INTOX Home Page

    WORLD HEALTH ORGANIZATION             FOOD AND AGRICULTURE ORGANIZATION
    ORGANISATION MONDIALE DE LA SANTE     ORGANISATION POUR L'ALIMENTATION
                                          ET L'AGRICULTURE

                                                      VBC/DS/82.49

                                                      ORIGINAL: ENGLISH






    DATA SHEETS ON PESTICIDES No. 49

    PIRIMIPHOS-METHYL






         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.
    R 185

                               CLASSIFICATION:

                               Primary use: Insecticide

                               Secondary use: Acaricide

                               Chemical group: Organophosphorus Compound

                               Date issued: January 1983

    1.  GENERAL INFORMATION

    1.1  COMMON NAME:

         Pirimiphos-methyl (BSI, ISO, ANSI)

    1.1.1  Identity:

         IUPAC          0,2-diethylamino-6-methylpirimidin-4-yl O,O-
                        dimethyl phosphorothioate
         CAS No. 1      phosphorothioic acid, O-(2-(diethylamino)-6-
                        methyl-4-pyridinyl) O,O-diethyl ester
         Cas Reg. No. 29232-93-7
         Mol. Formula C11H20N303PS
         Mol. Wt. 305.3

    CHEMICAL STRUCTURE

    1.1.2  Synonyms:

         ActellicR; ActellifogR; BlexR; PP511 (discontinued name);
    SilosanR; SybolR; OMS 1424.

    1.2  SYNOPSIS:

         Pirimiphos-methyl is a broad spectrum, non-cumulative
    organophosphorus pesticide; a cholinesterase inhibitor with fast
    acting fumigant, contact, and stomach action; and slightly toxic to
    mammals. Pirimiphos-methyl has translaminar action when sprayed on
    plants; short persistence on growing plants; and, long persistence
    on inert surfaces, including stored grain.

         It is fairly rapidly degraded in the environment.

    1.3  SELECTED PROPERTIES

    1.3.1  Physical characteristics

         The pure substance is a straw-coloured liquid. It has no
    characteristic odour; a M.P. of 15-18°C - it freezes to a white
    solid at 15°C; a density (d30) of 1.157; and, a refractive index
    (nD25) of 1.527. The U.V. spectrum is a strong absorption band
    at 248 nm and a weaker band at 300 nm. Weakly alkaline, it is
    slightly corrosive to tinplate and mild steel but not corrosive to
    brass, copper, stainless steel, nylon, polyethylene or aluminium.

    1.3.2  Solubility

         5.0 mg/l water at 30°C; miscible with, or very soluble in most
    organic solvents.

    1.3.3  Stability

         Stable for up to six months at normal room temperature, readily
    hydrolysed by concentrated acids and alkalis; decomposes in
    sunlight, low biological persistence on foliar surfaces and in plant
    tissues but excellent persistence on inert surfaces and on stored
    crops.

    1.3.4  Vapour pressure

         1.47 x 10-5 kPa (1.1 x 10-4 mm Hg) at 30°C.

    1.4  AGRICULTURE, HORTICULTURE AND FORESTRY

    1.4.1  Common formulations

         E.c. (250 and 500 g a.i./1), U.L.V. concentrate (500 g a.i./1),
    encapsulated formulation (200 g a.i./1), dusts (10 and 20 g
    a.i./kg), w.p. (250 and 400 g a.i./kg), a fog (100 g a.i./1), an
    aerosol (20 g a.i./1 with pyrethroids), a solvent free formulation
    (900 g a.i./kg) and a smoke generator formulation.

    1.4.2  Susceptible pests

         Pirimiphos-methyl is active against a wide variety of pests
    including ants, aphids, beetles, caterpillars, cockroaches, fleas,
    flies (including houseflies,  Drosophila, and biting flies), mites,
    mosquitos, moths, thrips, whiteflies and scales.

    1.4.3  Use pattern

         Pirimiphos-methyl is used as a general insecticide; in pre-
    harvest clean up of fruits and vegetables; and on horticultural
    plants. It is not recommended for use on celery. Pre-harvest

    withholding intervals of three to seven days are recommended
    following spray application, no such intervals are necessary
    following the use of fogs or smokes. Pirimiphos-methyl is also used
    for eradication of a wide range of stored product pests for long
    duration protection and, to control nuisance and disease vector
    insects.

    1.4.4  Unintended effects

         None reported.

    1.5  PUBLIC HEALTH USE

    1.5.1  Common formulations

         E.c. (250 and 500 g a.i./1), U.L.V. concentrate (500 g a.i./1),
    encapsulated formulation (200 g a.i./1), dusts (10 and 20 g
    a.i./kg), w.p. (250 and 400 g a.i./kg), a fog (100 g a.i./1), an
    aerosol (20 g a.i./1 with pyrethroids), a solvent-free formulation
    (900 g a.i./kg) and a smoke generator formulation.

    1.5.2  Susceptible pests

         Ants, beetles, bed-bugs, cockroaches, fleas, flies, lice,
    mites, mosquitos, and others as in 1.4.2.

    1.5.3  Use pattern

         Pirimiphos-methyl is used as a residual insecticide in malaria
    control programmes, applied indoors on walls and ceilings at 1 or 2
    g a.i./m2, usually as a 2.5-5% suspension at three-monthly
    intervals. It is also used as a U.L.V. spray and in thermal fogs to
    control mosquitos vectoring viral infections and, as a mosquito
    larvicide. It is extensively used as a residual spray in fly control
    programmes and as a 2% dust in rodent burrows to control DDT
    resistant fleas.  It should not be used directly on humans or on
    processed foods.

    1.5.4  Unintended effects

         None reported.

    1.6  HOUSEHOLD USE

    1.6.1  Common formulations

         It is available in emulsifiable concentrates (80 g a.i./1),
    dusts and aerosols (with pyrethroids) for home and garden use.

    1.6.2  Susceptible pests

         Ants, beetles, bed-bugs, cockroaches, fleas, flies, lice,
    mites, mosquitos, wasps, and many nuisance insects and other
    arthropods.

    1.6.3  Use pattern

         As recommended by manufacturer; do not use on processed food.
    Do not harvest food crops until at least seven days after the last
    spray application.

    1.6.4  Unintended effects

         None reported.

    2.  TOXICOLOGY AND RISKS

    2.1  TOXICOLOGY - MAMMALS

    2.1.1  Absorption route

         Pirimiphos-methyl may be absorbed from the gastrointestinal
    tract; through the intact skin; and less commonly, by inhalation of
    fogs, smokes or spray mists.

    2.1.2  Mode of action

         Cholinesterase inhibition by pirimiphos-methyl. The degradation
    products desethyl pirimiphos-methyl and pirimiphos-methyloxon are
    also active but of transient stability and have not figured
    significantly in mammalian studies.

    2.1.3  Excretion products

         Detoxification of pirimiphos-methyl by metabolism and excretion
    is very rapid in mammals. In 14C-labelled pirimiphos-methyl dosed
    rats, over 70% of the radioactivity was excreted within 24 hours and
    100% within five to six days, 85% in urine and 15% in faeces. Twelve
    metabolites, none with cholinesterase inhibiting activity, were
    detected in the urine of treated rats and dogs. Metabolism,
    quantitatively similar in both species, proceeds primarily by
    cleavage of the P-O bond. The oxon product appears to be an
    important active intermediary which is rapidly detoxified in
    homeotherms.

    2.1.4  Toxicity, single dose

         Oral:   LD50 Rat (M)               1450 mg/kg b.w.
         Rat (F)                       1840-2260 mg/kg b.w.
         Rabbit (M)                    1154-2300 mg/kg b.w.
         Mouse (M)                     1030-1360 mg/kg b.w.
         Guinea-pig (F)                1000-2000 mg/kg b.w.
         Dog (M)                          > 1500 mg kg b.w.
         Cat (F)                        575-1150 mg kg b.w.

         In acute oral toxicity studies on rats the onset of toxicity
    signs was delayed 12-14 hours after dosing and persisted for 10-12
    days.

         Dermal: LD50 Rat (F)            > 4500 mg/kg b.w.

         I.P.: LD50 Rat (M)                 800 mg/kg b.w.

         Most susceptible species: No appreciable species variability
    among the mammals tested; the hen (LD50 79-80 mg/kg) is the most
    susceptible.

    2.1.5  Toxicity, repeated doses

         Oral: Groups of male and female rats were dosed for two
    weeks, five days a week. At 200 mg/kg only mild signs were observed,
    toxicity was delayed and reversible. There were no mortalities; body
    weights and haemoglobin were reduced; reticulocytosis and spleenic
    haematopoesis were observed. At 400 mg/kg severe signs of poisoning
    appeared after the second dose; the severity of toxicity increased
    with each successive dose; the cumulative mortality was nine of 10
    rats from day 4 for males and three of 10 from day 6 for females.

         Inhalation: Male and female rats exposed to a nominal vapour
    concentration of 3.5 ppm for three weeks showed no signs of toxicity
    during the study period, no change in blood cholinesterase levels
    and no gross or histopathologic effects.

         Dermal: In rabbits, a daily application of 1000 mg/kg b.w. of
    pirimiphos-methyl for two weeks produced mild, reversible signs of
    poisoning and the onset of poisoning was delayed for several days.
    In a later 21-day study, the insecticide was applied to intact or
    abraded skin of male and female rabbits in occluded applications of
    0, 4, 40 or 400 mg/kg b.w. No treatment related adverse clinical
    signs, gross or histopathologic changes were observed. At the
    highest dose, on abraded skin, food consumption and plasma
    cholinesterase levels were depressed in both sexes; body weights
    were reduced in the females only. It was concluded that 40 mg/kg
    b.w. is a clear "no-effect" level for rabbits.

         Cumulation of compound: There was no evidence of accumulation
    of pirimiphos-methyl, or its metabolites in liver, kidney or adipose
    tissue of rats following four successive 7.5 mg/kg b.w. per oral
    daily doses of the 14C-labelled insecticide. In similar studies on
    domesticated animals there was no evidence of residue accumulation
    in either body tissues or animal produce.

         Cumulation of effects: Repeated exposure of rats to high
    doses of pirimiphos-methyl produced cumulative inhibitory effects on
    cholinesterase activity.

    2.1.6  Dietary studies

         Short-term: Pirimiphos-methyl was fed to four groups of rats
    (male and female) for 90 days at levels of 0, 8, 80 and 360 mg/kg
    diet. There were no mortalities in any of the dose groups. No
    effects were observed in the 8 mg/kg diet group. In the groups fed
    80 and 360 mg/kg significant signs of toxicity were observed; plasma
    and brain cholinesterase were inhibited; and, in females, there was
    a significant reduction in weight gain. In the group fed 360 mg/kg
    diet, the same effects were observed as in the 80 mg/kg group, but
    they were more severe and more rapid in onset; and, erythrocyte
    cholinesterase was inhibited. With the exception of brain
    cholinesterase activity the above effects were rapidly reversed upon
    cessation of treatment.

         Pirimiphos-methyl was given groups of dogs, both male and
    female, for 90 days at dose levels of O, 2, 10 or 25 mg/kg b.w.
    There were no mortalities. Females in the 10 and 25 mg/kg groups and
    males in the 25 mg/kg group showed reduced weight gains which were
    easily reversed on cessation of treatment.  At all dose levels there
    was a mild and reversible depression of plasma cholinesterase
    activity. At 10 and 25 mg/kg erythrocyte cholinesterase depression
    was marked and recovery was slow. Bile duct proliferation was
    observed in four out of 16 high dose dogs, three of those had
    received the 25 mg/kg dose. In a repeat study at 25 mg/kg, minimal
    bile duct proliferation was seen in two of the 10 animals but it was
    not observed in two dogs whose dose had been progressively raised to
    50 mg/kg b.w. from the eighth week onwards.

         Long-term: Pirimiphos-methyl was fed to groups of female and
    male mice for 80 weeks at concentrations of 0, 5, 250 or 500 mg/kg
    of diet. Animal deaths and rumour incidence were comparable between
    controls and treatment groups. At 250 and 500 mg/kg, plasma and
    erythrocyte cholinesterase was inhibited. The mouse "no-effect"
    level was determined from the 5.0 mg/kg diet to be equivalent to 0.5
    (mg/kg b.w.)/day.

         Pirimiphos-methyl was fed to groups of male and female rats for
    two years at concentrations of 0, 10, 50 or 300 mg/kg of diet. A few
    animals from each test group were kept on normal diet for an

    additional four to eight weeks, for recovery observations. With one
    exception, in males at 300 mg/kg between weeks 54 and 72, there was
    no treatment related increase in cumulative mortalities within the
    test groups. No adverse effects were seen apart from cholinesterase
    inhibition. Marked plasma cholinesterase depression and some
    erythrocyte and brain cholinesterase inhibition were observed at 300
    mg/kg. At 50 mg/kg, only female plasma cholinesterase activity was
    depressed. In all cases these enzyme activities returned to normal
    within four weeks after cessation of dosing. On the 10 mg/kg diet,
    no ill-effects were observed and therefore this dose was selected
    for the "no-effect" level for rats, equivalent to 0, 5 (mg/kg
    b.w.)/day.

         In a two-year study of dogs, pirimiphos-methyl was given per
    oral in doses of 0, 0.5, 2 or 10 (mg/kg b.w.)/day. Mild signs of
    toxicity were seen in all the high dose animals. There was no
    increase in gross or histopathologic incidences in any of the
    treatment groups. Erythrocyte and plasma cholinesterase activities
    were depressed in the 2 and 10 mg/kg groups, brain cholinesterase
    was inhibited at the 10 mg/kg level only. Cholinesterase activity
    was normal at the lower dose level, 0.5 (mg/kg b.w.)/day was
    selected as the "no-effect" level for dogs.

    2.1.7  Supplementary studies of toxicity

         Carcinogenicity: No evidence of carcinogenic activity was
    observed in the several diet studies described in section 2.1.6. In
    addition, no evidence supportive of a carcinogenic potential for
    pirimiphos-methyl was found in several mammalian mutagenicity
    studies.

         Teratogenicity: No evidence of teratogenicity was observed in
    studies of pregnant rats and rabbits fed pirimiphos-methyl in their
    diets at concentration levels of 10 and 20 mg/kg and 1 and 16 mg/kg
    respectively, for the duration of gestation. In both studies the
    litter size was increased and the foetus weights were decreased by
    the treatment. Pirimiphos-methyl has been shown to be teratogenic in
    chick-egg injection studies only, inducing micromelia and abnormal
    feathering after dosing on the fourth day of incubation. However, no
    teratogenic effects were observed in a dietary study in laying-hens
    at dose levels of 4' to 40 mg/kg of diet.

         Reproduction: Pirimiphos-methyl was fed continuously to rats
    in two three-generation studies, in one the dose levels were 5, 10
    and 100 mg/kg (diet) and in the other were 20 and 200 mg/kg (diet).
    No treatment related embryotoxic effects were observed in either
    study. The pesticide had no adverse effect on reproduction
    performance at dose levels up to 100 mg/kg (diet), at 200 mg/kg
    (diet) the pregnancy rate was slightly depressed. (See also the
    section on teratogenicity above.)

         Mutagenicity: Pirimiphos-methyl showed no mutagenic potential
    in several mammalian studies including two three-generation studies,
    a micronucleus test in young female ICR mice, or in a mouse dominant
    lethal study. It was found to be mutagenically active in a plate
    assay of six out of seven  S. typhimurium strains but in none of
    the  E. coli strains used in microbial screening tests.

         Irritation and sensitization: There were no signs, of
    sensitization nor primary irritation in a 24-hour occluded patch
    test in which a 50% pirimiphos-methyl solution in olive oil was
    applied to the dorsal skin of guinea-pigs and in another study in
    which the undiluted compound was applied to the dorsal skin of rats.

         Neurotoxicity: Two groups of five hens were given single oral
    doses of pirimiphosmethyl at 50 and 60 mg/kg. One hen died in the
    first dose group and three in the latter, at 21 days the dead
    animals were replaced, all the hens in each group were redosed and
    protected with atropine and pralidoxime. The hens were observed for
    an additional 21 days, no neurotoxicity was found in the treatment
    groups that could be attributed to pirimiphos-methyl.

         In another study, 10 birds received 0, 0.5, 1.0, 2.5, 5.0 or 10
    mg/kg b.w. by direct intubation daily for 90 days. There were no
    clinical or histopathological findings associated with
    neurotoxicity.

    2.2  TOXICOLOGY - MAN

    2.2.1  Absorption

         It may be absorbed from the gastrointestinal tract; through the
    intact skin; and, by inhalation of fogs, smokes or spray mist when
    used in confined spaces.

    2.2.2  Dangerous doses

         Single: Not known.

         Repeated: Not known.

    2.2.3  Observations of occupationally exposed workers

         A total of 35 trained personnel participated in two separate
    WHO-supervised public health spray programmes, none showed any ill-
    effects attributable to pesticide poisoning. At the termination of
    one programme three of the 12 spraymen showed plasma cholinesterase
    activities which were 70-75% of the mean of two pre-exposure values.

    2.2.4  Observations on exposure of the general public

         The inhabitants of two locations involved in the above-
    mentioned pirimiphos-methyl spray programmes did not show or
    complain of any ill-effects attributable to pesticide poisoning; no
    observations of cholinesterase activity were reported.

    2.2.5  Observations on volunteers

         Liver function and blood test results were within the normal
    limits in two groups of volunteers given 0.25 (mg/kg)/day, five
    males for 28 days and three males and four females for 56 days. From
    these results, 0.25 (mg/kg)/day was accepted as the "no observed
    effect" level. The acceptable daily intake (ADI) was established at
    0.01 mg/kg; the ADI represents the sum of the oxygen analogue,
    n-desmethyl pirimiphos-methyl and the parent compound in total
    expressed as pirimiphos-methyl.

    2.2.6  Reported mishaps

         There are no reports of human poisoning attributed to
    pirimiphos-methyl.

    2.3  TOXICITY TO NON-MAMMALIAN SPECIES

    2.3.1  Fish

         LC50, static tests: Carp (24-hour)           1.6 mg/l
                             Carp (48-hour)           1.4 mg/l
                             Rainbow trout (48-hour)  0.25 mg/l

         LC50, flow through tests:  Rainbow trout (24-hour)   0.78 mg/l
                                    Rainbow trout (48-hour)   0.53 mg/l
                                    Fathead minnow (24-hour)  5.60 mg/l
                                    Fathead minnow (48-hour)  4.10 mg/l

         The threat to fish is greatly reduced by the strong tendency of
    pirimiphos-methyl to decompose in aqueous solutions and, to undergo
    photo-oxidation.

    2.3.2  Birds

         Oral: LD50 Chickens                       79-80 mg/kg
                    Japanese quail                   140 mg/kg
                    Green finches                200-400 mg/kg

         I.P.: LD50 Japanese quail               140 mg/kg

         Diet: LC50 Mallard ducklings                630 mgkg
                    Bobwhite quail chicks            207 mg/kg

         In two diet studies, chickens were fed pirimiphos-methyl in
    doses ranging from 4 to 40 ppm, there was no lasting adverse effect
    on hens, chicks; or, egg production, quality, or hatchability.

         The relatively high toxicity of pirimiphos-methyl to birds
    appears to be related to a deficiency of esterases that hydrolyze
    pirimiphos-methyloxon. In 14 species of birds representing six avian
    orders the rate of hydrolysis of the oxon by  in vitro plasma
    A-esterase ranged from a non-detectable-level to 71 (nmoles/min.)/ml
    plasma, at best it was less than 10% of the lowest recorded
    mammalian rate.

    2.3.3  Other species

         No information.

    3.  FOR REGULATORY AUTHORITIES - RECOMMENDATIONS ON REGULATION
        OF COMPOUND

    3.1  RECOMMENDED RESTRICTIONS ON AVAILABILITY

         (For definitions of categories, see introduction).

         Liquid and solid formulations above 10 and 30% respectively:
    category 4.

         Other formulations: category 5.

    3.2  TRANSPORT AND STORAGE

         Formulations in category 4 - Should be transported and stored
    in clearly labelled, rigid and leakproof containers, under lock and
    key, secure from access by unauthorized persons and children. No
    food or drink should be transported or stored in the same
    compartment.

         Formulations in category 5 - Should be transported and stored
    in clearly labelled leak-proof containers out of reach of children,
    away from food and drink.

    3.3  HANDLING

         Formulations in category 4 - Protective clothing (see 4.1.3-
    4.1.4) should be used by all persons handling the compound. Adequate
    facilities should be available at all times during the handling and
    should be close to the site of handling. Eating, drinking and
    smoking should be prohibited during handling and before washing of
    hands and face.

         Formulations in category 5 - No facilities other than those
    needed for handling of any chemical are required.

    3.4  DISPOSAL AND/OR DECONTAMINATION OF CONTAINER

         Containers may be decontaminated. Decontaminated containers
    should not be used for food or drink. If not decontaminated, empty
    containers should be burned or crushed and buried below topsoil.
    Care must be taken to avoid subsequent contamination of water
    resources.

    3.5SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS

         Formulations in category 4 - Pre-employment medical
    examination of workers is desirable. Workers suffering from active
    hepatic or renal disease should be excluded from contact. Special
    account should be taken of workers' mental ability to comprehend and
    follow instructions. Training of workers in techniques to avoid
    contact is essential.

         Formulations in category 5 - No pre-employment medical
    examination for workers is necessary. Warning to workers to minimize
    contact is essential.

    3.6  ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT

         All formulation - Pilots and loaders should have special
    training in application methods and in recognition of early symptoms
    of poisoning. Loaders must wear overalls, rubber gloves and goggles.
    Flagmen should wear overalls and an impermeable brimmed hat; and
    should be located well away from the dropping zone.

    3.7  LABELLING

         Formulations in category 4 - Minimum cautionary statement -
    Pirimiphos-methyl is an organophosphorus compound. It is of low
    toxicity and should not be used by people under medical advice not
    to work with such compounds. Avoid all mouth contact, skin contact
    or inhalation of spray, dust, fog or smoke. Wash splashes from skin
    and eyes immediately wash hands before eating or smoking after
    handling the pesticide and, wash oneself and change clothing
    immediately after work.

         When handling concentrates wear protective gloves, a face
    shield, and clean protective clothing. When using foggers or when
    fumigating indoors, wear protective gloves, rubber boots, a rubber
    coat, sou'wester and a respirator and do not re-enter treated spaces
    until they have been thoroughly ventilated.

         Remove or cover all food and animal feedstuffs prior to
    application and do not apply to food preparation surfaces or
    utensils.

         Store pesticide in the original container, tightly closed and
    in a safe place away from children. Wash out empty containers
    thoroughly and dispose of safely. Do not contaminate ponds,
    waterways, ditches or ground waters with either the chemical
    directly or the used container.

         Do not harvest the indicated food crops for human consumption
    before the specified interval has elapsed between last application
    and harvest. Avoid application when bees are active.

         If poisoning occurs take the patient to the hospital
    immediately. Atropine and pralidoxime are specific antidotes. No
    sedatives should be given. Oxygen and artificial respiration may be
    necessary.

         Formulations in category 5 - Minimum cautionary statement -
    This formulation contains pirimiphos-methyl, a cholinesterase
    inhibitor. Avoid all mouth and skin contact, or inhalation of spray
    mist, dust, fog or smoke. Wash hands after use. Store in the
    original container in a safe place away from children and pets. Wash
    out empty container thoroughly and dispose of safely. In addition,
    for aerosol preparations, keep away from heat (including sun) and do
    not puncture or incinerate even when empty. Do not apply directly on
    to food, food utensils or food preparation surfaces. Do not harvest
    food crops until at least seven days after the last application.

    3.8  RESIDUES IN FOOD

         Maximum residue limits for pirimiphos-methyl have been
    recommended by the WHO/FAO Meeting on Pesticide Residues.

    4.  PREVENTION OF POISONING IN MAN AND EMERGENCY AID

    4.1  PRECAUTIONS IN USE

    4.1.1  General

         Pirimiphos-methyl is an organophosphorus pesticide of low
    mammalian toxicity which inhibits cholinesterase activity.

    4.1.2  Manufacture and formulation

         T.L.V.: 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, care should be
    taken to avoid contact with the mouth and eyes. If necessary, a
    facial visor and gloves should be worn. Mixing, if not mechanical,
    should always be carried out with a paddle of appropriate length.
    Splashes should be washed immediately from the skin or eyes with
    large quantities of water. Before eating, drinking or smoking, hands
    and exposed skin should be washed. If contaminated, clothing should
    be washed at the end of a working day.

    4.1.4  Other associated workers (including flagmen in aerial
           operations)

         Persons exposed to pirimiphos-methyl and associated with its
    application should wear clean overalls and observe the precautions
    described above in 4.1.3 under "Mixers and applicators".

    4.1.5  Other populations likely to be affected

         With correct use in agriculture, public health and in the home,
    the general population should not be exposed to hazardous amounts of
    pirimiphos-methyl. Harvesting intervals should be observed, as shown
    on the label they range from three to seven days depending upon the
    crop.

    4.2  ENTRY OF PERSONS INTO TREATED AREAS

         Unprotected persons may enter a treated area immediately after
    spraying, however, they should not enter premises recently treated
    by sprays, fogs or smokes before those premises have been thoroughly
    ventilated.

    4.3  DECONTAMINATION OF SPILLAGE AND CONTAINERS

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

    4.4  EMERGENCY AID

    4.4.1  Early symptoms of poisoning

         These may include excessive sweating, headache, weakness,
    giddiness, nausea, vomiting, stomach pains, blurred vision, slurred
    speech and muscle twitching. Later there may be convulsions, coma,
    loss of reflexes and loss of sphincter control.

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

         The person should stop work immediately, remove contaminated
    clothing and wash contaminated skin with soap and water, if
    available, and flush with large quantities of water. Vomiting should
    not be induced unless it is reasonably certain that a potentially
    lethal dose has been swallowed and, provided that the person is
    conscious - inhalation of the solvent must be avoided. In the event
    of collapse artificial respiration should be given bearing in mind
    that if mouth to mouth respiration is used, vomit may contain toxic
    amounts of pirimiphos-methyl.

    5.  FOR MEDICAL AND LABORATORY PERSONNEL

    5.1  MEDICAL DIAGNOSIS AND TREATMENT IN CASE OF POISONING

    5.1.1  General information

         Pirimiphos-methyl is an organophosphorus pesticide of low
    mammalian toxicity which may be absorbed from the gastrointestinal
    tract; through the intact skin; and by inhalation when fog and smoke
    generators are used or when spraying in a confined space. It acts by
    inhibiting acetycholinesterase. Continuous exposure to low amounts
    may inhibit blood cholinesterase to hazard levels.

    5.1.2  Symptoms and signs

         Initial symptoms of poisoning may include excessive sweating,
    headache, weakness, giddiness, nausea, 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 in activity of blood
    cholinesterases. Urinary levels of organic phosphorus containing
    metabolites could also be used as a measure of exposure. Neither
    method is specific for pirimiphos-methyl.

    5.1.4  Treatment

         If a potentially lethal dose has been ingested, unless the
    patient is vomiting, rapid gastric lavage should be performed. For
    skin contact, the skin should be washed with soap and water. If the
    compound has entered the eyes, they should be washed with isotonic
    saline. Persons without signs of respiratory inefficiency but with
    manifest peripheral symptoms should be treated with 2-4 mg of
    atropine sulfate and 1000-2000 mg of pralidoxime chloride or 250 mg
    of toxogonin (adult dose) by slow intravenous injection. More
    atropine may be given as needed. Persons with severe intoxication
    and 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 five to 10 minute intervals.
    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
    sulfate. The airways should be kept free and artificial respiration
    may be required, preferably by mechanical means. If necessary,
    intubation should be perforated. Contraindications are morphine,

    barbiturates, phenothiazine, tranquillizers and central stimulants
    of all kinds.

    5.1.5  Prognosis

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

    5.1.6  References to previously reported cases

         None.

    5.2  SURVEILLANCE TESTS

    Test                          Normal       Action      Symptomatic
                                  level*       level*      level*
                                                                      

    Plasma cholinesterase          100%          50%       variable

    Whole blood or erythrocyte
      cholinesterase               100%          70%
                                                                      

    * Expressed as percentage of pre-exposure activity.

         Urinary levels of ether-extractable phosphorus compounds may
    also be used to determine the degree of exposure.

    5.3  LABORATORY METHODS

         References only are given,

    5.3.1  Detection and assay of compound

         Yuen, S. A. (1976) Analyst (London), 101, 533

         Bullock, D. J. W. (1976) Analytical methods in pesticides and
    plant growth regulators, Vol. VIII, Chapter 9, 185

         Kirasnykh, A. A. (1978) Kimiya V Sel'Skom Khozaistve, 16, 36

    5.3.2  Other tests in cases of poisoning

         The level of cholinesterase in the blood, particularly the
    plasma, provides the most useful diagnosis of poisoning, see:
    Ellman, G. L. et al. (1961) Biochem. Pharmacol., 7, 88. Michel, N.
    O. (1949) J. Lab. Clin. Med., 34, 1564.

         Plasma and urine levels of methanol extractable pirimiphos-
    methyl and pirimiphos-methyl metabolites may also be useful in
    diagnosis of poisoning, see: Brealey, C. J. & Lawrence, D. K. (1979)
    Journal of Chromatography, 168, 461.


    Note:   This data sheet was drafted in the Bureau of Chemical
            Standards, Environmental Health Directorate, Health and
            Welfare, Canada, and subsequently underwent medical,
            scientific, and industrial review.

See Also:
        Pirimiphos methyl (PIM 361)