Health and Safety Guide No. 61






    This is a companion volume to Environmental Health Criteria 129:

    Published by the World Health Organization for the International
    Programme on Chemical Safety (a collaborative programme of the United
    Nations Environment Programme, the International Labour Organisation,
    and the World Health Organization)

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

    WHO Library Cataloguing in Publication Data

    Isobenzan : health and safety guide.

    (Health and safety guide ; no. 61)

    1. Insecticides, Organochlorine - standards
    2. Insecticides, Organochlorine - toxicity
    3. Hazardous substances   I. Series

    ISBN 92 4 151061 7          (NLM Classification: WA 240)
    ISSN 0259-7268

    (c) World Health Organization 1991

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    welcomes such applications.

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

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



         1.1. Identity
         1.2. Physical and chemical properties
         1.3. Analytical methods
         1.4. Production and uses



         4.1. Main human health hazards, prevention and protection,
              first aid
              4.1.1. Symptoms of poisoning
              4.1.2. Medical advice
              4.1.3. Health surveillance advice
         4.2. Explosion and fire hazards
              4.2.1. Explosion hazard
              4.2.2. Fire hazard
         4.3. Storage
         4.4. Transport
         4.5. Spillage and disposal
              4.5.1. Spillage
              4.5.2. Disposal


         6.1. Previous evaluations by international bodies
         6.2. Exposure limit values
         6.3. Specific restrictions
         6.4. Labelling, packaging, and transport
         6.5. Waste disposal
         6.6. Other measures



    The Environmental Health Criteria (EHC) documents produced by the
    International Programme on Chemical Safety include an assessment of
    the effects on the environment and on human health of exposure to a
    chemical or combination of chemicals, or physical or biological
    agents.  They also provide guidelines for setting exposure limits.

    The purpose of a Health and Safety Guide is to facilitate the
    application of these guidelines in national chemical safety
    programmes. The first three sections of a Health and Safety Guide
    highlight the relevant technical information in the corresponding EHC. 
    Section 4 includes advice on preventive and protective measures and
    emergency action; health workers should be thoroughly  familiar with
    the medical information to ensure that they can act efficiently in an
    emergency.  Within the Guide is a Summary of Chemical Safety
    Information which should be readily available, and should be clearly
    explained, to all who could come into contact with the chemical.  The
    section on regulatory information has been extracted from the legal
    file of the International Register of Potentially Toxic Chemicals
    (IRPTC) and from other United Nations sources.

    The target readership includes occupational health services, those in
    ministries, governmental agencies, industry, and trade unions who are
    involved in the safe use of chemicals and the avoidance of
    environmental health hazards, and those wanting more information on
    this topic.  An attempt has been made to use only terms that will be
    familiar to the intended user.  However, sections 1 and 2 inevitably
    contain some technical terms.  A bibliography has been included for
    readers who require further background information.

    Revision of the information in this Guide will take place in due
    course, and the eventual aim is to use standardized terminology. 
    Comments on any difficulties encountered in using the Guide would be
    very helpful and should be addressed to:

    The Manager
    International Programme on Chemical Safety
    Division of Environmental Health
    World Health Organization
    1211 Geneva 27



    1.1  Identity

    Common name:             Isobenzan

    Molecular formula:       C9H4Cl8O

    Chemical structure:


    Chemical names:          1,3,4,5,6,7,8,8-octachloro-4,7-methylene-

                             hydro-4,7-endomethylene-naphthalene (IUPAC)

    Developmental codes:     BAS-4402; CP 14957; ENT-25545; OMS-206;
                             OMS-618; SD-4402, WL 1650

    Trade names:             Telodrin (technical product), Omtan

    Purity (technical):      not less than 95% (w/w)

    CAS registry number:     297-78-9

    Conversion factors:      1 ppm = 17 mg/m3 at 20C
                             1 mg/m3 = 0.06 ppm at 20C

    RTECS registry number:   PC1225000

    1.2  Physical and Chemical Properties

    Isobenzan is a whitish to light-brown crystalline powder, with a mild
    chemical odour.  It is relatively stable to acids, but liable to
    dehydrochlorination under strongly alkaline conditions.

    Some physical properties of isobenzan are given in Table 1.

    Table 1. Physical properties


    Relative molecular mass     411.73
    Melting point (C)          120-122
    Flash-point                 non-flammable
    Explosion limits            non-explosive
    Specific gravity            1.87
    Vapour pressure (20C)      6.7 x 10-4 Pa (5 x 10-6 mmHg)
    Solubility in water         practically insoluble

    Solubility in organic solvents: slightly soluble in kerosene and
    ethanol; soluble in acetone, benzene, toluene, xylene, heavy aromatic
    naphtha, and ethyl ether.

    1.3  Analytical Methods

    The method of choice is gas-liquid chromatography with
    electron-capture detection.

    1.4  Production and Uses

    Isobenzan is a broad spectrum contact and stomach insecticide, which
    was manufactured from 1958 to 1965 and was used throughout the world. 
    Its agricultural use was restricted, because of its persistence and


    As far as is known, isobenzan, an organochlorine insecticide, was only
    manufactured during the period 1958-65.  Existing stocks were used for
    several years after this.  At present, the only major sources of
    exposure are believed to be the original waste-disposal sites of
    industrial wastes, and dredgings from contaminated sediments.

    Following the application of isobenzan to the soil, a rapid initial
    loss occurs, after which the remaining compound decays at a much
    slower rate.  Isobenzan persists in the soil from 2 to 7 years,
    depending on the type of soil.  Under laboratory conditions, isobenzan
    decomposes in surface water within a few weeks, when exposed to
    natural and artificial light.

    Soil, ground water, and surface water from polders built up using
    sediment contaminated with organochlorines, including chlorinated
    cyclodiene compounds, still contained minor residues of isobenzan some
    years later.  Sediments of rivers in the Netherlands did not contain
    any detectable isobenzan (less than 0.01 mg/kg dry weight).  Crop
    residues, resulting from soil treatment, are usually low (below
    0.05 mg/kg crop), but higher levels may be found in some root crops
    (up to 0.2 mg/kg in carrots).  No residues were detected (less than
    0.01 mg/kg) in food items analysed in market surveys that were carried
    out when isobenzan was being used in agriculture.

    When domestic animals were introduced to pastures treated with
    isobenzan, the dairy products contained residues of the compound.  Two
    samples of butter contained 0.07-0.15 mg isobenzan/kg product.  In
    milk, the levels were 0.005-0.07 mg/kg (whole milk).  Dried milk
    contained only 0.005 mg/kg.  Up to 50% of the residue was lost during
    the processing of dairy products, depending on the type of treatment.

    No data were available on the levels of isobenzan in the blood and
    adipose tissue of the general population.  Operators of manufacturing
    and formulation plants exposed to isobenzan had mean whole blood
    levels of isobenzan of up to 0.041 mg/litre.  In whole blood samples
    from people living in the neighbourhood of one plant, the
    concentration of isobenzan was below the limit of detection of
    0.001 mg/litre.

    Isobenzan is well absorbed through the gastrointestinal wall.  It is
    transported in the blood as the unchanged compound.  Hydrophilic
    metabolites are formed, one of which has been identified as isobenzan
    lactone.  Isobenzan accumulates in the tissues and organs of rats and
    dogs in the following order: fat > liver = muscle > brain > blood. 
    In general, the concentrations are higher in the tissues of female
    rats than in those of male rats, especially in the body fat.  The
    biological half-life in the body fat was 10.9 days in male rats and
    16.6 days in female rats.  A female dog pup that had fed only on its
    mother's milk (containing 0.7 mg/litre of whole milk) showed

    convulsions 15 days after birth.  The blood of the pup contained
    0.09 mg/litre.  These effects in the pup were also seen in a rat
    reproduction study.  Isobenzan is excreted via the milk of cows.

    Mosquito larvae and soil fungi metabolize isobenzan in the same way as
    vertebrates, yielding isobenzan-lactone.

    Isobenzan is very persistent in the environment and bioaccumulates. 
    It is highly toxic for fish, shrimps, and birds.  In the Netherlands,
    the country where isobenzan was produced, residues in the eggs of
    terns living along the Dutch coast ranged up to 0.45 mg/kg (mean,
    0.09 mg/kg); mean residues in mussels and fish were 0.05 mg/kg in
    1965.  Earthworm numbers were reduced in field plots treated with
    isobenzan at 2 kg/ha.  Nitrification was reduced, with a consequent
    increase in inorganic nitrogen, in soils treated with isobenzan in the
    field at 1 kg/ha; laboratory studies did not show any effects on
    nitrification at doses equivalent to 250 g/ha.

    The acute toxicity of isobenzan is high in mammals exposed via the
    oral or percutaneous route.  The mode of action is an overstimulation
    of the central nervous system, resulting in convulsions.  The acute
    toxicity of formulations of isobenzan varies according to the
    percentage of active ingredient present.

    Isobenzan is not a skin irritant, but some formulations may cause

    Limited short- and long-term oral studies on mice, rats, and dogs have
    been carried out.  Isobenzan may cause histological changes in the
    liver of the classical type associated with organochlorine
    intoxication.  In a long-term rat study, a no-observed-effect level
    (NOEL) of 5 mg/kg diet (ca 0.25 mg/kg body weight) was found.  In a
    2-year study on dogs, a NOEL of 0.025 mg/kg body weight was

    A one-generation reproduction study on rats indicated a NOEL of
    0.1 mg/kg diet (ca 0.005 mg/kg body weight).  A higher dose level of
    1 mg/kg diet (ca 0.05 mg/kg body weight) decreased survival of pups.

    No teratogenicity or mutagenicity studies have been reported.

    No carcinogenic potential was demonstrated in a 2-year oral study on
    rats and an oral study on mice; both these studies were inadequate for
    the evaluation of carcinogenicity.

    The toxicological data base for isobenzan is incomplete. The Task
    Group considered that the quality of the data was generally poor, by
    today's standards, and that the data were inadequate to make an
    evaluation of the hazards of isobenzan for human health or for the

    Data on exposed human beings are limited to observations on workers in
    a factory in the Netherlands during the manufacture and formulation of
    isobenzan and related "drins".  No cases of skin irritation were
    reported. Convulsions occurred in several cases of intoxication, but
    the changes in the EEG pattern were reversible.  The intoxication
    threshold level (for convulsions) was estimated to be 0.015 mg
    isobenzan/litre blood.  The biological half-life of isobenzan in human
    blood was estimated to be of the order of 2.8 years.


    Isobenzan is highly toxic and very persistent.  The available
    information on the hazards of isobenzan is incomplete.  However,
    available data are sufficient to indicate that the hazards posed to
    those handling isobenzan, and to the environment, are such that any
    human or environmental exposure to this substance, either as an
    insecticide or for any other purpose, should not be allowed.


    4.1  Main Human Health Hazards, Prevention and Protection, First Aid

    Isobenzan is an organochlorine insecticide.  It is highly toxic (rat
    oral LD50: 5-10 mg/kg) and can be very hazardous for human beings if
    incorrectly or carelessly handled.  It is therefore essential that the
    correct precautions should be observed in its handling and use.

    The human health hazards of isobenzan exposure, together with
    preventive and protective measures and first aid, are listed in
    Table 2.

    4.1.1  Symptoms of poisoning

    Isobenzan is readily absorbed by mouth, by skin contact (especially
    liquid formulations), and by inhalation (especially dust or mist).  It
    acts as a stimulant of the central nervous system.  It is eliminated
    from the body very slowly.

    Following accidental ingestion or gross overexposure, symptoms may
    include headache, dizziness, nausea, vomiting, weakness in legs, and

    Respiratory depression may lead to metabolic acidosis and, if
    necessary, blood gases should be checked.  The use of an ECG monitor
    is recommended, if the symptoms are severe.

    4.1.2  Medical advice

    Medical treatment is largely symptomatic and supportive, and directed
    against convulsions and hypoxia.

    If isobenzan is swallowed, the stomach should be emptied as soon as
    possible by careful gastric lavage (with a cuffed endotracheal tube
    already in place), avoiding aspiration into the lungs.  In a rural
    situation, where this is not feasible, and if the victim is conscious,
    vomiting should be induced immediately.  This should be followed by
    intragastric administration of 50 g of activated charcoal and 30 g
    magnesium or sodium sulfate in a 30% aqueous solution.  Oily
    purgatives are contraindicated.  No fats, oils, or milk should be



    HAZARDS/SYMPTOMS                        PREVENTION AND PROTECTION                    FIRST AID

    SKIN: may cause poisoning in            Avoid contact with skin; wear                After contact with skin, wash immediately
    contact with skin                       suitable impervious protective               with plenty of water and soap; remove all
                                            clothing and gloves                          contaminated clothing immediately, and 
                                                                                         launder separately before re-use

    EYES: may cause irritation to           Avoid contact with eyes; wear                In case of contact with eyes, rinse 
    eyes                                    eye protection                               immediately with plenty of water and seek
                                                                                         medical advice

    INHALATION: dusts may cause             Wear appropriate dust mask or
    poisoning by inhalation                 respirator

    INGESTION: unlikely occupational        Do not eat, drink, or smoke during
    hazard                                  work; wash hands before eating,
                                            drinking, or smoking

    Accidental or intentional ingestion                                                  If swallowed, seek medical advice
    may cause poisoning                                                                  immediately and show container or label;
                                                                                         keep at rest, and ensure a clear airway;
                                                                                         if, in a rural situation, gastric lavage is
                                                                                         not possible, and the victim is
                                                                                         conscious, induce vomiting

        If convulsions occur, anti-convulsants should be given immediately,
    e.g., 10 mg of diazepam, slowly, intravenously (children 1-5 mg),
    repeated as necessary; or thiopental sodium or hexobarbital sodium
    slowly, intravenously, in a dose of 10 mg/kg with a maximum total dose
    of up to 750 mg for an adult, or paraldehyde 5 ml by intramuscular
    injection.  These short-acting anticonvulsants should always be
    followed by phenobarbital given orally at 3 mg/kg (up to 200 mg for an
    adult), or phenobarbital sodium given intramuscularly at 3 mg/kg (also
    up to 200 mg for an adult).

    Morphine and its derivatives, adrenaline, and noradrenaline should
    never be given.

    An unobstructed airway must be maintained.  Respiratory inadequacy,
    which may be accentuated by barbiturate anticonvulsants, should be
    corrected; oxygen and/or artificial ventilation may be needed.

    4.1.3  Health surveillance advice

    A complete medical history and physical examination of regularly
    exposed workers should be made, on an annual basis.

    4.2  Explosion and Fire Hazards

    4.2.1  Explosion hazard

    The explosion hazard will depend on the solvent used in the
    formulation, or on the characteristics of the dust.

    4.2.2  Fire hazard

    Liquid formulations containing organic solvents may be flammable. 
    Extinguish fires with alcohol-resistant foam, carbon dioxide, or
    powder.  With sufficient burning or external heat, isobenzan will
    decompose, emitting toxic fumes.  Fire-fighters should be equipped
    with self-contained breathing apparatus, eye protection, and full
    protective clothing.

    The use of water spray should be confined to the cooling of unaffected
    containers, thus avoiding the accumulation of polluted run-off from
    the site.

    4.3  Storage

    Products should be stored in locked buildings, preferably dedicated to
    insecticides, and in compliance with labelling recommendations.

    Keep the products out of reach of children and unauthorized personnel. 
    Do not store near foodstuffs or animal feed.

    4.4  Transport

    Comply with any national or local requirements regarding movement of
    hazardous goods or wastes.  Do not transport in the same compartment
    as foodstuffs or animal feed.  Check that containers are sound, and
    labels undamaged, before dispatch.

    4.5  Spillage and Disposal

    4.5.1  Spillage

    Before dealing with any spillage, precautions should be taken as
    required, and appropriate personal protection should be used
    (Table 2).  Empty any product remaining in a damaged or leaking
    container into a clean empty drum, which should then be tightly closed
    and suitably labelled.

    Prevent liquid from spreading or contaminating other cargo and
    vegetation, and avoid pollution of surface waters and ground water by
    using the most suitable available material, e.g., earth or sand.

    After emptying, leaking containers should be rinsed with at least
    1 litre water per 20-litre drum.  Swirl round to rinse the walls of
    the container, empty, and add the rinsings to the sawdust or earth. 
    Puncture or crush the container to prevent re-use.

    As soon as possible after the spillage, and before re-use, cover all
    contaminated areas with damp sawdust, sand, or earth.  Sweep up and
    place in a closeable container for later transfer to a safe place for

    4.5.2  Disposal

    Any surplus product, contaminated absorbents, and containers should be
    disposed of in an appropriate way.  Waste material should be burned in
    a proper incinerator designed for organochlorine waste disposal, with
    effluent gas scrubbing.  If this is not possible, bury in an approved
    dump or landfill where there is no risk of contamination of surface or
    ground water.  Comply with any local requirements regarding disposal
    of toxic wastes.  Puncture or crush container to prevent re-use.


    Isobenzan is very persistent in the environment and in biota.  It is
    highly toxic for aquatic and terrestrial organisms.

    Discharges from the manufacture, formulation, or use of isobenzan, and
    any spillage or unused product, must be prevented from spreading to
    vegetation or waterways, and must be treated and disposed of properly
    (section 4.5.2).


    The information given in this section has been extracted from the
    International Register of Potentially Toxic Chemicals (IRPTC) legal
    file and other United Nations sources.  Its intention is to give the
    reader a representative, but not an exhaustive, overview of current
    regulations, guidelines, and standards.

    The reader should be aware that regulatory decisions about chemicals,
    taken in a certain country, can only be fully understood in the
    framework of the legislation of that country.  Furthermore, the
    regulations and guidelines of all countries are subject to change and
    should always be verified with the appropriate regulatory authorities
    before application.

    6.1  Previous Evaluations by International Bodies

    Not available.

    6.2  Exposure Limit Values

    No data available.

    6.3  Specific Restrictions

    In the Federal Republic of Germany, isobenzan has been prohibited for
    use as a plant protectant.  It has not been registered as a pesticide
    in, among others, Canada, the Netherlands, Sweden, the United Kingdom,
    and the USA (where it had previous approval for use on alfalfa, corn,
    and tobacco).

    6.4  Labelling, Packaging, and Transport

    The United Nations Committee of Experts on the Transportation of
    Dangerous Goods classifies isobenzan in:

    Hazard Class 6.1:        poisonous substance;

    Packing Group I:         substances and preparations presenting a very
                             severe risk of poisoning, when the content of
                             active ingredient is 10-100%;

    Packing Group II:        substances and preparations presenting a
                             serious risk of poisoning, when the content
                             of active ingredient is 2-10%;

    Packing Group III:       substance presenting a relatively low risk of
                             poisoning in transport, when the content of
                             active ingredient is 0.4-2%.

    The labels should be as follows:

    FIGURE 1

    FIGURE 2

    The European Economic Community legislation requires labelling as a
    dangerous substance using the symbol:

    FIGURE 3

    The label must read:

          Very toxic by inhalation, in contact with skin and if swallowed;
          irritating to eyes and skin; keep locked up; keep away from
          food, drink and animal feeding stuffs; if you feel unwell, seek
          medical advice (show the label where possible).

    The European Economic Community legislation on the labelling of
    pesticide preparations classifies isobenzan in Class 1A for the
    purpose of determining the label for preparations containing isobenzan
    and other active ingredients.

    6.5  Waste Disposal

    No information is available.

    6.6  Other Measures

    The European Economic Community legislation concerning the major
    accident hazards of certain industrial activities foresees that the
    manufacturer must take all necessary measures to prevent accidents and
    to limit their consequences for man and the environment, when
    processing isobenzan in quantities equal to or over 100 kg. 
    Notification must be made to the competent authorities, giving
    information on the substance, the installation, information on
    possible major accident situations, and emergency plans.


    FAO (1985a)  Guidelines for the packaging and storage of pesticides.
    Rome, Food and Agriculture Organization of the United Nations.

    FAO (1985b)   Guidelines for the disposal of waste pesticides and
     pesticide containers on the farm. Rome, Food and Agriculture
    Organization of the United Nations.

    FAO (1985c)   Guidelines on good labelling practice. Rome, Food and
    Agriculture Organization of the United Nations.

    GIFAP (1982)   Guidelines for the safe handling of pesticides during
     their formulation, packing, storage and transport. Brussels,
    Groupement International des Associations Nationales des Fabricants de
    Produits Agrochimiques.

    GIFAP (1983)   Guidelines for the safe and effective use of
     pesticides. Brussels, Groupement International des Associations
    Nationales des Fabricants de Produits Agrochimiques.

    GIFAP (1984)  Guidelines for emergency measures in cases of pesticide
     poisoning. Brussels, Groupement International des Associations
    Nationales des Fabricants de Produits Agrochimiques.

    IARC (1972-present)  IARC monographs on the evaluation of carcinogenic
     risk of chemicals to man. Lyon, International Agency for Research on

    IRPTC (1985)  IRPTC file on treatment and disposal methods for waste
     chemicals. Geneva, International Register of Potentially Toxic
    Chemicals, United Nations Environment Programme.

    IRPTC (1987)   IRPTC legal file 1986. Geneva, International Register
    of Potentially Toxic Chemicals, United Nations Environment Programme.

    PLESTINA, R. (1984)   Prevention, diagnosis, and treatment of
     insecticide poisoning. Geneva, World Health Organization
    (unpublished document VBC/84.889).

    SAX, N.I. (1984)   Dangerous properties of industrial materials. New
    York, Van Nostrand Reinhold Company, Inc.

    UNEP/IEO (1990)   Storage of hazardous materials: a technical guide
     for safe warehousing of hazardous materials. United Nations
    Environment Programme, Industry and Environment Office, Paris. 80 pp.

    UNITED NATIONS (1984)   Consolidated list of products whose
     consumption and/or sale have been banned, withdrawn, severely
     restricted or not approved by governments. 1st ed. revised, New
    York, United Nations.

    UNITED NATIONS (1986)   Recommendations on the transport of dangerous
     goods. 4th ed. New York, United Nations.

    US NIOSH/OSHA (1981)   Occupational health guidelines for chemical
     hazards. 3 Vol., Washington, DC, US Department of Health and Human
    Services, US Department of Labor (Publication No. DHHS(NIOSH) 01-123).

    WHO (1990)   The WHO recommended classification of pesticides by
     hazard and guidelines to classification 1990-91. Geneva, World
    Health Organization (unpublished document WHO/PCS/90.1).

    WHO (in press)   Environmental Health Criteria 129: Isobenzan.
    Geneva, World Health Organization.

    WORTHING, C.R. & WALKER, S.B. (1987)   The  pesticide  manual. 8th
    ed. Lavenham, Lavenham Press Limited, British Crop Protection Council.


    See Also:
       Toxicological Abbreviations
       Isobenzan (EHC 129, 1991)