4:

    SULTAN, M.F., CAIN, C.A., & TOMPKINS, W.A.F. (1983b) Immunological
    effects of amplitude-modulated radiofrequency radiation: B lymphocyte
    capping. Bioelectromagnetics, 4: 157-166.

    SZMIGIELSKI, S. & OBARA, T. (1989) The rationale for the Eastern
    European radiofrequency and microwave protection guides. In:
    Franceschetti, G., Gandhi O.P., & Grandolfo, M., ed. Electromagnetic
    biointeraction - Mechanisms, safety standards, protection guides. New
    York, London, Plenum Press, pp. 135-151.

    WREMBEL, J.K. (1982) Accelerated development of spontaneous and
    benzopyrene-induced skin cancer in mice exposed to 2450 MHz microwave
    radiation. Bioelectromagnetics, 3: 179-191.

    Immunologic and cancer-related aspects of exposure to low-level
    microwave and radiofrequency fields. In: Marino, A.A., ed. Modern
    bioelectricity. New York, Marcel Dekker, Inc., pp. 861-925.

    & SZMIGIELSKI, S. (1982) Acceleration of the development of
    benzopyrene-induced skin cancer in mice by microwave radiation. Arch.
    dermatol. Res., 274: 303-312.

    TAKASHIMA, S., ONARAL, B., & SCHWAN, H.P. (1979) Effects of modulated
    RF energy on the EEG of mammalian brains. Radiat. environ. Biophys.,
    16: 15-27.

    Dielectric behaviour of DNA solutions at radio and microwave
    frequencies (at 20 °C). Biophys. J., 46: 29-34.

    TELL, R.A. (1983) Instrumentation and measurement of electromagnetic
    fields: Advanced Study Institute, series A. Life Sci., 49: 95-162.

    TELL, R.A. (1990) RF hot spot fields: The problem of determining
    compliance with the ANSI radiofrequency protection guide. NAB
    Engineering Conference Proceedings, pp. 419-431.

    TELL, R. A. & MANTIPLY, E. D. (1980) Population exposure to VHF and
    UHF broadcast radiation in the United States. Proc. IEEE, 68: 6-12.

    TELL, R.A., MANTIPLY, E.D., DURNEY, C.H., & MASSOUDI, H. (1982)
    Electric and magnetic field intensities and associated induced body
    currents in man in close proximity to a 50 kW AM standard broadcast
    station. Las Vegas, Nevada, US Environmental Protection Agency,
    Electromagnetic Radiation Analysis Branch, and Salt Lake City, Utah,
    Departments of Electrical Engineering and Bioengineering, University
    of Utah.

    TENFORDE, T.S. & BUDINGER, T.F. (1986) Biological effects and physical
    safety aspects of NMR imaging and  in vivo spectroscopy. In: Thomas,
    S.R. & Dixon, R.L., ed. NMR in medicine: Instrumentation and clinical
    applications. New York, American Association of Physicists in Medicine
    (Medical Monograph No. 14).

    TENFORDE, T.S. & KAUNE, W.T. (1987) Interaction of extremely low
    frequency electric and magnetic fields with humans. Health Phys., 53:

    THOMAS, J.R., YEANDLE, S.S., & BURCH, L.S. (1976) Modification of
    internal discriminative stimulus control of behaviour by low levels of
    pulsed microwave radiation. In: Johnson, C.C. & Shore, M.L., ed.
    Biological effects of electromagnetic waves. Selected papers of the
    USNC/URSI Annual Meeting, Boulder, Colorado, October 1975. Rockville,
    Maryland, US Department of Health, Education, and Welfare, Vol. 1, pp.
    201-214 (HEW Publication (FDA) 77-8010).

    THOMAS, J.R., BURCH, L.S., & YEANDLE, S.S. (1979) Microwave radiation
    and chlordiazepoxide: Synergistic effects on fixed-interval behaviour.
    Science, 203: 1357-1358.

    TINTINALLI, J. E., KRAUSE, G., & GURSEL, E. (1983) Microwave radiation
    injury. Ann. emerg. Med., 12(10): 645-647.

    TOFANI, S., AGNESOD, G., OSSOLA, P., FERRINI, S., & BUSSI, R. (1986)
    Effects of continuous low-level exposure to radiofrequency radiation
    on intrauterine development in rats. Health Phys., 51: 489-499.

    SGOUTAS, D. (1988) Long-term study of 435 MHz radio-frequency
    radiation on blood-borne end points in cannulated rats. Part II:
    Methods, results, and summary. J. microwave Power, 23: 105-136.

    TRIBUKAIT, B., CEKAN, E., & PAULSSON, L.E. (1987) Effects of pulsed
    magnetic fields on embryonic development in mice. In: Knave, B. &
    Wideback, P.G., ed. Work with display units 86. Amsterdam, Elsevier,
    p. 129.

    US EPA (1986) Federal radiation protection guidance; Proposed
    alternatives for controlling public exposure to radiofrequency
    radiation; Notice of proposed recommendations. Fed. Reg., Part II,
    51(146): 27318-27339 (July 30, 1986).

    VAN ZANDT, L.L. (1986) Resonant microwave absorption by dissolved DNA.
    Phys. Rev. Lett., 57: 2085-2087.

    VENDRIK, A.J.H. & VOS, J.J. (1958) Comparison of the stimulation of
    the warmth sense organ by microwave and infrared. J. appl. Physiol.,
    13: 435-444.

    WACHTEL, H. (1985) Synchronization of neural firing patterns by
    relatively weak ELF fields. In: Grandolfo, M., Michaelson, S.M., &
    Rindi, A. ed. Biological effects and dosimetry of static and ELF
    electromagnetic fields. New York, London, Plenum Press, pp.313-328.

    WACHTEL, H., SEAMAN, R., & JOINES, W. (1975) Effects of low-intensity
    microwaves on isolated neurons. Ann. N. Y. Acad. Sci., 247: 46-62.

    WACHTEL, H., BEBIO, D., VARGAS, C., BASSEN, H., & BROWN, D. (1989)
    Comparison of the efficacy of pulsed versus CW microwave fields in
    evoking body movements. In: The Eleventh Annual International IEEE
    Engineering in Medicine and Biology Society Conference Proceedings.

    WAY, W.I., KRITIKOS, H., & SCHWAN, H. (1981) Thermoregulatory
    physiologic responses in the human body exposed to microwave
    radiation. Bioelectromagnetics, 2: 341-356.

    WEAVER, J.C. & ASTUMIAN, R.D. (1990) The response of living cells to
    very weak electric fields: The thermal noise limit. Science, 247:

    W., CURTIS. R., MALLINGER, S., ROBBINS, A., & BINGHAM, E. (1980)
    Radiofrequency (RF) heaters and sealers: potential health hazards and
    their prevention. Am. Ind. Hyg. Assoc. J., 41: A22-A38.

    WHITE, D.R.J. (1980) A handbook on electromagnetic shielding material
    and performance. Gainesville, Don White Consultants, p. 164.

    WHO (1981) Environmental health criteria 16: Radiofrequency and
    microwaves. Geneva, World Health Organization, 134 pp.

    WHO (1984) Environmental health criteria 35: Extremely low frequency
    (ELF) fields. Geneva, World Health Organization, 131 pp.

    WHO (1987) Environmental health criteria 69: Magnetic fields. Geneva,
    World Health Organization, 197 pp.

    WIKE, E.L. & MARTIN, E.J. (1985) Comments on Frey's "Data analysis
    reveals significant microwave-induced eye damage in humans". J.
    microwave Power electromag. Eng., 20(3): 181-184.

    K.W. (1977a) Immune response of mice to 2450-MHz radiation: Overview
    of immunology and empirical studies of lymphoid splenic cells. Radio
    Sci., 12(S): 209-219.

    (1977b) Microwaves induce an increase in the frequency of complement
    receptor-bearing lymphoid spleen cells in mice. J. Immunol., 118:

    K.W. (1980) Effect of microwaves (2450-MHz) on the immune system in
    mice: Studies of nucleic acid and protein synthesis.
    Bioelectromagnetics, 1: 161-170.

    WILLIAMS, R.J., MCKEE, A., & FINCH, E.D. (1975) Ultrastructural
    changes in the rabbit lens induced by microwave radiation. Ann. N.Y.
    Acad. Sci., 247: 166-174.

    Effect of 2450 MHz microwave energy on the blood-brain barrier to
    hydrophilic molecules. A. Effect on the permeability to sodium
    fluorescein. Brain Res. Rev., 7: 165-170.

    WILLIAMS, W.M., DEL CERRO, M., & MICHAELSON, S.M. (1984b) Effect of
    2450 MHz microwave energy on the blood-brain barrier to hydrophilic
    molecules. B. Effect on the permeability to HRP. Brain Res. Rev., 7:

    WILLIAMS, W.M., PLATNER, J., & MICHAELSON, S.M., (1984c), Effect of
    2450 MHz microwave energy on the blood-brain barrier to hydrophilic
    molecules. C. Effect on the permeability to (14C) sucrose. Brain Res.
    Rev., 7: 183-190.

    WILLIAMS, W.M., LU, S-T., DEL CERRO, M., & MICHAELSON, S.M. (1984d)
    Effect of 2450 MHz microwave energy on the blood-brain barrier to
    hydrophillic tracers. Brain Res. Rev., 7: 191-212.

    WISSLER, E.H. (1964) A mathematical model of the human thermal system.
    Bull. Math. Biophys. 26: 147-166.

    WISSLER, E.H.(1981) Mathematical simulation of thermoregulatory
    behaviour. Houston, Texas, American Society of Mechanical Engineers.

    WONG, L.S., MERRIT, J.H., & KIEL, J.L. (1985) Effects of 20-MHz
    radiofrequency radiation on rat haematology, splenic function, and
    serum chemistry. Radiat. Res., 103: 186-195.

    YANG, H.K., CAIN, C.A., LOCKWOOD, J., & TOMPKINS, W.A.F., (1983)
    Effects of microwave exposure on the hamster immune system. I. Natural
    killer cell activity. Bioelectromagnetics, 4: 123-139.

    YAO, K.T.S. (1982). Cytogenetic consequences of microwave irradiation
    on mammalian cells incubated  in vitro. J. Hered., 73: 133-138.

    YEE, K-C., CHOU, C.K., & GUY, A.W. (1984) Effect of microwave
    radiation on the beating rate of isolated frog hearts.
    Bioelectromagnetics, 5: 263-270.

    YEE, K-C., CHOU, C-K., & GUY, A.W. (1988) Influence of microwaves on
    the beating rate of isolated rat hearts. Bioelectromagnetics, 9(2):


    1  Résumé

    1.1  Propriétés physiques et effets biologiques correspondants

         Le présent document porte sur les effets biologiques des champs
    électromagnétiques dans la gamme de fréquence de 300 Hz à 300 GHz,
    gamme qui comprend les radiofréquences (RF) (100 kHz à 300 GHz),
    traitées dans une précédente publication (OMS, 1981). Pour simplifier,
    on utilise dans la suite du document l'abréviation RF pour désigner
    les champs électromagnétiques de fréquences comprises entre 300 Hz et
    300 GHz. Ce domaine de fréquences comprend notamment les micro-ondes
    dont les fréquences se situent entre 300 MHz et 300 GHz.

         Pour définir le niveau d'exposition à des champs
    électromagnétiques qui se situent dans le domaine des micro-ondes
    (appelées également hyperfréquences) on utilise en général la "densité
    de puissance" qui s'exprime normalement en watts par mètre carré
    (W/m2) ou encore en milliwatts ou microwatts par mètre carré
    (mW/m2 ou µW/m2). Toutefois, à proximité des sources RF de plus
    grande longueur d'onde, il est nécessaire de préciser l'intensité du
    champ électrique (V/m) et du champ magnétique (A/m) pour décrire le
    champ électromagnétique.

         Les conditions d'exposition peuvent être fortement modifiées par
    la présence d'objets, le degré de perturbation dépendant de la taille,
    de la forme, de l'orientation dans le champ et des propriétés
    électriques de ces objets. La distribution du champ résultant peut
    donc être très complexe tant à l'intérieur qu'à l'extérieur des
    systèmes biologiques exposés aux champs électromagnétiques. La
    réfraction des ondes à l'intérieur de ces systèmes peut focaliser
    l'énergie transmise ce qui entraîne une hétérogénéité importante du
    champ et de pl'énergie cédée à la matière. Des différences dans les
    taux d'absorbtion de l'énergie peuvent entraîner l'apparition de
    gradients thermiques générateurs d'effets biologiques locaux,
    difficiles à prévoir et probablement spécifiques. La géométrie et les
    propriétés électriques des systèmes biologiques jouent également un
    rôle déterminant dans l'intensité et la répartition des courants
    induits à des fréquences inférieures à celles des micro-ondes.

         Lorsqu'un champ électromagnétique passe d'un milieu à un autre,
    il peut être réfléchi, réfracté, transmis ou absorbé en fonction de sa
    fréquence et de la conductivité de l'objet placé dans ce champ.
    L'énergie RF absorbée peut être transformée en d'autres formes
    d'énergie et perturber le fonctionnement du système biologique. Pour
    l'essentiel, cette énergie est transformée en chaleur. Toutefois on ne
    peut pas expliquer tous les effets des champs électromagnétiques par
    un simple mécanisme biophysique où l'énergie est absorbée puis
    transformée en chaleur. On a montré qu'aux fréquences inférieures à
    environ 100 kHz, il y a induction de champs électriques qui peuvent
    stimuler les tissus nerveux. Au niveau microscopique, on pense qu'il

    peut y avoir d'autres interactions susceptibles de perturber les
    systèmes biologiques macromoléculaires complexes (membranes
    cellulaires, structures infracellulaires).

    1.2  Sources de l'exposition

    1.2.1  Collectivité

         Des études approfondies menées aux Etats-Unis au sein de la
    collectivité afin de déterminer la valeur de fond du champ
    électromagnétique ambiant a fait ressortir une exposition médiane de
    l'ordre de 50 µW/m2. Ce sont principalement les émissions de radio
    à haute fréquence qui sont à l'origine des champs électromagnétiques
    ambiants. Les enquêtes ont montré que moins de 1 % de la population
    était exposé à des densités de puissance dépassant 10 mW/m2. A
    proximité immédiate des émetteurs (c'est-à-dire à une distance de
    l'ordre d'une demi-longueur d'onde du champ incident) l'exposition
    peut être plus importante et être accrue par la présence de
    conducteurs avoisinants. Une étude s'impose dans chaque cas

    1.2.2  Environnement domestique

         Dans l'environnement domestique, les sources de radiofréquences
    sont constituées de divers appareils: fours à micro-ondes, réchauds à
    induction, alarmes électroniques, installations vidéo et téléviseurs.
    Les fuites provenant des fours à micro-ondes peuvent atteindre 1,5
    W/m2 à 0,3 m et 0,15 W/m2 à 1 m. Le meilleur moyen de limiter
    l'exposition au rayonnement émis par les appareils domestiques
    consiste à améliorer leur conception et à effectuer des contrôles à la

    1.2.3  Lieu de travail

         Sur divers lieux de travail on utilise des corps de chauffe
    diélectriques pour le formage du bois et le soudage des plastique, des
    chauffages à induction pour le travail des métaux ainsi que des
    installations vidéo. Les installations vidéo produisent des champs
    électriques et magnétiques dont la fréquence se situe entre 15 et 35
    kHz ainsi que des champs modulés de très basse fréquence. Les
    personnels qui travaillent sur ou près des tours ou des antennes de
    radio-télévision peuvent être exposés à des champs importants allant
    respectivement jusqu'à 1 kV/m et 5 A/m. A proximité des installations
    de radar, les travailleurs peuvent être exposés à des densités
    importantes de puissance de crête s'ils se trouvent dans le faisceau
    de radio fréquence à quelques mètres de l'antenne émettrice (jusqu'à
    10 mW/m2). En général, la densité moyenne de puissance à proximité
    des radars de contrôle du trafic aérien est de l'ordre de 0,03-0,8

         Dans les ambiances de travail, le meilleur moyen d'assurer la
    protection du personnel est de s'en tenir aux spécifications

    d'émission relatives aux différents équipements et le cas échéant,
    d'assurer un contrôle continu au moyen d'instruments de mesure

         Des risques d'exposition particuliers existent en milieu
    médicalisé lorsqu'on utilise des appareils de diathermie pour traiter
    la douleur et l'inflammation des tissus. Les personnes qui manipulent
    ces appareils risquent une exposition professionnelle relativement
    importante au rayonnement parasite que l'on peut réduire au moyen
    d'écrans appropriés ou par une conception convenable de l'appareil. On
    a mesuré des champs de 300 V/m et de 1 A/m à 10 cm des électrodes. De
    même les chirurgiens qui utilisent du matériel électrochirurgical
    fonctionnant à des fréquences voisines de 27 MHz peuvent être exposés
    à des champs supérieurs aux limites recommandées plus haut. Ces
    valeurs diminuent très rapidement à mesure que s'accroît la distance
    aux électrodes.

         La plupart des matériels utilisés pour l'imagerie par résonnance
    magnétique (IRM) utilisent des champs magnétiques statiques dont les
    densités de flux atteignent 2 T avec des gradients d'intensité
    magnétique à basse fréquence allant jusqu'à 20 T/s et des champs RF
    compris entre 1 et 100 MHz. La puissance délivrée au malade peut être
    importante mais l'exposition du personnel est beaucoup plus faible et
    dépend des caractéristiques de l'imageur.

    1.3  Effets biologiques

         Les champs électromagnétiques de fréquence comprise entre 300 Hz
    et 300 GHz interagissent avec les systèmes biologiques humains ou
    animaux soit directement soit indirectement. Les interactions
    indirectes sont importantes au dessous de 100 MHz mais ne
    correspondent qu'à des situations particulières. Lorsque des charges
    électriques sont induites dans des objets métalliques (comme une
    automobile, une grille, etc.) plongés dans un champ électromagnétique,
    ces objets peuvent se décharger lorsqu'un corps entre en contact avec
    eux. Ces décharges peuvent produire localement des densités de courant
    susceptibles de causer un état de choc et des brûlures.

         L'un des principaux mécanismes d'interaction consiste dans
    l'induction de courants intratissulaires, dont les effets sont liés à
    la fréquence, à l'intensité et à la forme de l'onde. Pour les
    fréquences inférieures à environ 100 kHz, les interactions avec le
    tissu nerveux sont à prendre en considération du fait qu'ils sont
    alors plus sensibles aux courants induits. Au dessus de 100 kHz, le
    tissu nerveux perd de sa sensibilité à la stimulation direte par le
    champ électromagnétique et ce sont alors les phénomènes liés à la
    transformation de l'énergie électromagnétique en énergie thermique qui

         Un certain nombre d'études montrent qu'il existe également des
    interactions dans le cas des champs faibles. On a émis diverses
    hypothèses sur la nature de ces interactions mais on en ignore encore

    le mécanisme exact. Ces interactions avec les champs faibles résultent
    de l'exposition aux champs de basse fréquence modulés en amplitude.

    1.4  Etudes en laboratoire

         La plupart des effets biologiques observés en cas d'exposition
    aiguë à des champs électromagnétiques traduisent différents types de
    réponse au réchauffement induit: élévation de la température
    intratissulaire locale ou de la température centrale d'environ 1 °C ou
    davantage ou encore réactions destinées à réduire l'apport thermique
    total. La plupart de ces réactions ont été observées à des taux
    d'absorption spécifiques (TAS) supérieurs à environ 1-2 W/kg chez
    différentes espèces animales exposées dans diverses conditions
    d'ambiance. Les données obtenues sur l'animal (en particulier les
    primates) permettent de prévoir les réactions susceptibles de se
    produire chez des sujets humains soumis à un apport thermique
    suffisamment élevé. Toutefois, il est difficile d'extrapoler
    directement à l'homme les donnés quantitatives obtenus car les
    réactions varient généralement d'une espèce à l'autre, notamment en ce
    qui concerne l'aptitude thermorégulatrice.

         Les réponses les plus sensibles de l'organisme animal à la charge
    thermique consistent dans la mise en oeuvre de mécanismes
    thermorégulateurs tels qu'une réduction de la thermogénèse et une
    vasodilatation, les valeurs seuil oscillant autour de 0,5-5 W/kg, en
    fonction des conditions ambiantes. Toutefois, il s'agit là de
    réactions qui correspondent à des réponses thermorégulatrices normales
    destinées à maintenir la température centrale dans des limites

         On a observé chez les animaux exposés des effets transitoires qui
    correspondent aux réactions suscitées par une augmentation de la
    température centrale de 1 °C ou davantage (avec des TAS dépassant
    environ 2 W/kg chez les primates et les rats); il s'agit d'une
    diminution de l'aptitude à effectuer certaines tâches après
    apprentissage, et d'une augmentation des taux sanguins de
    corticostéroïdes. Les effets thermiques peuvent également se traduire
    par l'apparition de réponses temporaires au niveau du système
    hématopoiétique et immunitaire, peut être par suite de l'élévation des
    taux de corticostéroïdes. Les effets les plus régulièrement observés
    consistent en une réduction du nombre de lymphocytes circulants, une
    augmentation des neutrophiles, une altération fonctionnelle des
    cellules NK (tueuses naturelles) et des macrophages. On a également
    fait état d'une augmentation de la réponse primaire en anticorps des
    lymphocytes B. Au niveau cardiovasculaire, les réactions observées
    correspondent bien à une élévation de la charge thermique:
    accroissement du rythme et du débit cardiaques, avec réduction de
    l'effet des médicaments tels que les barbituriques dont l'action peut
    être modifiée par les changements au niveau circulatoire.

         La plupart des données de l'expérimentation animale montrent
    qu'il est très peu probable que la nidation et le développement de

    l'embryon ou du foetus soient affectés par une augmentation de la
    température centrale de la mère qui ne dépasse pas 1 °C. Au-delà, des
    effets indésirables tels que des retards de croissance et des
    modifications postnatales affectant le comportement peuvent se
    produire, les effets étant d'autant plus graves que la température
    centrale de la mère était plus élevée.

         La plupart des ces mêmes données incitent à penser qu'une
    exposition à de faibles champs RF qui n'entraînent pas une
    augmentation de la température centrale au-delà des limites
    physiologiques, n'est pas mutagène. Une exposition de ce genre ne peut
    pas entraîner de mutations somatiques ou d'effets héréditaires. On est
    en revanche beaucoup moins bien renseigné sur les effets à long terme
    d'une exposition de faible intensité. Toutefois jusqu'ici, il ne
    semble pas qu'une exposition qui n'entraîne aucun effet thermique
    significatif puisse avoir d'effet à long terme. Les données obtenues
    sur l'animal montrent que chez les mâles, la fertilité ne devrait pas
    être affectée par une exposition à long terme à des intensités qui ne
    provoquent pas d'élévation de la température centrale ou de la
    température des testicules.

         On n'a pas observé la formation de cataracte chez des lapins
    exposés pendant six mois à 100 W/m2 ou des primates exposés pendant
    plus de trois mois à 1,5 kW/m2.

         On a exposé 100 rats pendant la majeure partie de leur existence
    à un champ électromagnétique correspondant à 0,1 W/kg, sans observer
    d'augmentation dans l'incidence des lésions non-néoplasiques ou de
    l'ensemble des lésions néoplasiques par rapport aux animaux témoins;
    la longévité était analogue dans les deux groupes. Il y avait certes
    des différences dans l'incidence globale des tumeurs malignes
    primitives mais elles n'étaient pas nécessairement imputables à

         La possibilité que l'exposition à des champs RF puisse intervenir
    dans le processus de la cancérogénèse est une question
    particulièrement préoccupante. Jusqu'ici rien n'indique de manière
    définitive que cet effet existe. Toutefois, il est à l'évidence
    nécessaire de poursuivre les études. Un grand nombre de données
    expérimentales montrent que ces champs n'ont pas d'effets mutagènes et
    que, par ailleurs, ils n'ont selon toute probabilité aucun rôle comme
    initiateurs de la cancérogénèse; les quelques études consacrées à ce
    problème ont consisté principalement à rechercher s'il y avait
    accroissement de l'effet exercé par tel ou tel cancérogène. Chez les
    souris longuement exposées à 2-8 W/kg on a observé une plus forte
    progression des tumeurs mammaires spontanées parmi les animaux dont la
    peau avait été traitée par un cancérogène chimique.

         Les études  in vitro ont révélé que, après une exposition à des
    champs RF à raison de 4,4 W/kg (seuls ou en association avec une
    irradiation X) il se produisait une augmentation du taux de
    transformation cellulaire après traitement par un promoteur chimique.

    Dans ce dernier cas, il n'y a pas toujours accord entre les
    différentes études. Il est cependant clair qu'il faut s'efforcer de
    reprendre et d'approfondir les études relatives au problème de la

         On possède une somme importante de données relatives aux réponses
    biologiques suscitées par des champs RF modulés en amplitude ou des
    champs de micro-ondes à des taux d'absorption spécifiques trop faibles
    pour produire un effet thermique. Dans certaines de ces études, on a
    observé des effets lorsque le taux d'absorption spécifique était
    inférieur à 0,01 W/kg, effets qui se produisaient à l'intérieur de
    "fenêtres" de modulation de fréquence (généralement entre 1-100 Hz) et
    quelques fois à l'intérieur de "fenêtres" de densité de puissance; des
    résultats analogues ont été obtenus aux fréquences vocales (300 Hz-3
    kHz). Les modifications obervées concernaient les paramètres suivants:
    électroencéphalogramme chez le chat et le lapin, mobilité des ions
    calcium dans le tissu cérébral  in vitro et  in vivo, cytotoxicité
    lymphocytaire  in vitro, activité d'une enzyme intervenant dans la
    croissance et la division cellulaire. Certaines de ces réponses ont
    été difficiles à confirmer et leur portée physiologique n'est pas
    clairement établie. Quoi qu'il en soit, toute étude toxicologique doit
    se fonder sur des épreuves menées avec une exposition d'intensité
    appropriée. Il importe que ces études soient confirmées et que leurs
    conséquences sur la santé - si elles en ont - soient dûment établies.
    Il serait particulièrement important de relier les effets des très
    basses fréquences, des champs modulés en amplitude, des champs RF ou
    des champs de micro-ondes au niveau de la surface cellulaire, à des
    modifications intervenant dans la synthèse ou la transcription de
    l'ADN. Il est bon de noter que ce type d'interaction implique une
    "démodulation" du signal RF au niveau de la membrane cellulaire.

    1.5  Etudes chez l'homme

         Assez peu d'études portent directement sur les effets d'une
    exposition aiguë ou à long terme à des champs RF. Dans les études
    effectuées en laboratoire, on a observé une perception des champs au
    niveau cutané dans le domaine allant de 2 à 10 GHz. Le seuil
    d'apparition d'une sensation de chaleur se situerait à des densités de
    puissance de 270 W/m2 à 2000 W/m2, selon la dimension de la
    surface irradiée (13 à 100 cm2) et la durée de l'exposition (1 à 180
    secondes). Lorsque le taux d'absorption spécifique est de 4 W/kg
    pendant 15 à 20 minutes, on constate chez les volontaires humains, une
    augmentation de la température centrale moyenne de 0,2 à 0,5 °C, ce
    qui est tout à fait surportable pour des sujets en bonne santé. On
    ignore quel impact cette charge thermique accrue pourrait avoir sur
    des sujets dont le système thermorégulateur est défficient et qui sont
    placés dans une ambiance où la thermorégulation par sudation est

         Les quelques études épidémiologiques effectuées sur des
    populations exposées à des champs RF n'ont pas permis d'attribuer à ce
    type d'exposition une influence quelconque sur la santé, qu'il

    s'agisse d'une réduction de l'espérance de vie ou, d'une surmortalité
    pour une raison déterminée, sauf toutefois dans le cas des décès par
    cancer où l'on a noté un accroissement d'incidence qui, il est vrai,
    pourrait s'expliquer par une confusion avec l'action de certaines
    substances chimiques. Selon certaines études, ce type d'exposition
    n'entraînerait aucune augmentation dans l'incidence des accouchements
    prématurés ou des malformations congénitales alors que selon d'autres,
    il y aurait une association entre l'intensité de l'exposition et
    certains accidents obstétricaux. Ces études pêchent par un certain
    nombre de points, notamment une mauvaise évaluation de l'exposition et
    une appréciation insuffisante des autres facteurs de risque.

    1.6  Evaluation des dangers pour la santé

         L'évaluation globale des dangers pour la santé résultant d'une
    exposition aux champs de RF s'articule comme suit.

    1.6.1  Effets thermiques

         Lorsque de l'énergie électromagnétique est absorbée par le corps
    humain elle tend à accroître la température centrale. Dans ces
    conditions, la thermogénèse métabolique peut atteindre 3 à 5 W/kg.
    Dans une ambiance thermique normale, un taux d'absorption spécifique
    de 1 à 4 W/kg pendant 30 minutes ne produit qu'une augmentation
    moyenne de la température centrale inférieure à 1 °C chez un adulte en
    bonne santé. Par conséquent, une valeur indicative d'exposition
    professionnelle aux champs RF correspondant à un taux d'absorption
    spécifique de 0,4 W/kg, laisse une marge de sécurité qui permet de se
    garantir contre les complications qui peuvent se produire dans une
    ambiance thermique défavorable. En ce qui concerne la population en
    général, au sein de laquelle peuvent se trouver des groupes plus
    sensibles tels que les nourrissons et les personnes âgées, un taux
    d'absorption spécifique de 0,08 W/kg donne une marge supplémentaire de
    sécurité et garantit contre les effets thermiques indésirables des
    champs RF.

    1.6.2  Champs pulsés

         On a montré, dans un certain nombre de circonstances que le seuil
    d'apparition des effets biologiques aux fréquences supérieures à
    plusieurs centaines de MHz diminuait lorsque l'énergie était délivrée
    sous la forme de brèves impulsions (1 à 10 µs). Par exemple,
    l'émission d'un train d'impulsions délivrant plus de 400 mJ/m2
    chacune durant moins de 30 µs produit des effets auditifs. Il n'est
    pas possible de définir une limite de sécurité pour ces trains
    d'impulsions sur la base des données disponibles.

    1.6.3  Champs RF modulés en amplitude

         Les effets de ce type de champ observés au niveau cellulaire,
    tissulaire et organique ne semblent pas correspondre à des effets
    nocifs pour la santé. Comme il n'est pas possible d'établir de

    relation dose-effet qui mette en évidence un seuil quelconque, on
    n'est en mesure d'émettre des recommandations particulières en
    fonction des données disponibles.

    1.6.4  Effets des champs RF sur l'induction et la promotion des

         Il n'est pas possible d'après ce que l'on sait des effets que les
    champs RF exercent sur certaines lignées cellulaires, sur la
    transformation des cellules, sur l'activité enzymatique ainsi que sur
    l'incidence et la progression es tumeurs chez l'animal, de conclure
    que l'exposition à ces champs puisse avoir un effet quelconque sur
    l'incidence du cancer chez l'homme ni d'en déduire que des
    recommandations particulières seraient nécessaires pour limiter
    l'intensité de ces champs en raison du risque de cancer.

    1.6.5  Densités de courant induites par les champs RF

         Dans la gamme de fréquence de 300 Hz à 100 kHz, le paramètre le
    plus important pour l'évaluation du risque est l'induction de champs
    et de courants dans les tissus excitables. Le seuil de stimulation du
    tissu nerveux et musculaire dépend fortement de la fréquence et la
    densité de courant nécessaire varie de 0,1 à 1 mA/m2 à 300 Hz à
    environ 10-100 A/m2 à 100 kHz. Toutefois, pour ce qui concerne les
    autres effets observés en-dessous de ces seuils, on ne dispose pas de
    données suffisantes pour émettre des recommandations particulières.

    1.6.6  Chocs et brûlures provoqués par contact avec des objets plongés
           dans un champ RF

         Les objets conducteurs plongés dans un champ RF peuvent acquérir
    une charge électrique. Lorsqu'une personne touche un tel objet ou s'en
    approche suffisamment près, un courant électrique non négligeable peut
    s'établir entre l'objet et la personne. En fonction de la fréquence,
    de l'intensité du champ électrique, de la taille et de la forme de
    l'objet ainsi que de l'aire des surfaces en contact, le courant
    résultant peut provoquer un choc par stimulation des nerfs
    périphériques. Si le courant est suffisamment fort, il peut entraîner
    des brûlures. A titre de précaution, on peut éliminer tout objet
    conducteur présent dans un champ intense de RF, le placer dans une
    enceinte ou en limiter l'accès.

    1.7  Normes d'exposition

    1.7.1  Limites de base

         Afin de protéger les travailleurs et la population générale
    contre les effets éventuels d'une exposition aux champs
    électromagnétiques, on a défini des limites de base qui s'appuient sur
    les effets biologiques observés. Diverses considération scientifiques
    sont à la base des limites fixées pour les fréquences supérieures ou
    inférieures à MHz. Au-dessus de 1 MHz, on a étudié les effets

    biologiques sur l'animal afin de déterminer quelle est la valeur la
    plus faible du taux d'absorption spécifique moyen pour le corps entier
    qui est susceptible d'avoir un effet nocif sur la santé. Cette valeur
    est de 3 à 4 W/kg.

         La majeure partie des résultats concerne des expositions à des
    champs qui se situent à la limite inférieure du domaine gigahertzien.
    Ainsi, pour déterminer les effets qui s'excercent à fréquences plus
    basses, il faut poser par hypothèse que les effets biologiques sont
    liés à la fréquence. Etant donné que les effets biologiques observés
    dans les limites de 1 à 4 W/kg sont supposées être thermiques, on
    suppose que la valeur seuil du taux d'absorption spécifique est
    indépendante de la fréquence. On estime que l'exposition d'un être
    humain à 4 W/kg pendant 30 minutes entraîne une augmentation de moins
    de 1°C de la température centrale. Cet acccroissement de la
    température centrale est considéré comme acceptable.

         Afin de tenir compte des effets défavorables, des effets
    thermiques et des effets d'ambiance ou des effets éventuels à long
    terme, on a introduit un coefficient de sécurité de 10, d'où une
    limite de base égale à 0,4 W/kg. En ce qui concerne la population en
    général, il faudrait introduire une marge de sécurité supplémentaire
    pour tenir compte des sujets qui sont plus ou moins sensibles à
    l'exposition. En général pour le grand public, on propose un
    coefficient de sécurité de 5 ce qui entraîne une limite de base de
    0,08 W/kg. On trouvera aux tableaux 34 et 35 de la présente
    publication les limites d'exposition qui en dérivent.

         Les limites relatives au taux d'absorption spécifique moyen pour
    le corps entier ne sont pas suffisamment restrictives, étant donné que
    la distribution de l'énergie absorbée dans l'organisme peut être
    hétérogène et liée aux conditions d'exposition. En cas d'exposition
    partielle du corps et en fonction de la fréquence, l'énergie absorbée
    peut se concentrer dans un volume limité de tissu, même si le taux
    d'absorption spécifique moyen pour le corps entier est inférieur à 0,4
    W/kg. Par conséquent, il est recommandé d'observer une limite de base
    supplémentaire de 2 W/100 g pour toute zone délimitée de l'organisme
    afin d'éviter une élévation excessive de la température locale. L'oeil
    constitue un cas à part.

         Aux fréquences inférieures à environ 1 MHz, les limites
    d'exposition ont été choisies pour éviter une stimulation des cellules
    nerveuses et musculaires. Les limites d'exposition concernent les
    densités de courant induites dans les tissus. Elles doivent comporter
    un coefficient de sécurité suffisant pour limiter la densité de
    courant à 10 mA/m2 à 300 Hz. Cette valeur est du même ordre de
    grandeur que celle des courants naturels de l'organisme. Au-dessus de
    300 Hz, la densité de courant nécessaire à l'excitation du tissu
    nerveux croît avec la fréquence jusqu'à ce que les effets thermiques
    prennent le relai. Aux fréquences situées alentour de 2 à 2 Mhz, la
    limite de base pour la densité de courant correspond à la limite
    relative au taux d'absorption spécifique maximal de 1 W/100 g. Etant

    donné qu'il est difficile, en pratique, de mesurer un taux
    d'absorption spécifique ou une densité de courant, on s'efforce
    d'obtenir, à partir des limites de base, des limites d'exposition qui
    s'expriment sous la forme d'une grandeur aisément mesurable. Ces
    limites "dérivées" permettent de savoir quelles sont les limites à
    fixer aux paramètres mesurés ou calculés du champ pour satisfaire aux
    limites de base.

    1.7.2  Limites d'exposition professionnelle

         Les populations exposées de par leur profession sont constituées
    d'adultes exposés dans des conditions contrôlées et qui sont
    conscients des risques qu'ils encourent. Etant donné la gamme étendue
    de fréquences qui fait l'objet de la présente publication, il n'est
    pas possible de donner une valeur unique pour l'exposition
    professionelle. On trouvera au tableau 34 une liste des limites
    professionelles dérivées pour les fréquences de 100 kHz à 300 GHz.
    Dans le cas des champs pulsés, la prudence est recommandée et
    l'intensité des champs électriques et magnétiques est limitée à 32
    fois les valeurs du tableau 34 (en moyenne calculée sur une largeur
    d'impulsion). Quant à la densité de puissance, elle est limitée à 1000
    fois la valeur correspondante du tableau 34 ramenée à sa moyenne sur
    la largeur d'une impulsion.

    1.7.3  Limites d'exposition pour la population générale

         La population générale est constituée de personnes d'âge
    différente, d'état de santé variable et de femmes enceintes.
    L'éventualité d'une sensibilité particulière du foetus mérite une
    attention spéciale.

         Les limites d'exposition pour la population générale devraient
    être inférieures aux limites d'exposition professionelle. Par exemple,
    les limites dérivées recommandées pour les fréquences de 100 kHz à 300
    GHz (tableau 35), sont généralement inférieures d'un facteur 5 aux
    limites d'exposition professionelle.

    1.7.4  Application des normes

         Pour faire appliquer les normes d'exposition professionnelle ou
    celle qui concernent la santé publique, il faut préciser qui est
    chargé de mesurer les champs, d'interpréter les résultats et d'établir
    les codes de sécurité détaillés correspondantes ou des manuels
    d'hygiène et de sécurité qui indiquent le cas échéant comment procéder
    pour réduire l'exposition.

    1.8  Mesures de protection

         Au nombre des mesures de protection figurent la surveillance du
    lieu de travail (enquêtes), les contrôles techniques, les mesures
    administratives, la protection individuelle et la surveillance
    médicale. Lorsque les enquêtes indiquent que l'exposition sur le lieu

    de travail dépasse les limites recommandées pour la population
    générale, il faut mettre en place une surveillance. Si ces mêmes
    enquêtes indiquent que l'exposition sur les lieux de travail dépasse
    les limites recommandées, on prendra des mesures pour protéger les
    travailleurs. Il faut, en premier lieu, prendre des mesures techniques
    qui ramènent les émissions à un niveau acceptable. Ces mesures
    consistent tout d'abord en une conception générale respectueuse de
    l'hygiène et de la sécurité et, si nécessaire, dans l'utilisation de
    dispositifs de vérouillage ou autres types de sécurités.

         Sur le plan administratif, on peut prendre des mesures visant à
    limiter l'accès à l'appareillage, et faire utiliser des systèmes
    d'alarme sonores ou visuels, en plus des mesures techniques. En ce qui
    concerne les mesures de protection individuelle (port de vêtements
    protecteurs), si elles peuvent rendre des services dans certains cas,
    on doit considérer qu'elles ne constituent qu'un recours ultime. Dans
    la mesure du possible on privilégiera les mesures techniques et
    administratives. Lorsque les travailleurs risquent de subir une
    exposition dépassant les limites applicables à la population générale,
    on envisagera de les soumettre à une surveillance médicale appropriée.

         La prévention des risques liés à l'utilisation des champs RF
    nécessite également l'établissement et le respect d'un certain nombre
    de règles: a) veiller à ce qu'il n'y ait pas d'interférences avec les
    dispositifs de sécurité et les appareils médicaux électroniques (par
    exemple les stimulateurs cardiaques); b) veiller à éviter le
    déclenchement des détonateurs à commande électronique; et enfin c)
    prendre des mesures contre les incendies et les explosions dus à la
    présence de matériaux qui pourraient s'enflammer au contact des
    étincelles produites par des champs induits.

    2  Recommandations en vue de recherches futures

    2.1  Introduction

         On s'inquiète d'un certain nombre d'effets que les champs RF
    pourraient avoir sur la santé: promotion et progression des tumeurs
    cancéreuses, effets indésirables sur la fonction de reproduction
    (avortements spontanés et malformations congénitales), et effets sur
    le fonctionnement du système nerveux central. Les connaissances dans
    tous ces domaines restent trop fragmentaires pour que l'on puisse se
    prononcer sur l'existence de ces effets, aussi ne dispose-t-on
    d'aucune base rationnelle pour proposer des recommandations visant à
    protéger la population générale contre d'éventuels effets nocifs.

         Il faudrait assurer une très bonne coordination des efforts de
    recherche concernant les interactions faibles avec les processus
    biologiques d'une part et les études consacrées aux effets sur la
    cancérogénèse et la fonction de reproduction chez l'animal et chez
    l'homme d'autre part. Ce type de coordination pourrait être assuré en
    favorisant le financement de propositions de recherches
    pluri-disciplinaires ou pluriinstitutionnelles. Les études consacrées

    aux champs RF pourraient être coordonnées avec les programmes du même
    type consacrés aux effets des champs de très basse fréquence (50 à
    60Hz). On devrait accorder une priorité élevée aux recherches qui
    portent principalement sur l'établissement de relations causales et
    sur les effets de seuil.

         De l'avis du Groupe de travail, les secteurs suivants doivent
    être considérés comme prioritaires.

    2.2  Champs pulsés

         Nos connaissances sont très insuffisantes au sujet des effets
    produits par de très fortes densités de puissance de crête séparées
    par des périodes où la puissance est nulle. On ne dispose que de
    quelques rapports isolés sur les effets des champs pulsés et il n'est
    pas possible de déterminer si c'est la fréquence ou la puissance de
    crête qui est la plus importante. Il est d'une nécessité urgente de
    disposer de données concernant les risques pour la santé humaine liés
    à des facteurs tels que la puissance de crête du champ pulsé, la
    fréquence de répétition, la longueur des impulsions et la fréquence du
    champ, du fait des applications de plus en plus larges de systèmes
    utilisant des impulsions de grande puissance (essentiellement des
    radars), systèmes qui entraîneny une exposition professionnelle et une
    exposition de la population générale.

    2.3  Etudes sur les cancers, la fonction de reproduction et le système

         On s'inquiète de plus en plus du rôle que l'exposition aux champs
    RF pourrait avoir dans l'apparition ou la promotion de certains
    cancers, notamment au niveau des organes hématopoïétiques ou du
    système nerveux central. Il existe des incertitudes du même genre à
    propos d'effets possibles sur la reproduction, par exemple un
    accroissement des avortements spontanés et des malformations

         Les effets d'une exposition aux champs RF sur le système nerveux
    central et notamment sur les fonctions cognitives, sont également
    entachés d'incertitude. En raison de l'importance potentielle de ces
    interactions et compte tenu de l'influence néfaste que le flou qui les
    entourne pourrait avoir sur le corps social, il importe de considérer
    ce secteur comme tout à fait prioritaire. Il faudrait que les efforts
    de recherche soient coordonnés afin de lever toutes ces incertitudes
    au lieu de les accroître. On s'efforcera de coordonner étroitement les
    recherches sur les mécanismes à la base de ces effets, notamment
    l'action des champs faibles, avec des études toxicologiques bien
    conçues sur l'animal et des études épidémiologiques chez l'homme.

    2.4  Interactions avec les champs faibles

         Très peu de personnes sont exposées à des champs RF qui suscitent
    des effets thermiques importants; dans la très grande majorité des

    cas, le niveau d'exposition susceptible d'entraîner des effets nocifs
    sur la santé n'implique que des interactions avec des champs faibles.
    On possède un nombre important de données expérimentales qui indiquent
    l'existence de réactions aux champs de RF modulés en amplitude,
    données qui font ressortir l'existence de fenêtres de fréquence et
    d'amplitude; certaines réactions sont liées à une exposition
    concommitante à des agents physiques ou chimiques. Il est d'une
    importance capitale d'établir la portée de ces effets pour la santé
    humaine et de déterminer les relations dose-réponse qui peuvent
    exister. Des travaux sont nécessaires afin d'identifier les mécanismes
    biophysiques qui sous-tendent ces interactions en les étendant à
    l'expérimentation animale et humaine afin de mettre en évidence les
    risques éventuels pour la santé.

    2.5  Epidémiologie

         Les études épidémiologiques sur la reponsabilité éventuelle des
    champs RF dans certaines cancers et accidents obstétricaux sont
    rendues difficiles par un certain nombre de facteurs:

    -    Pour la plupart des membres de la population, l'exposition aux
         champs RF est de plusieurs ordres de grandeur inférieure aux
         valeurs qui produiraient des effets thermiques sensibles.

     -   Il est très difficile d'établir qu'elle est l'exposition subie
         par des individus sur une période de temps représentative.

     -   Il est très difficile de tenir compte des principaux facteurs de

         Moyennant des études cas-témoins convenablement conçues et
    menées, il est possible de surmonter ces difficultés, du moins en
    partie. Un certain nombre d'études de ce genre sont en cours ou en
    prévision pour ce qui concerne les cancers de l'enfance et les effets
    éventuels des champs électriques de basse fréquence. Il est important
    de prévoir dans ces études, une évaluation de l'exposition aux champs


    1.  Resumen

    1.1  Características físicas en relación con los efectos biológicos

         El presente documento se ocupa de los efectos que tienen en la
    salud los campos electromagnéticos de la banda de frecuencias
    comprendidas entre 300 Hz y 300 GHz, que abarca el espectro de
    radiofrecuencias (RF) (100 kHz-300 GHz) tratado en la publicación
    anterior (OMS, 1981). Para mayor sencillez, en el presente documento
    se utiliza la abreviatura RF para los campos electromagnéticos de
    frecuencia 300 Hz-300 GHz. Dentro de esas frecuencias se encuentran
    las microondas, cuyas frecuencias están comprendidas entre 300 MHz y
    300 GHz.

         Los niveles de exposición en la gama de microondas suelen
    describirse respecto de la «densidad de potencia» y suelen expresarse
    en vatios por metro cuadrado (W/m2), o milivatios o microvatios por
    metro cuadrado (mW/m2, µW/m2). Sin embargo, en las proximidades de
    fuentes de RF con longitudes de onda superiores, se necesitan para
    describir el campo los valores de intensidades de los campos eléctrico
    (V/m) y magnético (A/m).

         Las condiciones de exposición pueden verse considerablemente
    alteradas por la presencia de objetos; el grado de perturbación
    depende de su tamaño, forma, orientación en el campo, y propiedades
    eléctricas. Pueden producirse distribuciones sumamente complejas del
    campo, tanto dentro como fuera de los sistemas biológicos expuestos a
    campos electromagnéticos. La refracción dentro de estos sistemas puede
    centrar la energía transmitida, dando lugar a campos notablemente
    heterogéneos y a deposición de energía. Los distintos índices de
    absorción energética pueden originar gradientes térmicos causantes de
    efectos biológicos que pueden ser generados localmente, difíciles de
    prever y tal vez singulares, La geometría y las propiedades eléctricas
    de los sistemas biológicos serán también factores que determinen la
    magnitud y la distribución de corrientes inducidas en frecuencias
    inferiores a la banda de microondas.

         Cuando los campos electromagnéticos pasan de un medio a otro,
    pueden ser reflejados, retractados, transmitidos o absorbidos,
    atendiendo a la conductividad del objeto expuesto y a la frecuencia
    del campo. La energía RF absorbida puede convertirse en otras formas
    de energía y causar interferencias con el funcionamiento del sistema
    vivo. La mayor parte de esta energía se convierte en calor. No
    obstante, no todos los efectos de los campos electromagnéticos pueden
    explicarse basándose en los mecanismos biofísicos de la absorción
    energética y la conversión térmica. En frecuencias inferiores a unos
    100 kHz, se ha demostrado que los campos eléctricos inducidos pueden
    estimular el sistema nervioso. A escala microscópica, se han postulado
    otras interacciones causantes de perturbaciones en los sistemas

    biológicos macromoleculares complejos (membranas celulares,
    estructuras subcelulares).

    1.2  Fuentes y exposición

    1.2.1  Comunidad

         En estudios comunitarios amplios sobre los niveles de fondo de
    los campos electromagnéticos en los Estados Unidos, se encontró una
    exposición mediana del orden de 50 µW/m2. Se observó que los
    principales contribuyentes a los campos electromagnéticos del ambiente
    eran las radiodifusiones de frecuencias muy altas. Menos del 1 % de la
    población estaba expuesta a densidades ambiente superiores a 10
    mW/m2. La exposición en las proximidades inmediatas (a una distancia
    de aproximadamente media longitud de onda de los campos incidentes) de
    estaciones transmisoras puede ser superior, y verse aumentada por
    objetos próximos con carácter conductor. Esas condiciones deben
    evaluarse para cada situación concreta.

    1.2.2  Hogar

         Entre las fuentes de RF en el hogar figuran los hornos de
    microondas, las cocinas que calientan por inducción, las alarmas
    antirrobo, las pantallas de computadora y los receptores de
    televisión. Los escapes a partir de hornos de microondas pueden
    elevarse hasta 1,5 W/m2 a 0,3 m y 0,15 W/m2 a una distancia de 1
    metro. La mejor manera de limitar la exposición a las radiaciones
    procedentes de electrodomésticos es cuidar su diseño y vigilar los
    escapes en el punto de fabricación.

    1.2.3  Lugar de trabajo

         Los calentadores dieléctricos para el tratamiento de madera y el
    sellado de plásticos, los calentadores por inducción para calentar
    metales, y las pantallas de computadora tienen un uso sumamente
    extendido en distintas situaciones ocupacionales. Las pantallas de
    computadora crean campos eléctricos y magnéticos en las frecuencias
    comprendidas en la banda 15-35 kHz y las frecuencias moduladas en la
    banda ELF. El personal que trabaja en el interior o en las
    proximidades de torres o antenas emisoras pueden verse expuestos a
    campos de intensidad considerable, de hasta 1 kV/m y 5 A/m,
    respectivamente. En las cercanías de instalaciones de radar, los
    trabajadores pueden estar expuestos a máximos considerables de
    densidad de potencia si se encuentran en el rayo de RF a pocos metros
    de las antenas de radar (hasta decenas de MW/m2). Por lo general, la
    densidad de potencia media en las proximidades de los radares que
    controlan el tráfico aéreo, por ejemplo, se encuentra en el orden de
    0,03-0,8 W/m2.

         En el medio laboral, la mejor manera de proteger a los
    trabajadores es respetar las especificaciones de emisión en todos y

    cada uno de los elementos del equipo y, cuando sea necesario, el
    monitoreo y la vigilancia utilizando los aparatos apropiados.

         Se produce un caso especial de exposición en el entorno médico
    con el uso de tratamientos diatérmicos contra el dolor y la
    inflamación en tejidos orgánicos. Los operarios de estos aparatos
    están probablemente expuestos a niveles relativamente elevados de
    radiación dispersa, que pueden reducirse mediante vestimenta
    protectora adecuada o por el diseño de la máquina. Se han llegado a
    medir intensidades de campo de 300 V/m y 1 A/m a 10 cm de los
    aplicadores. Del mismo modo, los cirujanos que utilizan instrumentos
    electroquirúrgicos que funcionan a frecuencias próximas a 27 MHz
    pueden verse expuestos a niveles superiores a los límites
    recomendados. Estas intensidades de campo disminuyen muy rápidamente
    al aumentar la distancia desde los aplicadores.

         La mayoría de los sistemas de imaginaría por resonancia magnética
    utilizan campos magnéticos estáticos con densidades de flujo de hasta
    2 T, campos de gradiente de baja frecuencia de hasta 20 T/s, y campos
    de RF en la banda de frecuencias de 1 a 100 MHz. Aunque la deposición
    de potencia en el paciente puede ser considerable, la exposición del
    personal es mucho menor y viene determinada por las características
    del equipo.

    1.3  Efectos biológicos

         Los campos electromagnéticos en la banda de frecuencias de 300
    Hz-300 GHz interaccionan con los sistemas humanos y otros sistemas
    animales por vías directas e indirectas. Las interacciones indirectas
    son importantes en frecuencias inferiores a 100 MHz, pero se producen
    en situaciones particulares. Cuando un objeto metálico (como un
    automóvil, una valla) que se encuentra en un campo electromagnético
    adquiere carga eléctrica por inducción, puede descargarse al entrar un
    cuerpo en contacto con él. Esas descargas pueden originar densidades
    de corriente locales capaces de provocar un choque o quemaduras.

         Uno de los principales mecanismos de interacción es mediante las
    corrientes inducidas en los tejidos, de modo que los efectos dependen
    de la frecuencia, la forma de las ondas y la intensidad. Con
    frecuencias inferiores a unos 100 kHz, revisten interés las
    interacciones con el tejido nervioso, debido a su mayor sensibilidad
    a las corrientes inducidas. Por encima de 100 kHz, el tejido nervioso
    se hace menos sensible al estímulo directo por campos
    electromagnéticos y la termalización de la energía se convierte en el
    principal mecanismo de intericción.

         Se ha observado en varios estudios que también existen
    interacciones por campos débiles. Se han postulado diferentes
    mecanismos para esas interacciones, pero no se ha elucidado el
    mecanismo preciso. Esas interacciones de campos débiles se deben a la
    exposición a campos de RF, de amplitud modulada a frecuencias

    1.4  Estudios en el laboratorio

         Muchos de los efectos biológicos de la exposición aguda a campos
    electromagnéticos son coherentes con las respuestas al calentamiento
    inducido, y dan lugar a elevaciones de la temperatura de los tejidos
    o el cuerpo de alrededor de 1 °C o más, o a respuestas encaminadas a
    reducir la carga térmica total. La mayoría de las respuestas se han
    notificado a índices de absorción específica (IAE) superiores a unos
    1-2 W/kg en distintas especies animales expuestas bajo diversas
    condiciones ambientales. Los datos obtenidos en animales
    (especialmente primates) indican los tipos de respuestas probables en
    humanos sometidos a una carga térmica suficiente. No obstante, la
    extrapolación cuantitativa directa al ser humano es difícil, dadas las
    diferencias entre unas especies y otras en las respuestas en general
    y en la capacidad termorreguladora en particular.

         Las respuestas animales más sensibles a la carga térmica son las
    adaptaciones termorreguladoras, como la reducción de la producción
    térmica en el metabolismo y la vasodilatación, con umbrales entre 0,5
    y 5 W/kg, según las condiciones ambientales. No obstante, esas
    reacciones forman parte del repertorio natural de respuestas
    termorreguladoras que sirven para mantener la temperatura normal.

         Entre los efectos transitorios observados en animales expuestos,
    que son acordes con las respuestas a aumentos de la temperatura
    corporal de 1 °C o más (y/o IAE superiores a unos 2 W/kg en primates
    y ratas), figuran el menor rendimiento en la ejecución de tareas
    aprendidas y el aumento de los niveles plasmáticos de
    corticosteroides. Entre otros efectos relacionados con el calor
    figuran respuestas hematopoyéticas e inmunitarias temporales, debidas
    posiblemente al aumento de los niveles de corticosteroides. Los
    efectos más uniformemente observados son la redución de los niveles de
    linfocitos circulantes, el aumento de los niveles de neutrófilos, y la
    alteración de la función natural de las células asesinas y los
    macrófagos. También se ha comunicado un aumento de la respuesta
    primaria con anticuerpos de los linfocitos B. Se han observado
    alteraciones cardiovasculares coherentes con el aumento de la carga
    térmica, como la aceleración del ritmo cardiaco y la mayor producción
    cardiaca, junto con una reducción del efecto de ciertos fármacos, como
    los barbitúricos, cuya acción puede verse modificada por los cambios

         La mayoría de los datos en animales indican que la implantación
    y el desarrollo del embrión y el feto probablemente no se vean
    afectados por exposiciones que aumenten la temperatura del cuerpo
    materno en menos de 1 °C. Por encima de estas temperaturas pueden
    presentarse efectos adversos, como retraso del crecimiento y cambios
    conductuales postnatales, con efectos más graves cuanto mayor es la
    temperatura de la madre.

         La mayoría de los datos en animales sugieren que las exposiciones
    bajas a RF que no aumentan la temperatura corporal por encima del

    margen fisiológico no son mutagénicas: esas exposiciones no darán
    lugar a mutaciones somáticas ni a efectos hereditarios. Se dispone de
    mucha menos información que describa los efectos de exposiciones de
    bajo nivel a largo plazo. No obstante, hasta el momento, no parece que
    la exposición a niveles inferiores a los térmicamente significativos
    produzca efectos a largo plazo. Los datos en animales indican que la
    fecundidad de los machos no se ve afectada por la exposición
    prolongada a niveles insuficientes para elevar la temperatura del
    cuerpo y de los testículos.

         No se indujo catarata en conejos expuestos a 100 W/m2 durante
    6 meses, ni en primates expuestos a 1,5 kW/m2 durante más de 3

         En un estudio realizado en 100 ratas expuestas durante casi toda
    su vida a unos 0,4 W/kg no se observó aumento de la incidencia de
    lesiones no neoplásicas ni de neoplasias totales en comparación con
    los animales testigo; la longevidad fue similar en ambos grupos. Se
    observaron diferencias en la incidencia general de tumores malignos
    primarios pero no pudieron atribuirse necesariamente a la irradiación.

         La posibilidad de que la exposición a campos de RF pueda influir
    en el proceso de la carcinogénesis es motivo de particular inquietud.
    Hasta el momento no hay pruebas concluyentes de que la irradiación
    ejerza efecto alguno, pero es a todas luces necesario llevar a cabo
    más estudios. Muchos datos experimentales indican que los campos de RF
    no son mutagénicos, y por ello es poco probable que actúen como
    desencadenantes de carcinogénesis; en los pocos estudios realizados,
    se han buscado sobre todo pruebas de un aumento del efecto de un
    carcinógeno conocido. La exposición prolongada de ratones a 2-8 W/kg
    dio lugar a un aumento de la progresión de tumores espontáneos de la
    mama y de tumores cutáneos en animales tratados con un carcinógeno
    químico por vía cutánea.

         Los estudios  in vitro han revelado índices mayores de
    transformación celular tras la exposición a RF de 4,4 W/kg (por sí
    sola o combinada con rayos X) seguida por un tratamiento con un
    promotor químico. Los últimos datos no siempre han sido uniformes de
    unos estudios a otros. Está claro, no obstante, que es necesario
    reproducir y profundizar los estudios sobre la carcinogénesis.

         Se dispone de un gran volumen de información que describe las
    respuestas biológicas a RF de amplitud modulada o campos de microondas
    con IAE demasiado bajos para desencadenar respuestas al calentamiento.
    En algunos estudios, se han notificado efectos tras la exposición a
    IAE inferiores a 0,01 W/kg, que han aparecido dentro de «ventanas» de
    frecuencia de modulación (generalmente entre 1 y 100 Hz) y a veces
    dentro de «ventanas» de densidad de potencia; se han comunicado
    resultados similares con frecuencias dentro del espectro de la voz
    humana (VF) (300 Hz-3 kHz). Se han notificado cambios en: los
    electroencefalogramas de gatos y conejos; la movilidad del ion calcio
    en el tejido cerebral  in vitro e  in vivo; la citotoxicidad de los

    linfocitos  in vitro; y la actividad de una enzima que participa en
    el crecimiento y la división celular. Algunas de estas respuestas han
    resultado difíciles de confirmar, y sus consecuencias fisiológicas no
    están claras. No obstante, toda investigación toxicológica que se
    emprenda debe basarse en ensayos llevados a cabo con niveles de
    exposición apropiados. Importa que esos estudios se confirmen y que se
    determinen, si existen, las repercusiones para la salud de las
    personas expuestas. Sería particularmente importante realizar estudios
    que vinculen las interacciones de frecuencias extremadamente bajas,
    modulación de amplitud, RF o microondas en la superficie celular con
    los cambios en la síntesis o la transcripción del ADN. Cabe destacar
    que esta interacción entraña una «desmodulación» de la señal de RF en
    la membrana celular.

    1.5  Estudios en el ser humano

         Existen relativamente pocos estudios que se ocupen directamente
    de los efectos de la exposición aguda o prolongada del ser humano a
    los campos de RF. En estudios realizados en el laboratorio, se ha
    notificado percepción cutánea de campos en la banda 2-10 GHz. Se han
    fijado umbrales para sensibilidad al calor con densidades de potencia
    de 270 W/m2-2000 W/M2@ según la superficie irradiada (13-100
    cm2) y la duración de la exposición (1-180 s). Cuando se expone a
    voluntarios humanos a IAE de 4 W/kg durante 15-20 minutos, la
    temperatura corporal media asciende 0,2-0,5 °C, que resulta totalmente
    admisible en personas sanas. Se desconoce el efecto que esta carga
    térmica añadida tendría en individuos que padecen trastornos en la
    termorregulación en ambientes que reducen al mínimo los mecanismos de
    enfriamiento basados en la transpiración.

         Los pocos estudios epidemiológicos que se han llevado a cabo en
    poblaciones expuestas a campos de RF no han permitido establecer
    asociaciones significativas entre esas exposiciones y resultados como
    disminución de la longevidad o excesos en causas particulares de
    defunción, salvo una mayor incidencia de muerte por cáncer, en la que
    la exposición a sustancias químicas puede haber sido un factor de
    confusión. En algunos estudios, no se observó aumento de la incidencia
    de partos prematuros ni malformaciones congénitas, si bien otros
    estudios indicaron que existía una asociación entre el nivel de
    exposición y el resultado adverso del embarazo. Esos estudios suelen
    adolecer de una mediocre evaluación de la exposición y una deficiente
    identificación y determinación de otros factores de riesgo.

    1.6  Evaluación de riesgos para la salud

         En una evaluación general de los riesgos para la salud asociados
    a las exposiciones a RF se han definido las siguientes categorías de
    riesgo para la salud:

    1.6.1  Efectos térmicos

         La deposición de energía RF en el organismo humano tiende a
    aumentar la temperatura corporal. Durante el ejercicio, la producción
    de calor metabólico puede alcanzar niveles de 3-5 W/kg. En entornos
    térmicos normales, un IAE de 1-4 W/kg durante 30 minutos produce
    aumentos medios de la temperatura corporal inferiores a 1 °C en
    adultos sanos. Así, una norma ocupacional de RF de 0,4 W/kg IAE deja
    un margen de protección contra complicaciones debidas a condiciones
    ambientales térmicamente desfavorables. Para la población general, que
    comprende las subpoblaciones sensibles como los lactantes y los
    ancianos, un IAE de 0,08 W/kg daría un margen adicional de seguridad
    contra los efectos térmicos adversos de los campos RF.

    1.6.2  Campos pulsátiles

         Se ha demostrado, en diversas condiciones, que los umbrales para
    la aparición de efectos biológicos en frecuencias superiores a varios
    cientos de MHz disminuyen cuando la energía se libera en pulsos cortos
    (1-10 µs). Por ejemplo, se producen efectos auditivos cuando en pulsos
    de menos de 30 µs de duración se liberan más de 400 mJ/m2 por pulso.
    Con arreglo a las pruebas disponibles, no puede definirse un límite
    inocuo para esos pulsos.

    1.6.3  Campos RF de amplitud modulada

         Los efectos descritos para este tipo de campo en los niveles
    celular, tisular y orgánico no pueden relacionarse con efectos
    adversos para la salud. No pueden formularse relaciones dosis-efecto
    en las que se observen niveles umbral; así, con la información
    disponible no pueden formularse recomendaciones específicas.

    1.6.4  Efectos de los campos RF en la inducción y la promoción de

         A partir de los informes sobre los efectos de la exposición a RF
    en ciertas líneas celulares, en la transformación celular, en la
    actividad enzimática y en la incidencia y la progresión de tumores en
    animales, no es posible concluir que la exposición a RF tenga efecto
    alguno en la incidencia del cáncer en el ser humano ni que sean
    necesarias recomendaciones específicas para limitar esos campos a fin
    de reducir los riesgos de cáncer.

    1.6.5  Densidades de corrientes inducidas por RF

         En la banda de frecuencias de 300 Hz-100 kHz, la inducción de
    campos y densidades de corriente en tejidos excitables es el mecanismo
    más importante para evaluar los riesgos. Los umbrales de estimulación
    de tejido nervioso y muscular dependen en gran medida de la
    frecuencia, y van desde 0,1-1 mA/m2 a 300 Hz hasta unos 10-100
    A/m2 a 100 kHz. No obstante, en lo que se refiere a otros efectos,

    observados por debajo de esos umbrales, no se dispone de bastante
    información para formular recomendaciones específicas.

    1.6.6  Choques y quemaduras por contacto en campos RF

         En un campo de RF, los objetos conductores pueden adquirir carga
    eléctrica. Cuando una persona toca un objeto cargado o se acerca mucho
    a él, puede producirse una corriente de importancia entre el objeto y
    esa persona. Según la frecuencia, la intensidad del campo eléctrico,
    la forma y el tamaño del objeto, y la superficie de contacto, la
    corriente resultante puede provocar un choque por estimulación de los
    nervios periféricos. Si la corriente tiene bastante intensidad, pueden
    producirse quemaduras. Como medida de protección deben eliminarse o
    aislarse los objetos conductores que se encuentren en campos intensos
    de RF, o limitarse el acceso físico.

    1.7  Normas de exposición

    1.7.1  Límites básicos de exposición

         Para proteger a los trabajadores y a la población general de los
    posibles efectos en la salud que tiene la exposición a los campos
    electromagnéticos, se han determinado límites básicos de exposición
    basándose en el conocimiento de sus efectos biológicos. Se utilizaron
    distintas bases científicas para fijar los límites correspondientes a
    frecuencias superiores e inferiores a aproximadamente 1 MHz. Por
    encima de 1 MHz, se estudiaron los efectos biológicos en animales para
    determinar el menor valor del IAE medio para el organismo entero que
    provocaba efectos nocivos en los animales. Se encontró que ese valor
    estaba comprendido entre 3 y 4 W/kg.

         La gran mayoría de los resultados correspondían a las
    exposiciones en la región inferior de GHz. Así, para determinar los
    efectos a frecuencias más bajas es necesario suponer una cierta
    dependencia de la frecuencia en la respuesta biológica. Como se cree
    que los bioefectos observados en la banda 1-4 W/kg son de carácter
    térmico, se supuso que el umbral para el IAE era independiente de la
    frecuencia. Se consideró que la exposición del ser humano a 4 W/kg
    durante 30 minutos daría lugar a un ascenso de la temperatura corporal
    inferior a 1 °C. Este aumento de la temperatura corporal se considera

         Para dar cabida a posibles efectos desfavorables, térmicos,
    ambientales y a largo plazo, así como a otras variables, se ha
    introducido un factor de seguridad de 10, con lo que se obtiene un
    límite básico de 0,4 W/kg. Debería introducirse un factor de seguridad
    adicional para la población general, que comprende personas con
    distintas sensibilidades a la exposición a RF. Normalmente, para el
    público en general se recomienda un límite básico de 0,08 W/kg,
    obtenido al añadir un factor de seguridad de 5. En los cuadros 34 y 35

    de la presente publicación se ofrecen los límites de exposición

         Las limitaciones para el IAE medio para todo el organismo no son
    lo bastante restrictivas, puesto que la distribución de la energía
    absorbida en el organismo humano puede ser muy heterogéneo y depender
    de las condiciones de exposición a RF. En situaciones de exposición
    parcial del cuerpo, atendiendo a la frecuencia, la energía absorbida
    puede concentrarse en una cantidad limitada de tejido, aunque el IAE
    medio para todo el organismo se restrinja a menos de 0,4 W/kg. Así
    pues, se recomiendan límites básicos adicionales de 2 W/100 g en
    cualquier otra parte del organismo, a fin de evitar que se produzcan
    elevaciones excesivas de la temperatura a nivel local. Tal vez haya
    que prestar especial atención a los ojos.

         En el caso de las frecuencias inferiores a alrededor de 1 MHz, se
    han fijado límites de exposición que permitan prevenir la estimulación
    de células nerviosas y musculares. Los límites básicos de exposición
    se refieren a densidades de corriente inducidas dentro de los tejidos
    orgánicos. Los límites de exposición deben tener un factor de
    seguridad suficiente para restringir la densidad de corriente a 10
    mA/m2 a 300 Hz, valor que se encuentra en el mismo orden de magnitud
    que las corrientes naturales del organismo. Por encima de 300 Hz, la
    densidad de corriente necesaria para excitar el tejido nervioso
    aumenta con la frecuencia, hasta que se alcanza una frecuencia en la
    que dominan los efectos térmicos. Para las frecuencias en torno a 2-3
    MHz, el límite básico para la densidad de corriente equivale al límite
    para el IAE máximo de 1 W/100 g. Como en las situaciones prácticas de
    exposición es difícil medir los valores del IAE y de la densidad de
    corriente inducida, los límites de exposición en función de cantidades
    fácilmente medibles deben derivarse de los límites básicos. Estos
    «límites derivados» indican los límites aceptables, respecto de los
    parámetros medidos y/o calculados en el campo, que permiten respetar
    los límites básicos.

    1.7.2  Límites de exposición ocupacional

         Las poblaciones expuestas en el lugar de trabajo están formadas
    por adultos expuestos en condiciones controladas y que están al tanto
    de los riesgos que ello supone. Dada la amplitud de la gama de
    frecuencias de que se ocupa la presente publicación, no es posible dar
    una cifra única como límite de exposición ocupacional. En el cuadro 34
    figuran los límites ocupacionales derivados recomendados en la banda
    de frecuencias comprendida entre 100 kHz y 300 GHz. Se recomienda
    abordar con prudencia los campos pulsátiles en los que las
    intensidades de los campos eléctricos y magnéticos se limitan a 32
    veces los valores ofrecidos en el cuadro 34, promediados sobre la
    duración del pulso, y la densidad de potencia se limita a un valor de
    1000 veces el valor correspondiente del cuadro 34, promediado sobre la
    duración del pulso.

    1.7.3  Límites de exposición para la población general

         La población general comprende personas de distintos grupos de
    edad, distintos estados de salud, y mujeres embarazadas. La
    posibilidad de que el feto en desarrollo pueda ser particularmente
    sensible a la exposición a RF merece especial consideración.

         Los límites de exposición para la población general deben ser más
    bajos que los correspondientes a la exposición ocupacional. Por
    ejemplo, los límites derivados recomendados en la banda de frecuencias
    de 100 kHz-300 GHz figuran en el cuadro 35, y son en general
    inferiores por un factor de 5 a los límites ocupacionales.

    1.7.4  Aplicación de normas

         La aplicación de las normas protectoras ocupacionales y de salud
    pública respecto de los campos de RF exige designar responsables de la
    medición de la intensidad de los campos y de la interpretación de los
    resultados, así como establecer códigos y guías de seguridad
    detallados sobre protección contra los campos, que indiquen, según
    convenga, los modos y medios de reducir la exposición.

    1.8  Medidas de protección

         Entre las medidas de protección figuran la vigilancia en el lugar
    de trabajo (encuestas sobre exposición), los controles técnicos, los
    controles administrativos, la protección personal y la vigilancia
    médica. Cuando las encuestas sobre los campos de RF indiquen niveles
    de exposición en el lugar de trabajo superiores a los límites
    recomendados para la población general,, debe ponerse en marcha la
    vigilancia ocupacional. Cuando indiquen niveles de exposición
    superiores a los límites recomendados, deben adaptarse medidas para
    proteger a los trabajadores. En primer lugar, deben aplicarse
    controles técnicos, cuando sea posible, a fin de reducir las emisiones
    hasta niveles aceptables. Entre esos controles figuran un buen control
    del diseño en lo que respecta a la seguridad y, cuando sea necesario,
    el uso de dispositivos cortacorrientes u otros similares.

         Los controles administrativos, como la limitación del acceso y el
    uso de alarmas auditivas y visuales, deben usarse en conjunción con
    los controles técnicos. A pesar de su utilidad en ciertas
    circunstancias, el uso de protección personal (vestimenta protectora)
    debe considerarse un último recurso para velar por la seguridad del
    trabajador. Siempre que sea posible, debe darse prioridad a los
    controles técnicos y administrativos. Cuando exista la posibilidad de
    que los trabajadores estén expuestos a niveles superiores a los
    límites aplicables a la población general, debe examinarse la
    posibilidad de poner a su disposición vigilancia médica apropiada.

         La prevención de los riesgos para la salud relacionados con los
    campos de RF exige asimismo establer y aplicar normas para velar por:
    a) la prevención de la interferencia con el equipo y los dispositivos

    electrónicos de seguridad y médicos (inclusive los marcapasos
    cardiacos); b) la prevención de la detonación de dispositivos
    electroexplosivos (detonadores); y c) la prevención de incendios y
    explosiones a partir de chispas provocadas por los campos inducidos.

    2.  Recomendaciones para estudios ulteriores

    2.1  Introducción

         Preocupan los posibles efectos de los campos de RF en lo que se
    refiere a la promoción y la progresión del cáncer, a las disfunciones
    reproductivas, como los abortos espontáneos y las malformaciones
    congénitas, y a los efectos en el funcionamiento del sistema nervioso
    central. No se conocen lo bastante estas cuestiones como para
    determinar si existen esos efectos y, por tanto, no hay ninguna base
    racional sobre la que formular recomendaciones para proteger a la
    población general de los posibles efectos adversos.

         Todas las investigaciones que se emprendan sobre los mecanismos
    de interacción débil por una parte y los estudios de los efectos sobre
    la carcinogénesis y la reproducción en animales y humanos por otra
    parte, deben estar sumamente coordinadas. Esa coordinación puede
    conseguirse concentrando la asignación de fondos en las propuestas de
    investigación que tengan carácter multidisciplinario y
    multiinstitucional. Los estudios sobre los efectos de los campos de RF
    podrían coordinarse con programas semejantes sobre los efectos de los
    campos de ELF (50/60 Hz). Debe darse gran prioridad a las
    investigaciones que se ocupen de las relaciones causases y los
    umbrales y coeficientes dosis/efecto.

         A continuación figura una lista de aspectos prioritarios que, a
    juicio del grupo de trabajo, necesitan estudiarse más a fondo.

    2.2  Campos pulsátiles

         Aún no se comprenden los efectos de los campos pulsátiles en los
    que se dan máximos de densidad de potencia muy elevados separados por
    periodos de potencia cero. Sólo se dispone de algunos informes
    aislados sobre los efectos de estos campos y no es posible identificar
    ni la frecuencia ni el dominio de importancia de los máximos de
    potencia. Se necesitan con urgencia datos para evaluar los riesgos
    para la salud humana referidos a los máximos de potencia de los
    pulsos, la frecuencia de repetición, la longitud de los pulsos y la
    frecuencia de la RF en el pulso, en vista de la aplicación cada vez
    más difundida de sistemas que utilizan pulsos de alta potencia
    (principalmente radares), y que entrañan la exposición tanto
    ocupacional como de la población general.

    2.3  Estudios sobre el cáncer, la reproducción y el sistema nervioso

         Cada vez preocupa más seriamente la posibilidad de que la
    exposición a RF pueda intervenir como causante o favorecedor del

    cáncer, especialmente de los órganos hematopoyéticos o en el sistema
    nervioso central. Tampoco se conocen a ciencia cierta los posibles
    efectos en la reproducción, como las mayores tasas de aborto
    espontáneo y de malformaciones congénitas.

         Los efectos de la exposición a RF en la función del sistema
    nervioso central, con los cambios correspondientes en las funciones
    dcognitivas, también están envueltos en la incertidumbre. En vista de
    la posible importancia de esas interacciones y de los trastornos
    causados por esa incertidumbre en la sociedad, debe darse gran
    prioridad a las investigaciones en este campo. Importa coordinar los
    esfuerzos de investigación para aclarar los conocimientos en lugar de
    aumentar el nivel de incertidumbre. Las investigaciones sobre los
    posibles mecanismos, como las interacciones de campos débiles, deben
    coordinarse estrechamente con estudios de toxicología en animales
    debidamente diseñados y con epidemiología humana.

    2.4  Interacciones de campos débiles

         Muy pocas personas están expuestas a niveles térmicamente
    significativos de RF; la gran mayoría de las exposiciones se dan a
    niveles en los que las interacciones de campos débiles serían la única
    fuente posible de respuestas adversas en la salud. Hay un volumen
    considerable de datos experimentales que implican respuestas a los
    campos de RF de amplitud modulada, que muestran ventanas de frecuencia
    y de amplitud; algunas respuestas dependen de la coexposición a
    agentes físicos y químicos. Es de primera importancia establecer los
    efectos para la salud humana y sus relaciones dosis/respuesta. Se
    necesitan estudios que definan los mecanismos biofísicos de
    interacción y que amplíen los estudios en animales y en el ser humano,
    a fin de determinar los riesgos para la salud.

    2.5  Epidemiología

         Los estudios epidemiológicos sobre la asociación entre los campos
    de RF y el cáncer y los efectos adversos en la reproducción se ven
    dificultados por varios factores:

    -    La mayoría de los miembros de cualquier población se ven
         expuestos a niveles de RF que se encuentran a varios órdenes de
         magnitud por debajo de los niveles que revisten importancia desde
         el punto de vista térmico.

    -    Es muy difícil establecer la exposición a RF en individuos
         durante un periodo de tiempo significativo.

    -    Es muy difícil controlar los principales factores que inducen a

         Algunas de las fuentes de dificultades, aunque no todas, pueden
    salvarse mediante un estudio de control de casos bien diseñado y
    aplicado. Se están realizando o planificando estudios de ese tipo para

    estudiar el cáncer durante la infancia y los efectos de los campos de
    ELF. Importa que en esos estudios se evalúen las exposiciones a la
    radiación RF.

    See Also:
       Toxicological Abbreviations