Lead (EHC 3, 1977)

INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

ENVIRONMENTAL HEALTH CRITERIA 3

Lead

This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of either the World Health Organization or the United Nations
Environment Programme

Published under the joint sponsorship of
the United Nations Environment Programme
and the World Health Organization

World Health Organization
Geneva 1977

ISBN 92 4 154063 X

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CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR LEAD

1. SUMMARY AND RECOMMENDATIONS FOR FURTHER RESEARCH

1.1. Summary
1.1.1. Analytical problems
1.1.2. Sources and pathways of exposure
1.1.3. Metabolism
1.1.4. Experimental studies on the effects of lead
1.1.5. Clinical and epidemiological studies on the effects
of lead. Evaluation of health risk to man from
exposure to lead

1.2. Recommendations for further research
1.2.1. Analytical methods
1.2.2. Sources of lead intake
1.2.3. Epidemiological studies
1.2.4. Interactions of lead with other environmental
factors
1.2.5. Significance of biological effects

2. PROPERTIES AND ANALYTICAL METHODS

2.1. Physical and chemical properties of lead and its compounds

2.2. Analytical procedures
2.2.1. Sampting
2.2.2. Analytical methods for lead
2.2.3. Methods for the measurement of some biochemical
effects of lead

3. SOURCES OF LEAD IN THE ENVIRONMENT

3.1. Natural occurrence
3.1.1. Rocks
3.1.2. Soils
3.1.3. Water
3.1.4. Air
3.1.5. Plants
3.1.6. Environmental contamination from natural sources

3.2. Production of lead
3.2.1. Lead mining
3.2.2. Smelting and refining
3.2.3. Environmental pollution from production

3.3. Consumption and uses of lead and its compounds
3.3.1. Storage battery industry
3.3.2. Alkyllead fuel additives
3.3.3. Cable industry
3.3.4. Chemical industry
3.3.5. Miscellaneous
3.3.6. Environmental pollution from consumption and uses of
lead

3.4. Waste disposal

3.5. Miscellaneous sources of environmental pollution

4. ENVIRONMENTAL TRANSPORT AND DISTRIBUTION

5. ENVIRONMENTAL LEVELS AND EXPOSURES

5.1. Exposure of the general population
5.1.1. Air
5.1.2. Water
5.1.3. Food
5.1.4. Miscellaneous

5.2. Exposure of infants and young children
5.2.1. Soil, dust, and taint
5.2.2. Miscellaneous

5.3. Occupational exposures
5.3.1. Lead mining, smelting and refining
5.3.2. Electric storage battery manufacturing
5.3.3. Shipbreaking and welding
5.3.4. Printing
5.3.5. Alkyllead manufacture
5.3.6. Other industrial exposures

5.4. Blood lead concentrations of various populations
5.4.1. Adult populations
5.4.2. Children

6. METABOLISM OF LEAD

6.1. Absorption
6.1.1. Absorption by inharation
6.1.1.1 Human studies
6.1.1.2 The relationship of air lead to blood lead
in the general population
6.1.1.3 The relationship of air lead to blood lead
in occupational exposure
6.1.1.4 Animal studies

6.1.2. Absorption of lead from the gastrointestinal tract
6.1.2.1 Human studies
6.1.2.2 The relationship of oral intake of lead to
blood lead levels in man
6.1.2.3 Animal studies

6.2. Distribution and retention
6.2.1. Human studies
6.2.2. Studies in animals

6.3. Elimination of lead
6.3.1. Human studies
6.3.2. Animal studies

6.4. "The metabolism of alkyllead compounds

7. EXPERIMENTAL STUDIES ON THE EFFECTS OF LEAD

7.1. Animal studies
7.1.1. Haemopoietic system
7.1.2. Nervous system
7.1.2.1 Inorganic lead
7.1.2.2 Alkyllead compounds
7.1.3. Renal system
7.1.4. Gastrointestinal tract
7.1.5. Cardiovascular system
7.1.6. Respiratory system
7.1.7. Reproductive system
7.1.8. Endocrine organs
7.1.9. Carcinogenicity
7.1.9.1 Inorganic lead compounds
7.l.9.2 Alkyllead compounds
7.1.10. Mutagenicity
7.1.11. Teratogenicity

7.2. Acquisition of tolerance to lead

7.3. Factors influencing lead toxicity
7.3.1. Age and sex
7.3.2. Seasonal variations
7.3.3. Nutrition
7.3.4. Intercurrent disease, alcohol, and other metals

7.4. Human studies

8. EFFECTS OF LEAD ON MAN--EPIDEMIOLOGICAL AND CLINICAL STUDIES

8.1. Retrospective studies of lead-exposed populations
8.1.1. Epidemiology of lead poisoning in industry

8.1.2. Epidemiology of lead poisoning in the general adult
population
8.1.3. Epidemiology of lead poisoning in infants and young
children

8.2. Clinical and epidemiological studies of the effects of lead
on specific organs and systems
8.2.1. Haemopoietic system
8.2.1.1 delta-aminolevulinic acid dehydratase (ALAD)
8.2.1.2 Free erythrocyte porphyrins (FEP)
8.2.1.3 delta-aminolevulinic acid excretion in urine
(ALA-U)
8.2.1.4 Coproporphyrin excretion in urine (CP-U)
8.2.1.5 Effects of lead on cell morphology
8.2.1.6 Effects of lead on erythrocyte survival
8.2.1.7 Effects of lead on haem synthesis
8.2.1.8 Relationship between lead exposure and
anaemia
8.2.2. Nervous system
8.2.2.1 Central nervous system
8.2.2.2 Peripheral nervous system
8.2.3. Renal system
8.2.4. Gastrointestinal tract
8.2.5. Liver
8.2.6. Cardiovascular system
8.2.7. Reproduction
8.2.8. Endocrine organs
8.2.9. Carcinogenicity
8.2.10. Effects on chromosomes
8.2.11. Teratogenicity

8.3. Factors influencing lead toxicity
8.3.1. Acquisition of tolerance to lead
8.3.2. Age
8.3.3. Seasonal variation
8.3.4. Nutrition
8.3.5. Intercurrent disease, alcohol, and other metals

9. EVALUATION OF HEALTH RISKS TO MAN FROM EXPOSURE TO LEAD AND ITS
COMPOUNDS

9.1. Relative contributions of air, food, water and other
exposures to total intake
9.1.1. Adult members of general population groups
9.1.2. Infants and children
9.1.3. Occupationally exposed population groups

9.2. Evaluation of haematological effects

9.3. Dose-effect relationships

9.4. Dose-response relationships

9.5. Diagnosis of lead poisoning and indices of exposure and/or
effects for epidemiological studies
9.5.1. Concentration of lead in blood (Pb-B)
9.5.2. Aminolevulinic acid dehydratase (ALAD)
9.5.3. Aminolevulinic acid (ALA) and coproporphyrin (CP)
excretion in the urine
9.5.4. Lead excretion in the urine
9.5.5. Haematological changes (stippled cells, anaemia)
9.5.6. Lead in tissues (teeth and hair)
9.5.7. Some practical aspects
9.5.7.1 General population studies
9.5.7.2 Occupationally-exposed persons
9.5.7.3 Reliability of the sampling and analytical
methods
9.6. The problem of alkyllead compounds

REFERENCES

NOTE TO READERS OF THE CRITERIA DOCUMENTS

While every effort has been made to present information in the
criteria documents as accurately as possible without unduly delaying
their publication, mistakes might have occurred and are likely to
occur in the future. In the interest of all users of the environmental
health criteria documents, readers are kindly requested to communicate
any errors found to the Division of Environmental Health, World Health
Organization, 1211 Geneva 27, Switzerland, in order that they may be
included in corrigenda which will appear in subsequent volumes.

In addition, experts in any particular field dealt with in the
criteria documents are kindly requested to make available to the WHO
Secretariat any important published information that may have
inadvertently been omitted and which may change the evaluation of
health risks from exposure to the environmental agent under
examination, so that that information may be considered in the event
of updating and re-evaluating the conclusions contained in the
criteria documents.

WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR LEAD

Geneva, 29 April-5 May 1975

Participants

Professor M Berlin, Department of Environmental Health, University of
Lund, Sweden

Professor A. David, Centre of Industrial Hygiene and Occupational
Diseases, Institute of Hygiene and Epidemiology, Prague,
Czechoslovakia (Vice-Chairman)

Dr. F. A. Fairweather, Division of Chemical Contamination of Food and
Environmental Pollution, Department of Health and Social Security,
London, England

Professor R. A. Goyer, Department of Pathology, University of Western
Ontario, London, Ontario, Canada (Chairman)

Dr. L. Graovac-Leposavic, Institute of Occupational and Radiological
Health, Belgrade, Yugoslavia

Dr. R. J. M. Horton, Environmental Protection Agency, Research
Triangle Park, NC, USA

Dr. C. H. Nordman, Institute of Occupational Health, Helsinki, Finland
(Rapporteur)

Dr. H. Sakabe, Department of Industrial Physiology, National Institute
of Industrial Hygiene, Kawasaki, Japan

Professor H. W. Schlipköter, Institute of Air Hygiene and Silicosis,
Düsseldorf, Federal Republic of Germany

Professor N. Ju. Tarasenko, First Moscow Medical Institute, Moscow,
USSR

Professor R. L. Zielhuis, Coronel Laboratory, Faculty of Medicine,
University of Amsterdam, Amsterdam, Netherlands

Representatives of other agencies

Dr. A. Berlin, Health Protection Directorate, Commission of the
European Communities, Centre Louvigny, Luxembourg

Professor R. Bourdon, International Union of Pure and Applied
Chemistry, Commission on Toxicology, Laboratoire de Biochimie-
Toxicologie, Centre Anti-Poison de l'Hôpital Fernand Widal, Paris,
France

Dr. D. Djordjevic, Occupational Safety and Health Branch,
International Labour Office, Geneva, Switzerland

Dr. R. Morf, International Union of Pure and Applied Chemistry,
Liaison Officer with WHO, 8311 Kyburg Zh, Switzerland

Secretariat

Professor Paul B. Hammond, Department of Environmental Health,
University of Cincinnati, The Kettering Laboratory, Cincinnati,
Ohio, USA (Temporary Adviser)

Dr. Y. Hasegawa, Medical Officer, Control of Environmental Pollution
and Hazards, Division of Environmental Health, World Health
Organization, Geneva, Switzerland

Dr. J. E. Korneev, Scientist, Control of Environmental Pollution and
Hazards, Division of Environmental Health, World Health
Organization, Geneva, Switzerland

Dr. V. Krichagin, Scientist, Promotion of Environmental Health, WHO
Regional Office for Europe, Copenhagen, Denmark

Dr. B. Marshall, Medical Officer, Occupational Health, Division of
Environmental Health, World Health Organization, Geneva.

Professor L. A. Timofievskaja, Institute of Occupational Health,
Moscow, USSR (Temporary Adviser)

Dr. V. B. Vouk, Chief, Control of Environmental Pollution and Hazards,
Division of Environmental Health, World Health Organization,
Geneva (Secretary)

List of abbreviations

ALA delta-aminolevulinic acid

ALA-U delta-aminolevulinic acid in urine

ALAD porphobilinogen synthase (EC 4.2.1.24), delta-aminolevulinate
dehydratase, delta-aminolevulinic acid dehydratase

ALAS delta-aminolevulinate synthase (EC 2.3.1.37), aminolevulinic
acid synthetase

CP coproporphyrins

CP-U coproporphyrin in urine

CPG coproporphyrinogen III

EDTA ethylenediaminetetraacetic acid

FEP free erythrocyte porphyrins

Hb haemoglobin

LD₅₀ median lethal dose

PP protoporphyrin IX

PBG porphobilinogen

Pb-B lead in blood

Pb-U lead in urine

RBC red blood cells

SGOT aspartate aminotransferase (EC 2.6.1.1), serum glutamic
oxaloacetic transaminase

ENVIRONMENTAL HEALTH CRITERIA FOR LEAD

A WHO Task Group on Environmental Health Criteria for Lead met in
Geneva from 29 April to 5 May 1975. Dr B. H. Dieterich, Director,
Division of Environmental Health, opened the meeting on behalf of the
Director-General. The Task Group reviewed and revised the second draft
criteria document and made an evaluation of the health risks from
exposure to lead and its compounds.

The first and second drafts were prepared by Professor Paul B.
Hammond of the Department of Environmental Health, The Kettering
Laboratory, University of Cincinnati, Ohio, USA. The comments on which
the second draft was based were received from the national focal
points for the WHO Environmental Health Criteria Programme in
Bulgaria, Czechoslovakia, Federal Republic of Germany, Greece, Japan,
The Netherlands, New Zealand, Poland, Sweden, USA, and the USSR, and
from the United Nations Educational, Scientific and Cultural
Organization (UNESCO), Paris, from the United Nations Industrial
Development Organization (UNIDO), Vienna, from the Centro Panamericano
de Ingenieria Sanitaria y Ciencias del Ambiente (CEPIS) at Lima, Peru,
and from the Health Protection Directorate of the Commission of the
European Communities (CEC), Luxembourg. Comments were also received,
at the request of the Secretariat from: Professor R. Goyer and
Professor H. Warren, Canada; Professor J. Teisinger, Czechoslovakia;
Dr S. Hernberg, Finland; Dr K. Cramer and Dr B. Haeger-Aronsen,
Sweden; Dr D. Barltrop, Professor B. Clayton, Professor R. Lane, and
Professor P. J. Lawther, United Kingdom; Dr J. J. Chisholm, Professor
H. L. Margulis, and Dr G. Ter Haar, United States of America; and Dr
D. Djuric and Professor K. Kostial, Yugoslavia.

Valuable comments were received on the third draft, resulting from
the task group, from: Mr Joseph E. Faggan, Director of Petroleum
Chemicals Research, Ethyl Corporation, Ferndale, Michigan, USA, and
from Mr R. L. Stubbs, Director-General, Lead Development Association,
London and Chairman, Statistical Committee, International Lead and
Zinc Study Group.

The collaboration of these national institutions, international
organizations, WHO collaborating centres, and individual experts is
gratefully acknowledged. Without their assistance this document would
not have been completed. The Secretariat wishes to thank, in
particular, Professor Hammond for his continued help in all phases of
the preparation of the document, and Dr H. Nordman of the Institute of
Occupational Health, Helsinki, who assisted the Secretariat in the
final scientific editing of the document.

This document is based primarily on original publications listed
in the reference section. However, several recent publications broadly
reviewing health aspects of lead and its compounds have also been

used. These include publications by Kehoe (1961), NAS-NRC (1972), NRC-
Canada (1973), Goyer & Rhyne (1973), WHO Working Group (1973), Inter-
Department Working Group on Heavy Metals (1974), SCEP (1974),
Nordberg, ed. (1976). In addition, the document draws on comprehensive
and useful data from the proceedings of several symposia and meetings,
e.g. the "International Symposium on Environmental Aspects of Lead",
Amsterdam, 1972, arranged by the Commission of the European
Communities and the US Environmental Protection Agency; the
"International Symposium on Recent Advances in the Assessment of the
Health Effects of Environmental Pollution", Paris, 1974, jointly
organized by the Commission of the European Communities, US
Environmental Protection Agency, and the World Health Organization;
the University of Missouri's Annual Conferences on Trace Substances in
Environmental Health, Columbia, Missouri, 1967-1975; and the
"International Symposium on Environmental Lead Research", Dubrovnik,
1975, organized by the Institute for Medical Research and Occupational
Health, under the auspices of the Yugoslav Academy of Sciences and
Arts.

Details of the WHO Environmental Health Criteria Programme,
including some of the terms frequently used in the documents, may be
found in the introduction to the publication "Environmental Health
Criteria 1-Mercury", published by the World Health Organization,
Geneva, in 1976.

1. SUMMARY AND RECOMMENDATIONS FOR FURTHER RESEARCH

1.1 Summary

1.1.1 Analytical problems

The procurement of environmental and biological samples requires
careful consideration of the special problems relating to the
particular material to be analysed. In air sampling, it is most
important to ensure that the sampler is placed at the breathing zone
of the population group under study. For all sampling procedures and
particularly for blood, external contamination is a major problem.

The most successful analytical method in recent years has been
atomic absorption spectroscopy. It has proved to be versatile and
sufficiently sensitive for most purposes, but reliable results,
particularly for biological specimens such as blood, can be obtained
only after considerable experience has been acquired.

Determinations of haem intermediates and of porphobilinogen
synthase (EC 4.2.1.24) (ALAD)^a,b activity in blood are important
methods for estimating the biological consequences of overexposure to
lead. There is a great need for standardization of both these methods
and of ways of expressing the results.

1.1.2 Sources and pathways of exposure

The major sources of lead in the environment that are of
significance for the health of man, arise from the industrial and
other technological uses of lead. The major dispersive non-recoverable
use of lead is in the manufacture and application of alkyllead fuel
additives. Because of current legislative actions with respect to the
maximum permissible concentration of lead in gasoline, the consumption
of lead for the production of alkyllead additives decreased from 1973
to 1975 and a further decline for the latter half of the 1970s may
occur as more cars equipped with catalysts which require lead-free
gasoline will come into use.

^a "In the first instance, enzymes are named according to the 1972
recommendations of the Commission on Enzyme Nomenclature but
throughout the rest of the document the more familiar names or
abbreviations are used.

^b Formerly known as delta-aminolevulinate dehydratase or
delta-aminolevulinic acid dehydratase.

From a mass balance point of view, the transport and distribution
of lead from stationary or mobile sources is mainly via air.
Although large amounts are probably also discharged into soil and
water, lead tends to localize near the points of such discharge. Lead
that is discharged into the air over areas of high traffic density
falls out mainly within the immediate metropolitan zone. The fraction
that remains airborne (about 20%, based on very limited data) is
widely dispersed. Residence time for these small particles is of the
order of days and is influenced by rainfall. In spite of widespread
dispersion, with consequent dilution, there is evidence of lead
accumulation at points extremely remote from human activity, e.g. in
glacial strata in Greenland.

The biota acquires lead both by surface deposition and by
secondary transfer from soil to plants and from plants to animals.
However, the impact of man-made lead pollution on the lead content of
plants and animals is not perceptible except in localized areas of
intense air pollution, e.g. around smelters and in the immediate
vicinity of roads with heavy traffic.

The concentration of lead in air varies from 2-4 µg/m³ in large
cities with dense automobile traffic to less than 0.2 µg/m³ in most
suburban areas and still less in rural areas. The concentration of
lead in drinking water is generally less than 10 µg/litre, but in some
areas where the water is soft (low in calcium and magnesium) and
where, at the same time, lead pipes and lead-lined water storage tanks
are used, the concentration may reach 2000-3000 µg/litre. At this
concentration (and even at concentrations of several hundred µg/litre)
a perceptible rise in the body burden of lead occurs, which is
reflected in elevated values of lead in the blood (Pb-B).

The contribution of food to man's exposure to lead is highly
variable. Some recent studies in the USA have estimated the daily oral
intake in food and beverages to be about 100 µg whereas earlier
studies and some recent European studies indicated the intake to be in
the range of 200-500 µg/day. However, a recent Swedish study reported
volumes of the order of 20 µg/day. No specific category of food has
been identified as being especially high in lead content other than
wine and foods that are stored in lead-soldered cans or lead-glazed
pottery. Processed milk contains considerably more lead than fresh
cow's milk which has a similar concentration to human milk. The
reported lead concentrations range from less than 5 µg/litre to
12 µ/litre. If this information is correct, milk could be a
significant source of lead for infants.

Various miscellaneous sources of lead have been identified as
being highly hazardous. These include lead-glazed ceramics used for
beverage storage, illicitly-distilled whisky, and discarded automobile
battery casings when used for fuel.

In certain countries, gross overexposure of some infants and young
children has been recorded. The major sources are lead-based paint in
old houses and in the soil surrounding these homes, and the soil
surrounding lead smelters. Lead in street dust due to atmospheric
fallout, and miscellaneous lead-containing objects chewed or eaten by
children are other possible sources of exposure, but their relative
importance is not clear.

The highest exposure occurs in workers who come into contact with
lead during mining, smelting, and various manufacturing processes
where lead is used. The major pathway of exposure is inhalation. The
concentration of air lead in the working environment of smelters and
storage battery factories often exceeds 1000 µg/m³. For other
industries, data are either not available or indicate a lower level of
exposure.

Extensive surveys have been made on blood concentrations in both
adults and young children. Such data are useful indicators of overall
exposure to lead.

1.1.3 Metabolism

A number of studies have been made which indicate that 35% of the
lead inhaled by man is deposited in the lungs. The relative importance
of the mucociliary escalator mechanism and of direct absorption from
pulmonary deposition is poorly understood and the contribution of
airborne lead to total daily intake cannot be estimated from metabolic
data. But when sustained Pb-B is used as a measure of lead absorption,
it can be assumed from human data that continuous exposure to 1 µg of
lead per m³ of air would contribute lead levels of about
1.0-2.0 µg/100 ml of blood.

About 10% of lead taken in from food and beverages is absorbed.
However, using data from several sources, the dietary contribution to
Pb-B can only be roughly estimated as 6-18 µg of lead per 100 ml of
blood per 100 µg of dietary lead intake.

From both animal and human studies, the general features of lead
distribution and excretion are fairly clearly defined. The body burden
of lead can be subdivided into a large, slow-turnover compartment and
a smaller more rapidly-exchanging compartment. Anatomically, the
larger compartment is mainly located in bones. The amount of lead in
this compartment increases throughout life. The smaller compartment
consists of the soft tissues and includes the blood. Lead levels in
soft tissues and in blood continue to increase up to early adulthood
and then change little. Elimination of lead from the body is mainly by
way of the urine (about 76%) and the gastrointestinal tract (about
16%). The other 8% is excreted by miscellaneous routes (sweat,
exfoliation of the skin, loss of hair) about which little is known.

Alkyllead compounds (tetraethyllead and tetramethyllead) are
dealkylated both to trialkyl derivatives and to inorganic lead.
Details of alkyllead metabolism have been learned from animal studies
and have not been defined in man.

1.1.4 Experimental studies on the effects of lead

The extensive animal studies that have been conducted concerning
the biological effects of lead indicate that, with rare exceptions,
the toxic phenomena that have been observed in man have also been
successfully reproduced in animals. Although animal studies have
provided a more profound understanding of the effects of lead than
could be learned from studies of man himself, they have not been of
much use in the elucidation of dose-effect and dose-response
relationships in man.

Major differences that have been noted are as follows: (1) benign
and malignant tumour induction has occurred in rats and mice exposed
to lead acetate and in rats exposed to lead subacetate and lead
phosphate but carcinogenic effects have not been seen in man; (2)
clear-cut reductions in fertility have been observed in experimental
animals but not in man, although data have been reported which suggest
that this might be so; (3) hyperactivity and other behaviourial
disturbances have been observed in rats, mice, and sheep without prior
encephalopathy. This is especially important because of current
suspicions that widespread, slight brain damage occurs in young
children with relatively low exposure not preceded by encephalopathy.
Evidence also exists for compensatory increases in ALAD in animals
with continuing exposure to lead whereas all human studies to date
have been negative in this respect.

1.1.5 Clinical and epidemiological studies on the effects of lead:
Evaluation of health risk to man from exposure to lead

Studies of the effects of lead on man may be divided into two
general types. The first type is the retrospective study of the causes
of mortality in lead-exposed populations in contrast with those in
matched control groups. Several studies showed that at high exposure
levels (Pb-B>80 µg/ 100 ml^a), a slightly higher number of deaths
occurred due to cerebrovascular disease and chronic nephritis. In one
study, where the mortality rate due to cancer was observed, no
statistically significant differences were found between the
industrially exposed workers and the control group.

^a In this document, the concentrations of lead in blood are
expressed in µg/100 ml although in some original papers the values
are given in µg/100 g. For practical purposes, the difference of
about 5% can be neglected.

The second type of study concerns morbidity rates due to the
effects of lead on specific organs and systems. In some cases, it has
been possible to estimate the level of the exchangeable body burden
(expressed as Pb-B) at which a given intensity of effect (dose-
response relationship) has been observed in certain sections of a
selected group. For other effects it has only been possible to specify
the Pb-B level at which no effect was observed in reasonably large
groups of people (no-detected-effect level).

The haematopoietic system shows effects at lower Pb-B levels than
any other system. The effects are, in order of sensitivity: inhibition
of erythrocyte ALAD, elevation of erythrocyte protoporphyrin IX (FEP),
rise in urinary delta-aminolevulinic acid (ALA) and coproporphyrin
(CP) excretion, inhibition of erythrocyte sodium-potassium adenosine
triphosphatase (EC 3.6.1.3) (Na-K-ATP'ase), and fall in haemoglobin
level. A fall in haemoglobin level is clearly an indication of adverse
effects. The no-detected-effect level for this effect is a Pb-B
concentration equivalent to 50 µg/100 ml in adults and 40 µg/100 ml in
children.

The effects of inorganic lead on the central nervous system have
been under intensive investigation in recent years, particularly with
regard to subtle effects on behaviour, mainly in children, but also to
some extent in adults. Substantial doubts remain as to the validity of
some of the studies because the relationship between the exposure to
lead at the time the damage occurs and at the time the effects are
first observed is not known. Nevertheless, a no-detected-effect level
has been specified that is lower than for classical lead
encephalopathy. The no-detected-effect level is estimated to be at
Pb-B values of about 60-70 µg/100 ml for adults and of about
50-60 µg/100 ml for children.

The renal effects of lead are of two general types. The first is
tubular, characterized by the Fanconi triad of aminoaciduria,
hyperphosphaturia, and glycosuria. It occurs with relatively short-
term exposure and is reversible. The second type of renal effect is
characterized anatomically by sclerotic changes and interstitial
fibrosis. Functionally, filtration capacity is reduced. These changes
are of a progressive nature and may lead to renal failure. It is
probable that exposures leading to this type of nephropathy are rarely
encountered even in industry today. A no-detected-effect level cannot
be specified.

The problem of the toxic effects of alkyllead is almost entirely
restricted to workers who are occupationally exposed. There is very
little information concerning dose-effect and dose-response
relationships and even the frequency of occurrence of toxic effects
and their relation to specific work activities is not well documented.

1.2 Recommendations for Further Research

1.2.1 Analytical methods

One of the major needs is for the standardization of analytical
methods, particularly with regard to the haem intermediates, ALAD, and
erythrocyte Na-K-ATP'ase. At the present time, it is often impossible
to compare studies conducted in one laboratory with those of another.
This is particularly true for enzymatic methods that give different
results depending on pH, oxygen tension, and the presence or absence
of other factors, e.g. other metals that can influence the action of
lead. It is of equal importance that a standard mode of expressing
results be introduced in order to achieve valid interlaboratory
comparisons. Thus, measurements involving urine should be expressed
per unit of creatinine excreted per unit time; this would probably
take body mass into consideration.

In view of the highly variable results that have been obtained in
the interlaboratory comparisons conducted to date, more cooperative
efforts should be undertaken and maintained on a continuous basis. It
is recommended that all published data include interlaboratory
comparison results for the methods used. International standard
specimens of the commonly investigated biological media with reliably
determined concentrations of lead should be developed and made
available to investigators.

Finally, standardized methods of statistical treatment of
analytical data should be adopted and adhered to.

1.2.2 Sources of lead intake

It is apparent that the estimations of lead in the diet of man
vary greatly. Future studies should include specifications concerning
the characteristics of the individuals for whom lead consumption data
are being reported, including sex, age, weight, and physical activity.
Since the ultimate purpose of food studies is to evaluate the
contribution made to the total dose, it is important that future
reports also include the observed Pb-B levels and, preferably, other
indices, such as delta-aminolevulinic acid in urine (ALA-U), PP and
ALAD in erythrocytes. Food studies should also include estimates of
the lead concentration of various components of the total diet. Only
with such studies will it be possible to arrive at decisions regarding
the control of lead in foods.

More precise information is available concerning the contribution
of airborne lead to Pb-B and although this seems to be a minor
contributor to Pb-B for the general population compared with diet,
additional studies are needed both in occupational situations, and for
the general population. The studies should be of a relatively long-

term nature and should be done, as far as possible, with personal air
samplers maintained in operation continuously throughout the day
during the period of study.

There is a great need to study the sources of lead affecting
infants and young children including the contributions of food, milk
and other beverages, and air, and also miscellaneous sources, e.g.
paint, soil, and dust.

1.2.3 Epidemiological studies

Prospective studies are needed of the health effects of both
inorganic and organolead compounds, with particular reference to a
more thorough estimation of the nature of the lead exposure, Pb-B
levels, and measurable effects. It would seem particularly useful to
make further studies on occupational groups, beginning at the time of
their entry into the high lead environment.

1.2.4 Interactions of lead with other environmental factors

In both epidemiological studies and in experimental studies on
animals, not enough emphasis has been placed on the environmental
variables that can affect man's response to lead. The list of such
variables is long and is documented in this report. Particular
attention should be paid to the influence of other metals, air
pollutants, and the nutritional status of the subjects, since these
factors have been identified as interacting with lead either in regard
to its deposition in the body or in regard to its biological effects
in target organs.

1.2.5 Significance of biological effects

Numerous abnormalities have been identified, the toxic
significance of which is obscure, e.g. elevated free erythrocyte PP
and marginal erythrocyte ALAD inhibition. There is an urgent need to
study the significance of these findings in relation to human health.

2. PROPERTIES AND ANALYTICAL METHODS

2.1 Physical and Chemical Properties of Lead and its Compounds

Lead (atomic number, 82; atomic weight, 207.19; specific gravity,
11.34) is a bluish or silvery grey soft metal. The melting point is
327.5°C and the boiling point at atmospheric pressure 1740°C. It has
four naturally occurring isotopes (208, 206, 207, and 204 in order of
abundance), but the isotopic ratios for various mineral sources are
sometimes substantially different. This property has been used to
carry out non-radioactive-tracer environmental and metabolic studies.

Although lead has four electrons in its valence shell, only two
ionize readily. The usual oxidation state of lead in inorganic
compounds is therefore + 2 rather than + 4. The inorganic salts of
lead (II), lead sulfide, and the oxides of lead are generally poorly
soluble. Exceptions are the nitrate, the chlorate and, to a much
lesser degree, the chloride (Table 1). Some of the salts formed with
organic acids, e.g. lead oxalate, are also insoluble.

Under appropriate conditions of synthesis, stable compounds are
formed in which lead is directly bound to a carbon atom.
Tetraethyllead and tetramethyllead are well-known organolead
compounds. They are of great importance owing to their extensive use
as fuel additives. Both are colourless liquids. Their volatility is
lower than for most gasoline components. The boiling point of
tetramethyllead is 110°C and that of tetraethyllead is 200°C. By
contrast, the boiling point range for gasoline hydrocarbons is
20-200°C. Thus evaporation of gasoline tends to concentrate
tetraethyllead and tetramethyllead in the liquid residue.

Both tetramethyllead and tetraethyllead decompose at, or somewhat
below, the boiling point. Analysis of automobile exhaust gases shows
that the ratio of tetramethyllead to tetraethyllead increases as the
engine warms up, indicating that tetramethyllead is more thermostable
than tetraethyl-lead (Laveskog, 1971). These compounds are also
decomposed by ultraviolet light and trace chemicals in air such as
halogens, acids, or oxidizing agents (Snyder, 1967).

2.2 Analytical Procedures

2.2.1 Sampling

Particular attention should be paid to the cleanliness of the
instruments and the purity of chemicals to prevent the appearance of
artifacts due to the secondary contamination by lead, especially in
the sampling of foods and biological media.

Table 1. Some physical and chemical data on lead and selected lead compounds^a

Solubility
Name Synonym and Molecular Melting Boiling in cold Soluble in
formula weight point (°C) point (°C) water (g/litre)

lead Pb 207.19 327.502 1740 insoluble HNO₃; hot concentrated H₂SO₄
acetate Pb(C₂H₃O₂)₂ 325.28 280 -- 443 hot water; glycerine; alcohol
(slightly)
azide Pb(N₃)₂ 291.23 explodes 350 0.23 acetic acid; hot water
(0.9 g/litre)
carbonate cerrusite PbCO₃ 267.20 315 (decomposes) 0.0011 acid; alkali; decomposes in
hot water
chlorate Pb(ClO₃)₂ 374.09 230 (decomposes) very soluble alcohol
chloride cotunite PbCl₂ 278.10 501 950 9.9 NH₄ salts; slightly in dilute
HCl and in NH₃; hot water
(33.4 g/litre)
chromate crocoite, chrome 328.18 844 decomposes 0.000058 alcohol; alkali
yellow PbCrO₄
nitrate Pb(NO₃)₂ 331.20 470 (decomposes) 376.5 alcohol; alkali; NH₃; hot water
(1270 g/litre)
ortophosphate Pb₃(PO₄)₂ 811.51 1014 0.00014 alkali; HNO₃
oxalete PbC₂O₄ 295.21 300 (decomposes) 0.0016 HNO₃
oxide: di- plattnerite PbO₂ 239.19 290 (decomposes) insoluble dilute HCl; acetic acid (slightly)
mono- litharge PbO 223.19 888 0.017 HNO₃; alkali; NH₄Cl
red mioium Pb₃O₄ 685.57 500 (decomposes) insoluble HCl; acetic acid
sesqui- Pb₂O₃ 462.38 370 (decomposes) insoluble decomposes in acid and hot water
stearate Pb(C₁₈H₃₅O₂)₂ 774.15 115.7 0.5 hot water (0.6 g/litre); ether
(0.05 g/litre)
sulfate anglesite PbSO₄ 303.25 1170 0.0425 NH₄ salts; concentrated H₂SO₄
(slightly)
sulfide galena PbS 239.25 1114 0.00086 acid

Table 1. (Cont'd)

Solubility
Name Synonym and Molecular Melting Boiling in cold Soluble in
formula weight point (°C) point (°C) water (g/litre)

tetraethyllead Pb(C₂H₅)₄ 323.44 -136.80 200 insoluble benzene; petroleum; alcohol; ether
decomposes;
91
tetramethyllead Pb(CH₃)₄ 267.3 -27.5 110 insoluble benzene; petroleum; alcohol; ether

^a Adapted from Weast, R. C., ed. Handbook of Chemistry and Physics, 55th edition, Cleveland, Ohio, Chemical Rubber Company, 1974.

In air sampling, high-volume samplers are preferable for accuracy
(when it is necessary), but the low-volume technique is also useful
for obtaining extensive data. As in all sampling for suspended
particulate matter, the accuracy of volume meters should be checked
periodically. The size of the pores of filters for collecting lead-
containing particles should be small, possibly less than 0.2 µm for
glass-fibre filters (Lee & Goransen, 1972). Liquid scrubbers
containing iodine monochloride and solid scrubbers with activated
carbon, cristobalite, or iodine crystals have been used for sampling
organic lead compounds in air, in the range of about 1 µg/m³ or less
(Snyder, 1967; ASTM, 1970; Laveskog, 1971; Coleville & Hickman, 1973;
Purdue et al., 1973) up to 10 µg/m³ (Harrison et al, 1974).

Depending on the purpose of sampling, care should be taken to
select the appropriate site for sampling devices and to achieve the
best possible sampling conditions by:

-- estimating the required amount of particulates before deciding on
the sample volume and the sampling procedure;

-- placing the sampling devices in the appropriate position (e.g.
breathing air level, level of inlet tubes of house ventilators,
window level in the case of a traffic-laden town street, at a
reasonable distance from the highway in uninhabited zones, etc),

-- taking the samples at appropriate rates and volumes (e.g. daily
breathing volumes, daily ventilating capacities of installations)
and for a sufficient time to make possible the estimation of the
average concentration (e.g. during a work shift, or a 24-hour or
longer period for general population exposure);

-- taking into account the use of appropriate areas (cattle grazing,
recreational zones, children's playgrounds etc.)

In addition, whenever possible, a procedure should be used that
makes it possible to evaluate particle-size distribution and the
physico-chemical properties of the lead compounds involved, including
the shape of the particles and the state of their aggregation.

Stationary samplers can provide general indices of the exposure of
individuals within a certain area. For estimating exposure through
inhalation, personal samplers are highly desirable (Azar et al.,
1973).

Techniques for sampling water are less complex than for air. The
major question is whether or not the water should be filtered before
analysis since it is known that lead occurs in water both in the
particulate fraction and in solution. For most purposes at least, it
is reasonable to sample water without any fractionation of the
material collected.

However, in some cases it may be necessary to determine the
biological availability for absorption of the various forms of lead
that occur in water, and in soil. The latter is a dust source and may
be a food contamination source as well.

The preparation of soil and soil dust samples for lead analysis
usually involves drying (at 100°c), homogenization by grinding, and
sieving (Thornton & Webb, 1975; Bolter et al., 1975).

For the study of lead in foods, two general methods have been
used. These are the duplicate portions technique and the equivalent
composite technique (theoretical diet). These two general techniques
and others have been reviewed recently with reference to their
advantages and disadvantages (Pekkarinen, 1970). The duplicate
portions technique involves the collection for analysis of duplicates
of the meals actually consumed by the individual. When carried out
over a long enough period, the technique has the advantage of defining
variability in consumption. Kehoe (1961) used this method for the
daily determination of lead consumption over long periods.
Considerable variation in lead consumption was found in individuals
even when consumption was averaged for four- or eight-week collection
periods. The disadvantages of the method are the expense and the
exacting nature of the method of collecting samples; these factors
tend to limit the numbers of individuals included in such studies.

The equivalent composite technique consists of formulating the
ingredients of meals typical for subpopulations and analysing them.
The advantages are economy and ease of collection. This approach may
or may not include the cooking process. The disadvantage is
uncertainty as to how typical or representative the formulation is.
Even when the cooking process is included, there may be significant
differences in the manner of preparation for the study in comparison
with that carried out under actual home conditions.

The main problem in the sampling of body fluids and tissues for
lead analysis is potential secondary contamination with lead. Special
precautions must be taken to ensure that all blood-collecting and
blood-storage materials are as free from lead as possible. All glass
equipment involved in blood collection and storage should be made of
lead-free silicate glass, rinsed first in mineral acid, then with
copious amounts of glass-distilled or deionized water. Polypropylene
syringes have been recommended (NAS-NRC, 1972). Needles should be of
stainless steel with polypropylene hubs. Blood is often drawn directly
from the needle into vacuum tubes. It is wise to confirm periodically
the absence of significant amounts of lead in the anticoagulant used
in the blood container, although this has not been reported as a
problem.

New analytical techniques make it possible to determine lead
concentrations in microlitre quantities of blood. The trend towards
the procurement of micro-samples of blood by skin prick increases the

hazard of secondary contamination of the blood. Only one systematic
investigation on the significance of this problem has been reported.
Mitchell et al. (1974) describe a procedure whereby sample
contamination appears to be avoided. This is achieved by spraying
collodion over the cleansed skin before lancing. The correlation
between the concentration of lead in micro-samples and in macro-
samples obtained by venipuncture was fairly good (r = 0.92). The same
general precautions must be taken in the collection of urine samples
as in the collection of blood samples.

Ceramic surfaces are analysed to determine the quantity of lead
likely to be leached by different foods and beverages. In all cases
acetic acid solutions are used but the concentrations vary from 1 to
4%. The temperature of the tests ranges from 20 to 100°C and the
duration from 30 minutes to more than 24 hours (Laurs, 1976; Merwin,
1976).

2.2.2 Analytical methods for lead

The analytical methods currently in use for the estimation of lead
content are of two general types, destructive and non-destructive. In
the former, the sample is first oxidized to destroy all organic
matter. The ash is then usually dissolved in an aqueous medium, either
for further preparative steps or for direct instrumental analysis.
Non-destructive methods are of more recent origin and are still too
complicated for routine studies. They include X-ray fluorescence
analysis and fast neutron activation. In selecting methods,
consideration must be given to the cost of the equipment and the time
involved in performing the analyses.

The oldest and best known of the general methods currently in wide
use are those based on the formation of the red complex that lead
forms with dithizone (diphenylthiocarbazone). Numerous specific
procedures have been developed based on the spectrophotometric
determination of lead dithizonate. A typical example is the "US Public
Health Service" method commonly used for the determination of lead in
biological materials (NAS-NRC, 1972). The method has evolved over many
years. A study of its reliability was reported by Keenan et al.
(1963). An interlaboratory comparison was made of analyses of blood
and urine with and without the addition of lead. Ten laboratories
participated in the study. For blood, the concentration of lead
calculated in the principal laboratory was 20 µg/100 ml. The average
reported by the participating laboratories was 26 µg/100 ml with a
standard deviation of ± 0.82 µg/100 ml. For samples of blood to which
lead was added, the average result was right on the mark,
70 µg/100 ml ± 0.78. For "spiked" urine, determined by the primary
laboratory to contain 750 µg/litre, the average reported result was
679 ± 5.5 µg/litre.

Perhaps no method of instrumental analysis for lead has enjoyed
such a rapid acceptance in recent years as atomic absorption
spectroscopy. In conventional atomic absorption spectroscopy, the
source of heat is a flame into which the sample solution is aspirated.
More recently, various procedures have been developed whereby the
receptacle containing the sample is heated electrically. This type of
modified procedure is termed flameless atomic absorption spectroscopy.
The main advantage of this approach is that sample size is reduced
from the millilitre to the microlitre range with no commensurate loss
of sensitivity. Another advantage is that the heated receptacle can be
used for ashing the sample immediately prior to the spectrophotometric
analysis. Numerous reports have appeared describing various kinds of
flameless instrumentation and their application in the analysis of the
lead content of blood and other materials (Cernik, 1974; Delves, 1970;
Ediger & Coleman, 1973; Matousek & Stevens, 1971; Kubasik et al.,
1972; Hwang et al., 1971; Sansoni et al., 1973; Schramel, 1973;
Schramel, 1974). It has been reported that the analytical capabilities
of this method for determining lead in whole blood are comparable with
that of the conventional flame atomic absorption method (Kubasik et
al., 1972; Hicks et al., 1973).

Electroanalytical methods have also been found useful for lead
determinations. These include polarography and, more recently, anodic
stripping voltametry. The polarographic method was developed
specifically for lead by Teisinger (1935). The low sensitivity of the
method as applied to lead in blood and urine required working close to
the detection limits. This is obviously a disadvantage when
determining the normal levels of lead in blood and urine. Various
modifications of the original method have been used for the evaluation
of industrial exposures (Weber, 1947; Baker, 1950; Brezina & Zuman,
1958). This method found wide application until more effective masking
procedures were developed to increase the specificity of the dithizone
method. Anodic stripping voltametry is gaining in popularity for lead
analysis. Results have been compared using a dithizone method, an
atomic absorption method, and anodic stripping voltametry (Matson,
1971). Generally, there was good agreement between all three methods
in the estimation of the lead contents of blood and urine. In another
study, anodic stripping voltametry was compared with atomic absorption
spectroscopy and polarography for the analysis of lead in blood and
urine (Horiuchi et al., 1968). The authors concluded that there were
no significant differences between the results obtained by the various
methods. Anodic stripping voltametry has also been compared with
conventional and flameless atomic absorption spectroscopy and with
potentiometric determination using ion-specific electrodes to estimate
the lead content of water (Kempf & Sonnenborn, 1973).

Two non-destructive methods for lead analysis have been under
investigation in recent years. These are neutron activation and X-ray
fluorescence. The first of these is not likely to find wide
application for lead analysis in the near future because of the cost

and the need for access to a fast neutron source. Its advantage is
that the concentration of many elements can be determined
simultaneously.

X-ray fluorescence is also theoretically capable of detecting,
non-destructively, all elements in a substance. A major obstacle to
the wide application of this method is the profound matrix effect of
the substances being analysed. Another problem is the backscatter from
the exciting source. These design problems and approaches to their
solution have been discussed recently by Kneip & Laurer (1972). Lead
analysis by means of X-ray fluorescence with proton excitation has
been successfully used with biological samples (Möller et al., 1974).
It has also been used as the standard method for the determination of
lead on filters from air sampling equipment by the Warren Springs
Laboratory in the United Kingdom. In the USA, the most extensive
application of X-ray fluorescence for lead analysis has been for
estimating the concentration and amount of lead on the walls of
houses. For this purpose, several portable units have been designed
and are being used in surveys of dwellings for hazardous
concentrations of lead. Since the instruments in question scan
surfaces, instrument response is in terms of lead detected per unit
area and not per unit weight or volume of paint film. This creates
difficulties, since the thickness of the total paint film varies
depending on how many times a surface has been painted. Ordinances
should perhaps be revised to specify tolerances based on surface area.
The accuracy of these instruments is severely limited. These factors
have been studied using one of the commercially available instruments
(Spurgeon, 1973). In another report from the US National Bureau of
Standards (Rasberry, 1973), four commercial instruments were tested as
received from the manufacturer. It was found that all the instruments
had a detection limit below 1 mg/cm², but that between 1 and
6.6 mg/cm², errors as large as 30-50% occurred. It is difficult to
evaluate the adequacy of such instruments since it is not at all clear
where the cut-off is between hazardous and non-hazardous amounts of
lead per unit area of paint film. Thus, if the cut-off were known to
be at or above 1 mg/cm², the instruments would clearly be useful.

The accuracy and precision of various methods for the lead
analysis of biological materials have been appraised in a number of
interlaboratory comparison programmes both at the national (Keppler et
al., 1970; Donovan et al., 1971) and international levels (Berlin et
al., 1973). In general, these published studies have indicated that
the accuracy of the measurements is unsatisfactory, with less than
half of the laboratories performing adequately. More recently, in a
programme involving sixty-six European laboratories, it was observed
that even when only the laboratories that measured lead in blood and
urine with a precision of greater than 10% were selected, the
interlaboratory variability still remained high. It is possible that

the performance could be improved by rapid distribution of the sample
and by improved sample preparation techniques, e.g. by subjecting
blood samples to ultrasonic irradiation prior to despatch to
participating laboratories.

The paper punch disc microtechnique (Cernik & Sayers, 1971;
Cernik, 1974) was used in a population survey of blood lead content
performed in Western Ireland (Grimes et al., 1975). Over 400 duplicate
samples were analysed double-blind by one laboratory. The assay showed
a satisfactory agreement with the results obtained by other
laboratories using various techniques.

Comparisons have also been reported of the agreement between
results obtained by the same investigator using different analytical
methods. Yeager et al. (1971) compared the results obtained using a
standard dithizone procedure and flame atomic absorption spectroscopy.
The results from common digests of the same material were compared.
The materials included blood, urine, tissue, faeces, food, and bone.
Since the two methods are based on entirely different analytical
principles, a straight line with a slope equal to 1 and an intercept
equal to 0, obtained when the results of atomic absorption
spectroscopy analyses were plotted against the results of the
dithizone method, suggested that the two methods were equally
accurate.

These studies show that blood sample preparation is important to
ensure sufficient homogeneity for microanalytical techniques.

2.2.3 Methods for the measurement of some biochemical effects of lead

The classic method for the urinary delta-aminolevulinic acid (ALA)
determination was developed by Mauzerall & Granick (1956). The major
procedural difficulty was separation from interfering substances. A
number of modifications and simplifications have been made by several
authors (Davis & Andelman, 1967; Grabecki et al., 1967; Williams &
Few, 1967; Sun et al., 1969; Tomokumi & Ogata, 1972).

The original Mauzerall & Granick method does not discriminate
between ALA and aminoacetone, a fact that these authors were careful
to point out. This is probably not very important when ALA excretion
is greatly increased due to lead exposure, but for marginal
elevations, it may be a serious problem. In healthy humans on a normal
diet, the urinary excretion of ALA and that of aminoacetone are nearly
equal (Marver et al., 1966). These authors and also Urata & Granick
(1963) separated ALA from aminoacetone by chromatography.

One interlaboratory comparison study of ALA methods has been
reported (Berlin et al., 1973). The methods used by the laboratories
were those of Mauzerall & Granick (1956), Davis & Andelman (1967) and
of Grabecki et al. (1967). The results using the Grabecki method were

significantly higher than those using the Mauzerall & Granick method.
Results with the Davis & Andelman method gave a mean value
intermediate between the other two. The coefficients of variation were
quite high: 33%, Grabecki; 28%, Mauzerall & Granick; and 49%, Davis &
Andelman. It should also be noted that in the case of the Grabecki
method, the colorimetric reaction was influenced by various
interfering substances in the individual urine samples. This source of
error was not considered in the interlaboratory comparison (Mappes,
1972).

Comparisons have also been reported between these different
techniques by Roels et al. (1974) who evaluated the critical factors
in the urine preparation which affected the different methods. The
ionic strength and pH of the urine can affect the results of some of
the methods.

In the methods used for the determination of ALAD activity, the
amount of porphobilinogen (PBG) formed per unit time by a standard
amount of enzyme source is measured. Limited data indicate that ALAD
in blood is stable for several hours, even at room temperature
(Hernberg et al., 1970); however, storage at lower temperatures
improves the stability. The major variables reported to influence the
activity of the enzyme are pH (Nikkanen et al., 1972), oxygen tension
(Gibson et al., 1955), the nature of the anticoagulant (Collier,
1971), and the presence or absence of activators (Bonsignore et al.,
1965; Collier, 1971; Granick et al., 1973; Hapke & Prigge, 1973).
Measurement of ALAD activity in erythrocytes is a relatively simple
procedure that can be conducted without sophisticated equipment. This
makes it attractive as a measure of the haematological effects of
exposure to lead. A number of investigators have shown it to be fairly
specific for lead.

In its simplest and most frequently used form, the method of
Bonsignore et al. (1965) requires the incubation of a mixture of
blood, ALA, and water under aerobic conditions at 38°C. However, many
investigators have modified the procedure and results from different
laboratories are not necessarily comparable. In a recent
interlaboratory comparison (Berlin et al., 1973), nine participants
used various modifications of the Bonsignore method. Thus, it was only
possible to compare the activity ratios between different blood
samples. For two blood samples this ratio showed a coefficient of
variation of only 13%.

Recently a "European standardized method" has been developed,
tested in a collaborative study, and agreed upon by nineteen
laboratories. The results of these tests compare very favourably with
blood lead determinations. The interlaboratory coefficient of
variation for ALAD was 10% (Berlin et al., 1974).

Porphyrins exhibit intense fluorescence when excited by light at
approximately 400 nm (Soret band). They may be quantitatively
determined either by measurement of light absorption in the Soret band
region or by the measurement of fluorescence (Sassa et al., 1973;
Chisolm, 1974).

A number of methods have been reported for the measurement of
protoporphyrin IX. Some of these methods discriminate between
different porphyrins, measuring specifically the concentration of
protoporphyrin IX in erythrocytes (Schwartz & Wikoff, 1952; Wranne,
1960; Schlegel et al., 1972; Granick et al., 1972; Sassa et al.,
1973). Other methods measure the total concentration of free
erythrocyte porphyrins including copro- and uro-porphyrins (Kammholtz
et al., 1972; Piomelli, 1973; Schiele et al., 1974b). It is, however,
scarcely necessary to make a distinction between the two kinds of
procedure as over 90% of the free erythrocyte porphyrins are made up
of protoporphyrin IX (Baloh, 1974). A particular advantage of the more
recently developed procedures for the measurement of FEP is that they
can be performed on microcapillary samples of blood (Kammholz, 1972;
Granick et al., 1972; Sassa et al., 1973: Piomelli, 1973; Schiele et
al., 1974a). The Piomelli procedure utilizes two successive
extractions into ethylacetate-acetic acid with subsequent transfer of
porphyrins into hydrochloric acid. The procedure of Granick et al.
(1972) is simpler. Ethylacetate-acetic acid and hydrochloric acid are
successively added to the sample of blood. In both procedures the
ethylacetate serves to remove and retain interfering impurities in the
blood. The data obtained by these two methods are not strictly
comparable.

All the methods described measure protoporphyrin in the free base
form. Lamola & Yamane (1974) have recently demonstrated that the
protoporphyrin IX associated with iron deficiency and lead
intoxication is present as a zinc chelate. This is not so in the case
of erythropoietic porphyria. On the basis of these observations they
developed a fluorimetric method for zinc chelate (Lamola et al.,
1975). The major advantage of this method is its simplicity and
rapidity. Microlitre samples are analysed fluorimetrically, after
dilution, without any extraction steps.

The measurement of coproporphyrins in urine is generally done by
extraction of the porphyrins into either ethylacetate-acetic acid
(Sano & Rimington, 1963) or diethyl ether (Askevold, 1951) followed by
transfer into hydrochloric acid. Absorbance is then measured at 401 nm
with the corrections recommended by Rimington & Sveinsson (1950). The
method is apparently specific, since uroporphyrins, the most likely
source of interference, are not extracted into the organic phase under
these conditions (Rimington & Sveinsson, 1950). An alternative method
has been reported whereby the fluorescence of the hydrochloric acid
extract is measured after adsorption on to magnesium hydroxide
(Djuric, 1964). Certain precautions are necessary if urine is to be

analysed for coproporphyrins. Coproporphyrins are unstable in acid
urine and, furthermore they are light-sensitive (Schwartz et al.,
1951). They may be stored safely in the dark at 4°C if the pH is
maintained between 6.5 and 8.5.

3. SOURCES OF LEAD IN THE ENVIRONMENT

3.1 Natural Occurrence

3.1.1 Rocks

Lead occurs naturally in the earth's crust in the concentration of
about 13 mg/kg. As with all elements, there are some areas with much
higher concentrations including the lead ore deposits scattered
throughout the world.

The most important sources of lead are igneous and metamorphic
rocks, with lead concentrations in the range of 10-20 mg/kg (Wedepohl,
1956, Vinogradov, 1956, 1962; Turekian & Wedepohl, 1961). The
concentration of lead in sedimentary rocks is of the same order of
magnitude. The lead content of carbonaceous shales from the United
States of America and Europe ranges from 10mg/kg to 70mg/kg (Wedepohl,
1971; Davidson & Lakin, 1962). The lead contents of shale and
sandstone are similar but that of phosphate rocks is higher, and may
exceed 100 mg/kg (Sheldon et al., 1953). Unconsolidated sediments in
bodies of freshwater and in shallow marine areas have a similar lead
content to shales. Deep marine sediments have quite a high lead
content by comparison, commonly containing 100-200mg/kg (Riley &
Skirrow, 1965).

The lead content of coal is relatively low. However, when
expressed on an ash-weight basis, the concentration is generally
higher than that of igneous, metamorphic, and sedimentary rocks, but
not more than ten-fold (Abernethy et al., 1969).

3.1.2 Soils

Surface soils are in direct contact with the contemporary
environment; thus, special care must be taken to distinguish between
soils that acquire lead only from natural sources and soils that are
polluted by man. Acidic soils generally have a lower lead content than
alkaline soils. The nature of the organic matter in soil also has a
considerable influence on its lead content. Some organic matter is
rich in chelating components, and it binds lead, either promoting its
movement out of the soil or fixing the metal, depending on the
solubility properties of the complex. Although all of these factors no
doubt play a role in determining the lead content of specific soils,
the concentrations usually encountered in areas, remote from human
activity, are similar to concentrations found in rocks, with an
average range of 5-25 mg/kg (Swaine, 1955). More recent data from
various parts of the world have confirmed this estimate.

3.1.3 Water

Analyses of groundwater have revealed lead concentrations varying
from 1 to 60 µg/litre (Kehoe et al., 1933, 1944; Bagchi et al., 1940).
Most data refer to water that has been filtered to remove particulate
matter. Colloidal lead is only partially removed by filtration and to
different degrees. Water that is pumped from the ground is usually not
filtered prior to analysis. The content of colloidal material is
probably insignificant in such samples owing to natural filtration
which removes colloidal particles fairly effectively.

There have been a large number of investigations concerning the
concentration of lead in natural surface waters. From the data
available, Livingstone (1963) estimated that the global mean lead
content in lakes and rivers is 1-10 µg/litre. Although this estimate
includes man-made pollution, it probably still represents a fair
approximation of natural conditions since water flowing through the
ecosystems has a considerable self-cleaning capacity.

The concentration of lead in sea water has been found to be lower
than in freshwaters. Tatsumoto & Patterson (1963) report
0.08-0.4 µg/litre in seawaters off the coast of California. In deep
waters the concentration was even lower. According to Chow (1968)
surface waters off Bermuda, which are free from continental
influences, have lead concentrations averaging 0.07µg/litre, while
central Atlantic waters contain an average of 0.05 µg/litre. Although
there seem to be somewhat higher lead concentrations in the surface
waters of the Pacific and the Mediterranean, compared with the central
Atlantic, the concentrations at depths below the 1000-m level are very
similar, i.e. around 0.03-0.04 µg/litre (Chow, 1968).

3.1.4 Air

The atmospheric concentration of lead measured at points most
remote from civilization is of the order of 0.0001-0.001 µg/m³
(Jernigan et al., 1971; Chow et al., 1969; Egorov et al, 1970;
Murozumi et al., 1969). The sampling sites in these studies were
mainly over remote areas of oceans and over Greenland. Patterson
(1965) estimated from geochemical data that the concentration of lead
in air of natural origin is about 0.0006 µg/m³. If that is a correct
estimate, even the air over uninhabited, remote, continental areas may
be contaminated by human activities. For example, Chow et al. (1972)
reported that the concentration of lead in the air over remote,
uninhabited mountains of southern California had a concentration of
0.008 µg/m³.

3.1.5 Plants

Lead occurs naturally in all plants, as well as in soil, air, and
water. Extremely variable concentrations of lead in plants have been
reported but nevertheless, certain generalizations have been made.
Warren & Delavault (1962) have concluded that the normal concentration
of lead in leaves and twigs of woody plants is 2.5 mg/kg on a dry
weight basis. For vegetables and cereals they estimated normal
concentrations to be 0.1-1.0 mg/kg dry weight. Mitchell (1963) found
that the usual concentration of lead in pasture grasses was 1.0 mg/kg
dry weight. These figures should be multiplied by a factor of 20 to
convert concentration on a dry weight basis to an ash weight basis.

3.1.6 Environmental contamination from natural sources

The contribution of natural sources of lead to lead concentrations
in the environment is small. As regards exposure of man, these sources
are negligible. Through various breakdown processes, rocks yield lead
which is transferred to the biosphere and the atmosphere and
ultimately back to the earth's crust in the form of sedimentary rocks.
Soluble lead has for thousands of years entered the oceans with river
discharges, and the amount has been estimated by Patterson (1965) at
some 17 000 tonnes per year. Sources contributing to airborne lead are
silicate dusts, volcanic halogen aerosols, forest fires, sea salts
aerosol, meteoric and meteoritic smoke, and lead derived from the
decay of radon. The last mentioned source generates the lead isotope
²¹⁰Pb in trace amounts, the mean air residence time of which has
been calculated to be about four weeks; the radioactive half-life is
22 years (Hill, 1960).

3.2 Production of Lead

3.2.1 Lead mining

Lead is produced from ores and recycled lead products. Lead occurs
in a variety of minerals the most important of which are galena (PbS),
cerrusite (PbCO₃) and anglesite (PbSO₄). Galena is by far the most
important source of primary lead. It occurs mostly in deposits
associated with other minerals, particularly those containing zinc.
Mixed lead and zinc ores account for about 70% of total primary lead
supplies. Ores containing mainly lead account for about 20% and the
remaining 10% is obtained as a by-product from other deposits, mainly
zinc and copper-zinc deposits (Federal Institute for Minerals Research
and German Institute for Economic Research, 1972). The proportions of
various metals may differ in the ores of different countries. Silver
is the most important of the other metals frequently present in lead
deposits but copper may also be present in concentrations high enough
to be commercially important. Other minor constituents of lead ores
are gold, bismuth, antimony, arsenic, cadmium, tin, gallium, thallium,

indium, germanium, and tellurium. The lead content of ores is
comparatively low, i.e. 3-8%, but even ores with lower lead contents
may be commercially valuable.

The level of world mine production of lead concentrates from ores
has increased in recent years. According to the International Lead and
Zinc Study Group and the World Bureau of Metal Statistics, the world
mine production of lead (lead content) was about 3.6 million tonnes in
1975, as compared with about 2.6 million tonnes in 1965. These figures
include production estimates for socialist countries with a planned
economy made by the World Bureau of Metal Statistics. The most
important lead mining countries, producing over 100 000 tonnes each in
1975, were Australia (10% of the total world output), Bulgaria (3%),
Canada (9.6%), China (3.8%), Mexico (4.5%), Peru (5.5%), United States
of America (16%), USSR (14.5%), and Yugoslavia (3.5%). In addition,
some other countries had a production of over 2% of the world total,
e.g. Ireland, Japan, Democratic People's Republic of Korea, Morocco,
Poland, Spain, and Sweden. There are about 40 countries producing only
small amounts each, making together only some 12% of the world
production. One estimate of proven lead reserves of the world is 93
million tonnes of lead metal content. (Federal Institute for Minerals
Research and German Institute for Economic Research, 1972.)

3.2.2 Smelting and refining

Smelting and refining is classified as primary or secondary, the
former producing refined lead from concentrates (primary lead); the
latter recovering lead from scrap (secondary lead). The raw materials
for secondary lead are process (new) scrap arising during
manufacturing processes, and recycled (old) scrap which arises when
lead-containing manufactured goods are discarded. Old material makes
up the bulk of the scrap, the most important source being storage
batteries, which account for 70-80% of the total supply of scrap.

Secondary lead accounts for about half the consumption in the
United States of America and it has been estimated that about 35% of
the total world lead supply comes from secondary sources (Federal
Institute for Minerals Research and German Institute for Economic
Research, 1972). Table 2 gives the production of lead ore, the total
metal production, and the consumption of some industrialized
countries.

Table 2. Lead production and consumption in some industrialized countries (kilotonnes)^a

Country Lead ore production Metal production Consumption
(metal content) (refined metal)

1973 1974 1975^b 1973 1974 1975b 1973 1974 1975^b

EUROPE 1134 1134 1069 2054 2115 1871 2118 2125 1831
Belgium - - - 98 95 103 52 64 54
Bulgaria 105 110 108 100 105 108 80 85 91
Denmark - - - 13 15 13 19 23 20
France 25 24 22 186 178 150 214 199 188
Germany, Federal
Republic of 40 35 37 300 319 260 290 260 210
Ireland 53 34 55 - - - 1 3 2
Italy 27 24 27 100 112 70 234 242 200
Netherlands - - - 25 26 20 38 41 38
Poland 70 70 72 68 70 66 87 90 40
Spain 64 65 58 120 102 85 121 116 90
Sweden 74 73 69 42 41 37 34 36 32
UK - - - 265 277 229 282 266 238
USSR 570 590 504 640 660 600 600 620 544
Yugoslavia 106 109 117 97 115 130 66 80 84

AFRICA 223 183 178 116 117 93 65 66 75
Morocco 90 86 - 1 1 - - - -
South Africa 63 55 53 64 64 49 27 31 39

AMERICA 1430 1412 1379 1666 1677 1565 1718 1706 1339
Canada 388 314 348 187 127 172 69 63 55
Mexico 168 169 163 177 204 179 88 83 74
Peru 199 201 185 83 80 72 10 9 10
USA 570 616 575 1100 1128 1008 1423 1374 1027

Table 2. (Cont'd)

Country Lead ore production Metal production Consumption
(metal content) (refined metal)

1973 1974 1975^b 1973 1974 1975b 1973 1974 1975^b

ASIA 273 284 291 413 423 395 457 412 386
Democratic Republic
of Korea 90 100 100 60 65 60 20 20 20
Japan 53 44 51 228 228 195 267 217 186
People's Republic
of China 130 140 140 125 130 140 170 175 180

OCEANIA 396 360 384 221 225 191 82 79 75
Australia 396 360 384 221 225 191 74 72 68

Other countries 55 53 48 102 108 88 189 203 233

TOTALS 3617 3569 3497 4642 4723 4260 4883 4882 4154

^a Sources: International Lead, Zinc Study Group, and World Bureau of Metal Statistics.
^b Estimated.

3.2.3 Environmental pollution from production

Mining, smelting, and refining, as well as the manufacture of
lead-containing compounds and goods, can give rise to lead emissions.
According to a study of the industrial sources of air pollution by
lead in the USA, Davis (1973) reported that 9% of the total of 18 000
tonnes generated from such sources was attributable to the production
of primary lead.

Smelters of lead ores are well known to create pollution problems
in local areas. Their influence on the surrounding air and soil
depends to a large extent on the height of the stack, the trapping
devices in the stacks, the topography, and other local features. The
emissions can cover a considerable area. The zone of air pollution for
one large smelter in the USA extended to approximately 5 km from the
smelter while soil contamination extended as far as 10 km (Landrigan
et al., 1975b). The larger area of the zone of soil pollution compared
to the zone of air pollution probably was due to the fact that current
emission control devices are more effective than earlier ones used to
be. The opposite situation was found around the Mezica mine and
smelter in Yugoslavia (Djuric et al., 1971; Kerin, 1972, 1973). In
this case, the zone of air pollution extended as far as 10 km from the
smelter stack. Soil was grossly contaminated (>200 mg/kg) as far away
as 7 km. There was also heavy pollution of water courses through
effluents.

Secondary smelters producing lead from scrap are comparatively
small, numerous, and frequently situated close to human settlements.
Several studies showed that pollution in the surroundings of such
smelters had been severe enough to produce an increase in the intake
of lead by people living nearby (section 5.1.1).

3.3 Consumption and Uses of Lead and its Compounds

Figures for the consumption of lead are available for most
industrialized countries. The estimated total world consumption of
lead in 1975 was about 4.1 million tonnes (Table 2). The use of lead
is greatly influenced by the growth of the automobile industry which
in 1974 took about 56% of total consumption. Table 3 is compiled from
statistics of lead consumption for the Federal Republic of Germany,
France, Italy, Japan, the United Kingdom, and the United States of
America. There has been a notable increase in the consumption for
batteries over the period 1969-1974.

3.3.1 Storage battery industry

The manufacture of electric storage batteries is responsible for
the largest consumption of lead (Table 3). This industry uses both
metallic lead in the form of a lead-antimony alloy, and lead oxides in
about equal proportions. The metallic lead is in the grids and lugs,

while the oxides, litharge (PbO), red lead (Pb₃0₄), and grey oxide
(PbO₂), are used in the active material that is pasted on the
plates. The demand for lead batteries decreased in 1974 and 1975
concomitantly with the decline in total consumption (Table 2) as a
result of the economic recession in several of the major lead-
producing countries. However, the fall in the demand for batteries has
also been attributed to the longer life-time of batteries, (Stubbs,
1975) which in 1967 was considered to be about 29 months (US Bureau of
Mines, 1969) but according to Stubbs is, at present, close to 4 years.
The battery industry also constitutes the major source of lead for
secondary lead production. It has been estimated that up to 80% of the
lead in storage batteries is recovered at secondary smelters
(Ziegfeld, 1964).

Table 3. Percentage of total lead consumption by different
industries in six major industrial countries

Industry 1969^a 1974^b

Batteries 35.9 44
Alkyllead 12.0 12.0
Cable sheathing 10.9 9.2
Chemical pigments 10.9 12.0
Alloys 8.1 10.8
Semi-manufacturers 16.5 12.0

^a Federal Institute for Minerals Research and German Institute
for Economic Research, 1972.
^b Based on data provided by Stubbs, R. L., Lead Development
Association, London.

The lead battery is likely to retain its position as a convenient
source of electricity in the foreseeable future. The nickel-cadmium
battery does offer some advantages but is about three times more
expensive. Better battery design, improvements in the electrical
systems in cars and lower mileages because of higher gasoline costs
are factors that may retard the growth rate for lead consumption by
the battery industry. New applications for batteries may, on the other
hand, increase demand.

3.3.2 Alkyllead fuel additives

Alkyllead compounds have been in use as anti-knock additives in
gasoline for almost 50 years. Use of these compounds (almost
exclusively tetraethyllead and tetramethyllead) increased steadily up
to 1973 (Table 4). In 1973, the world consumption of refined lead for

the manufacture of lead additives was about 380 000 tonnes
(International Lead and Zinc Study Group, 1976). The moderate decrease
in consumption in 1974 was almost entirely attributable to a decrease
of 22 000 tonnes in the use of lead for gasoline additives in the USA.
A further decline in the consumption was estimated in the USA in 1975,
amounting to some 50 000 tonnes (Table 4); thus, the consumption in
1975 declined by 30% in comparison with the 1973 consumption (Stubbs,
1975). In the USA, the manufacture of alkylleads is, after batteries,
the largest lead consuming industry. By comparison, lead additives
make up only 6% of the European market for lead (International Lead
and Zinc Study Group, 1973). The decrease in the use of lead for fuel
additives is likely to continue in the latter half of the 1970s as
more cars fitted with catalysts requiring lead-free gasoline will come
into use, The regulations on the maximum permissible concentrations of
lead in gasoline will further affect the consumption of lead in fuels.
The US Environmental Protection Agency's reduction programme aiming at
0.13 g of lead per litre of gasoline by 1 January 1979 was ratified in
March 1976 by the US Court of Appeals. The maximum permissible level
in the Federal Republic of Germany has been 0.15 g of lead per litre
since 1 January 1976, and in Japan has been, 0.31 g of lead per litre
since July 1971. Some European countries introduced limits of 0.4 g of
lead per litre (e.g. Austria, Norway, Sweden, Switzerland) but most
European governments have deferred their decision because of the
economic implications of lowering the lead content (International Lead
and Zinc Study Group, 1976).

Table 4. Consumption of refined lead for the manufacture of
alkylleads (kilotonnes)^a

Country 1972 1973 1974 1975^b

USA 253 249 227 175
Europe: (total) (87) (89) (89) (91)
France 13 14 14 14
Germany, Federal Republic of 9 9 10 9
Italy 15 12 10 10
United Kingdom 50 54 56 58
Others n.a.^b 40^b 40^b 35^b

Total 340 378 357 301

^a From: International Lead and Zinc Study Group, 1976
^b Estimated data; n.a.=not available.

3.3.3 Cable industry

The relative importance of the cable industry as a lead consumer
has declined considerably (Table 3), mainly owing to the introduction
of plastic sheathing/insulation. However, the total amount of lead
used is still notable (Table 5). The use of lead in cable production
is comparatively greater in Europe and several developing countries
than in the United States of America. Alloys used for cable sheathing
contain small amounts of many other elements including cadmium,
tellurium, copper, antimony, and arsenic.

3.3.4 Chemical industry

Although a wide range of lead pigments are still produced they are
increasingly being substituted by other, less toxic, pigments. Red
lead (minium) is used extensively in the painting of structural steel
work and lead chromate is often used as a yellow pigment. The use of
lead for pigment manufacture in 1974 is given in Table 5.

Lead arsenate was, at one time, an important insecticide but is
now little used and current consumption figures are not available.

Table 5. Consumption of lead in cables and pigments in five
industrial countries in 1974 (kilotonnes)^a

Country Cable Pigments

France 40 32
Germany, Federal Republic of 52 80
Italy 50 47
Japan 21 50
United Kingdom 44 35

Total 205 244

^a Data from International Lead Zinc Study Group statistics.

The use of lead for the manufacture of alkyllead additives was
discussed in section 3.3.2. The petroleum industry also uses a small
amount of litharge dissolved in sodium hydroxide solution to remove
sulfur compounds in the refining of petroleum.

3.3.5 Miscellaneous

Industries producing semi-manufactured components account for an
important proportion of the total consumption. The surface of lead
oxidises readily and is then very resistant to corrosion. The building
and construction industries use lead sheet for roofing and other
flashings, wall cladding, and sound insulation. Lead also forms alloys
readily and is used in solder, bearing metals, brasses, type metal,
collapsible tubes, and for radiation shielding. The ammunition
industry is another major consumer of lead. There are many minor uses
of lead compounds but these account for only a very small proportion
of total lead consumption.

3.3.6 Environmental pollution from consumption and uses of lead

The combustion of alkyllead additives in motor fuels accounts for
the major part of all inorganic lead emissions. The consumption of
lead for the manufacture of alkylleads was estimated at 380 000 tonnes
in 1973 and 300 000 tonnes in 1975 (section 3.3.2). Of this amount,
over 70% is like to enter the environment immediately after
combustion, the rest being trapped in the crank case oil and in the
exhaust system of the vehicles (Davis, 1973; Huntzicker et al., 1975).
Moreover, part of the lead retained in the lubricating oil will enter
the environment through different pathways (section 3.4). The degree
of pollution from the combustion of alkyllead naturally differs from
country to country, depending on the car density. The importance of
alkyllead combustion is exceptionally high in the USA, where 20% of
the total lead consumed is for the manufacture of alkyllead compounds,
the corresponding values in 1969 being only 5% for France and 11% for
Italy and the United Kingdom. The estimated total world emissions from
this source were, according to the figures mentioned above, at least
266 000 tonnes in 1973 and 210 000 tonnes in 1975.

In the study by Davis (1973) on lead emissions into the air from
industrial sources in the USA, 11% (1900 tonnes) was attributed to the
processing of alkyllead additives. The manufacture of storage
batteries emitted smaller amounts (480 tonnes) and emissions were
still smaller in the production of lead oxide, lead pigments, type
metal, solder, etc. The amounts of effluent from these industries were
not studied. The dispersion of lead through the exhausts of workrooms
should also be considered. These emissions although not very large may
still contribute significantly to the pollution of the surrounding
areas. The possibility of contamination of the home environment
through working clothes should be borne in mind.

The magnitude of the pollution arising from the vast number of
lead containing items that are subjected to weathering or are
decomposed in the course of time is difficult to appraise. According
to one estimate, about 50% of paint is removed from surfaces protected
by lead pigments in a period of about seven years before re-painting

(Patterson, 1965). Heavy contamination of the dust and soil around
houses painted with lead paints has been consistently reported (Ter
Haar & Aranow, 1974).

Only an unknown, but probably small fraction of the lead used in
metallic form for the production of sheeting, cable, printing metal,
etc. is ever released into the environment. Contamination of domestic
water supplies, foods, and beverages resulting from the use of lead
pipes, PVC pipes, glazed ceramics, and from cans with lead containing
solders may under certain conditions be hazardous to man's health
(sections 5.1.2 and 5.1.4).

The lead content in tobacco has been attributed to lead residues
present in the soils of tobacco fields as a result of the former use
of lead arsenate as an insecticide (section 5.1.4).

3.4 Waste Disposal

A substantial part of lead wastes are remelted in secondary
smelters (see section 3.2.2).

Municipal incinerators have recently been investigated for lead
emissions. An unknown proportion of the non-recycled, lead containing,
consumer products, e.g. collapsible tubes, bottle caps, cable scrap,
battery casings, and products painted with lead pigments, are
incinerated. Depending on the type of furnace and on purification
devices, these emissions may be considerable (Davies, 1973; Mattsson &
Jaakkola, 1974).

Waste lubricating oil has been contaminated through the combustion
of lead alkyls. Over 50% of the oil is dumped or used as road oil. In
1970, the total amount of waste oil generated in the USA was about
2400 million litres. Waste crankcase oil contains about 1% lead. Thus,
the estimated amount of lead discharged into the environment from this
source in the USA was nearly twice the amount originating from, for
instance, the production of primary lead (Davis, 1973).

The extent of environmental pollution by lead arising from the
incineration of sewage and sludge is not known.

3.5 Miscellaneous Sources of Environmental Pollution

When studying all industrial sources emitting lead into air, Davis
(1973) reported that out of a total of 18 000 tonnes, copper smelting
accounted for 8% and the production of steel and iron another 8%.
Smaller amounts were generated in the production of primary zinc and
also in the production of cement.

Coal contains small amounts of lead with a wide range of
concentrations in different coals. Concentrations found by Abernethy
et al. (1969) in coal from various districts in the USA ranged from
0.6 to 33.1 mg/kg. According to Patterson (1965) about 5% of the ash
leaving boilers as stable fly-ash aerosols is made up of small
particles of a few micrometres. This silicate matter contains about
100 mg of lead per kg. Large quantities of coal are burnt to produce
steam in power stations, steel works, and in manufacturing industries.

Small amounts of lead are generated from burning oil, which also
has a very broad range of lead concentrations. The average
concentrations in oil appear to be below 0.5 mg/kg (Davis, 1973). The
possible future use of sewage sludge as fertilizer is discussed in
section 4.

4. ENVIRONMENTAL TRANSPORT AND DISTRIBUTION

From a mass-balance point of view, the transport and distribution
of lead from stationary or mobile sources into other environmental
media is mainly through the atmosphere. Large discharges may also
occur directly into natural waters and on to the land but, in such
cases, lead tends to localize near the points of discharge owing to
the very low solubility of the compounds that are formed upon contact
with soil and water. The mass transfer of lead from air to other media
is as yet poorly defined and the various mechanisms involved in the
removal of lead from air are not fully understood. Although some data
indicate that an important proportion of the lead may be removed
through sedimentation (Atkins, 1969) the most efficient clearing
mechanism is probably rain (Ter Haar et al., 1967). In a study of the
concentration of lead in rainfall at 32 stations in the United States
of America the average was 34 µg/litre (Lazrus et al., 1970). Most of
these data were collected in areas with a high population density.
Over rural areas of the USA the concentration was found to be
approximately 18 µg/litre (Ter Haar et al., 1967).

Lead is rapidly removed from water when it passes through soil and
bottom sediments. This is due to the high capacity of organic matters
to bind the lead firmly. Because of this clearing mechanism, lead
concentrations in both natural waters and water supplies are generally
low (section 5.1.2).

Table 6. Distribution of lead from motor vehicles in the Los
Angeles basin^a

Environmental area Fractional
fallout

Retained in car 0.25
Near fallout 0.40
Far fallout 0.08
Airborne 0.24
Unaccounted for 0.03

^a Adapted from Huntzicker et al., 1975.

An attempt was made to account for the lead emitted by automobiles
in the Los Angeles Basin (Huntzicker et al., 1975) which is an area of
exceptionally dense motor traffic. Limited environmental monitoring
data tended to confirm the approximate correctness of the
calculations. The transport pattern was classified as "near fallout",
"far fallout" and "airborne". "Near fallout" was defined as the
deposition in the immediate vicinity of roadways. "Far fallout" was

defined as the fallout away from roadways, but within the basin, and
"airborne" designated small particles carried away from the basin and
ultimately deposited elsewhere. The data are shown in Table 6 and
indicate that most of the emission was deposited within the basin. The
fallout figures are calculated from the estimated behaviour of the
airborne particles based on particle size distribution. If these
results are approximately valid for other metropolitan areas, soil and
water pollution from automobile emission fallout is predominantly
limited to the immediate metropolitan area. The particles carried away
from the area by air transport are probably widely dispersed and
diluted since the atmospheric retention time of small particles is
probably fairly long. It has been estimated that the residence time of
airborne particles ranges from 6 days to 2 weeks in the lower
troposphere and from 2 to 4 weeks in the upper troposphere (SCEP,
1970). Residence time will vary with a number of factors such as wind
currents and rainfall. Yamamoto et al. (1968) demonstrated that
atmospheric turbidity varied inversely with rainfall, owing to the
washout effect of rain.

In spite of the great dilution of airborne lead that occurs during
transport from centres of human activity, there is evidence indicating
that a long-term global accumulation of lead has occurred. This long-
term accumulation has been studied in glacial ice and snow deposits.
Studies in Greenland showed that ice formed in about 1750 had lead
concentrations 25 times greater than ice estimated to have been formed
in about 800 B.C. From 1750, the concentration increased steadily to
about 1940. From 1940 to the present day, the rate of increase has
risen even more sharply. The most recent ice layers examined (about
1968) had a concentration 400 times greater than the natural
background. Similar studies in the region of the Antarctic have also
shown a rise, but it has not been so dramatic (Murozumi et al., 1969).
Jaworowski (1968) conducted studies of Polish glaciers similar to
those conducted in Greenland. He observed an approximate 16-fold
increase in the lead concentration over the past 100 years.
Chronological increases in the lead content of Swedish mosses have
also been reported from 1860 to 1968 (Ruhling & Tyler, 1968). These
increases, about 4-fold in the past hundred years, were thought to
reflect first the increase in coal combustion and later the
introduction of leaded gasoline.

The transfer of air lead to the biota may be direct or indirect.
For plants, the fallout contribution may be direct via the above
ground parts, or it may be indirect by way of the soil. The pattern
and degree of lead accumulation appears to be substantially influenced
by the state of growth. Mitchell & Reith (1966) found that the lead
content of certain plants increased 10-fold or more from the period of
active growth to the time when growth ceased in the late fall. Some
trees apparently have the capacity to accumulate high concentrations
of lead. Kennedy (1960) reported that the tips of larches, firs, and
white pines contained 100 mg of lead per kg dry weight, when grown in

the lead mining areas of Idaho where the soil lead concentration was
20 000 mg/kg. The total concentration of lead in soil does not
correlate well with the concentration in the plant but a correlation
does exist when adjustment is made for the degree to which the soil
lead can be brought into an aqueous solution of ammonium lactate and
acetic acid (Kerin et al., 1972).

Thus, there is no doubt that plants acquire lead from the soil and
air, but interspecies differences are prominent (Dedolph et al.,
1970). It does not seem likely, however, that lead deposited on the
leaves of plants transfers readily to other parts. Thus, Ter Haar
(1970) showed in greenhouse studies that atmospheric lead at
1.45 µg/m³ did not influence the lead content of tomatoes, beans,
carrots, potatoes, wheat, and cabbage heads, but did have an effect on
the lead content of lettuce and bean leaves.

Transfer of lead from plants to animals is not well-defined.
However, the concentration of lead in meat and eggs is quite similar,
on a wet weight basis, to the concentration found in vegetables and
grains (Schroeder et al., 1961). There is no evidence of biological
accumulation proceeding from plants to animals.

Much remains to be learned about the environmental transport and
distribution of lead. The potential pathways of lead from air to man
are indicated in Fig. 1. Special attention should be given to the
potential transfer of the fallout lead in cities that is washed into
the sewage systems. Sewage sludge is currently being considered for
use as fertilizer. Most cities have dual sewage system, i.e., storm
and sanitary sewers, and it was shown in the report of the US
Environmental Protection Agency Office of Research and Monitoring
(1972) that storm runoff is far from being clean and probably warrants
being treated in many instances. However, lead is not currently viewed
as a hazard in this case because sludges have a high phosphate content
which tends to minimize the bio-availability of the lead for plants
(Chaney, 1973).

Little information exists with regard to the biotransformation of
lead by microorganisms in the environment. However, Wong and his
collaborators (1975) have reported that microorganisms in lake
sediments can transform certain inorganic and organic lead compounds
into volatile tetramethyllead. The authors were not able to explain
completely the pathways of this transformation. A possible mechanism
for the conversion of trimethyllead acetate into tetramethyllead in
anaerobic systems was presented by Jarvie et al. (1975), who proposed
that this takes place through the formation of an intermediate sulfide
which decomposes into tetramethyllead. There is need for further
research along these lines.

5. ENVIRONMENTAL LEVELS AND EXPOSURES

In the preceding chapter the general pattern of the environmental
transport and distribution of lead was described. This chapter is more
specifically concerned with the different circumstances under which
people are exposed to lead to a degree that may be hazardous to their
health.

5.1 Exposure of the General Population

The general population is exposed to lead by ingestion of food,
and water, and by inhalation. In addition, children are exposed by
eating non-food items, and those working in the lead industries suffer
exposure over and above their exposure as members of the general
population. These categories of exposure will be considered
separately.

5.1.1 Air

The highest concentrations of lead in ambient air are found in
dense population centres. The larger the city, the higher the ambient
air lead concentration. As one moves away from the centre of the city,
the concentration falls progressively. For urban stations, an average
concentration of 1.1 µg/m³ has been reported; for non-urban stations
(near the city) the average was 0.21 µg/m³; for stations somewhat
farther removed it was 0.10 µg/m³, and for remote areas,
0.02 µg/m³ (McMullen et al., 1970). Air over streets with heavy
traffic contained more lead than air over streets with light traffic,
and considerably more than the ambient air over rural areas.

There is a clear pattern in this picture, the non-urban sites
showing less than 0.5 µg/m³, while the urban sites have values
ranging from 1 to 5-10 µg/m³. The highest levels have been recorded
on highways during rush hours, 14-25 µg/m³ (WHO Expert Committee,
1969).

The results of continuous monitoring for 1971-72, in 27 European
cities, by 43 uniform sampling stations are summarized in Table 7
(Commission of European Communities, 1973).

The ambient air lead levels at 15 national sampling stations in
Japan in 1973 were 0.30 µg/m³ for the average 24-hour value,
2.72 µg/m³ for the maximum 24-hour value, and 0.01 µg/m³ for the
minimum (Environment Agency, Japan, 1975).

Table 7. Air lead concentrations in some cities of the European Community (1971-72)^a

Location Continuous measurements Traffic-hour measurements

Non-urban monthly averages < 0.5 µg/m³ -
daily maxima < 1 µg/m³ -

Small cities
residential areas monthly averages < 1 µg/m³ -
daily maxima < 2 µg/m³
traffic areas - monthly averages < 3 µg/m³
individual measurements < 8 µg/m³

Metropolitan areas
residential areas monthly averages < 2 µg/m³ individual measurements < 4 µg/m³
daily averages
up to 8 µg/m³
traffic areas monthly averages monthly averages < 10 µg/m³