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                                                      ORIGINAL: ENGLISH


    December 1976


         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.

    Part 1 - General Information

                             Primary use:      Insecticide

                             Secondary use:    Avicide, Acaricide

                             Chemical group:   Organophosphorus compound

                             Data sheet No.    23

                             Date issued:      December 1976


    1.1.1  Identity:

         dimethyl 3-methyl-4-methylthiophenyl phosphorothionate.



    Synonyms     Local synonyms

    1.2  SYNOPSIS

    An organophosphorus insecticide of moderate mammalian toxicity which
    may be absorbed through the skin, from the gastrointestinal tract
    and by inhalation. It is active upon metabolism into the more toxic
    oxygen analogue. Symptoms after acute poisoning tend to be


    1.3.1  Physical characteristics

    When pure, colourless, almost odourless liquid of boiling point 87°C
    at 0.01 mm Hg. The technical material is 95-98% pure, a brown oily
    liquid with a weak garlic odour.

    1.3.2  Solubility

    Water at 20°C, 54-56 ppm, readily soluble in most organic materials
    and glyceride oils.

    1.3.3  Stability

         It is stable up to 160°C and is resistant to light and alkaline

    1.3.4  Vapour pressure (volatility)

    4 x 10-5 mm Hg at 20°C. It has a low vapour pressure but is
    slightly volatile


    1.4.1  Common formulations

    Fogging concentrates between 40% and 60%: wettable powders 25% to
    40%; emulsifiable concentrates 50%; dusts 3%; ultra low volume
    application 1000 g per litre.

    1.4.2  Pests mainly controlled

    Used as a contact and stomach insecticide and is highly persistent.
    Effective against fruit flies, leaf hoppers, cereal bugs, weaver
    birds, animal parasites, mites, aphids, codling moth.

    1.4.3  Use pattern

    Used preharvest on sugar cane, rice, field corn, beets, pome and
    stone fruit, citrus fruits, pistachio, cotton at rates up to
    2 kg/ha. Active matter - also on olives, coffee, cocoa, vegetables,
    vines and corn at rates up to 1 kg/ha.

    1.4.4  Unintended effects

    Not phytotoxic if used at the recommended dose rates. Applications
    are not likely to give rise to contamination of food.


    Mainly as larvicide in mosquito control. Not recommended for
    residual indoor application due to rather high mammalian toxicity.


    Not recommended for indoor use.

    Part 2 - Toxicology and risks


    2.1.1  Absorption route

    Absorbed by the intact skin as well as by inhalation and from the
    gastro-intestinal tract.

    2.1.2  Mode of action

    Cholinesterase inhibition after conversion into the more toxic
    oxygen analogue in the body.

    2.1.3  Excretion

    In rats 86% of an oral dose is eliminated in seven days (urine 45%
    and faeces 40%). Metabolites include the sulfone and sulfoxide of
    both the parent compound and its oxygen analogue.

    2.1.4  Toxicity, single dose

    Oral LD50 rat  (M) 215 mg/kg     Dermal LD50 rat (M) 330 mg/kg
                   (F) 245 mg/kg                 rat (F) 330 mg/kg

    Dermal LD50 rabbit (M) 150 mg/kg

    Most susceptible species

    Calf - oral LD50 approximately 40 mg/kg

    2.1.5  Toxicity, repeated doses


    Rats of both sexes were given repeated oral doses of 10, 25, 50 and
    100 mg/kg for five days. No deaths were observed at 10 and 25 mg/kg.
    One out of four animals died at 50 mg/kg and all died at 100 mg/kg.
    Fasciculations were observed after a single dose of 25 mg/kg.

    Daily oral doses of 25 mg/kg for 75 days, six days a week to 30 rats
    killed 12 animals. Daily administration of 30 mg/kg five days a week
    for 13 weeks to male rats gave a 30% mortality and 80-90% reduction
    of cholinesterase activity. Cholinesterase recovery was slow, up to
    40 days.


    Female rats tolerated a daily one-hour inhalation exposure to
    fenthion of 0.163 mg/l for 30 days with inhibition of cholinesterase
    but no deaths. At 0.415 mg/l, all animals died within 10 days.


    Dermal administration of fenthion at 14.5 and 25 mg/kg for 60 days
    to rats resulted in 40% mortality in the higher dosed group. Blood
    cholinesterase activity was reduced to 20% of normal in the lower
    group. The five-day repeated dermal LD50 has been given as
    73 mg/kg/day to rats (total dose 365 mg/kg).

    Cumulation of compound

    Fenthion is not cumulative to any marked degree. However,
    cholinesterase recovery is slow after inhibition by this compound.

    Cumulation of effect

    Repeated exposure may produce cumulative effect on cholinesterase.

    2.1.6  Dietary studies


    Male and female rats were fed fenthion at dietary levels of 0.25,
    0.50, 2.5 and 5.0 mg/kg for three months. Reduction of erythrocyte
    cholinesterase activity was observed at all dose levels. At the
    lowest level, 0.25 mg/kg, the inhibition, approximately 10-20%, was
    not progressive with time. Mortalities were observed in the females
    at 5.0 mg/kg, the animals died manifesting muscarinic and nicotinic
    effects. Histological examination revealed reduced spermatogenesis
    in the testis and atrophic prostate glands at the highest feeding
    levels (2.5 and 5.0 mg/kg).


         Six groups of 25 males and 25 female rats were fed for one year
    on diets of 2, 3, 5, 25 and 100 ppm fenthion. Survival of male rats
    at 25 ppm was slightly decreased and cholinesterase activity was
    reduced at the 5 ppm level and above with only those animals at 2
    and 3 ppm showing no adverse enzyme effects. Haemosiderosis was
    evident in the spleen of the rats at the 100 ppm level.

    2.1.7  Supplementary studies of toxicity


    No information available.


    A three generation study in rats at 3.15 and 75 ppm involving two
    litters per generation produced no adverse effects on rat
    reproduction. Only slight growth depression was observed at the
    highest dietary level.


    No neurological disruption in hens was observed when fenthion was
    administered orally as a single dose of 25 mg/kg and at up to
    100 ppm in the diet for 30 days.

    2.1.8  Modifications of toxicity

    Fenthion potentiates the acute intraperitoneal toxicity of malathion
    dioxathion and coumaphos in rats. The greatest - almost threefold -
    potentiation was with coumaphos. Reduction of cholinesterase
    activity was also potentiated by a combination of fenthion and
    coumaphos when fed to dogs.


    2.2.1  Absorption

    Ingestion has proved to be the important cause of severe poisoning
    with this compound. It may also be absorbed through the skin and by
    inhalation of dust particles.

    2.2.2  Dangerous doses

    Single: not known.

    Repeated: not known.

    2.2.3  Observations on occuptionally exposed workers

    Fenthion has been widely used in many parts of the world for control
    of household pests and mosquitos. Twenty-seven out of 28 workers who
    sprayed fenthion as residual indoor application for 15 days in a
    malaria control operational trial without taking adequate
    precautions, demonstrated various degrees of poisoning. These
    included headache, vertigo, blurred vision, muscle and abdominal
    pains, cramps, diarrhoea and prolonged vomiting. Very severe
    reduction of whole blood cholinesterase activity was observed, and
    it was still reduced a month after the end of spraying. However, in
    a second smaller spraying operation when precautions were more
    stringent, only one out of 12 men showed mild symptoms.

    In mosquito larviciding operations, dermal exposure was found to
    average 3.6 mg/h with both power and hard sprayers and 12.3 mg/h
    using a granular formulation dispersed by hand. Some workers showed
    some plasma cholinesterase depression but in no case was erythrocyte
    cholinesterase depressed.

    2.2.4  Observations on exposure of the General population

    No information available.

    2.2.5  Observations of volunteers

    No information available.

    2.2.6  Reported mishaps

    Apart from the incident when applied in a trial as a residual indoor
    insecticide, most incidents have been from ingestion of quantities
    of fenthion. In these separate incidents there has been recovery
    although the patients were suffering from severe poisoning (one was
    comatose and cyanosed at presentation). However, extensive treatment
    with pralidoxime, atropine, artificial respiration, and in one case
    endotracheal intubation, were necessary. In these cases the acute
    effects were prolonged; in one case, recovery took 30 days.


    2.3.1  Fish

    Information being obtained.

    2.3.2  Birds


    2.3.3  Other species

    Information being obtained.

    Part 3 - For regulatory authorities



    (For definition of categories, see introduction.)

    Liquid formulations above 10%, category 3. All others, category 4.
    Solid formulations above 10%, category 4. All others, category 5.


    All formulations

    United Nations Classification 6.1.

    Should be transported or 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.

    3.3  HANDLING

    Formulations in categories 3 and 4

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

    Formulations in category 5

    No facilities other than those needed for handling of any chemical
    may be required.


    Containers must either be 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 permitted.


    Formulations in categories 3 and 4

    Pre-employment medical examination of workers necessary. Workers
    suffering from active hepatic or renal disease should be excluded
    from contact. Pre-employment and periodic plasma and erythrocyte

    cholinesterase determinations 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 essential.

    Formulations in category 5

    No special cholinesterase monitoring of workers necessary. Warning
    of workers to minimize contact essential.


    All formulations

    Pilots and loaders should have special training in application
    methods and recognition of early symptoms of poisoning and must wear
    a suitable respirator. Use of flagmen not recommended. Flagmen, if
    used, should wear overalls and be located away from the dropping

    3.7  LABELLING

    Formulations in categories 3 and 4

    Minimum cautionary statement

    Fenthion is an organophosphorus compound which inhibits
    cholinesterase. It is poisonous if swallowed. It may be absorbed
    through the skin or inhaled as dusts or mists. Avoid skin contact;
    wear protective gloves, clean protective clothing and a respirator
    when handling the material. Wash thoroughly with soap and water
    after using. Keep the material out of reach of children, and well
    away from foodstuffs, animal feed and their containers. If poisoning
    occurs, call a physician. Atropine and pralidoxime are the specific
    antidotes and artificial respiration may be needed.

    Formulations in category 5

    Minimum cautionary statement

    This formulation contains fenthion, a toxic substance which is
    poisonous if swallowed. Keep the material out of reach of children
    and well away from foodstuffs, animal feed and their containers.


    Maximum residue limits for fenthion have been recommended by the
    Joint FAO/WHO Meeting on Pesticide Residues.

    Part 4 - Prevention of poisoning in man and emergency aid


    4.1.1  General

    Fenthion is an organophosphorus pesticide of moderate toxicity which
    penetrates the intact skin and is also absorbed by inhalation of
    dusts and from the gastrointestinal tract. Most formulations should
    be handled by trained personnel wearing protective clothing.

    4.1.2  Manufacture and formulation


    No information.

    Closed system and forced ventilation may be required to reduce as
    much as possible the exposure of workers to the chemical.
    Formulation should not be attempted without advice from the

    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
    hood, 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,
    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 fenthion and associated with its application
    should wear protective clothing and observe the precautions
    described above in 4.1.3 under "mixers and applicators".

    4.1.5  Other populations likely to be affected

    With good agricultural practice subject to 4.2 below, other
    populations should not be exposed to hazardous amounts of fenthion.


    Unprotected persons should be kept out of treated areas for at least
    one day. (Does not apply when used as a larvicide.)


    Residues in containers should be emptied in a dilute form into a
    deep pit taking care to avoid contamination of ground waters.
    Decontamination of containers in order to use them for other
    purposes should not be permitted. Spillage should be removed by
    washing with 5% sodium hydroxide solution and then rinsing with
    large quantities of water.


    4.4.1  Early symptoms of poisoning

    Early symptoms of poisoning are headache, vertigo, blurring of
    vision, tightness in the chest, joint and muscle pains, abdominal
    cramps, diarrhoea and repeated vomiting. Other symptoms that may
    occur include insomnia, loss of appetite, weakness, slurred speech,
    constriction of the pupils and generalized anxiety.

    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, vomiting should be induced if the person is conscious. 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 fenthion.

    Part 5 - For medical and laboratory personnel


    5.1.1  General information

    An organophosphorus pesticide of moderate toxicity which is absorbed
    through the intact skin as well as by inhalation and from the
    gastrointestinal tract. It is converted in vivo to its oxygen
    analogue which is an active cholinesterase inhibitor. Continued
    exposure to small amounts may inhibit blood cholinesterases to
    hazard levels.

    5.1.2  Symptoms and signs

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

    5.1.3  Laboratory

    The most important laboratory finding is reduction in activity of
    blood cholinesterases. Direct measurement can be made of metabolites
    in urine and faeces.

    5.1.4  Treatment

    If the pesticide has been ingested, unless the patient is vomiting,
    rapid gastric lavage should be performed using 54 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 isotonic saline or water.

    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 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. 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,
    artificial respiration should be given first and then atropine

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

    Contraindications are morphine, barbiturates, phenothiazine,
    tranquillizers and central stimulants of all kinds.

    5.1.5  Prognosis

    If the acute toxic effects are survived and these may be prolonged,
    and adequate artificial respiration has been given, the chances of
    complete recovery are good. However, in very severe cases,
    particularly if artificial respiration has been inadequate,
    prolonged hypoxia may give rise to permanent brain damage.

    5.1.6  References of previously reported cases

    Case histories and methods of treatment can be found in:

    Dean et al. (1967) So. African Med. J., 1017-1019

    Von Clarmann, M. et al. (1966) Arch. Toxik., 22, 2-11

    Pickering, E. N. (1966) Can. 3. Med. Tech., p. 174


            Test                  Normal level*    Action level*,+    Symptomatic level*

    Plasma cholinesterase           100%              50%                 variable

    Erythrocyte cholinesterase      100%              70%               usually < 40%

    +The level at which action has to be taken to terminate exposure of the men until
    recovery of cholinesterase occurs.

    *Expressed as percentage of pre-exposure activity.


    References only are given.

    5.3.1  Detection and assay of compound

    It is unlikely that unchanged fenthion will be detectable in human
    tissues after exposure. Determination of the level of blood
    cholinesterase is probably the most suitable method in cases of
    suspected poisoning. Levels of metabolites can be measured in urine
    or faeces. Most methods of residue analysis involve gas-liquid

    Thornton, 3. S. Chemagro Corp., Research Department, Report No.
    20.420 (revised 21 October, 1968)

    Bowman & Beroza (1968) J. Ag. Food Chem., 16, 399-402

    Additional information will be found in:

    Analytical methods for pesticides, Plant Growth Regulations and Food
    Additives, ed. Zweig, G., Vol. II, 1964, Academic Press

    5.3.2  Other tests in cases of poisoning

    Levels of cholinesterase in the blood provides the most useful
    diagnosis of poisoning for methods of estimation. See:

    Michel, N. O. (1969) J. Lab. Clin. Med., 34, 1566-1568

    Ellman et al. (1961) Biochem. Pharmacol. I., 88-95

                                    * * *

See Also:
        Fenthion (PIM 780)