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    IPCS INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
    Health and Safety Guide No. 97

    METHOMYL
    HEALTH AND SAFETY GUIDE






    UNITED NATIONS ENVIRONMENT PROGRAMME

    INTERNATIONAL LABOUR ORGANISATION

    WORLD HEALTH ORGANIZATION




    WORLD HEALTH ORGANIZATION, GENEVA 1995

    This is a companion volume to Environmental Health Criteria 178:
    Methomyl

    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

    Health and safety guide for Methomyl

         (Health and safety guide ; no. 97)

    1.Methomyl - toxicity    2.Insecticides - Carbamate

    3.Environmental exposure    I.Series

    ISBN 92 4 151097 8   (NLM Classification: WA 240)
    ISSN 0259-7268

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

    (c) World Health Organization 1995

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

    The designations employed and the presentation of the material in this
    publication do not imply the 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
    boundaries.

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

    CONTENTS

    INTRODUCTION

    1. PRODUCT IDENTITY AND USES
        1.1. Identity
              1.1.1. Primary constituent
              1.1.2. Technical product
        1.2. Physical and chemical properties
        1.3. Analytical methods
        1.4. Production and uses

    2. SUMMARY AND EVALUATION
        2.1. Exposure
        2.2. Uptake, metabolism, and excretion
        2.3. Effects on non-target organisms in the environment
        2.4. Effects on experimental animals and  in vitro
              test systems
        2.5. Effects on human beings

    3. CONCLUSIONS AND RECOMMENDATIONS
        3.1. Conclusions
        3.2. Recommendations

    4. HUMAN HEALTH HAZARDS, PREVENTION AND PROTECTION, EMERGENCY
        ACTION
        4.1. Main human health hazards, prevention and
              protection, first aid
        4.2. Advice to physicians
              4.2.1. Symptoms of poisoning
              4.2.2. Medical treatment
              4.2.3. Health surveillance advice
        4.3. Explosion and fire and hazards
        4.4. Storage
        4.5. Transport
        4.6. Spillage and disposal
              4.6.1. Spillage
              4.6.2. Disposal

    5. HAZARDS FOR THE ENVIRONMENT AND THEIR PREVENTION

    6. CURRENT REGULATIONS, GUIDELINES, AND STANDARDS
        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

    BIBLIOGRAPHY
    

    INTRODUCTION

    The Environmental Health Criteria (EHC) monographs 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 Director
    International Programme on Chemical Safety
    World Health Organization
    1211 Geneva 27
    Switzerland

    THE INFORMATION IN THIS GUIDE SHOULD BE CONSIDERED AS A STARTING POINT
    TO A COMPREHENSIVE HEALTH AND SAFETY PROGRAMME

    1. PRODUCT IDENTITY AND USES

    1.1  Identity

    1.1.1  Primary constituent

    Common name (ISO):       methomyl

    Chemical structure:

                                       O
                                       "
                                       "
                             CH3-C=N-O-C-NH-CH3
                                 '
                                 '
                                 S - CH3

    Molecular formula:       C5H10N2O2S

    Relative molecular
     mass:                   162.2

    IUPAC chemical name:      S-methyl- N-(methylcarbamoyloxy)
                             thioacetimidate

    CAS chemical name:       methyl  N-[[(methylamino)
                             carbonyl]oxy]ethanimido-thioate

    CAS registry number:     16752-77-5

    RTECS number:            AK2975000

    Synonyms:                metomil, mesomil, OMS 1196

    1.1.2  Technical product

    Major trade names:       Flytek, Golden Fly Bait, Lannate, Methomex,
                             Nudrin, Pillarmate

    Purity:                  >98% w/w

    Impurities:               S-methyl- N-hydroxy-thioacetimidate (0.2%)
                             1,3-dimethylurea (0.4%)

    1.2  Physical and Chemical Properties

    Methomyl is a white crystalline solid with a melting point of 77C. It
    is soluble in water and in many organic solvents. It is stable at
    temperatures up to 140C; the autoignition temperature is 265C.
    Methomyl is stable in sterile distilled water at pH values of 5-7 but
    decomposes increasingly with higher pH and temperature levels. Its
    half-life in water at pH 9 is 30 days.

    Some physical properties of methomyl are listed in Table 1.

                                                               

    Table 1.  Physical properties of methomyl
                                                               

    Physical state                   crystalline solid

    Colour                           white

    Odour                            slight sulfurous

    Melting point                    77C

    Vapour pressure (at 25C)        6.65 mPa

    Henry's Law constant             2.1  10-11 atm-m3/mole

    Octanol-water partition
     coefficient (Kow)               1.24

    Solubility:

      water                          54.7 g/litre
      toluene                        30 g/litre
      isopropanol                    220 g/litre
      ethanol                        420 g/litre
      acetone                        720 g/litre
      methanol                       1000 g/litre
                                                               

    1.3  Analytical Methods

    The principal analytical procedure for the determination of methomyl
    residues in foods, crops, and environmental solid media consists of
    extraction with an organic solvent followed by solvent partition and
    then, usually, a column cleanup. Water samples are mainly submitted
    directly to solid phase extraction. The cleaned up samples are
    analysed using HPLC or GLC methods, in some cases, after conversion to
    the oxime derivative.

    Methomyl as technical material and in formulations can be determined
    by reverse phase HPLC followed by UV analysis.

    1.4  Production and Uses

    Methomyl is a monomethyl carbamate insecticide that has been in use
    since 1966. It is used in many countries to control insects on fruit,
    vines, hops, vegetables, grain, soyabeans, cotton, and ornamentals.
    Methomyl is mainly formulated as water-soluble powders and
    water-miscible liquids. These products are diluted with water and
    applied using ground or aerial spraying equipment. Typical application
    rates are 0.15-1.0 kg active ingredient per hectare.

    2.  SUMMARY AND EVALUATION

    2.1  Exposure

    Methomyl is photolysed rapidly in water with a half-life of 2-3 days.
    It is broken down rapidly in the aquatic environment; analysis of
    various water sources in the vicinity of methomyl applications has
    shown non-detectable (<0.02 mg/kg) or very low concentrations of the
    compound.

    When applied in the field, methomyl is not very mobile in the soil and
    remains mostly in the top 15-cm layer. Under these conditions, it is
    broken down rapidly with a half-life of 11-30 days. Carbon dioxide is
    an end product of the degradation. Very low levels of methomyl may be
    found in the soil after aerial or ground application to crops at
    recommended rates.

    Methomyl has a low octanol:water partition coefficient and has shown
    no evidence for bioaccumulation in fish. It is not likely to
    accumulate in the environment.

    After its application to crops, methomyl is broken down on plant
    foliage to give carbon dioxide and acetonitrile. The remaining residue
    is incorporated into natural plant components, such as Krebs cycle
    acids and sugars. Methomyl's half-life on growing foliage is 1-7 days.
    Any remaining residue is composed mainly of methomyl itself, which may
    be present in low concentrations in food crops at harvesting. These
    residues may be reduced further during transport, storage, and
    processing. Total diet and individual food analyses show undetectable
    or very low methomyl residues. Thus, exposure of the general
    population to methomyl is expected to be very low.

    After re-entry into treated vineyards, the areas of workers' bodies
    that received the highest exposure to dislodgeable foliar residues of
    methomyl were the upper body and head, during grape girdling and
    the upper body and hands, during raisin harvesting. Inhalation
    exposure was minimal. One day after methomyl application to cucumbers
    and tomatoes in green-houses, the ambient air concentration was
    4.7 g/m3. Hand wash sampling was considered to be the most reliable
    indicator of operator exposure in these circumstances.

    2.2  Uptake, Metabolism, and Excretion

    Methomyl is absorbed very rapidly after oral administration to rats.
    Distribution to tissues and the excretion of breakdown products also
    occur very rapidly. The main excretory routes are expired air (as
    carbon dioxide and acetonitrile in the ratio 2:1), 34% in 5 days, and
    urine, 54% in 7 days. The main urinary metabolite is the mercapturic
    acid derivative of methomyl. It is probable that the  S-methyl group

    on methomyl is displaced by glutathione followed by enzymatic
    transformation to give the mercapturic acid derivative. The expired
    air products are probably derived from the hydrolysis of methomyl to
    its oxime followed by breakdown to carbon dioxide, and, by conversion
    of methomyl to its anti-isomeric form, which undergoes hydrolysis,
    rearrangement, and elimination reactions to give acetonitrile.

    In mice, the penetration of 14C-methomyl through the skin was
    estimated to be 85%, one hour after its dermal application in acetone.
    Despite this, the dermal toxicity of methomyl is low (section 2.4),
    probably because of its rapid metabolism and excretion. Total
    radioactivity excreted was 54% within 8 h of application.

    Methomyl is also rapidly broken down and eliminated from ruminants
    after oral administration. Lactating cows, given 80 mg/kg feed for 28
    days, showed no detectable residues of methomyl (<0.02 mg/kg) in milk
    or tissues.

    Overall, the absorption, metabolism, and excretion of methomyl is very
    rapid in mammals. Much of an oral dose is eliminated within 24 h and
    its half-life is a few hours. Tissue levels of methomyl are low and
    less than that in blood. There is no evidence for accumulation of
    methomyl in the body.

    2.3  Effects on Non-target Organisms in the Environment

    There is no apparent effect on soil microorganisms when methomyl is
    applied at recommended rates.

    Methomyl is moderately to highly toxic for fish with 96-h LC50s
    mostly in the range of 0.5-2 mg/litre. In an early life stage, 28-day,
    toxicity study on fathead minnows, the maximum acceptable toxicant
    concentrations (MATC) were >57 and <117 g/litre, respectively.
     Daphnia magna appears to be the most susceptible of other aquatic
    organisms with a 48-h LC50 of 31.7 g/litre. The Fidler crab was one
    of the least susceptible with a 96-h LC50 of 2380 g/litre. In a
    21-day study on survival, growth, and reproductive capacity in
     Daphnia magna, the MATC was >1.6 and <3.5 g/litre.

    The contact and oral toxicity of methomyl is high for honey bees.
    Field observations indicate that early morning or evening application
    of methomyl to flowering crops is advisable, because bees are less
    active and the spray has time to dry before exposure occurs.

    Methomyl is toxic for birds with acute oral LD50s of 10 mg/kg body
    weight for the pigeon and 34 mg/kg body weight for the Japanese quail.
    It is relatively less toxic by the dietary route with 8-h LC50s of
    1100 mg/kg and 2880 mg/kg for the bobwhite quail and mallard duck,
    respectively. No effects were seen on birds in field studies, when
    methomyl was sprayed at recommended rates from the air or using ground
    equipment.

    Although methomyl is likely to have high acute oral toxicity for
    wildlife mammals, it is unlikely to have any significant effect on
    them in normal usage, apart from a small depression of blood
    cholinesterase activity.

    2.4  Effects on Experimental Animals and  in vitro Test Systems

    Methomyl is a carbamate cholinesterase inhibitor, depressing
    cholinesterase activity in the blood and brain. It causes signs
    typical of anticholinesterase action, depending upon the dose,
    including pupil constriction, profuse salivation, lacrimation, and
    tremor. Recovery from the toxic effects is rapid in surviving animals
    after acute doses, because of the rapid reversibility of
    cholinesterase inhibition.

    The acute oral toxicity of methomyl in the rat is high with an LD50
    of 17-45 mg/kg body weight. It is also toxic for the rat via
    inhalation with a 4-h LC50 of 0.26 mg/litre, in aerosol form. The
    dermal toxicity of methomyl in the rabbit is low with an LD50 of
    >2000 mg/kg body weight. Methomyl is not a skin irritant or
    sensitizer and is only mildly irritant to the eye.

    The repeated administration of methomyl does not show any accumulated
    or increased toxic action. Rats showed mild to moderate toxic effects
    when given methomyl at 250 mg/kg diet for 13 weeks. Rabbits given
    repeated dermal applications of 500 mg/kg body weight per day for 21
    days showed hyperactivity and depressed plasma and brain
    cholinesterase activity. No effects were observed at 5 mg/kg body
    weight per day. In long-term studies, no-observed-effect levels
    (NOELs) were established at 100 mg/kg diet for the rat and the dog,
    and, at 50 mg/kg for the mouse.

    There was no evidence for a carcinogenic effect in 2-year rat and
    mouse studies.

    Methomyl was not mutagenic in several types of  n vitro assay with
    various end-points, or in an  in vivo rat bone-marrow chromosome
    study.

    Neither embryotoxic nor teratogenic effects were produced in rats or
    rabbits at doses of up to 400 mg/kg diet or 16 mg/kg body weight per
    day (by gavage), respectively. Rat reproduction studies over 2 or 3
    generations did not show any morphological effects. In a 3-generation
    study, reproductive indices were not affected at a dietary level of
    100 mg/kg.

    Delayed neurotoxicity was not shown in any of the above studies or in
    studies on the hen. Measurements of plasma, erythrocyte, and brain
    cholinesterase activity during the toxicity studies showed that
    cholinesterase inhibition was not increased with repeated dosing.
    Atropine was the most effective antidote on the evidence of studies on
    several species.

    2.5  Effects on Human Beings

    Reports of accidental or suicidal poisoning have shown that victims
    exhibited cholinergic symptoms following acute overexposure. Survivors
    recovered rapidly from the effects. In some cases, effective treatment
    was provided by the administration of atropine. Analysis of tissues
    and excreta and estimates of the amount ingested indicated that doses
    as low as 12-15 mg/kg body weight could be lethal. Reports of
    occupational effects usually indicate non-observance of recommended
    safety precautions as a causal factor.

    3.  CONCLUSIONS AND RECOMMENDATIONS

    3.1  Conclusions

    Methomyl is a monomethyl carbamate insecticide that is highly toxic by
    the oral and inhalation routes. Misuse or disregard of label safety
    instructions may therefore lead to severe poisoning.

    Its low dermal toxicity and the application of correct handling and
    use procedures ensure a low potential for occupational hazard.

    Exposure of the general population is expected to be very low and
    should not constitute a health hazard.

    Methomyl is moderately to highly toxic for aquatic species, bees,
    birds, and mammals in laboratory studies. The results of field studies
    and observations indicate that methomyl does not give rise to
    long-lasting adverse effects, when used as recommended. Methomyl
    residue levels in the environment are very low or undetectable.

    3.2  Recommendations

    Continued emphasis should be given to the correct handling and use of
    methomyl so that workers and users apply good work practices, hygiene
    measures, and recommended safety precautions.

    Observations on regularly exposed workers should be maintained.

    Unnecessary contamination of the environment should be avoided by
    following appropriate disposal practices. The insecticide must be
    applied at recommended rates in field use and, where necessary, any
    special precautions to avoid environmental overexposure should be
    observed.

    4.  HUMAN HEALTH HAZARDS, PREVENTION AND PROTECTION, EMERGENCY ACTION

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

    Methomyl is a monomethyl carbamate insecticide. The acute toxicity of
    technical methomyl by the oral and inhalation routes is high. The oral
    toxicity of formulations for laboratory mammals is lower. Both
    technical and formulated methomyl products can be hazardous for
    humans, if incorrectly handled or misused. Poisoned individuals may
    show symptoms typical of anti-cholinesterase action and their onset
    may be rapid in cases of over-exposure. Although the dermal toxicity
    of methomyl is low and it is not a skin irritant or sensitizer,
    adequate precautions should be taken to prevent skin and eye
    contamination or to remove any such contamination quickly.

    The human health hazards associated with methomyl exposure together
    with preventive and protective measures and first aid recommendations
    are shown in Table 2.

    4.2  Advice to Physicians

    4.2.1  Symptoms of poisoning

    Methomyl directly inhibits cholinesterase activity, therefore signs of
    poisoning can arise very quickly, sometimes within minutes. Early
    symptoms include malaise, muscle weakness, dizziness, and sweating.
    Headache, salivation, nausea, vomiting, abdominal pain, and diarrhoea
    are often prominent. Constriction of pupils (miosis), blurred vision,
    and muscle twitching are other symptoms reported. Dyspnoea,
    bronchospasm, and chest tightness, leading to pulmonary oedema in the
    more severe cases, can also occur. Severe neurological indications
    including convulsions and coma are less commonly observed than with
    organophosphate poisoning.

    The effects of poisoning are likely to be of shorter duration than
    those of organophosphorus toxicity. Because blood cholinesterase
    activity can return to normal within a few hours of exposure, its
    measurement may not be a helpful indicator of poisoning and recovery.
    However, it may be of some use if measured within an hour or so of a
    severe poisoning, provided that a rapid assay method is used that
    takes into account the rapid enzyme reactivation, which can occur in
    blood samples as well as  in vivo. A normal blood cholinesterase
    activity value does not disprove the diagnosis of symptoms and
    treatment of a suspected poisoning should proceed immediately.

    4.2.2  Medical treatment

    For each case, the appropriate emergency first aid (as shown in
    Table 2) should be applied. In the case of a swallowed dose, when the
    patient is conscious, induce vomiting or perform gastric lavage and
    administer activated charcoal. If the patient has difficulty in
    breathing or is unconscious, give oxygen and begin cardiopulmonary
    resuscitation (CPR) as needed.

    Administer atropine sulfate intravenously or intramuscularly as soon
    as possible. 

    N.B. The use of oximes, e.g., pralidoxime (2-PAM), is not recommended
    for carbamate poisonings. 

    Initially, administer 1-2 mg atropine sulfate intravenously or
    intra-muscularly to adults. Repeat dosage at 10 to 30-min intervals
    until symptoms are relieved and full atropinization is achieved. For
    severe intoxication, initially administer 2-4 mg atropine sulfate
    intravenously or intramuscularly and give repeated 2 mg doses every
    3-10 min until signs of cholinesterase inhibition disappear. For mild
    intoxication of children (<13 years), administer atropine sulfate at
    0.05 mg/kg body weight and repeat every 15-30 min until atropinization
    is achieved. Maintain a mild degree of atropinization until the
    patient recovers by administering 0.02 mg/kg body weight as repeated
    doses.

    Observe the patient for at least 24 h to ensure that cholinergic
    symptoms do not recur.

    If the insecticide consists of methomyl in combination with an
    organophosphorus pesticide and the poisoning is due partly, or wholly,
    to the organophosphate, then the use of oximes, e.g., 2-PAM is
    recommended.

        Table 2.  Human health hazards, preventive and protective measures, and first aid

                                                                                                                                         

    HAZARDS/SYMPTOMS                         PREVENTION AND PROTECTION                   FIRST AID
                                                                                                                                         

    GENERAL: readily absorbed following      Avoid exposure
    ingestion or inhalation, or
    through the skin; if absorbed may
    cause cholinesterase inhibition
    poisoning: weakness, headache,
    vomiting, diarrhoea, excessive
    sweating, salivation, pinpoint
    pupils, muscular twitching; in
    severe cases, dyspnoea, broncospasm,
    and chest tightness

    SKIN: extensive contamination may       Wear clothing covering most of the           Remove and wash contaminated clothing; wash
    cause poisoning                         body, protective gloves, and apron           contaminated skin with plenty of soap and
                                                                                         water; obtain medical attention, if necessary

    EYES:  pupil constriction, mild         Wear safety goggles or face shield           Flush eyes with clean water for at least 15 min;
    irritation                                                                           obtain medical attention if effects persist

    INHALATION: overexposure may            Avoid breathing dust or aerosol, use         Move into fresh air immediately; use oxygen
    cause poisoning                         adequate ventilation, use recommended        or artificial respiration, if needed; obtain 
                                            respiratory equipment, if required           medical attention

    INGESTION: an unlikely occupational     Wash hands before eating, drinking,
    hazard                                  using the toilet, and after work

    Accidental or intentional ingestion     Keep the insecticide out of reach of         Obtain medical attention immediately; if
    may rapidly lead to severe              children and under lock and key              breathing has stopped, apply artificial
    poisoning                                                                            respiration; induce vomiting, if person is
                                                                                         conscious
                                                                                                                                         
        4.2.3  Health surveillance advice

    Unlike most organophosphorus compounds, the use of blood
    cholinesterase activity monitoring is of limited value for the
    assessment of occupational exposure to methomyl and many other
     N-methylcarbamates. This is because of the fast reversal of enzyme
    inhibition  in vivo and the difficulty of submitting blood samples
    quickly enough for instantaneous assay. It may be useful, however, to
    help in differential diagnosis in eliminating poisoning with an
    anticholinesterase compound.

    4.3  Explosion and Fire Hazards

    Technical methomyl is not sensitive to impact. Its lower explosion
    limit is 0.269 g/litre and its autoignition temperature is 265C.
    Dusts may form an explosive mixture in air. Hazardous gases and
    vapours may be produced under fire conditions including sulfur oxides,
    HCN, and methylisocyanate. Liquid formulations may be combustible and
    heating releases vapours that are ignitable.

    In case of fire, evacuate personnel to a safe area. Use water squirts,
    dry powder, foam, or dry ice to control/extinguish fire. Warn
    fire-fighting personnel to wear full protective equipment, including
    self-contained breathing apparatus. Prevent contamination of local
    water sources.

    4.4  Storage

    Keep containers tightly closed in dry, cool, well-ventilated areas set
    aside for pesticide storage. Do not store them near foodstuffs or
    animal feed. Keep products out of reach of children and unauthorized
    personnel. Liquid formulations should be kept at a temperature above
    0C.

    4.5  Transport

    Comply with any local regulations regarding the movement of hazardous
    goods. Do not load into transport units containing foodstuffs or
    animal feed. Ensure that containers are undamaged and sound and that
    labels are securely fixed and intact before transportation.

    4.6  Spillage and Disposal

    4.6.1  Spillage

    Check any fire and explosion hazards and safety precautions before
    clean up. Wear appropriate personal protective equipment. Evacuate
    personnel and thoroughly ventilate the area. Keep upwind of the

    spillage and remove sources of heat, sparks, flame, impact, friction,
    and electricity. Use sawdust, sand, or other absorbent material to
    help clean up; transfer to a clean, dry, empty container and label it.

    Contain any liquid spillage with a barrier of soil, sand, or other
    suitable, available material and prevent it from reaching drainage
    systems and waterways. If any product remains in crevices, treat with
    sodium hydroxide solution, allow to stand for 4 h, then flush out with
    water (caution: sodium hydroxide causes skin burns and eye
    damage).

    4.6.2  Disposal

    Disposal must comply with any local or government legislation. Methods
    recommended are those described by FAO and GIFAP. Ensure that disposal
    does not contaminate drinking-water and food or animal feed and that
    there is no danger of run-off or seepage into drainage systems or
    watercourses.

    Contaminated absorbents, containers, and surplus product should be
    burnt in an efficient high temperature incinerator (950-1200C)
    equipped with an effluent gas scrubber. Alternatively, bury in an
    approved dump or landfill, or, burn, if allowed by the local
    authority.

    After agricultural use, excess pesticide, spray mixture, or rinsate
    must be used up by further application according to label
    instructions. If it is not possible to dispose of the concentrate or
    spray mixture in this way, they may be decomposed by the addition of
    sodium hydroxide solution (after appropriate dilution of concentrate).
    Allow to stand for 4 h, above pH 10, and then incinerate, or, after
    neutralization to about pH 7, dispose of according to local
    regulations (caution: sodium hydroxide causes skin burns
    and eye damage).

    5.  HAZARDS FOR THE ENVIRONMENT AND THEIR PREVENTION

    Methomyl is moderately to highly toxic for aquatic organisms. Its
    acute toxicity for birds is high, but dietary toxicity is
    comparatively low. Methomyl is broken down rapidly in the environment
    and does not bioaccumulate. Only very low levels have been found in
    soil, water, and plant foliage. It is unlikely that methomyl will pose
    a threat to aquatic or bird life at recommended rates of usage.
    However, direct, or unnecessary, contamination of streams, rivers,
    ponds, lakes, and other natural water-courses should be avoided.
    Follow disposal advice outlined in section 4.6.2.

    Methomyl is acutely toxic for bees. Do not spray during periods when
    bees are foraging; apply methomyl in the early morning or evening when
    bees are less active and the spray has time to dry.

    6.  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

    The FAO/WHO Joint Meeting on Pesticide Residues (JMPR) evaluated
    methomyl at its meetings in 1975, 1976, 1977, 1978, 1986, 1987, 1988,
    1989, 1990, and 1991. In 1989, an acceptable daily intake (ADI) of
    0-0.03 mg/kg body weight was established. See the table on pp. 24-25
    for Codex maximum residue limits (MRL).

    Methomyl is listed in Class IB, "Highly Hazardous" category, in the
    WHO Recommended Classification of Pesticides by Hazard on the basis of
    its acute oral LD50.

    6.2  Exposure Limit Values

    Some exposure limit values for methomyl are given in the table on
    pp. 24-25.

    6.3  Specific Restrictions

    Methomyl has been approved for use as a pesticide in many countries.
    In some countries, specific uses are defined as well as limitations
    and precautions, particularly for products with a high concentration
    of the active ingredient.

    6.4  Labelling, Packaging, and Transport

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

    -Hazard Class 6.1:                      poisonous substance

    -Packing Group II:                      a substance presenting a
                                            relatively medium risk of 
                                            poisoning in transport

    The label should be as follows:

    FIGURE 1

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

    FIGURE 2

    The label must read:

     Very toxic by inhalation and if swallowed.

    6.5  Waste Disposal

    In the USA, methomyl waste is regarded as acutely hazardous. Improper
    disposal of excess pesticide, spray mixture, or rinsate is a violation
    of Federal law. If the wastes cannot be disposed of according to the
    label instruction, contact the appropriate Pesticide or Environmental
    Control Agency or Hazardous Waste representative for guidance. Do not
    contaminate water, food, or animal feed during storage or disposal.

        CURRENT REGULATIONS, GUIDELINES, AND STANDARDS
                                                                                                                                         

    Exposure limit values
                                                                                                                                         

    Medium      Specification       Country/            Exposure limit description                   Value                Effective
                                    organization                                                                          date
                                                                                                                                         

    AIR         Workplace           United              Long-term exposure (8-h TWA)                 2.5 mg/m3            1993
                                     Kingdom

                                    USA/ACGIH           Threshold limit value (TLV)
                                                        - Time-weighted average (TWA)                2.5 mg/m3            1977

                                    USA/OSHA            Permissible exposure limit (PEL)
                                                        - Time-weighted average (TWA)                2.5 mg/m3


    FOOD        Intake from         FAO/WHO             Acceptable daily intake (ADI)                0-0.03 mg/kg         1989
                residues                                                                             body weight

                                    FAO/WHO             Maximum residue limit (MRL)                                       1991
                                                        (methomyl + oxime as methomyl)
                                                        - meats, milks                               0.02 mg/kg
                                                        - cottonseed, peanuts, potatoes, soyabeans,  0.1 mg/kg 
                                                          beans (dry), sugar beet, sweet corn
                                                        - cucumbers, egg plants, melons, onion       0.2 mg/kg
                                                          bulbs, pineapples, sorghum, squashes
                                                        - barley, oats, onions (Welsh), peas         0.5 mg/kg
                                                          (shelled), tomatoes, wheat 
                                                                                                                                         

    FOOD (contd)
                                                                                                                                         

    Medium      Specification       Country/            Exposure limit description                   Value                Effective
                                    organization                                                                          date
                                                                                                                                         

                                                        - citrus, peppers, sorghum, forage           1 mg/kg
                                                        - asparagus, cauliflowers, celery,           2 mg/kg
                                                          common beans (pods and/or immature
                                                          seed), mint hay, pome fruits
                                                        - barley straw and fodder (dry), cabbage     5 mg/kg
                                                          (head), grapes, kale, lettuce (head),
                                                          nectarines, oat straw & fodder (dry),
                                                          peaches, peanut forage (green), peas,
                                                          spinach, wheat straw and fodder (dry)
                                                        - alfalfa forage, green hops (dry), pea      10 mg/kg
                                                          vines (green) soyabean forage (green)

    WATER       Drinking-           Australia           "Standard" maximum residue level             0.06 mg/litre        1987

                                    USA/EPA             Health advisory, longer term                 0.2 mg/litre         1992
                                                                                                                                         
        BIBLIOGRAPHY

    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 for pesticides.
    Rome, Food and Agriculture Organization of the United Nations.

    FAO (1990) International code of conduct on the distribution and use
    of pesticides (Amended version). Rome, Food and Agriculture
    Organization of the United Nations.

    FAO/WHO (1964-present) Evaluation of some pesticide residues in food.
    Rome, Food and Agriculture Organization of the United Nations.

    FAO/WHO (1989) Guide to Codex recommendations concerning pesticide
    residues. Part 8. Recommendations for methods of analysis of pesticide
    residues. 4th ed., Rome, Codex Committee on Pesticide Residues.

    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.

    GIFAP (1987) Guidelines for the safe transport of pesticides,
    Brussels, Groupement International des Associations Nationales des
    Fabricants de Produits Agrochimiques.

    IPCS (1986) Environmental Health Criteria 64: Carbamate pesticides - a
    general introduction. Geneva, World Health Organization.

    IPCS (1995) Environmental Health Criteria 178: Methomyl, Geneva, World
    Health Organization.

    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 Organisation (unpublished document
    WHO/VBC/84.889).

    United Nations (1989) Recommendations on the transport of dangerous
    goods. 6th 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 (1994) The WHO recommended classification of pesticides by hazard
    and guidelines to classification, 1994-95. Geneva, World Health
    Organization (unpublished document WHO/PCS/94.2)

    Worthing CR & Hance RJ, ed. (1991) The pesticide manual, 9th ed.,
    Farnham, United Kingdom, The British Crop Protection Council.
    


    See Also:
       Toxicological Abbreviations
       Methomyl (EHC 178, 1996)
       Methomyl (ICSC)
       Methomyl (WHO Pesticide Residues Series 5)
       Methomyl (Pesticide residues in food: 1976 evaluations)
       Methomyl (Pesticide residues in food: 1977 evaluations)
       Methomyl (Pesticide residues in food: 1978 evaluations)
       Methomyl (Pesticide residues in food: 1986 evaluations Part II Toxicology)
       Methomyl (Pesticide residues in food: 1989 evaluations Part II Toxicology)
       Methomyl (JMPR Evaluations 2001 Part II Toxicological)