Health and Safety Guide No. 69






    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

    Dimethylarsinic acid, methanearsonic acid, and salts: health and
    safety guide.

    (Health and safety guide ; no. 69)

    1. Arsenicals - standards    2. Arsenicals - toxicity
    3. Environmental exposure    I.Series

    ISBN 92 4 151069 2          (NLM Classification: QV 294)
    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 1992

    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




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

         2.1. Human exposure
         2.2. Effects on organisms in the environment
         2.3. Uptake, metabolism, and excretion
         2.4. Effects on experimental animals
         2.5. Effects on humans

         3.1. Conclusions
         3.2. Recommendations

         4.1. Human health hazards, prevention and
              protection, first aid
              4.1.1. First aid
         4.2. Advice to physicians
              4.2.1. Treatment
         4.3. Explosion and fire hazards
         4.4. Storage and transport
         4.5. Spillage
         4.6. Disposal


         6.1. Previous evaluations by international bodies
         6.2. Exposure limit values
         6.3. Specific restrictions
         6.4. Transport and labelling



    This Health and Safety Guide is not based on an existing
    Environmental Health Criteria document, but on critical national
    reviews. The hazard evaluation in the Health and Safety Guide was
    made on the basis of carefully selected studies, after scrutiny of
    the original publications.

    In order to assist the peer-review process of the present Health and
    Safety Guide, a background companion document was prepared by the
    IPCS and can be obtained from the Director on request; the IPCS does
    not intend that the background document should be published.

    The first three sections of this Health and Safety Guide present
    essential technical information and the hazard evaluation. 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. 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.

    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



    Organic arsenic compounds comprise a large number of alkyl and aryl
    derivatives; these have widely different uses and toxicological
    properties and do not form a homogeneous group. Also, the available
    information on most of these compounds is insufficient to allow for
    an adequate evaluation of the health and environmental hazards
    associated with their use. For these reasons, this Health and Safety
    Guide deals only with dimethylarsinic acid, methanearsonic acid, and
    their sodium salts.

    It is important to emphasize, however, that some of the compounds
    not covered in this Guide are more hazardous than the derivatives
    that are described, and should be handled with great caution.


    1.1  Identity

    The formulas, chemical names, CAS numbers, synonyms and trade names
    of the dimethylarsinic and methanearsonic acids and their sodium
    salts are included in Table 1.

    1.2  Physical and chemical properties

    Dimethylarsinic acid is stable in storage. Nascent hydrogen, formed
    by the action of acids on active metals, will reduce the substance
    to highly toxic dimethylarsine. Aqueous solutions are mildly
    corrosive. Some physical properties of these compounds are shown
    above, in Table 2.

    1.3  Analytical methods

    The most common method involves reduction to the corresponding
    arsine by sodium-borohydride, followed by determination of the
    latter by atomic-absorption spectroscopy.

    Another sensitive method for the separation and quantitative
    determination of arsenical pesticide residues and their metabolites
    is based on the use of high-pressure liquid chromatography coupled
    with graphite furnace, atomic-absorption spectroscopy.

    Paper chromatographic separation and detection methods, as well as
    the use of ion-exchange chromatography in combination with
    thin-layer chromatography, have been described for the determination
    of dimethyl-arsinic acid and other organic arsenical compounds.

    1.4  Production and uses

    Substantial amounts of methanearsonic acid, dimethylarsinic acid
    (cacodylic acid), and their salts, are used as non-selective contact
    herbicides, especially for the control of Johnson grass in cotton
    fields. Dimethylarsinic acid is used extensively in some areas for
    cotton defoliation. It has also been used as an insecticide (e.g.,
    against bark beetles), as a soil sterilant, and as a silvicide in
    forest control (timber thinning).

    Dimethylarsinic acid (cacodylic acid) is available as a technical
    grade product, containing 65% active ingredient and the following
    possible impurities: sodium chloride, sodium sulfate, methanearsonic
    acid, and arsenic acid.

        Table 1. Formulas, chemical names and synonyms of dimethylarsinic and methanearsonic acids
             and their sodium salts


    Chemical name       Formula           CAS-No.           Synonyms and trade names


    Dimethylarsinic     (CH3)2AsO(OH)     75-60-5           Arsine oxide, hydroxydimethyl-;
    acid                                                    arsinic acid, dimethyl-; cacodylic
                                                            acid; hydroxy-dimethylarsine oxide;
                                                            Agent Blue; Ansar 138; Arsan; Dilic;
                                                            Phytar 138; Phytar 560; Rad-E-Cate
                                                            25; Silvisar 510

    Methanearsonic      CH3AsO(ONa)2      144-21-8          arsinyl; arsonic acid, methyl-,
    acid, disodium                                          disodium salt; disodium
    salt                                                    methanearsenate; disodium
                                                            methanearsonate; disodium
                                                            methylarsonate; Arrhenal; Ansar 184;
                                                            Ansar 8100; Ansar DSMA Liquid;
                                                            Arsynal; Cacodyl New; Chipco Crab
                                                            Kleen; Cralo-E-Rad; Dal-E-Rad 100;
                                                            Diarsen; Disomear; Di-Tac; DMA;
                                                            DMA 100; DSMA; DSMA Liquid;
                                                            Methar; Metharsan; Metharsinat;
                                                            Namate; Neo-Asycodile; Sodar;
                                                            Somar; Stenosine; Tonarsen; Tonarsin;
                                                            Weed Broom; Weed-E-Rad;
                                                            Weed-E-Rad DMA Powder;
                                                            Weed-E-Rad 360; Weed-Hoe

    Table 1 (continued)

    Chemical name       Formula           CAS-No.           Synonyms and trade names


    Methanearsonic      CH3AsO(OH)ONa     2163-80-6         Arsonic acid, methyl-, monosodium
    acid, mono-                                             salt; monosodium acid
    sodium salt                                             methanearsonate; sodium
                                                            monosodium acid metharsonate;
                                                            monosodium methanearsonate;
                                                            monosodium methylarsonate; MSMA;
                                                            sodium acid methanearsonate;
                                                            methylarsenic acid, sodium salt;
                                                            Ansar 170H.C.; Ansar 170 L; Ansar
                                                            529 H.C.; Arsonate Liquid; Bueno 6;
                                                            Daconate 6; Dal-E.Rad; Herb-All;
                                                            Merge 823; Mesamate; Mesamate
                                                            H.C.; Mesamate Concentrate;
                                                            Mesamate 400; Mesamate 600;
                                                            Phyban H.C.; Silvisar 550; Target
                                                            MSMA; Trans-Vert; Weed 108;
                                                            Weed-E.Rad; Weed-Hoe

    Sodium              (CH3)2AsO(ONa)    124-65-2          Arsine oxide, hydroxydimethyl-,
    cacodylate                                              sodium salt; arsinic acid, dimethyl-
                                                            sodium salt; cacodylic acid, sodium
                                                            salt; [(dimethylarsino)oxy]-sodium-As-
                                                            oxide; hydroxydimethylarsine oxide,
                                                            sodium salt; sodium dimethylarsinate;
                                                            sodium dimethylarsonate; Alkarsodyl;
                                                            Arsecodile Arsicodile; Arsycodile;
                                                            Boll's Eye; Phytar 560; Rad-E-Cate 25;

    Table 2: Physical properties of dimethylarsinic acid and its sodium salt and of methanearsonic
             acid monosodium and disodium salts


    Compound            Melting point (C)        Description       Solubility (g/litre)


    Dimethylarsinic     195-196                   white,            very soluble in water (2000),
    acid                                          crystalline       ethanol; insoluble in ether

    Methanearsonic      132-139                   crystalline       very soluble in water (1000),
    acid disodium                                 solid             methanol; insoluble in organic
    salt                                                            solvents

    Methanearsonic      115-119                   crystalline       soluble in water (570), methanol;
    acid mono-                                    solid             insoluble in organic solvents
    sodium salt

    Sodium              200                       crystalline       very soluble in water (2000);
    cacodylate                                    solid             soluble in ethanol

    Methanearsonic acid, disodium salt, is available for farm
    applications as a solution containing added surfactant.
    Methanearsonic acid, monosodium salt, is available for farm
    applications as a technical grade product in combination with a
    surfactant, or in combination with sodium cacodylate,
    dimethylarsinic acid, and a surfactant.

    Sodium cacodylate is available for farm applications as concentrated
    solutions, as a 25% solution with surfactant, in combination with
    dimethyl-arsinic acid or in combination with methane-arsonic acid,
    monosodium salt, and surfactant.


    2.1  Human exposure

    Since inorganic arsenic can be converted to methylated species by
    living organisms, human exposure to these compounds through food is
    universal. Arsenic in fish is mainly present as organic compounds,
    which, in general, are less toxic than the inorganic derivatives.
    Marine fish and crustaceans commonly contain 2-20 mg arsenic/kg on a
    wet weight basis, although higher values (up to 50-100 mg/kg) have
    been reported.

    In occupational exposure, inhalation is the main route of

    2.2  Effects on organisms in the environment

    The acute toxicities of dimethylarsinic acid and its salts for fish
    are moderate to low. The long-term effect of methylated arsenicals
    on non-target organisms is not known. Biological transformations in
    soil result in the production of more toxic arsenic compounds, such
    as the volatile dimethyl- and trimethylarsines, as well as inorganic
    arsenic. In a model ecosystem, algae and daphnia accumulated these
    compounds. Methyl arsenic derivatives are phytotoxic. Very few
    studies are available on the environmental effects of organoarsenic

    2.3  Uptake, metabolism, and excretion

    Following ingestion or inhalation, methylated arsenic compounds are
    rapidly and extensively taken up by mammals, including humans. They
    are eliminated, mainly in the urine, within a period of 2-4 days.
    Apart from species-related retention in the red blood cells of rats,
    no appreciable accumulation seems to occur in mammals.
    Dimethylarsinic acid penetrates the intact skin, and has been shown
    to cross the placental barrier. In the hamster, dimethylarsinic acid
    forms small amounts of volatile arsines, such as trimethylarsine.

    2.4  Effects on experimental animals

    In contrast to most inorganic arsenic compounds, the acute oral,
    dermal, and inhalation toxicities of methylated arsenic compounds
    for mammals are low to very low. Ruminants appear to be more
    susceptible, and several reports of intoxication of domestic animals
    have been published; the clinical signs and histological findings
    seem to have been similar to those induced by inorganic arsenic.
    The long-term administration of methylated arsenic compounds to
    rabbits and rats has induced signs of toxicity at relatively low
    doses. However, the carcinogenicity of these compounds in animals
    has not been sufficiently investigated.

    Although the results from most tests for genotoxicity using
    dimethylarsinic acid have been negative, some positive findings have
    been reported. Embryotoxic as well as teratogenic effects of
    dimethylarsinic acid have been reported in mice and hamsters. In
    rats, a no-effect level for embryotoxicity of 15 mg/kg body weight
    per day has been found in one oral study. No reproduction studies
    have been found in the literature.

    2.5  Effects on humans

    No data are available on toxic effects in humans; the risk
    evaluation is based on the demonstrated effects of these substances
    on experimental animals. It is likely that if poisoning does occur
    in humans, the effects will be similar to those produced by
    inorganic arsenic compounds.


    3.1  Conclusions

    Dimethylarsinic acid and methanearsonic acid salts are characterized
    by a low acute toxicity in mammals, although ruminants appear to be
    more susceptible. Although insufficiently investigated, there are
    indications that the toxicity is higher with long-term exposure.
    Information on the toxicological properties of methanearsonic acid
    salts is fragmentary, but these substances seem to have
    toxicological properties similar to those of the dimethyl

    Dimethylarsinic acid is decomposed in the environment to either
    inorganic arsenic, or highly toxic volatile arsines. Thus, extensive
    use as a pesticide may result in undesired long-term effects by
    increasing the total arsenic load in the ecosystem.

    3.2  Recommendations

    Methylated arsenic compounds and their salts should be replaced by
    less hazardous substitutes, wherever this is feasible.


    4.1  Human health hazards, prevention and protection, first aid

    In order to interrupt the chain of generation/release/transmission
    of the hazardous agent, the main goal should be primary prevention
    through interventions in the work environment. These include
    measures such as exhaust ventilation, closed systems, enclosure of
    sources, and good housekeeping practices. Local exhaust ventilation
    systems must include air cleaning devices to prevent environmental

    When these measures are not technically feasible, as is the case in
    the formulation or application of pesticides, or in the case of
    temporary operations, the use of personal protective clothing and
    equipment (e.g., disposable dust masks) is recommended.

    The following precautions should be observed during handling and

    *    Avoid contact with the skin and eyes by using a face-mask and
         complete protective clothing.

    *    Do not smoke, drink, or eat in the workplace. Wash hands and
         any exposed skin before eating, drinking, or smoking, and after

    Regular medical supervision of workers occupationally exposed to
    organic arsenic compounds is recommended.

    4.1.1  First aid

    Medical attention should be obtained; in the meantime, first aid
    should be provided immediately. If material has been spilled on the
    skin, immediately remove the patient from the source of
    contamination, remove all contaminated clothing, and wash the
    affected areas with soap and water. If the material is in the eyes,
    flush with clean water for 5-10 minutes. In the case of ingestion,
    immediate action is imperative: if the patient is conscious, give
    two glasses of milk or water, or a beaten egg, induce vomiting, and
    subsequently administer activated charcoal, if possible. Transport
    the patient to a hospital.

    4.2  Advice to physicians

    Diagnosis is based on history, symptoms, signs, and laboratory
    confirmation of a raised arsenic level in the urine, but treatment
    should start on suspicion of poisoning.

    Although it is unlikely that in normal use these compounds will
    induce acute poisoning, signs of acute poisoning are likely to be
    similar to those of inorganic arsenic compounds and could include
    nausea, vomiting, abdominal pain, and diarrhoea.

    4.2.1  Treatment

    Prognosis is dependent on dose, as well as the time between
    ingestion of the arsenical compound and first treatment. Gastric
    aspiration and lavage with warm water, followed by administration of
    sodium sulfate (30 g) is indicated. Keep the patient warm and quiet;
    combat shock and dehydration. Apply artificial respiration, oxygen
    therapy, whole blood, or fluids as needed. It is unlikely that
    chelation will be required, but if it is, dimercaprol (BAL), by
    intramuscular injection, has been found to be useful in cases of
    intoxication. A number of side-effects have been associated with
    BAL, and the use of this antidote for the treatment of chronic
    intoxications is controversial. D-penicillamine has also been used,
    although its efficacy has been questioned. A water-soluble analogue
    of dimercaprol (meso-2,3-dimercaptosuccinic acid - DMSA) has proved
    to be more effective and less toxic; therefore, it is indicated as
    first-choice chelator, if available. The sodium salt of
    2,3-dimercaptopropanesulfonate (Unithiol, Dimaval, DMPS) has also
    been reported to be effective, and to induce less severe
    side-effects than dimercaprol.

    4.3  Explosion and fire hazards

    Organic arsenic compounds may give off highly toxic fumes when
    heated. Dimethylarsinic acid may be decomposed by powerful oxidizing
    or reducing agents. Most fire-extinguishing agents can be used to
    combat fires involving arsenic. However, the use of water sprays
    should be confined to the cooling of unaffected stock only, thus
    avoiding the accumulation of polluted run-off from the site.
    Fire service personnel should be advised that self-contained
    breathing apparatus and totally encapsulated protective clothing is

    4.4  Storage and transport

    All products should be stored in secure buildings, kept dry and out
    of reach of children and animals, and separated from food and animal
    feed. Containers should be sound and adequately labelled. Keep
    containers well closed. Do not store near fertilizers, seeds,
    insecticides, or fungicides. Storage vessels or tanks should not be
    made of steel, galvanized steel, tin, or aluminium. Suitable
    containers are high-density polyethylene bottles, resin-lined metal
    drums, and glass containers.

    4.5  Spillage

    Keep spectators away from any leakage. Prevent contamination of
    other goods or cargo, and of nearby vegetation and surface waters.
    Absorb spillage of liquid products with earth or sand, sweep up, and
    place in a separate container. Empty any product remaining in
    damaged or leaking containers into a clean empty container, which
    should be suitably labelled. Sweep up any spilt powder with damp
    sawdust, taking care not to raise a dust cloud. Place in a separate
    container for subsequent disposal. Contaminated absorbents, used
    containers, surplus product, etc., should not be incinerated.

    4.6  Disposal

    Arsenic-containing wastes should not be buried in landfill sites,
    except in very small quantities interspersed with large volumes of
    non-hazardous wastes. Do not incinerate and do not discharge to
    sewers or water courses.

    Precipitation and/or solidification are preferred methods of
    disposal, but should be undertaken by a specialist in toxic waste
    disposal because of the persistence and toxicity of arsenic.


    The acute toxicities of dimethylarsinic acid and its salts for fish
    are low. Methyl arsenic derivatives are phytotoxic. The long-term
    effects on a number of non-target organisms are not known.
    Biological transformations in soil result in the production of
    more-toxic arsenic compounds, such as the volatile dimethyl- and
    trimethylarsines, as well as inorganic arsenic.


    6.1  Previous evaluations by international bodies

    The International Agency for Research on Cancer evaluated the
    carcinogenic hazard of several organic arsenic compounds and
    concluded that no adequate data on the carcinogenicity of organic
    arsenic compounds are available.

    WHO (1992) has classified dimethylarsinic acid and methanearsonic
    acid as "slightly hazardous" pesticides with oral LD50s for the rat
    of 1350 mg/kg body weight and 1800 mg/kg body weight, respectively.
    No acceptable daily intakes (ADI) for organic arsenic pesticides
    have been established by the Joint FAO/WHO Meeting on Pesticide

    A guideline value of 0.05 mg As(total)/litre has been recommended in
    the WHO publication,  Guidelines for drinking-water quality.

    6.2  Exposure limit values

    In the USA, a time-weighted average of 0.5 mg/m3 has been
    established for occupational exposure to organic arsenic compounds.

    Residue limits of 0.7-2.8 mg/kg and 0.35-0.7 mg/kg, calculated as
    As2O3, in food and feed have been established in the USA for
    dimethylarsinic acid, and for the mono- and disodium salts of
    methanearsonic acid, respectively.

    Brazil has established tolerable limits of 0.2-0.7 mg/kg of
    monosodium methanearsonate in specified plant products.

    6.3  Specific restrictions

    Argentina prohibits the use of monosodium methanearsonate in the
    cultivation, commercial distribution, and industrial processing of
    tobacco. Mixtures of dimethylarsinic acid and its sodium salt may
    not be marketed in Portugal on account of their
    environmental/toxicological effects.

    In the USA, any solid waste (except domestic) containing
    dimethylarsinic acid must be listed as hazardous waste, and is
    subject to regulation and notification requirements, unless it is
    found that the waste cannot pose a threat to human health or the
    environment when improperly managed.

    6.4  Transport and labelling

    The United Nations Committee of Experts on the Transport of
    Dangerous Goods has classified dimethylarsinic acid and its sodium
    salt as "poisonous (toxic) substances". As such, strict regulations
    have been applied to their transportation. The International
    Maritime Dangerous Goods Code classifies such substances as marine
    pollutants, and requires appropriate warning labels.

    Canada classifies dimethylarsinic acid and its sodium salt as a
    "toxic substance"; the maximum amount per package that may be
    transported on a passenger aircraft, train, or road vehicle is 25
    kg; the maximum amount per package that may be transported on a
    cargo aircraft is 100 kg.


    IARC (1980) IARC monographs on the evaluation of carcinogenic risk
    of chemicals to humans - some metals and metallic compounds. Vol.
    23. Lyon, International Agency for Research on Cancer, pp. 39-41.

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

    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

    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.

    WHO (1981) Environmental Health Criteria 18: Arsenic. Geneva, World
    Health Organization, 174 pp.

    WHO (1984) Guidelines for drinking-water quality. Vol. 1:
    Recommendations. Geneva, World Health Organization, 130 pp.

    WHO (1987) Air quality guidelines for Europe. Copenhagen, WHO
    Regional Office for Europe, pp. 171-181 (European Series No. 23).

    WHO (1989) Toxicological evaluation of certain food additives and
    contaminants. Geneva, World Health Organization, pp. 155-162 (WHO
    Food Additives Series 24).

    WHO (1992) The WHO recommended classification of pesticides by
    hazard and guidelines to classification 1992-1993. Geneva, World
    Health Organization (unpublished document, WHO/PCS/92.14).

    See Also:
       Toxicological Abbreviations