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         It must be noted that the issue of a Data Sheet for a
    particular pesticide does not imply endorsement of the pesticide by
    WHO or FAO for any particular use, or exclude its use for other
    purposes not stated. While the information provided is believed to
    be accurate according to data available at the time when the sheet
    was compiled, neither WHO nor FAO are responsible for any errors or
    omissions, or any consequences therefrom.

    The issue of this document does    Ce document ne constitue pas une
    not constitute formal              publication. Il ne doit faire
    publication. It should not be      l'objet d'aucun compte rendu ou
    reviewed, abstracted or quoted     résumé ni d'aucune citation sans
    without the agreement of the       l'autorisation de l'Organisation
    Food  and Agriculture              des Nations Unies pour
    Organization of the United         l'Alimentation et l'Agriculture
    Nations or of the World Health     ou de l'Organisation Mondiale de
    Organization.                      la Santé.


                          Primary use: Insecticide

                          Secondary use: Acaricide

                          Chemical group: Organophosphorus compound


    1.1  COMMON NAME

    Demeton-S-methyl (ISO, BSI and JMAF; exception USSR - methyl-
    mercaptofos teolovy)

    1.1.1  Identity

    IUPAC and CAS:      S-2-ethylthioethyl O,O-dimethyl

    CAS Reg. No.:       919-86-8

    Molecular formula:  C6H15O3PS2     Molecular weight: 230.3

    Structural formula:

    Structural Formula

    1.1.2  Synonyms

    AzotoxR; Bayer 18436; Bayer 21/116; Bayer 25/154; Campbell's
    DsMR; Demeton-S-methyl; Demeton-S-metile; DemetoxR; DuratoxR;
    Isometasystox; Isomethylsystox; Metaisoseptox; MetaisosystoxR;
    Metasystox iR; Methyl demeton thioester; Methyl isosystox; Methyl
    mercaptofos teolovy

    1.2  SYNOPSIS

    Demeton-S-methyl is a broad spectrum, non-cumulative, systemic
    organophosphorus insecticide; a cholinesterase inhibitor with good
    contact and limited stomach action; highly toxic to mammals, other
    vertebrates and bees. Its toxicity is maintained after metabolism to
    the oxygen derivatives, i.e., sulfoxide and sulfone.


    1.3.1  Physical characteristics

    Demeton-S-methyl is a pale yellow oily liquid. It has a boiling
    point of 89°C at 0.15 mmhg; a density (d20) of 1.707; and a
    refractive index (n20 ) of 1.5065.

    1.3.2  Solubility

    In water, 3.3 g/litre at 25°C, it is readily soluble in
    conventional organic solvents.

    1.3.3  Stability

    Demeton-S-methyl has a half-life of 7.6 days in an ethanol-Ph 6
    buffer solution (1:4) at 70°C. In aqueous solutions, Ph 1-5, it has
    a half-life of 88 days. The shelf-life is quite short yielding the
    highly toxic sulfonium compound.

    1.3.4  Vapour pressure

    4.79 x 10-5 Kpa (3.6 x 10-4 mmhg) at 20°C.


    1.4.1  Common formulations

    These include emulsifiable concentrates of various
    concentrations in the range of 250 g a.i./kg.

    1.4.2  Pests controlled

    Aphid vectors of vital diseases, whiteflies, leafhoppers,
    sawflies, red spider mites and other pests of garden crops, fruit
    and hops.

    1.4.3  Use pattern

    It is recommended for use on alfalfa, almonds, apples,
    apricots, barley, beans, blackberries, broccoli, brussel sprouts,
    cabbage, cauliflower, celery, clover cotton, dewberries, eggplant,
    filberts, gooseberries, grapefruit, grapes, hops, lemons, lettuce,
    loganberries, muskmelons, nectarines, otas, oranges, peaches, pears,
    peas, pecans, peppers, pineapples, plums, potatoes, raspberries,
    sorghum, strawberries, sugar beets, walnuts, wheat, conifers and
    ornamentals. It is generally applied at 140-800 g/ha.

    1.4.4  Unintended effects

    Demeton-S-methyl is phytotoxic to ornamentals, especially
    certain chrysanthemum cultivars; it is toxic to bees.


    No recommended use.


    No recommended use.



    2.1.1  Absorption

    Demeton-S-methyl may be absorbed from the gastrointestinal
    tract; through the intact skin; and by inhalation of spray mist and

    2.1.2  Mode of action

    Demeton-S-methyl is a direct inhibitor of cholinesterase
    through phosphorylation of the esteratic site of the enzyme.
    Accumulation of acetylcholine at nerve synapses and myoneural
    junctions causes the toxic effects. Demeton-S-methyl and its
    oxidation products, the sulfoxide and the sulfone, are equally
    toxic. The thiono-isomer is less toxic than the thiolo-isomer.

    2.1.3  Excretion products

    The metabolism and excretion of demeton-S-methyl have not been
    extensively studied in mammals. By extrapolation from the ethyl
    homologue demeton, metabolism should involve oxidation of the
    thioether to the sulfoxide and, more slowly, to the sulfone by liver
    microsomal enzymes. In mice 97% of demeton-S-methyl sulfoxide was
    eliminated within 15 hours of dosing (per oral or subcutaneous),
    mostly in urine.

    2.1.4  Toxicity, single dose of demeton-S-methyl

    Oral LD50:

    Rat (H, F)                35-83 mg/kg bw; technical material
    Guinea-pig (M)              110 mg/kg bw; technical material
    Rabbit                    20-50 mg/kg bw; technical material
    Cat                        5-10 mg/kg bw; technical material
    Dog                          50 mg/kg bw; technical material

    Dermal LD50:

    Rat                      50-100 mg/kg bw; technical material
    Cat                       10-20 mg/kg bw; technical material

    I.P. LD50;

    Rat (M, F)                 2-10 mg/kg bw; technical material
    Rat (M, F)                 27.5 mg/kg bw (pure)
    Guinea-pig                 12.5 mg/kg bw; technical material

    I.V. LD50;

    Rat (M)                     8.4 mg/kg bw; technical material
    Rat (M)                    17.3 mg/kg bw (pure)
    Rat (F)                    64.5 mg/kg bw (pure)
    Mouse (M)                   4.1 mg/kg bw (purity unknown)
    Mouse (M)                  13.0 mg/kg bw (pure)

    Oral LD50:

    Rat                         676 mg/kg bw

    I.V. LD50;

    Rat                         216 mg/kg bw

    Inhalation LC50:

    Rat                         500 mg/m3/4 hours

    2.1.5  Toxicity repeated doses

    Oral: Groups of male rats were given doses of 0, 1, 5 or 10
    mg/kg bw for up to six months. Increased mortality was observed at
    the two highest doses only; no ill-effects were observed at 1

    Dermal: No information available on demeton-S-methyl.

    Demeton-S-methyl sulfoxide, a metabolite, was administered to
    male and female rats for 60 days at dosage levels of 25 or 50 mg/kg
    bw. The animals on the highest dose only showed signs of increased
    cholinergic activity for the initial two weeks of treatment only. No
    other ill-effects were observed.

    Oxydemeton, a metabolite, was also administered to male and
    female rats, approximately one-fifth of the LD50, five days a week
    for three weeks. A slight reduction in body weight and a marked
    inhibition of brain cholinesterase activity were observed at the end
    of the study. No other ill-effects or changes in tissue histology
    could be attributed to oxydemeton treatment.

    Inhalation studies: Groups of male and female rats were
    exposed to the metabolite demeton-S-methyl sulfone at concentrations
    of 0, 0.0068 and 0.017 mg/litre for four hours a day, five days per
    week for a period of 10 weeks. Cholinesterase depression was marked
    and body weight gain was significantly depressed in all treatment
    groups; no other ill-effects were observed.

    Cumulation of compound: Demeton-S-methyl does not accumulate
    in body tissues.

    Cumulation of effect: Dermal and oral studies indicate that
    there is none.

    2.1.6  Dietary studies

    Short-term: Groups of male rats were fed demeton-S-methyl at
    dietary levels of 0, 50, 100 or 200 mg/kg. Depression of
    cholinesterase activity was observed in all treatment groups;
    however, signs of cholinergic toxicity were evident at the highest
    dietary level only. Growth rates were depressed from 100 mg/kg
    (diet). There were no treatment-related changes in gross or
    microscopic anatomy.

    Groups of male and female weanling rats were maintained on
    diets containing 0, 2, 5, 10 or 20 mg/kg of demeton-S-methyl for
    three months. There were no signs of toxicity or laboratory findings
    that could be attributed to demeton-S-methyl at 10 mg/kg (diet) or

    Long-term: See section on Carcinogenicity.

    2.1.7  Supplementary studies of toxicity

    Carcinogenicity: Short-term dietary studies in rats have not
    shown a carcinogenic potential for demeton-S-methyl. Two-year rat
    studies with demeton-S-methyl sulfoxide have also not produced
    evidence of carcinogenic activity for that compound at dietary
    levels as high as 100 mg/kg. Mammalian mutagenicity and reproductive
    studies show no supportive evidence for an oncogenic role.

    Mutagenicity: Demeton-S-methyl has shown some mutagenic
    potential in non-mammalian systems at 5 mg/plate in an  E. coli and
    an  S. typhimurium plate test and in a  Drosophila melanogaster
    nondisjunction test. In mammalian systems, however, the sulfoxide
    analogue was not mutagenically active in a mouse dominant lethal
    assay (5 and 10 mg/kg bw).

    Teratogenicity: Pregnant female rabbits were given oral doses
    of oxydemetonthalidomide at 0, 0.1 and 0.2 mg/kg bw from days 6 to
    18 of gestation; a thalidomide positive control was also carried
    out. No clear treatment-related embryotoxic or teratogenic effects
    were observed nor were there any ill-effects observed among the

    Reproduction: No clear treatment-related adverse effects were
    observed in rats in a three-generation study at dosage levels of 10-
    50 mg/kg (diet), although cholinesterase depression was produced. At
    50 mg/kg (diet) the number of pregnancies and litter size were
    significantly reduced.

    Neurotoxicity: Demeton-S-methyl sulfone did not produce any
    delayed neurotoxic effects at doses up to and including 200 mg/kg

    2.1.8  Modifications of toxicity

    No evidence of acute potentiation was observed when oxydemeton-
    methyl was given in pairs with 15 other organophosphorus compounds,
    at one-half the LD50 dose, to male rats.


    2.2.1  Absorption route

    Demeton-S-methyl or related compounds may be absorbed from the
    gastrointestinal tract; through the intact skin; and by inhalation
    of spray mist or dusts.

    2.2.2  Dangerous doses

    Single: Not known.

    Repeated: Not known.

    2.2.3  Observations on occupationally exposed workers

    Over 700 cases of poisoning are known, including three
    fatalities which followed a one-week exposure in an agricultural
    spray programme. Lack of good personal hygiene was implicated as a
    cause. All others apparently recovered without sequelae, most after
    atroprine therapy and/or withdrawal from contact.

    2.2.4  Observations on exposure of the general population

    A group of teenagers and children living adjacent to a spray
    area were found to have depressed cholinesterase levels. The
    depression was attributed to air-borne contamination.

    2.2.5  Observations on volunteers

    The no-effect level for oxydemeton-methyl was found to be 0.05
    mg/kg bw after a 60-day period of administration. 0.4 mg/kg bw
    caused depression of serum and erythrocyte cholinesterase after
    several days but no signs of poisoning. A single application of 1
    mg/kg bw was tolerated without affecting cholinesterase activity,
    whereas a 2 mg/kg bw single dose inhibited the enzyme.

    2.2.6  Reported mishaps

    There have been several cases of suspected suicide. A 60-year-
    old man drank two liqueur glasses of demeton-S-methyl with two

    bottles of beer. Conventional treatment was given in hospital within
    two hours though there were no signs of toxicity at that time. In
    addition, the patient was treated for chronic illnesses. At 60 hours
    numbness developed, followed by diarrhoea at 72 hours and he died of
    cardiac failure at 81 hours post-administration. No laboratory
    findings were reported. A 65-year-old male ingested 15 ml of a
    mixture of demeton-S-methyl (25%) and benzene methyl chloride; there
    were no clinical signs of toxicity upon admission to hospital. After
    32 hours his condition deteriorated; signs and symptoms were
    consistent with anticholinesterase poisoning. Given conventional
    treatment, he appeared to be recovering but died nine days later of
    a pulmonary embolus.

    A farmer drank 90 ml of a 70% a.i. solution of demeton-S-
    methyl. Hospitalized within 30 minutes with the usual signs and
    symptoms of anticholinesterase poisoning, he responded well to
    conventional treatment including gastric lavage, recovering

    A 26-year-old male injected demeton-S-methyl into his upper arm
    at a rate of 44.6 mg/kg; surgical drainage released some of the
    fluid. The patient survived a protracted illness with conventional


    Fish, LC50 (96 hours);1
    Cyprinus carpio                         40-60 mg/litre
    Scardinius erythrothalmis               30-40 mg/litre
    Idis                                    20-40 mg/litre
    Carassius duratus                       20-40 mg/litre


    1 Data supplied by manufacturer.



    (For definition of categories, see the Introduction to Data

    Liquid formulations of 20.0% and over, Category 2

    Other liquid formulations, Category 3

    There are no solid formulations available.


    All formulations - Should be transported and stored in
    clearly labelled impermeable containers under lock and key, secure
    from access by children and other unauthorized persons. No food or
    drink should be stored in the same compartment.

    3.3  HANDLING

    All formulations - Full protective clothing (see section
    4.1.3) should be used by those handling the compound. Adequate
    washing facilities should be available at all times during the
    handling and should be close to site of handling. Eating, drinking
    and smoking should be prohibited during handling and before washing
    after handling.


    All formulations - Containers must be either burned or
    crushed and buried below topsoil. Care must be taken to avoid
    subsequent contamination of water sources. Decontamination of
    containers in order to use them for other purposes should not be


            All formulations - Pre-employment medical examination of
    workers necessary. Workers suffering from hepatic or renal disease
    should be excluded from contact. Pre-employment and periodic
    cholinesterase tests for workers desirable. Special account should
    be taken of the workers' mental ability to comprehend and follow
    instructions. Training of workers in techniques to avoid contact


            All formulations: Pilots and loaders should have special
    training in application methods and early symptoms of poisoning, and
    must wear a suitable respirator. Use of flagmen not recommended.
    Flagmen, if used, should wear protective clothing and be located
    well away from the dropping zone.

    3.7  LABELLING

            All formulations:

                             "DANGER - POISON"

                     (skull and cross-bones insignia)

            Demeton-S-methyl is an organophosphorus compound which inhibits
    cholinesterase. It is highly toxic. Contact with the skin,
    inhalation of dust or spray, or swallowing may be fatal. Wear
    protective gloves, clean protective clothing, and a respirator of
    the organic-vapour type when handling this material. Bathe
    immediately after work. Ensure that containers are stored under lock
    and key. Empty containers must be disposed of in such a way as to
    prevent all possibility of accidental contact with them. Keep the
    material out of reach of children and well away from foodstuffs,
    animal feed and their containers.

            In case of contact, immediately remove contaminated clothing
    and wash the skin thoroughly with soap and water; for eyes, flush
    with water for 15 minutes.

            If poisoning occurs, call a physician. Atropine sulfate and
    pralidoxime are specific antidotes; repeated doses may be necessary.
    Artificial respiration also may be needed.


            Maximum residue levels - Maximum residue levels have been
    recommended by the Joint FAO/WHO Meeting on Pesticide Residues.



    4.1.1  General

            Demeton-S-methyl is an organophosphorus pesticide of high
    toxicity. It penetrates the intact skin and is also absorbed by
    inhalation and from the gastrointestinal tract. Repeated exposure
    may have a cumulative effect on cholinesterase levels. Most
    formulations should be handled by trained personnel wearing
    protective clothing.

    4.1.2  Manufacture and formulation - TLV

            No information. Closed systems and forced ventilation may be
    required to reduce, as much as possible, the exposure of workers to
    the chemical.

    4.1.3  Mixers and applicators

            When opening the container and when mixing, protective
    impermeable boots, clean overalls, gloves and respirator should be
    worn. Mixing, if not mechanical, should always be carried out with a
    paddle of appropriate length. When spraying tall crops or during
    aerial application, a face mask should be worn as well as an
    impermeable hat, clothing, boots and gloves. The applicator should
    avoid working in spray mist and avoid contact with the mouth.
    Particular care is needed when equipment is being washed after use.
    All protective clothing should be washed immediately after use,
    separate from other laundry, including the insides of gloves.

            Splashes must be washed immediately from the skin, or eyes,
    with large quantities of water. Before eating, drinking or smoking,
    hands and other exposed skin should be washed.

    4.1.4  Other associated workers (including flagmen in aerial

            Persons exposed to the compound and associated with its
    application should wear protective clothing and observe the
    precautions described above in section 4.1.3 under "Mixers and

    4.1.5  Other populations likely to be affected

            With good application practice, subject to section 4.2 below,
    other persons are not likely to be exposed to hazardous amounts of
    the compound.


            Unprotected persons should be kept out of tall crops for four
    days and out of other crops for 24 hours after application.


            Residues in containers should be emptied in a diluted form into
    a deep pit, taking care to avoid groundwaters. The empty container
    may be decontaminated by rinsing two or three times with water and
    scrubbing the sides. An additional rinse should be carried out with
    5% sodium hydroxide solution which should remain in the container
    overnight. Impermeable gauntlets should be worn during this work and
    a soakage pit should be provided for the rinsings. Decontaminated
    containers should not be used for food or drink. Spillage of the
    compound and its formulations should be removed by washing with 5%
    sodium hydroxide solution and then rinsing with large quantities of


    4.4.1  Early symptoms of poisoning

            Early symptoms of poisoning may include excessive sweating,
    headache, weakness, giddiness, nausea, vomiting, hypersalivation,
    stomach pains, blurred vision, slurred speech and muscle twitching.
    Later there may be convulsions and coma.

    4.4.2  Treatment before person is seen by a physician; if these
           symptoms appear following exposure

            The person should stop work immediately, remove contaminated
    clothing and wash the affected skin with soap and water, if
    available, and flush the area with large quantities of water. If
    swallowed, and if the person is conscious, vomiting should be
    induced. In the event of collapse, artificial resuscitation should
    be given, bearing in mind that, if mouth-to-mouth resuscitation is
    used, vomit may contain toxic amounts of pesticide.



    5.1.1  General information

            Demeton-S-methyl is an organophosphorus pesticide of moderate
    mammalian toxicity which is active against a variety of agricultural
    and public health pests. It is readily absorbed from the
    gastrointestinal tract; through the intact skin; and by inhalation.
    It is converted  in vivo to the oxygen derivatives which inhibit
    cholinesterase. It does not accumulate in body tissues.

    5.1.2  Symptoms and signs

            Initial symptoms of poisoning may include excessive sweating,
    headache, weakness, giddiness, nausea, hypersalivation, vomiting,
    stomach pains, blurred vision, slurred speech and muscle twitching.
    More advanced symptoms of poisoning may be convulsions, coma, loss
    of reflexes and loss of sphincter control.

    5.1.3  Laboratory

            The most important finding is reduction of activity of blood
    cholinesterases. Urinary levels of organic phosphorus containing
    metabolites may also be used as a measure of exposure. Neither
    method is specific for the compound.

    5.1.4  Treatment

            If the pesticide has been ingested, unless the patient is
    vomiting, rapid gastric lavage should be performed using 5% sodium
    bicarbonate if available. For skin contact, the skin should be
    washed with soap and water. If the compound has entered the eyes,
    they should be washed with large quantities of isotonic saline or

            Persons without signs of respiratory inefficiency but with
    manifest peripheral symptoms should be treated with 2-4 mg of
    atropine sulfate by intravenous injection and 1000 mg pralidoxime
    chloride or 250 mg of toxogonin (adult dose) by slow intravenous
    injection. More atropine may be given as needed. Persons with severe
    intoxication, with respiratory difficulties, convulsions and
    unconsciousness should immediately be given atropine and a
    reactivator. In such severe cases, 4-6 mg of atropine sulfate should
    be given initially followed by repeated doses of 2 mg at 5-10 minute
    intervals. Diazepam may be given to control convulsions. The
    patient's condition including respiration, blood pressure, pulse
    frequency, salivation and convulsions should be carefully observed
    as a guide to further administration of atropine. If the patient is

    cyanotic, oxygen should be given at the same time as atropine

            The airways should be kept free and artificial resuscitation
    should be applied if required, preferably by mechanical means. If
    necessary, intubation should be performed.

            Contraindicated are morphine, barbiturates, phenothiazine,
    tranquillizers and central stimulants of all kinds. Pralidoxime and
    toxogonin alone are not regarded as effective antidotes in
    organophosphorus poisoning. In cases of severe poisoning, when
    administered early, pralidoxime may be used to relieve nicotinic

    5.1.5  Prognosis

            If the acute toxic effect is survived and adequate artificial
    resuscitation has been given if needed, the chances of complete
    recovery are good. However, in very severe cases, particularly if
    artificial resuscitation has been inadequate, prolonged anoxia may
    give rise to permanent brain damage.

    5.1.6  References of previously reported cases

            Demeton-S-methyl has been implicated in a number of cases of
    pesticide poisoning.

            Barr, A.M. (1964) M. J. Aust., 1, 792-796

            Tilsner, V. (1966) Vergiftung Argtliche Fosch., 20, 272-273

            United Kingdom Ministry of Agriculture, Fisheries and Food
    (1969) Report on the use of poisonous substances in agriculture and
    on the worker and of the Agriculture Regulations during 1969

            Hegazy, M. R. (1965) Br. J. Med., 22, 230-235

            Khasanor, V. K. & Li, A. P. (1970) Med. Zh. Uzb., 7, 12-13

            Readhead, I. H. (1968) Lancet, 1, 686-688


                                           Normal    Action    Symptomatic
            Test                          level*    level*       level*  

            Plasma cholinesterase                         100%            50%          variable

            Whole blood or erythrocyte
            cholinesterase                                100%            70%          usually 40%


    5.3.1  Detection and assay of compound

            Thin-layer chromatography and gas-liquid chromatography methods
    have been used to analyse demeton-S-methyl in technical products and
    in its formulations. Analysis of residues in plant and animal
    tissues gas chromatography and flame photometry methods.

            Boshoff, P. R. & Pretorium, V. (1979) J. Agric. Food Chem.,
            27(3), 626

            Brinkman, U. & De Vries, G. (1979) Chromatog., 161(1), 167

            CIPAC HANDBOOK (1970) Vol. 1, p. 312

            Fysh, R. R. & Jones, L. V. (1980) Forensic Toxicol., Eur.
            Meet. Int. Assoc. Forensic Toxicol., pp. 189-203

            Hild, J. & Thief, H. P. (1978) Z. Lebensom. Unters. Forsch.,
            166(1), 9

            Laws, E. Q. & Webley, D. J. (1959) Analyst (London), 84, 28

            MacDougal, D. (1964) Anal. Methods Pestic. Plant Growth
            Regulators Food Adit., 2, 295 Ramsay, J. D. et al. (1980) J.
            Chromatogr., 184(2), 185

            Stan, H. J. (1977) Z. Lebensom. Unters. Forsch., 164(3), 153

            Start, H. J. et al. (1977) Fresenius 'Z'. Anal. Chem.,
            287(4-5), 271

            Tietz, H. & Frehse, H. (1960) Hoefchen-Briefe (Eng. Edition),
            3, 212


    * Expressed as percentage of pre-exposure activity.

            Van der Merwe, J. H. & Taylor, W. B. (1977) Pflanzenschutz-
            Nachr. (Amer. Edition), 24, 259

            Wagner, K. & Thorton, J. S. (1977) Pflanzenschutz-Nachr.,
            30(1), 1

    5.3.2  Other tests in case of poisoning

            Levels of cholinesterase in the blood, particularly plasma,
    provide the most useful diagnosis of poisoning.

            Michel, N. O. (1949) J. Lab. Clin. Med., 34, 1564-1568

            Ellman, G. L. et al. (1961) Biochem. Pharmacol., 7, 88-95

            Measurement of urine metabolites may also be determined in
    order to give an indication of exposure. For methods, see section
    5.3.1, "Detection and assay of compound".

See Also:
        Demeton-s-methyl (PIM 760)