WHO Pesticide Residues Series, No. 1



    The evaluations contained in these monographs were prepared by the
    Joint Meeting of the FAO Working Party of Experts on Pesticide
    Residues and the WHO Expert Committee on Pesticide Residues that met
    in Geneva from 22 to 29 November 1971.1

    World Health Organization



    1 Pesticide Residues in Food: Report of the 1971 Joint Meeting of
    the FAO Working Party of Experts on Pesticide Residues and the WHO
    Expert Committee on Pesticide Residues, Wld Hlth Org. techn. Rep.
    Ser., No. 502; FAO Agricultural Studies, 1972, No. 88.

    These monographs are also issued by the Food and Agriculture
    Organization of the United Nations, Rome, as document AGP-1971/M/9/1.

    FAO and WHO 1972


    Chemical names:
    1.   dimethyl 3-methyl-4-methylthiophenyl

    2.   O,O-dimethyl-O-(4-methylmercapto-3-methyl-phenyl)-thiophosphate

    Synonyms:                (R)Lebaycid, (R)Baycid, (R)Baytex, (R)Entex,

                             BAY 29 493, S 1752



    Other information on identity and properties

    The pure active ingredient is a colourless liquid and the technical
    active ingredient is a brownish viscous liquid. The active ingredient
    has a boiling point of 87°C at 0.01 mm Hg. It is practically insoluble
    in water, and readily soluble in most organic solvents. It has a very
    low vapour pressure and slight volatility.

        Impurities in the technical active ingredient

    active ingredient (FAO-method No. 79/l/m/1.2)*                        95-97%

    O-methyl-O-(4-methylmercapto-3-methyl-phenyl)-thiophosphate           <0.5%

    5-hydroxy-2-methylmercapto-toluol                                     <0.5%

    O,S-dimethyl-O-(4-methylmercapto-3-methyl-phenyl)-thiophosphate       0.5-1.0%

    O,O,O,O-tetramethyl-dithiopyrophosphate                               <0.5%

    O,O-dimethyl-O-(4,6-bis-methylmercapto-3-methyl-phenyl)-thiophosphate 5-7%

    5-methoxy-2-methylmercapto-toluol                          <0.8%

    O,O,O-trimethyl-thiophosphate                              <0.5%

    Water                                                  max. 0.15%

    * By this analytical method the impurity
    is determined together with the active ingredient.

    Biochemical aspects

    Absorption, distribution and excretion

    The first studies on mammals (rats) were reported by Brady and Arthur
    (1961) who used a p32-labelled compound. Within a few hours of
    applying the compound, large amounts of p32-activity was found in
    the tissues including the bones, evidence that fenthion was rapidly
    degraded by rats. Fenthion or its oxidative metabolites were, however,
    not stored in tissues even when rats received daily doses of 10 mg/kg
    by the intraperitoneal route for 10 consecutive days. At 1.5 hours,
    following a single i.p. injection of 200 mg/kg, the following
    acetonitrile-soluble residues were observed:

                          liver            29.5 ppm
                          muscle            9.6 ppm
                          skin              6.1 ppm
                          kidney           26.9 ppm
                          heart             9.6 ppm

    The tissues from rats treated orally with 100 mg/kg (single dose)
    contained less than 0.01 ppm chloroform-soluble residues at three days
    after treatment, except for the liver (0.2 ppm); the blood, brain and
    fat of these animals contained no detectable acetonitrile-soluble
    residues, either. The orally treated animals eliminated 86% of the
    activity in the excreta by seven days after treatment. One to four per
    cent. of the activity in urine and faeces was chloroform-soluble.

    As a result of partial starvation, oxidative metabolism in rabbits was
    increased as evidenced by greater concentrations of fenthion-oxygen
    analogue in blood. The peak of radioactive substances in blood of
    normal rabbits following oral or subcutaneous administration of 35S
    fenthion was observed in six to nine hours following treatment while
    in starved rabbits the peak value was obtained one hour after
    treatment (Begum, 1967).


    Fenthion is activated through an enzymatic oxidation, in both plants
    and animals, to more active anti-cholinesterase compounds. The molar
    I50 fenthion for rat brain cholinesterase is 1.3 × 10-4m. (Dubois
    and Kinoshita, 1964). Following intraperitoneal administration of
    32p-labelled fenthion approximately 75% of the administered dose was
    recovered within three days in rat urine (60%) and faeces (15%). After

    oral administration 86% of the dose was excreted in urine (45%) and
    faeces (40%) with the majority excreted in three days (Brady and
    Arthur, 1961). Starvation of rabbits had no effect on elimination of
    fenthion (or metabolites) following oral or subcutaneous acute
    administration (Begum, 1967). Five metabolites (see Figure I) were
    isolated from rat urine and characterized as the sulfoxide (II) and
    sulfone (III) of the phosphorothioate (I), the oxygen analogue (IV) of
    the parent compound and its corresponding sulfoxide (V) and sulfone
    (VI) derivatives.

    In rabbits the major urinary metabolites were fenthion-sulfoxide (II),
    fenthion-O-sulfoxide (V) and sulfone (VI) (Begum, 1967). The metabolic
    scheme appears as shown in Figure I.

    Effects on enzymes and other biochemical parameters

    Fenthion and its metabolites are typical organophosphorus
    anticholinesterase agents. Typical of this class of agents the oxygen
    analogue is the most potent enzyme inhibitor of all the metabolites
    containing a phosphorus triester configuration (Francis and Barnes,
    1963)). Fenthion is unusual in that clinically and biochemically a
    prolonged effect following a single dose is manifest (recovery of
    blood and brain enzyme levels is very slow (Brady and Arthur, 1961).
    This effect may be as a result of inhibition of cholinesterase by
    metabolites which are released at different rates from storage in the
    body (Francis and Barnes, 1963), or a possible potentiation of its own
    antiesterase effects by selectively inhibiting phosphatase activity
    (Brady and Arthur, 1961), which is responsible for hydrolysis of the
    phosphate ester. Cholinesterase inhibitor cannot be reactivated by
    2-PAM, TMB-4 or P-2-S in vivo indicating that fenthion may inhibit
    cholinesterase in a manner differing from many of the other
    organophosphate esters. (Dubois, 1960; Dubois and Kinoshita, 1964;
    Francis and Barnes, 1963).

    FIGURE 1


    Special studies

    (a)  Acute toxicity of the metabolites

    Compound                         Acute LD50 (mg/kg)  150 (M)c
                                     Orala     i.p.b
    I. Fenthion                      220       325       >5   × 10-4
    II. Fenthion sulfoxide           125       250       4.5  × 10-5
    III. Fenthion sulfone            125       250       4.7  × 10-4
    IV. Oxygen analogue              125       26        2.65 × 10-6
    V. O-Sulfoxide                   50        22        4.8  × 10-5
    IV. O-Sulfone                    30        9         3.2  × 10-5
    VIII. 4-(methylthio)m-cresol     6500d
    IX. 4-methyl(thiosulfoxide)
        m-cresol                     3500d
    X. 4-methyl(thiosulfone)
       m-cresol                      7000d

    a Male rats - according to Francis and Barnes, 1963.
    b Female rats - according to Dubois and Kinoshita, 1964.
    c 150 = Molar concentration resulting in 50% inhibition of
      human RBC Cholinesterase (Francis and Barnes, 1963).
    d Female rats according to Nelson, 1967.

    (b)  Reproduction

    Except for a slight growth depression at the highest level in the
    diet, fenthion at levels of 0, 3, 15 and 75 ppm for three generations
    (two litters per generation), produced no adverse effect on rat
    reproduction (Loser, 1969). Microscopic examination of the tissues of
    the F3b generation did not reveal any significant abnormality (Spicer,

    (c)  Potentiation

    Fenthion potentiates the acute intraperitoneal toxicity of malathion,
    dioxathion, and coumaphos in rats. Intraperitoneal administration of
    13 other organophosphate or carbamate insecticides did not result in a
    greater than additive effect when administered with fenthion (Dubois
    and Kinoshita, 1964). Dietary combination of fenthion with coumaphos
    neither of which alone affected cholinesterase when fed to dogs for
    six weeks, was found to potentiate the anticholinesterase activity of
    serum and red blood cells. Less evident potentiation was observed when
    fenthion and malathion were fed and when fenthion was fed in
    combination with dioxathion no potentiation was noted (Doull et al.,
    1962), Fenthion (2 ppm) and malathion (100 ppm) resulted in moderate

    erythrocyte and serum cholinesterase activity inhibition (30-40%).
    When fenthion (2 ppm) and dioxathion (3 ppm) was fed cholinesterase
    activity was not depressed. When fenthion (2 ppm) and coumaphos
    (2 ppm) was fed to dogs, significant inhibition (75%) of serum
    cholinesterase and moderate inhibition (30%) of erythrocyte
    cholinesterase was evident. Oral administration to rats of a 75:25
    mixture of fenthion and dichlorvos did not result in a greater than
    theoretically additive toxicity (Kimmerle, 1967b).

    (d)  Neurotoxicity

    No evidence for delayed neurological disruption in hens was evident
    when fenthion was administered orally at a single dose of 25 mg/kg
    (Kimmerle, 1965a). When chickens were fed up to 100 ppm in the diet
    for 30 days, clinical examination of the animals and histological
    examination of nerve tissue indicated no demyelinating effect from
    fenthion (Kimmerle, 1965b; Dieckmann, 1971).

    (e)  Antidotes

    A number of antidotes which are commonly used for organophosphorous
    poisoning have been shown to be relatively inactive when used
    following fenthion intoxication. Studies with atropine, 2-PAM
    Toxogonin P-2-S, and TMB-4 (Dubois and Kinoshita, 1964; Francis and
    Barnes, 1963; and Dubois, 1960; Lorke and Kimmerle, 1969) administered
    alone and in combination showed that these materials did not
    successfully alleviate the parasympathomimetic signs of
    organophosphate poisoning. When BH-G (Merck; Darmstadt, Germany) was
    administered three to four times in combination with atropine, the
    LD50 value increased from 250 to 440 mg/kg (Kimmerle, 1963).
    Toxogonin was not effective as a cholinesterase reactivator following
    oral intoxication of dogs by fenthion (Hahn and Henschler, 1969).

    Acute toxicity

    Animal        Route     LD50            Reference
    Mouse  (M)    Oral      150             Francis and Barnes, 1963
                            227             Dubois, 1968
           (F)              190             Francis and Barnes, 1963
                            225             Dubois, 1968
           (F)    i.p.      150             Dubois and Kinoshita, 1964
           (M)              125             Dubois and Kinoshita, 1964

    Animal        Route     LD50            Reference
    Rat    (F)    Oral      245-310         (Dubois and Kinoshita, 1964
                                            (Gaines, 1960
                            615             Francis and Barnes, 1963
           (M)              175-470         (Dubois and Kinoshita, 1964
                                            (Klimmer, 1963
                                            (Gaines, 1969
                                            (Francis and Barnes, 1963
           (M)    i.p.      325             Dubois and Kinoshita, 1964
           (F)              260             Dubois and Kinoshita, 1964
           (M)              152             Klimmer, 1963
           (M)    Dermal    330-650         Gaines, 1969
                                            Klimmer, 1963
                                            Francis and Barnes, 1963
           (F)              330-500         Dubois and Kinoshita, 1964
                                            Gaines, 1969
                                            Francis and Barnes, 1963

           (M)    Oral      1000            Francis and Barnes, 1963
                            260             Dubois and Kinoshita, 1964
                  i.p.      310             Dubois and Kinoshita, 1964

    Rabbit (M)    Oral      150-175         Francis and Barnes, 1963
                  Dermal    150             Klimmer, 1963

    Duck          Oral      15              Dubois and Doull, 1960
                            1-2             Keith and Mulla, 1966

    Chicken                 30              Dubois and Doull, 1960
                            28              Sherman and Ross, 1961
                            30-40           Francis and Barnes, 1963

    Calf                    Approx. 40      McGrath, 1961
    Various solvents used to solubilize fenthion in combination with water
    or ethanol had no significant effect on the acute oral LD50
    (Kimmerle, 1967a).

    Fenthion is an organophosphorus insecticide of intermediate toxicity
    to mammals although it displays considerable differences in its
    toxicity to various species, e.g. fowls are very sensitive (Keith and
    Mulla, 1966).

    The rate of absorption through the skin of rabbits is slow. When
    fenthion was applied to a cotton plug and placed in a rabbit ear for

    four hours, swelling occurred. When it was left for 24 hours mortality
    resulted (Kimmerle, 1960).

    Female rats tolerated a daily one hour inhalation challenge of 0.163
    mg/l air for 30 days with cholinesterase depression but no mortality.
    At 0.415 mg/l air all animals were dead within 10 days (Dilley and
    Doull, 1961a).

    Exposure by inhalation daily for nine days, six hours per day at 210
    mg/M3 (initial concentration in a static inhalation chamber),
    resulted in signs of poisoning, but no mortality in cats, guinea pigs,
    rabbits and rats. Cholinesterase, which was severely depressed,
    recovered in three weeks (Klimmer, 1963). Fenthion exhibits a
    relatively low degree of acute mammalian toxicity. In only one
    instance was a sex difference in susceptibility noted and this is in
    contrast to the generally noted resistance of males to most other
    phosphorothioates (Dubois and Kinoshita, 1964). The signs of poisoning
    are typical of the central and peripheral cholinergic effects of
    organophosphorus esters with a gradual onset of the symptoms. The
    symptoms in humans and other animals include tremors, lacrymation,
    salivation, vomiting, diarrhoea and other signs of cholinergic

    Short-term studies


    Mallard ducks fed 25 ppm of fenthion in the diet for six weeks became
    emaciated and could not fly or walk; after two days on normal food,
    recovery was evident. A dietary level of 5 ppm produced no adverse
    clinical reaction (Keith and Mulla, 1966).


    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 and no
    mortality in the lower dosed group. However, blood cholinesterase
    levels were depressed to about 20% of normal at the lower treatment
    level (Dubois, 1961). Cholinesterase was depressed and mortality was
    absent when fenthion was applied to rats dermally for 12 days at 2.9
    mg/kg (Dubois and Puchala, 1960).

    Rats tolerated daily intraperitoneal administration of 10 mg/kg
    fenthion for 60 days with no mortality. At 20 mg/kg, 80% of the
    treated animals died within 20 days (Dubois and Kinoshita, 1964).

    Mortality (12 dead of 30 rats tested) occurred following daily oral
    administration of approximately 25 mg/kg (1/10 LD50) for 75 days
    (six days per week). Signs of poisoning were transient disappearing
    shortly after dosing (Klimmer, 1963).

    In a preliminary study, male rats were orally administered fenthion
    five days a week for 13 weeks at a dose of 30 mg/kg/day. Mortality

    occurred in approximately 30% of the rats over the course of the
    experiment and cholinesterase activity was depressed between 80-90% of
    normal. At the conclusion of the experiment cholinesterase recovery
    was very slow - up to 40 days (Kimmerle, 1961).

    Rats (22 male and 22 female per group) were fed dietary levels of
    fenthion at 0.25, 0.50, 2.5, and 5.0 mg/kg/day for three months.
    Cholinesterase activity depression was evident at 0.5 mg/kg in red
    blood cells, serum, liver and heart at all testing intervals. At the
    lowest feeding level (0.25 mg/kg) the inhibition (approx. 10-20%) did
    not progressively increase with time indicating lack of cumulative
    effects. Mortality in females was evident at 5.0 mg/kg. The animals
    died manifesting muscarinic and nicotinic effects. Body-weight gain
    was reduced in males at 0.25 mg/kg and above while in females it was
    evident only at 2.5 mg/kg. Behavioural effects were noted
    (piloerection) at 0.5 mg/kg and above (especially in females). This
    effect decreased with time and disappeared by week seven. Organ
    weights were all distinctly lower than the controls but as the
    body-weight was also reduced the organ to body-weight ratio did not
    appear to be affected. Histological examination showed the testis to
    have reduced spermatogenesis and atrophic prostate glands at the
    highest feeding levels (2.5 and 5.0 mg/kg). The ovary was not affected
    (Shimamoto and Hattori, 1969).

    Rats (six groups of 12 male and 12 female) were fed for 16 weeks on
    diets containing 0, 2, 3, 5, 25 and 100 ppm. Cholinesterase depression
    was evident at 25 ppm and absent at 5 ppm. No adverse effects were
    noted in food consumption, weight gain or gross and microscopic
    examination of tissues (Doull et al., 1961).

    Rats (six groups of 25 male and 25 female) were fed for one year on
    diets containing 0, 2, 3, 5, 25 and 100 ppm of fenthion. There was no
    evidence of significant changes in growth rate, food consumption,
    general appearance and gross of microscopic examination of tissues.
    Survival of male rats at 25 ppm was slightly depressed. Cholinesterase
    examinations indicated depression at the 5 ppm level and above with
    3 ppm showing no adverse enzyme effects. A mild extramedullary
    haematopoiesis was observed in controls and all dosage levels and
    haemosideresis was evident in the spleen of the rats at 100 ppm levels
    (Doull et al., 1963a).


    Dogs (four groups of two males and two females per group) were fed
    fenthion at 0, 2, 5 and 50 ppm for 12 weeks. Growth was not affected
    at any dietary level. Erythrocyte cholinesterase activity was
    depressed at 50 ppm while serum cholinesterase was depressed at 5 ppm
    and above. Little if any depression of the serum cholinesterase was
    evident before five weeks, after which it progressively decreased to
    about 40% inhibition (Doull et al., 1961).

    Dogs (four groups of two males and two females) were fed fenthion at
    0, 2, 5, and 50 ppm in the diet for one year. There was no effect of
    fenthion on food consumption or growth over the test interval.
    Erythrocyte and serum cholinesterase were significantly depressed at
    50 ppm with the serum also depressed at 5 ppm. An increase in the
    weight of the spleen, which was not dose dependent, was evident in all
    of the treated animals. Microscopic examinations of the tissues showed
    splenic congestion and some decrease in the cellularity of the red
    pulp was evident at all dose levels fed. Extramedullary haematopoiesis
    and haemosideresis was also observed in the spleen. Microscopic
    examination of other tissues did not reveal any significant change
    (Doull et al., 1963b).

    Long-term studies

    No data available.

    Observations in man

    Fenthion has been widely used in many parts of the world for control
    of household pests, mosquitos, etc. Cholinesterase studies conducted
    on individuals in areas treated by WHO for malaria eradication have
    shown that very slight plasma cholinesterase depression occurs when
    exaggerated spray schedules were followed. The plasma cholinesterase
    levels were depressed for up to six weeks after spraying (Elliot and
    Barnes, 1963). It was also evident that the children in the population
    (less than seven years old) were more susceptible to the
    anticholinesterase effects (Taylor, 1963). A man who ingested two
    ounces of fenthion (Entex)(R) recovered from severe
    organophosphorous poisoning after being in critical condition for the
    first six days after poisoning. Recovery was slow, lasting up to 30
    days. Cholinesterase measurements showed that at 22 days after
    poisoning the cholinesterase activity was still depressed (Pickering,
    1966). In humans, the signs of poisoning appear rapidly beginning with
    blurred vision, unsteady gait and slurred speech. After 72 hours of
    emergency treatment following an unknown quantity of fenthion, a man
    suffered extreme respiratory difficulty necessitating artificial
    ventilation and endotracheal intubation. The patient began to recover
    only after 11 days of treatment which included atropine, PAM and
    toxogonin (Dean et al., 1967). In another case, 45 minutes after
    ingestion of 30 ml of fenthion, a man was in a comatose state with
    pale skin, cyanotic mucous membranes, slow regular heart beat, no
    peripheral blood pressure and no reactions to pain or light
    stimulation on the pupils. Recovery took six days (von Clarmann and
    Geldmacher-von-Mallinkradt, 1966).


    Fenthion is slowly absorbed, metabolized by a complex series of
    reactions and excreted. It does not appear to accumulate in the body.
    In most instances the unhydrolysed metabolites containing a phosphorus
    atom are more toxic than the parent compound. The signs of
    intoxication from a single oral dose develop slowly, persist for a

    considerable period of time and are not readily alleviated by atropine
    or by most common oxime reactivators. Short-term studies in the rat
    and dog suggest that cholinesterase inhibition is the most sensitive
    criterion of biological effect. Anti-spermatogenesis in one rat study
    was not confirmed in other studies or in a reproduction study. The
    occurrence of an effect on the spleen in both rats and dogs was not
    considered to constitute evidence of significant toxicity. Of
    particular concern was the slow onset of symptoms of cholinergic
    stimulation, differences in susceptibility to acutely toxic doses in
    rodents and birds, the long lasting cholinesterase depression and the
    apparent lack of an effective antidote.

    Because of the apparently unusual effect on cholinesterase activity
    and the lack of long-term feeding studies only a temporary acceptable
    daily intake for man was established for this compound.


    Level causing no toxicological effect

         Rat - 3 ppm in the diet equivalent to 0.15 mg/kg per day.

         Dog - 2 ppm in the diet equivalent to 0.05 mg/kg per day.

    Estimate of temporary acceptable daily intake for man

         0-0.0005 mg/kg body-weight.


    Metabolites and possible products of decomposition

    A list of theoretically possible metabolites and primary products of
    hydrolysis is given [text missing]. These compounds are numbered and the
    numbers are used throughout this part of the text; thus (2).

    Use pattern

    Fenthion is an insecticide with a broad spectrum of activity. It is
    chiefly effective against Diptera, cereal bugs, rice stem borers. The
    main uses are as follows:

         50% field crops (rice, cereals, sugar beets, etc.)

         30% fruit and vine (i.e. pome and stone fruit, citrus, olives)

         20% other uses (i.e. ornamentals, public health, animal health)

    It is registered in 31 countries for use on crops.

    Application to plants

    The following formulations are available for application to crops:

         50  Emulsifiable Concentrate (550 g/l)

       1000  ULV (1000 g/l)

        40%  Wettable Powder

        25%  Wettable Powder

         3%  Dust

    Pre-harvest treatments

    The recommended application rates/concentrations for the major crops
    are as follows:

         Sugar cane          0.5-0.75 kg/ha
         Rice                0.04-0.075% and 0.6-1.2 kg/ha, resp.
         Field corn          0.75-1.0 kg/ha
         Beets               0.3-1.5 kg/ha
         Pome and stone      0.05-0.075%
         Citrus fruits       0.05-0.075% (or bait application, see olives)
         Pistachio           0.05%
         Cotton              0.25-2.0 kg/ha
         Olives              0.05% bait application at 0.15 kg + 0.3 kg
                             bait/20 litres of water for aerial
                             application or 0.25-0.3 kg + 0.75-1.0 kg
                             bait/100 litres of water for ground machine
         Coffee              0.05-0.075%
         Cocoa               0.05%
         Vegetables          0.05-0.075%, peas up to 0.1%
         Vines               0.75-1.0 kg/ha
         Corn                0.75-1.0 kg/ha

    The above-mentioned concentrations and rates of application refer to
    the active ingredient.

    Post-harvest treatments

    No recommendations are made for post-harvest treatments.

    Application to animals

    For use as an animal health product, fenthion is applied in the
    following formulations, concentrations and dosage rates and by the
    given methods for the control of ectoparasites and endoparasites on
    domestic animals and livestock.

         (1)    25% emulsifiable concentrate
         (2)    2 or 3% solution (pour-on)
         (3)    0.25%-5% dust                       (for experimental use)
         (4)    0.5-1% in oil (back-rubber)
         (5)    10% water-miscible feed premix      (for experimental use)
         (6)    Injectable solution
         (7)    0.32% Molasse-block                 (for experimental use)

    Fenthion EC is used at concentrations of 0.025-0.25% as a dip, spray
    and wash treatment for the control of ticks, biting and sucking lice,
    flies, keds, hornflies, mange and cattle grubs on horses, sheep,
    cattle, dogs and poultry.

    Fenthion 2 or 3% (pour-on) is used at dosages of 4-45 mg/kg for the
    control of cattle grubs, ticks, biting and sucking lice, flies and
    fleas on cattle.

    Fenthion Dust is used at concentrations of 0.25-5% for the control of
    ticks, hornflies, biting and sucking lice, flies, fleas and keds on
    horses, cattle, sheep, dogs and poultry.

    Fenthion in oil is used in the form of back-rubbers as a
    self-treatment for the control of hornflies, biting and sucking lice,
    flies and fleas on cattle.

    Fenthion 10% water-miscible and 1% premix is applied at dosages of
    1.2-30 mg/kg for the control of cattle grubs, hornflies, flies, fleas,
    biting and suckling lice, nose bots and endoparasites on cattle and

    Fenthion (injectable) is used at dosages of 4.4-15 mg/kg for the
    control of demodicosis, heart worms, Ancylostoma spp. and
    Uncinaria spp.in dogs.

    Fenthion is registered for the use on animals in the following
    countries: Australia, Austria, Belgium, Germany, Great Britain,
    Ireland, Italy, New Zealand, Spain, Switzerland, United States of
    America, Yugoslavia.

    Other uses

    Fenthion is widely used for the control of insects affecting public
    health, especially mosquitos and flies where a combination of high
    potency, persistence and stability when applied to surfaces of
    buildings, ditches, swamps, etc.

    These applications are not likely to give rise to contamination of

    Residues resulting from supervised trials

    On plants

    Detailed residue data are available from many countries, including
    England, Germany, Greece, Italy, New Zealand, South Africa, Spain,
    Switzerland and the United States of America on many important crops
    and have been deposited with FAO. The results showing the residue
    levels remaining after application of fenthion according to registered
    use patterns are reflected in the following typical examples:


    Crop             Country        Concentration  Formulation    No. of         Residue at harvest x days after application
                                                                                 0-1    2-6    7-12   13-20  21-30   >30(days)

    Apples           England        1´ lb/acre     EC 50          3              3.12          1.74   0.72           0 (84)
                     S. Africa      0.05%          WP 25          1              2.1           1.4
                     Switzerland    0.05%          EC 50          1              1.5    1.35   0.6           0.65    0.15(35)
    Grapes           S. Africa      1 kg/ha        D 5            1              1.15          0.15   0.05   <0.05
    Peaches          S. Africa      4 oz/100 gal   EC 50          1              2.1           0.9
                     S. Africa      8 oz/100 gal   EC 50          1              3.2           1.6
                     S. Africa      8 oz/100 gal   EC 50          1              2.3           0.9    0.25
    Oranges          Spain          300 g/ha       ULV            1              0.1           0.1           N.D.
    Oranges whole    Spain          0.025%         WP             1              0.55          0.5    0.3
         skin        Spain          0.025%         WP             1              2.4           2.4    1.4
         pulp        Spain          0.025%         WP             1              0.2           0.05   <0.05
         whole       Spain          300 g/ha       EC 50          1              0.13          0.13   0.03   0.04    0.03(54)
         skin        Spain          300 g/ha       EC 50          1              0.42          0.42   0.05   0.05    0.04(54)
    Cherries         Switzerland    0.05%          EC 50          1                     1.65   1.05   0.45   0.3
                     Gemany         0.05%          EC 50          1              4.75          0.95   0.55
                     Gemany         0.025%         EC 50          1              2.4           0.8    0.35
    Peas whole pod   England        0.125%         EC 50          2              4.52   0.85   0.38          0.02
       peas only     England        0.125%         EC 50          2              <0.02  0.23   <0.02
       pod           England        0.025%         EC 50          2              1.1    0.5    0.4    <0.1
       peas          England        0.025%         EC 50          2              <0.02  0.1    0.05   0.05
    Squash           S. Africa      0.065%         EC 50          1              0.25   <0.02  <0.02  <0.02
                     S. Africa      0.065%         EC 50          1                     0.25   <0.02  <0.02
    Lettuce          Gemany         0.05%          EC 50          2              3.85   3.46   2.46   0.42   0.05
                     Gemany         0.05%          EC 50          1                     3.2    2.3    1.45   0.3
                     Gemany         0.15%          EC 50          1                     10.2   3.9    2.75   0.8
    Cabbage          Germany        0.05%          EC 50          2              1.16   0.37   0.0
                     Germany        0.05%          EC 50          2              2.18   1.37   0.24

    TABLE (Continued)

    Crop             Country        Concentration  Formulation    No. of         Residue at harvest x days after application
                                                                                 0-1    2-6    7-12   13-20  21-30   >30(days)

    Sugar (roots)    Germany        0.05%          EC 50          2              8.09   1.23   0.82   0.15   0.0
    beet (tops)      Germany        0.05%          EC 50          2                                   0.50   0.16
    Wheat            Spain          0.65 kg/ha     EC 50          1                                   0.02   0.02    <0.01(63)
                     New Zealand    0.7 kg/ha      EC 50          1                                          0.4     0.2(32)
    Rice             USA            1.6 oz/acre    EC 50          3                                          <0.05
                     USA            2.4 oz/acre    EC 50          3                                                  <0.05(33)
                     USA            1.6 oz/acre    EC 50          1              0.48                 <0.01

    Olives           Turkey         0.06%          EC 50          1                                                  0.39(34)
                     Greece         0.04%          EC 50          4                                                  0.15(36)
                     Greece         0.04%          EC 50          4                                                  0.75(70)
                     Italy          0.05%          EC 50          1                                          1.3     0.8(32)

    On forage crops

    Extensive trials have been reported (Chemagro Reports 24 890; 24 891;
    24 915; Mulla et al.) to show that following registered uses of
    fenthion on alfalfa (0.1-0.5 kg/ha) residues on treated alfalfa range
    up to 6 ppm after 7 days, but by the fourteenth day these levels have
    declined to less than 2 ppm. In one typical experiment alfalfa was
    treated close to harvest with fenthion at 0.11 kg/ha and residues were
    18; 1.3; 1.7 and 0.7 ppm at 0; 2; 4; and 8 days after treatment.

    The levels in corn and grass forage are somewhat lower than in

    The occurrence of residues in milk and meat following the feeding of
    such treated forage is discussed under the heading uptake of the
    compound with feed.

    On animals

    Tissues and organs

    Details of many trials made to determine the level and fate of
    residues of fenthion in animal tissues, milk and eggs were available
    and were deposited with FAO. A selection of typical results has been
    reviewed to show the level of residues resulting from approved
    applications of fenthion for the control of ectoparasites of cattle,
    sheep and poultry and from the ingestion of fenthion residues on
    animal feeds and fodder.

    A single backline treatment with a 2% pour-on (6.25 mg of fenthion/kg)
    produced the following residues (Chemagro, 1965b):

                          Days after application (ppm)
                   1              3         7         14             28
    Brain          <0.1           n.d.      n.d.      n.d.           -
    Heart          <0.1           n.d.      n.d.      n.d.           -
    Liver          0.2            n.d.      n.d.      n.d.           -
    Kidney         <0.1           n.d.      n.d.      n.d.           -
    Loin steak     approx. 0.1    <0.1      0.1       n.d.           n.d.
    Round steak    <0.1           n.d.      <0.1      n.d.           n.d.
    Flank steak    0.2            0.1       <0.1      n.d.           n.d.
    Omental fat    0.8            0.5       0.2       <0.1           n.d.
    Back fat       0.7            0.4       1.5       n.d.           n.d.
    Renal fat      0.9            0.5       1.2       approx. 0.1    n.d.
                            Averages for 3 animals
    Backline treatment of cattle with a 3% pour-on (9.4 mg of fenthion/kg)
    resulted in the formation of the following residues in the tissues
    (Chemagro, 1968b):

                        Days after application (ppm)
                        1         3         7         28
    Brain               0.08      <0.01     <0.01     <0.01
    Heart               0.10      -         0.07      <0.02
    Liver               0.14      0.01      0.01      <0.01
    Kidney              0.15      0.06      0.10      0.02
    Loin steak          0.18      0.05      0.07      0.01
    Round steak         0.12      0.02      0.10      <0.01
    Flank steak         0.19      0.08      0.21      0.01
    Omental fat         0.19      0.14      0.31      0.02
    Renal fat           0.18      0.54      0.38      0.03
    Back fat            0.19      0.83      0.62      0.09

    The tabulated values represent the averages for three animals, and
    comprise the totality of the non-ionic residues.

    Another experiment with a 3% pour-on, equivalent to a dose rate of
    9.4 mg of fenthion/kg, at first showed that the residues were only
    slight (Chemagro, 1967e) but after 28 days they were of the same order
    of magnitude as in the first-mentioned experiment (Chemagro, 1968b):

                        Days after application (ppm)
                        7         14        28        42
    Brain               0.01      -         0.01      -
    Heart               <0.01     -         0.02      -
    Liver               0.01      <0.01     0.01      -
    Kidney              0.01      <0.01     <0.01     -
    Loin steak          <0.01     -         0.01      -
    Round steak         <0.01     -         <0.01     -
    Flank steak         <0.01     -         0.02      -
    Omental fat         0.10      -         0.07      <0.01
    Renal fat           0.12      -         0.15      <0.01
    Back fat            0.13      -         0.07      <0.01
    Averages for 3 animals

    The same organs and tissues were examined also 45 days after topical
    application to the skin using a 20% "Spotton solution" (5.8 mg of
    fenthion/kg); they were all found to be free of residues (Chemagro,

    Similar results were obtained in an experiment using a spray
    application (1 gal of 0.25% a.i. per animal). No residues were found
    (Chemagro, 1965c) in brain after three days; in liver after seven

    days; in heart and kidney after 14 days; in steaks after 14 days; in
    fat after 28 days.

    Following three spray applications of a 0.1% fenthion solution to the
    point of run-off, at intervals of two weeks, no detectable residues
    (less than 0.05 ppm) were present in brain, heart, liver and steaks
    after 28 days; omental fat contained on average 0.1 ppm, renal fat
    contained 0.05-0.1 ppm, and back fat contained 0.05 ppm. All fat
    samples were free of residues after 44 days (Chemagro, 1967d).

    Following daily backrubber application (1% a.i.) for four weeks, no
    residues were detected in the organs and tissues after the final
    application (Chemagro, 1965d).

    Elimination in milk

    The first results on the possible elimination of fenthion and its
    metabolites in milk were reported in the studies of Knowles & Arthur
    (1966) (see "Tissues and Organs").

    The concentration of acetonitrile-soluble materials, which represented
    predominantly fenthion or its oxidation products, was at its maximum
    six hours after dermal treatment (0.44 ppm) and 20 hours after
    intramuscular treatment (0.80 ppm). After 14 days, the residues in the
    milk amounted to less than 0.001 ppm (dermal) and 0.014 ppm (i.m.). Of
    the total activity administered, 1.1% was eliminated (as 32P) in the
    milk within 14 days after dermal treatment, and 2.2% was eliminated in
    the milk within 20 days after i.m. treatment.

    A daily backrubber application of 50 ml of a 1% fenthion solution for
    seven days resulted in acetonitrile-soluble residues of 0.06-0.36 ppm
    during treatment. Five days after treatment, these residues were below
    0.01 ppm (Chemagro, 1963).

    Backline application of a 3% pour-on, equivalent to a dose rate of
    9.4 mg of fenthion/kg., and, in a comparison experiment, of a three
    times higher concentration produced the following residues (in ppm) in
    the milk (Chemagro, 1969):

         Days after application        9.4 mg/kg      28 mg/kg
                   0.4                 0.81           2.82
                   1                   0.33           0.66
                   2                   0.13           0.15
                   3                   0.047          0.056
                   5                   0.011          0.017
                   7                   0.04(?)        0.003
                   10                  0.003          <0.002
                   14                  <0.002        <0.002
                   21                  <0.002        <0.002

    An experiment on six animals (single backline application with
    3% pour-on, 9.4 mg/kg) provided a good picture of the range of
    residues in the milk of the individual cows (Chemagro, 1968a).

                                    Residues in the milk (ppm)

         Days after application      Range            Average

                   1              0.055 - 0.106       0.072
                   2              0.129 - 0.167       0.150
                   3              0.012 - 0.023       0.019
                   7              <0.005             <0.005

    Daily backrubber treatment of cattle with 1% a.i., equivalent to
    approximately 0.5 g a.i. per animal and day, for a period of four
    weeks caused no formation of residues in the milk at the end of the
    treatment period (Chemagro, 1967a).

    The results presented here by and large agree with the data of
    Möllhoff (1970) who reports that following application of 10 mg of
    fenthion/kg (2% pour-on) the milk was free of residues after seven
    days and the edible tissues were free of residues after 13 days. All
    these observations can be accounted for by the physical properties of
    fenthion, on the one hand, and its metabolites, on the other hand. The
    oxidation products have a higher polarity. As a result of these
    properties, the penetration of fenthion through the skin is favourably
    influenced by the lipophilic properties of the parent compound, on the
    one hand, whereas, on the other hand, compounds (2) to (6), which are
    formed following penetration by metabolic processes, undergo faster
    degradation and elimination than unchanged fenthion would.

    Shillam et al. (1971) applied 125 ml fenthion as a 2% solution in
    liquid paraffin to each of three cows (equivalent to 2.5 ml fenthion
    per animal) and determined the level of fenthion in the milk. The cows
    were in low production (approximately 20 lbs milk per day when milked
    twice daily).

    It was found that milk drawn 15 hours post application contained 0.14
    ppm fenthion (0.08, 0.14, 0.20 ppm) but milk drawn 48 hours post
    treatment contained no measurable amount of fenthion (less than 0.005
    PPM). Pasteurization of the 15 hour milk reduced the fenthion residue
    level to 0.04 ppm. There was a further decline in the residue level
    when the pasteurized milk was analysed after 48 hours storage at 4°C.

    Shipp (1970) reported that the excretion of fenthion in milk reached a
    peak 12 hours after treating cows with 2% fenthion solution at the
    rate of 100 ml per cow (2 g per head). The concentration found in milk
    from four separate cows ranged from 1.1 ppm to 1.7 ppm in the
    butterfat of milk drawn 12 hours after application. The level had

    declined to 0.7-1.1 ppm at 24 hours and 0.2-0.3 ppm at 36 hours. At 48
    hours the residue level was less than 0.1 ppm in the fat of milk.

    Uptake of the compound together with feed

    A feed supplement treatment of two cows (two daily applications of
    0.72 mg of fenthion/kg in capsules) for 14 days resulted in residues
    of 0.02-0.36 ppm in the milk during treatment; two days
    post-treatment these residues were less than 0.01 ppm (Chemagro,

    Administration of fenthion-containing feed to cattle for six days (2.5
    mg of fenthion/kg) produced no detectable residues (less than 0.1 ppm)
    in the following organs: brain, heart, liver, kidney, steaks (loin,
    round, flank), fat (omental, renal, back) (Chemagro, 1965a). Daily
    administration of 5 ppm of fenthion in the feed for four weeks
    produced no residues in the milk at the end of the experiment
    (Chemagro, 1966d). Administration of 10 ppm of fenthion in the feed
    for seven days (0.5 mg/kg/day) likewise resulted in no residues in the
    milk on the final day of the experiment (Chemagro, 1966a).

    Bowman et al. (1970) investigated:

    (a)  whether residues of fenthion and its metabolites are secreted in
         the milk or excreted in the urine and faeces of cows fed silage
         made from corn treated with fenthion, and

    (b)  whether residues of fenthion in silage affect the physiological
         activity of lactating cows.

    The corn was sprayed with (A) 0.56, (B) 1.12, and (C) 2.24 kg of
    fenthion/hectare and ensiled in tower silos one day post-treatment.
    The ensiled corn was allowed to age 88 days before the silages were
    fed to the cows during a 56-day study. The residues of fenthion in
    corn and corn silage after field treatment at the three rates were as
    follows (in ppm):

                                              A      B      C

         day of treatment (forage)           4.3    17.6   34.6
         day after treatment (forage)        1.7    3.5    12.0
         ensiled 14 days (silage)            1.4    4.3    10.0
         ensiled 56 days (silage)            1.0    2.1    8.9
         ensiled 71 days (silage)            0.82   2.5    9.6
         silage fed first week               0.44   1.3    5.9
         silage fed third week               0.55   1.7    6.0
         silage fed fifth week               0.55   1.6    5.0
         silage fed eighth week              0.62   1.3    5.1

    In all cases, compound (2) accounted for most of the residue.

    One of the silages was assigned to each group of four cows. The
    animals ingested averages of (A) 0.03, (B) 0.07, and (C) 0.3 mg of
    residues/kg/day. No residues were detected in the milk from (A) and
    (B). Only low levels (maximum of 0.014 ± 0.003 ppm) were found in the
    milk from cows fed silage from corn treated at a rate of 2.24 kg of
    fenthion/hectare (C). Also, one week after feeding was terminated, no
    residues could be found in the milk in group (C).

    Only slight amounts of residues occurred also in the faeces and urine
    of the animals (expressed in ppm):


         Days fed treated feed      A        B        C

           26         faeces      0.003    0.015    0.09
                      urine       0.004    0.016    0.12

           55         faeces      0.014    0.03     0.16
                      urine       0.004    0.014    0.16

    No residues were detected in urine and faeces one week after feeding
    was terminated.

    The effect of diet on the metabolism of fenthion in laboratory
    animals (rabbits and rats) was studied by Begum (1968) 35S-labelled
    fenthion (Y position) was used in these experiments. When this
    compound was administered orally or subcutaneously to healthy,
    well-fed animals (group A), the peak concentration of the
    radioactivity appeared in the blood six to nine hours after treatment.
    The peak was observed in lean, half-starved animals (group B) one hour
    after treatment. There was more oxidized fenthion in the blood of
    group B rabbits than in the blood of group A rabbits. In both groups
    of animals, fenthion was eliminated primarily in the urine, and to a
    lesser extent in the faeces. There was a higher percentage of
    radioactive materials (mostly hydrolyzed products) excreted in the
    urine and faeces by group B animals. Apparently there was a more rapid
    breakdown and elimination from the system of lean animals than from
    fat ones.

    Experiments with sheep

    Sheep which were treated with a 2% pour-on (60 mg of fenthion/kg)
    showed no residues in brain, heart, liver, kidney, loin steak,
    shoulder, leg and fat (omental, renal, back) 44 days after the
    application (Chemagro, 1966c). Sheep treated with 50% powder applied
    as an oral drench at a dose level of 30 mg/kg also displayed no
    residues in the above-mentioned organs and tissues 14 days after the
    application (Chemagro, 1966b).

    When sheep were treated by dipping them in a 500 ppm solution of
    fenthion, only very slight residues appeared (Möllhoff, 1970). No
    residues were detected in the organs; in meat, residues were
    detectable only at seven days after treatment in one out of two
    animals (0.1 ppm). The concentration was highest in fat (up to 0.35
    ppm on the seventh day). When the same formulation was injected
    intravenously in two sheep at a rate of 5 mg of fenthion/kg 12 hours
    before slaughter, the highest residues again appeared in the fat
    (1.6 ppm) whilst in meat the residues amounted to a maximum of 0.7 ppm
    (Möllhoff, 1970).

    Experiments on poultry

    Fenthion is not eliminated in hen eggs. Hens were fed on a diet
    containing 2 ppm of fenthion for four weeks; at the end of the feeding
    period, there was no trace of residues in the eggs (Chemagro, 1967b).
    The tissues of six hens (giblets, muscle and fat) were also free of
    residues at the end of the feeding experiment (only exception: giblets
    contained 0.08 ppm in one out of six hens; fat contained 0.07 ppm in
    one out of six hens (Chemagro, 1967c)).


    The behaviour of the compound fenthion in living systems, like that of
    all pesticides which contain a thioether moiety, is determined by its
    readiness to form sulfoxides and sulfones. As an S-alkyl isomerization
    can also be reckoned with under thermal influences, the following
    non-ionic metabolites of fenthion (1) are theoretically to be


                 X      Y       Z

                 S      S       O      = (1) = fenthion
                 S      SO      O      = (2)
                 S      SO2     O      = (3)
                 O      S       O      = (4)
                 O      SO      O      = (5)
                 O      SO2     O      = (6)
                 O      S       S      = (7)
                 O      SO      S      = (8)
                 O      SO2     S      = (9)

    (See also the metabolic chart Figure 1, under "Biochemical Aspects").

    Isomerization to the P-S-aryl forms has not been observed so far.

    Of all these compounds, O-desmethyl forms are conceivable as
    metabolites. Whenever they are discussed, we shall mark them with a
    letter a), for example the compound will be marked 1a), and so on.


    The primary hydrolytic products that are theoretically to be expected
    are as follows:

    (10)  (CH3O)2 P (S) OH              (16)   HO-C7H6-S-CH3
    (11)  (CH3O)  P (S) (OH)2           (17)   HO-C7H7-SO-CH3
    (12)          P (S) (OH)3           (18)   HO-C7H6-SO2-CH3
    (13)  (CH3O)2 P (O) OH
    (14)  (CH3O)  P (O) (OH)2
    (15)          P (O) (OH)3

    In animals

    Knowles and Arthur (1966) applied fenthion dermally to two dairy cows
    each weighing 360 kg at a rate of approximately 13 mg/kg per cow, and
    treated two other lactating cows (each weighing 410 kg) by the
    intramuscular route with approximately 8.5 mg of fenthion/kg per cow.
    In the urine the peak concentration of radioactive materials occurred
    on the first day following either method of treatment. The total ppm
    of P32 materials from intramuscular treatment decreased from 33 ppm
    at one day to 1.6 ppm by 21 days. More than 95% of the radioactive
    materials eliminated in the urine consisted of hydrolytic products.
    The total P32-materials eliminated in the faeces peaked two days
    after both types of treatment. The cumulative percentage of the
    administered dose was about 4%. The peak concentration of
    acetonitrile-soluble radioactivity occurred one day after
    intramuscular treatment and three days after dermal treatment. The
    hair of the two cows treated dermally contained about 2000 ppm
    radioactive fenthion equivalents immediately after treatment. These
    residues declined to 16 ppm by 14 days after treatment. Chloroform to
    water partition data indicated that fenthion underwent little change
    on the hair to water-soluble components. The radioactivity in the
    blood after both types of treatment reached a peak during the first 24
    hours. Between 10 and 38% of the P32-materials partitioned into
    chloroform but no detectable chloroform-soluble P32-materials were
    present in the blood at seven days after either treatment.

    At 14 days after dermal treatment and 21 days after intramuscular
    treatment the cows were killed, and portions of liver, left and right
    sirloin steak, left and right round steak, T-bone steak, omental fat,
    and left and right subcutaneous fat were removed for analysis. None of
    these tissues contained acetonitrilesoluble radioactive materials
    following dermal treatment; all tissues contained less than 0.05 ppm
    of total radioactivity with the exception of the liver which contained
    0.44 ppm. The situation was vastly different in the tissues of the
    intramuscularly treated animals. The tissues from the left side (site
    of injection) of the cows contained considerably more P32-materials
    than those from the right side (e.g. left round steak contained 1.03
    ppm total radioactive materials, right round steak contained 0.11
    ppm). The acetonitrile-soluble compounds amounted to a maximum of 0.36
    ppm in the left steaks (less than 0.1 ppm in the right steaks); 0.2
    ppm in the left subcutaneous fat and 0.08 ppm in the right
    subcutaneous fat; 0.05 ppm in T-bone steak; 0.15 ppm in omental fat;
    and 0.76 ppm in liver. The injection sites contained high residues in
    both cases: skin 0.49 ppm total activity (0.08 ppm
    acetonitrile-soluble), injection site 164 ppm (76 pp.
    acetonitrile-soluble). The amount of the applied P32-materials
    remaining in the skin after dermal treatment was, however, only 0.14%.
    A similar calculation for the percentage remaining on the hair gave a
    figure of 0.73%.

    Following dermal and intramuscular treatment of cows with fenthion
    (Knowles and Arthur, 1966), fenthion constituted more than 50% of the
    non-ionic residues for three days after dermal and seven days after
    i.m. treatment in the milk. The remainder was composed chiefly of
    (3) + (5) + (6) and (2) [+ (4) ?]. In the urine, fenthion accounted
    for only a small percentage of the chloroform-soluble radioactivity.
    Some of (4) and/or (2) was present, but in most cases more than 70% of
    the activity consisted of (3) and/or (5) and/or (6). The hydrolytic
    products were composed of almost equal proportions of (10) and (13),
    and a small portion consisted of an unidentified compound (probably a
    O-desmethyl form of fenthion or one of its metabolites). More than 50%
    of the acetonitrile-soluble radioactive materials in the faeces
    consisted of the parent compound. The remainder was accounted for by
    the other metabolites just as in urine. The composition of the
    hydrolytic products was also very similar to that found in urine. In
    the tissues of the animals slaughtered 14 days after dermal treatment
    and 21 days after i.m. treatment, more than 50% of the radioactive
    acetonitrile-soluble materials was chromatographed as fenthion, but
    oxidation products were also present. At the injection site, (12) was
    the predominant product of the water-soluble materials.

    The silage feeding experiments performed by Bowman et al. (1970)
    referred to earlier, also provide certain indications of the
    transformation of fenthion metabolites in the cow. For example, the
    residue (total of six ppm) in the feed fed in the fourth week and in
    the resultant milk samples had the following composition:


                   Compound   Feed    Milk

                      (1)       8%    -
                      (2)      89%    <2%
                      (3)       2%    <2%
                      (4)        -    -
                      (5)       1%    97%
                      (6)        -    -

    Compound (5) accounted for 95% of the metabolites present in the
    urine. Those present in the faeces consisted almost exclusively of
    compound (1) (fenthion). Unfortunately the authors do not provide any
    data on the occurrence of metabolites in the blood of the animals;
    however, the cholinesterase activity of the animals of group C was
    significantly depressed during the feeding experiment but otherwise
    there were no changes in performance.

    In plants

    The transformation of fenthion in plants is basically similar to that
    in animals. The first studies performed to investigate transformation
    of fenthion in plants were made by Brady and Arthur (1961). Cotton
    plants were sprayed with an emulsion of P32-labelled fenthion at a
    rate of 2 kg of fenthion per hectare. The plants were growing under
    field conditions. Three days after spraying, 189 ppm fenthion
    equivalents were present on or in the leaves, but only 14 ppm were
    chloroform-soluble materials. The respective residues after 14 days
    were 71/5 ppm. Compound (3) was tentatively identified as by far the
    most prevalent metabolite (60-80%), followed in quantity by unchanged
    fenthion (28% after three days, 13% after 14 days). Compounds
    (5) + (6) appeared in smaller percentages (less than 10%). The
    hydrolytic products found were chiefly (10) and small amounts of (13)
    and an unknown compound.

    Experiments with P32-labelled fenthion on beans, in which the
    metabolites were separated by paper-chromatography (Niessen et al.,
    1962a) and quantitatively determined (Niesson et al., 1962b), produced
    the following results:

    The labelled parent compound contained 94.2% of (1), 4.5% of (7), 0.7%
    of (2) and 0.6% of ionic compounds. Bean plants (Phaseolus vulgaris)
    were either briefly dipped in a 0.2% emulsion of this compound by
    their stem, or placed in the emulsion by their roots. The
    chloroform-soluble extracts had the following composition (ppm):

    Days        (1)     (2)     (3)     (5)     (6)     (7)     (8)
    1/4         100     16      -       1.2     -       2.8     1.5
    2           27      25      2.1     3.5     0.06    -       0.4
    5           4.7     7.2     1.4     1.5     0.12    -       0.09
    8           1.6     4.7     1.4     1.2     0.11    -       0.05

    After eight days, only 1.6% of the parent compound was present; (2)
    was the principal metabolite. The impurity (7) was no longer
    detectable from the second day; however, it is also oxidized to the
    sulfoxide (8). The total residue decreased in the eight-day period
    from 122 ppm to a level of 9 ppm. The rate at which these
    transformations take place depends upon the temperature.

    Oxidation by plant enzymes preferably takes place at the thiono sulfur
    atom, while oxidation at the methylmercapto group seems chiefly to be
    a photosensitized reaction. The compound has a certain systemic
    action. (7) has a much stronger systemic action, but it is not found
    in the plant.

    Several experiments on glass plates confirmed that the formation of
    sulfoxide and sulfone is a light-induced reaction whilst (7) is formed
    from (1) and (8) is formed from (2) due to the influence of heat.
    These findings were later confirmed by Metcalf et al. (1963).

    At the same time as the studies of Niessen et al. (1962b) were
    conducted, Japanese research workers investigated the behaviour of
    P32-labelled fenthion in rice, tea and cabbage (Fukuda et al. 1962,
    Tomizawa et al., 1962). The neutral metabolites were separated by
    paper chromatography and the water-soluble metabolites were separated
    by ion exchange chromatography. Immediately after the treatment, the
    deposit of fenthion on the rice plants amounted to between 110 and 150
    ppm on the leaf blade and to between 18 and 28 ppm in the leaf sheath.
    (2) and (3) were the principal metabolites in the leaf blade and
    sheath. The accumulation of fenthion metabolites in ears and grains
    was examined in one variety which was treated a few days before
    heading. Four weeks after application, the distribution of
    radioactivity was as follows (ppm):


                               Total      Chloroform-extractable

              Husk                 2.4             n.d.
              Bran                60               0.9
              Polished rice        5.7             0.1

    The composition of the metabolite mixture in the ears 12 days after
    the application was as follows: 45% (2); 20% (7?); 18% (3); 17%
    unidentified. The water-soluble metabolites in the grains 14 days
    after the application were composed chiefly of (1a), plus a few
    percent. (less than 10) of (10), (13) and (12) and/or (15).

    The amounts of fenthion deposit on tea and cabbage after the
    application were as follows: 43 ppm on young tea leaves, 90 ppm on old
    tea leaves and 46 ppm on cabbage leaves. (2) and (3) were the
    principal metabolites also in these experiments. The appearance of
    O-desmethyl fenthion observed by the Japanese research workers seems
    astonishing and was never again reported by any other observers.

    In 1963, Metcalf et al. published qualitative results which they
    obtained on cotton. In these studies, too, (2) and (3) were the
    principal metabolites.

    With the improvement of analytical techniques, a better insight was
    gained into the metabolism of fenthion in plants. Leuck and Bowman
    (1968) treated Coastal bermudagrass and ensilage corn at rates of 0.56
    kg/hectare, 1.12 kg/hectare and 2.24 kg/hectare (a.i.). The ppm
    residues determined in Coastal bermudagrass treated at the highest
    application rate were as follows:


    Days                (1)       (2)       (3)       (5)       (6)
    0                   64        71        1.0       1.8       n.d.
    7                   0.31      10        4.0       2.0       0.34
    14                  0.07      2.1       2.3       0.48      0.18
    21                  0.03      0.59      1.3       0.08      0.11

    The corresponding residue levels for corn were as follows:

    Days             (1)      (2)    (3)    (5)      (6)
    0                0.41     26     0.22   0.63     <0.005
    7                0.04     2.4    0.68   1.03     0.16
    14               0.01     0.42   0.24   0.11     0.09
    21               <0.002   0.34   0.22   <0.02    0.04

    (4) was not detected (except on day 0 in bermudagrass when its level
    was 0.06 ppm). (2) and (3) were again the principal metabolites.

    The total residues were as follows (expressed in ppm):

    Days                    Bermudagrass               Corn
    post-treatment      0.56 kg/ha  1.12 kg/ha  0.56 kg/ha  1.12 kg/ha
    7                   3.3         8.5         0.65        1.95
    14                  1.3         3.2         0.15        0.4
    21                  0.5         1.3         0.1         0.2

    These findings were very largely confirmed by a study performed by
    Bowman et al. (1968), in which nine procedures for removal of
    phosphorus insecticides and their metabolites were compared. This
    study also provides an impressive picture of the differing effect of
    various extraction procedures. Soxhlet extraction with 10% methanol in
    chloroform proved to be the best one.

    The fate of phenolic hydrolytic products of fenthion in plants was not
    further studied. However, findings have been published by Wendel and
    Bull (1970) in respect of GC-6506 (dimethyl 4-methylthiophenyl
    phosphate). From some of the metabolites, substituted phenols could be
    liberated by hydrolysis with ß-glucosidase (Bull and Stokes, 1970).
    The predominant products were the glucosides of phenol-sulfoxide and
    phenol-sulfone. The glycone portions of the conjugates are further
    altered, possibly by the formation of a ß-gentiobiside.

    In soils

    The half-life of fenthion and its metabolites in soil is between 14
    and 40 days; only in one out of six experiments was a half-life of
    more than 30 days recorded. The experiments used various formulations
    including granules and emulsifiable solutions. (Chemagro - Summary
    under soils in main submission).

    In storage and processing

    Under frozen storage (-18 to -23°C), fenthion residues were shown to
    be stable in alfalfa for 28 weeks and in cattle fat for 11 weeks
    (Chemagro, 1966e,f). In liver from cattle, a decrease of 20% seemed to
    occur between the twelfth and twenty-sixth week of storage (Chemagro,

    Fenthion proved to be stable for four weeks at -18°C in cattle brain,
    heart, liver, kidney, steak and fat over a period of four weeks; (6)
    decreased slightly in brain, heart, steak and fat, by 30% in kidney,
    and by 80% in liver in six weeks (Olson, 1966).

    Following treatment of corn with fenthion at rates of 0.56, 1.12 and
    2.24 kg per hectare (Boman and Beroza, 1969), the plants treated at
    the highest rate contained 39 ppm of residues (1) + (2) + (3) + (5),
    in a ratio of 1.8 : 96.5 : 0.75 : 0.97. At 70 days after ensiling
    (which took place on the day after application), the residues amounted
    to 14.6 ppm (17 : 74 : 7.8 : 1.1); at 141 days, they amounted to 6.85
    ppm (9.7 : 85 : 4.7 : 0.5). The predominant metabolite throughout the
    whole period was (2). In another silage experiment with corn, the
    residues were consistently shown to be at a lower oxidation stage than
    were those in the field samples from which the silage was prepared
    (Leuck and Boman, 1968).

    The relatively high persistence of the residues in silage and the
    occurrence of (2) as the principal metabolite were again confirmed
    later (Bowman et al., 1970).

    Residues in canned and preserved peaches persist to a certain extent,
    especially when maintained at low temperatures (refrigerator) (Pigatti
    et al., 1967).

    Evidence of residues in commerce or at consumption

    Krause and Kirchhoff (1969) examined 78 market samples of different
    fruits and vegetables of domestic and foreign origin for residues of
    20 organophosphorus insecticides including fenthion. Residues of
    fenthion were not found in any of the samples.

    Total diet studies were carried out in England and Wales, in 1966/67,
    with altogether 66 samples of total diet. Each sample comprised seven
    sub-samples consisting of cereals, meats, fish, fats, fruits and
    preserves, root vegetables, green vegetables and milk. Fenthion and
    its immediate oxidation products could have been detected by the
    method employed, but they were not detected (Abbott et al., 1970).

    Methods of residue analysis

    Although the present-day gas chromatographic methods can be carried
    out largely without clean-up, it is nevertheless necessary in some
    cases to eliminate interfering substances. In this, consideration must
    be given to the greatly differing polarity of fenthion residues.
    Chemagro (1963) has published, for example, the following data on

                  n-hexane          water        n-hexane

    Compound    acetonitrile      chloroform       water

       (1)        1 :  8.4          1 : 1720    1  :  0.016
       (5)        1 :  300          1 : 88      1  :
       (6)        1 :  87           1 : 15      1  :  78

    Bowman and Beroza (1968) give the following p-values (=fractional
    amount in nonpolar phase):

                   n-hexane            n-hexane            n-hexane
    Compound       20% acetonitrile    40% acetonitrile    water
                   in water            in water
    (1)            0.98                0.92                1.00
    (2)            0.18                0.03                0.50
    (3)            0.61                0.12                0.94
    (4)            0.65                0.18                0.92
    (5)            0                   0                   0
    (6)            0                   0                   0.01

    Regarding the extraction of residues, attention is drawn to the study
    of Bowman et al. (1968) already referred to earlier.

    The first methods for the determination of fenthion and its
    metabolites were based on determination of total phosphorus (Frehse et
    al., 1962a for plant material; Frehse et al., 1962b for olives (oil);
    Adam (1967) for olives). In 1966, the first methods were published for
    the determination of fenthion in plant and animal tissues (Anderson et
    al., 1966) and milk (Katague, 1966), based on oxidation of the various
    compounds to the sulfone (6) which in turn was hydrolyzed to the
    corresponding phenol. The phenol was brominated and acetylated prior
    to detection measurement by electron-capture GLC. The methods were
    sensitive to 0.1 ppm (0.01 ppm for milk) but unavoidably very
    complicated and time-consuming.

    Therefore, Chemagro began in 1967 to develop methods using the
    thermionic phosphorus detector: for soil (Olson 1967a), rice grain
    (Olson 1967b), eggs and milk (Olson 1968), and animal tissues
    (Thornton 1967).

    These methods are based on oxidation of the residues to (6). The
    sensitivities are below 0.1 ppm for soil and rice, and about 0.005 ppm
    for eggs and milk. GLG conditions are:

    (a)  soil: 11 in × 3 mm i.d. column, packed with 6% DC-200 and 1% QF-1
         on 80/100 mesh Gas Chrom Q, 230°C;

    (b)  other material: 16 in × 3 mm i.d. column, packed with 10% DC-200
         and 0.2% QF-1 on 80/100 mesh Gas Chrom Q, 210°C, retention time
         3.5 minutes.

    Forty-five organophosphorus insecticides were examined for possible
    interference with the rice method (Olson, 1967b); no interferences
    were noted for any of the compounds except (R) Dasanit (Olson,

    Bowman and Beroza (1968) used a different principle of determination.
    Extracts from corn, grass and milk were separated by liquid
    chromatography into three fractions which then were analysed by GLC
    with a flame photometric detector: 90 cm × 4 mm i.d, column, packed
    with 10% DC-200 on 80/100 mesh Gas Chrom Q, 210°C for the two
    fractions (1) + (3) and (2) + (4) + (6); a 45 cm column is used for
    (5) (retention times (1) to (6) : 1.75, 4.2, 4.05, 1.45, 2.3 minutes).
    Ten per cent. QF-1 (50 cm), 1% Carbowax 20 M (50 cm) and 5% DEGS
    (50 cm) can also be used as the liquid phase. A complete separation of
    all six compounds was achieved by using liquid chromatography with a
    silica gel column and different elution systems. Later, Bowman and
    Beroza (1969) also used the oxidation method with m-chloroperbenzoic
    acid for the same substrates: 90 cm × 4 mm i.d. column packed with 10%
    OV-101 on 80/100 mesh Gas Chrom Q, 215°C. With this column, the
    metabolites can also be determined singly (retention times of
    0.7 - 2.75 minutes, 2.3 minutes for (6)); it was found that the
    results of the single metabolite determinations those of the total
    determination. The recoveries were above 90%. Excessive amounts of the
    oxidation mixture are removed on an alumina column.

    Further studies performed by Bowman and Beroza (1970) show that 2.4
    metre × 4 mm i.d. columns, packed with 5% OV-101 or OV-210 on Gas
    Chrom Q are also suitable for determination of the compounds (1) to

    Examples of national tolerances

    Country          Crop                            Tolerance      Safety
                                                     in ppm         Interval
                                                                    in days
    Algeria          General                                        15

    Australia        Fruit, vegetables               2              7
                     Meat of cattle                  1              1
                     Milk and milk products          2              1

    Austria          General                                        35

    Belgium          Fruit, vegetables excluding
                     potatoes                        0.3            21

    Brazil           General                                        14
                     Fruit                           1.0

    Country          Crop                            Tolerance      Safety
                                                     in ppm         Interval
                                                                    in days
    Bulgaria         Sugar beets                                    14
                     Cherries, cereals                              14

    Canada           Beef cattle                     N.R.

    Finland          General                                        14

    France           General                                        15
                     Olives                                         21

    Germany          Fruit                                          14
                     Vegetables, field & fodder
                     crops                                          10

    Israel           Fruit                                          21
                     Miscellaneous (e.g. dry onions
                     and cucurbits)                                 30

    Italy            General                                        20
                     Olives                                         30

    Morocco          General                                        15
                     Olives                                         30

    Netherlands      Fruit, vegetables excluding
                     potatoes                        0.3            -

    New Zealand      General                                        21

    Norway           General                                        14

    Poland           Fruit, vegetables, root crops                  30
                     Early cherries                                 14

    Portugal         General                                        14
                     Olives (as oil and preserves)                  42

    Russia           Cereals, cottonseed oil         0.35

    Spain            Fruit and olives                               30

    South Africa     General                         2.0
                     Apricots, peaches, apples,
                     pears, grapes                                  10
                     Subtropical crops & cucurbits                  7
                     Deciduous fruit                                10

    Country          Crop                            Tolerance      Safety
                                                     in ppm         Interval
                                                                    in days
    United States    Alfalfa (fresh), grass          5.0
    of America       Alfalfa (hay), grass hay        18.0
                     Animal products                 0.1
                     Milk                            0.01

    Yugoslavia       General                         0.5

    N.R. = registered for use on a no-residue basis.

    Fenthion is an organophosphorus insecticide with a broad spectrum of
    activity used against insects infesting field crops, fruit crops,
    vineyards, olives, cotton, insects of public health concern and
    ectoparasites of domestic animals. It is especially useful for control
    of fruit flies in many crops where its ability to penetrate plant
    tissues allows for destruction of larvae within the fruit. The
    concentrations/rate of use ranges from 0.5-2 kg/ha in the case of
    field crops and cotton and 0.05-0.1% solution on horticultural crops.
    Animals are treated with 0.25%-5% dust, 0.025%-0.25% solutions as dips
    or sprays and 2%-3% solutions in oil as pour-on preparations or back

    The residue data available to the meeting were obtained from many
    different countries, reflecting typical registered uses under a wide
    range of climatic and ecological conditions. Considerable information
    is available about the fate of fenthion residues in foods of plant and
    animal origin and extensive studies have been carried out on the
    nature of the degradation products formed under a variety of

    Little information is available about residues of fenthion in foods in

    The literature includes a number of methods of residue analysis based
    on gas-chromatographic procedures. The greatly differing polarity of
    the various fenthion metabolites has been investigated and
    recommendations for the most appropriate extraction procedures have
    been made.

    In order that all biologically active metabolites may be determined
    simultaneously the analytical procedure has been modified to provide
    for oxidation of the residues of the various compounds to the sulfone
    which is hydrolyzed to the corresponding phenol. The phenol is
    brominated and acetylated prior to measurement by electron-captive

    gas/liquid chromatography. The limit of detection is 0.1 ppm for most
    foods and 0.01 ppm for milk.

    Procedures which are less complicated and less time consuming have
    been developed using the thermionic phosphorus detector following
    oxidation to the sulfone. The limit of detection is below 0.1 ppm for
    soil and grain, and about 0.005 ppm for eggs, milk and animal tissues.

    These procedures appear suitable for regulatory purposes.


    Temporary tolerances

    The temporary tolerances are for fenthion and its major metabolites,
    determined separately or together and expressed as fenthion.

         Apples, peaches, cherries, lettuce,               2 ppm
         fat of meat
         Cabbage, cauliflower, olives,                     1 ppm
         olive oil
         Grapes, oranges, peas, meat                     0.5 ppm
         Squash                                          0.2 ppm
         Wheat, rice, milk products (fat basis)          0.1 ppm
         Milk (whole)                                   0.05 ppm

    Further work or information

    Required before 30 June 1975

    1.   Adequate two-year feeding studies in the dog and in one rodent

    2.   Establishment of the sequence of metabolic changes in man and
         laboratory animals in order to elucidate the mechanism of long
         lasting cholinesterase inhibition.


    Information on the frequency and level of fenthion residues in food
    commodities in commerce.


    Abbott, D. C., Crisp, S., Tarrant, K. R. and Tatton, J. O'G. (1970)
    Organophosphorus pesticide residues in the total diet. Pestic. Sci.
    1: 10-13

    Adam, N. Chr. (1967) Méthode de détermination des résidue de Lebaycid
    dans l'huile d'olive et lea olives. Ann. Inst. Phytopath. Benaki, N.S.
    8: 78-84

    Anderson, R. J., Thornton, J. S., Anderson, C. A. and Katague, D. B,
    (1966) Determination of fenthion residues in plant and animal tissues
    by electron-capture gas chromatography. J. Agr. Food Chem. 14:

    Begum, A. (1968) Effect of diet on metabolism of fenthion in animals.
    Ph.D. thesis, Auburn University, Auburn, Alabama. Dissert, Abstr.,
    Sect. B, 28: 4165

    Bowman, M. C. and Beroza, M. (1968) Determination of fenthion and five
    of its metabolites in corn, grass and milk. J. Agr. Food Chem. 16:

    Bowman, M. C. and Beroza, M. (1969) Rapid GLC method for determining
    residues of fenthion, disulfoton and phorate in corn, milk, grass and
    faeces, J.A.O.A.C. 52: 1231-1237

    Bowman, M. C. and Beroza, M. (1970) GLC retention times of pesticides
    and metabolites containing phosphorus and sulphur on four thermally
    stable columns. J.A.O.A.C. 53: 499-508

    Bowman, M. C., Beroza, M. and Leuck, D. B. (1968) Procedures for
    extracting residues of phosphorus insecticides and metabolites from
    field treated crops. J. Agr. Food Chem. 16: 796-802

    Bowman, M. C., Leuck, D. B., Johnson, J. C., jr and Knox, F. E. (1970)
    Residues in corn silage and effect of feeding dairy cows the treated
    silage. J. econ. Entomol. 63: 1523-1528

    Brady, U. E., jr and Arthur, B. W. (1961) Metabolism of O,o-dimethyl
    O-[4-(methylthio)-m-toly] phosphorothioate by white rats. J. econ.
    Entomol, 54: 1232-1236

    Bull, D. L. and Stokes, R. A. (1970) Metabolism of dimethyl
    p-(methylthio) phenyl phosphate in animals and plants. J. Agr. Food
    Chem. 18: 1134-1138

    Chemagro  Milk and tissue residues resulting from backline or oral
              treatment of Cattle with Bayer 29493, p. 32

    1963      Report No. 10. 946, December 3
    1965a     Report No. 16. 551, July 27 (revised January 10, 1968)
    1965b     Report No. 16. 990, October 21
    1965c     Report No. 17. 015, October 28
    1965d     Report No. 17. 062, November 3
    1966a     Report No. 17. 445, January 19 (revised April 28, 1966)
    1966b     Report No. 17. 969, April 21
    1966c     Report No. 18. 009, May 3
    1966d     Report No. 18. 067, May 12
    1966e     Report No. 18. 179, May 20
    1966f     Report No. 18. 191, May 24
    1967a     Report No. 20. 310, April 18
    1967b     Report No. 20. 738, June 20

    1967c     Report No. 20. 798, July 5
    1967d     Report No. 21. 113, September 13
    1967e     Report No. 21. 504, November 13
    1968a     Report No. 21. 796, January 25
    1968b     Report No. 22. 647, May 15
    1969      Report No. 24. 266, February 14 (revised April 2, 1969)
    1970      Report No. 28. 719, December 3

    Dean, G., Coxon, J. and Brereton, D. (1967) Poisoning by an
    organo-phosphorus compound. A case report. So. African Med. J.,

    Dieckmann, W. (1971) Neurotoxizctatsunter-suchungen an
    Huhnern-Histopathologie. Unpublished report of Farbenfabriken Bayer

    Dilley, J. and Doull, J. (1961a) Chronic inhalation toxicity of Bayer
    29493 to rats and mice. Unpublished report from Department of
    Pharmacology, University of Chicago

    Dilley, J. and Doull, J. (1961b) Acute inhalation toxicity of Bayer
    29493 to rats and mice. Unpublished report from Department of
    Pharmacology, University of Chicago

    Dubois, K. P. (1960) The absence of antidote activity by 2-PAM and
    TMB-4 against acute poisoning by Bayer 29493. Unpublished report from
    Department of Pharmacology, University of Chicago

    Dubois, K. P. (1961) Effects of repeated dermal application of Bayer
    29493 on rats. Unpublished report from Department of Pharmacology,
    University of Chicago

    Dubois, K. P. (1962) Acute oral toxicity of a sample of Bayer 29493 to
    female rats. Unpublished report from Department of Pharmacology,
    University of Chicago

    Dubois, K. P. (1968) Comparison of the acute oral toxicity of Bayer
    29493 and Sumithion to mice. Unpublished report submitted by
    Farbenfabriken Bayer A.G.

    Dubois, K. P. and Doull, J. (1960) The acute toxicity of Bayer 29493
    to chickens and ducks. Unpublished report from Department of
    Pharmacology, University of Chicago

    Dubois, K. P. and Puchala, E. (1960) Influence of Bayer 29493 on the
    cholinesterase activity of the blood of rats. Unpublished report from
    Department of Pharmacology, University of Chicago

    Dubois, K. P. and Kinoshita, F. (1964) Acute toxicity and
    anti-cholinesterase action of O,O-dimethyl O-4-(methylthio)-m-tolyl
    phosphorothioate (DMTP; Baytex) and related compounds. Tox. Appl.
    Pharmacol. 6: 86-95

    Doull, J., Root, M. and Cowan, J. (1961) Determination of the safe
    dietary level for Bayer 29493 for dogs. Unpublished report submitted
    by Farbenfabriken Bayer A.G.

    Doull, J., Root, M. and Cowan, J. (1962) Effect of adding Bayer 29493
    in combination with other cholinergic insecticides to the diet of male
    and female dogs. Unpublished report from Department of Pharmacology,
    University of Chicago

    Doull, J., Root, M., Cowan, N. J., Vesselinovitch, D., Fitch, F. W.
    (1963a) and Meskauskas, J. Chronic oral toxicity of Bayer 29493 to
    male and female rats. Unpublished report submitted by Farbenfabriken
    Bayer A.G.

    Doull, J., Root, M., Cowan, J. and Vesselinovitch, D. (1963b) Chronic
    oral toxicity of Bayer 29493 to male and female dogs. Unpublished
    report submitted by Farbenfabriken Bayer A.G.

    Doull, J., Vesselinovitch, D., Fitch, F., Cowan, J., Root, M. and
    Meskauskas, J. (1961) The effects of feeding diets containing Bayer
    29493 to rats for a period of 16 weeks. Unpublished report submitted
    by Farbenfabriken Bayer A.G.

    Elliott, R. and Barnes, J. M. (1963) Organophosphorus insecticides for
    the control of mosquitos in Nigeria. Bull. Wld Hlth Org. 28: 35-54

    Francis, J. I, and Barnes, J. M. (1963) Studies on the mammalian
    toxicity of fenthion. Bull. Wld. Hlth. Org. 29: 205-12

    Frehse, H. (1970) Ruckstande van pflanzenschutz mittein in nahrung und
    um welt in chemie der pflanzenschutz und schadlingshenamp-fungsmittel.
    Band 2-Wegler, R., Ed. Springer-Verlag, 1970

    Frehse, H., Niessen, H. and Tietz, H. (1962a) Method of determining
    residues of the insecticide Lebaycid(R) in plant material.
    Pflanzenschutz-Nachr Bayer 15: 148-159

    Frehse, H., Niessen, H. and Tietz, H. (1962b) Method of determining
    residues of the insecticide Lebaycid(R) in olives and olive oil.
    Pflanzenschutz-Nachr Bayer 15: 160-165

    Fukuda, H., Masuda, T., Miyahara, Y. and Tomizawa Ch. (1962) Fate of
    O,O-dimethyl O-(3-methyl-4-methylmercaptophenyl) thiophosphate sprayed
    on rice plant. Japan. J. appl. Entomol. Zool. 6: 230-236

    Gaines, T. B. (1969) Acute toxicity of pesticides. Toxicol. Appl.
    Pharmacol. 14: 515-34

    Hahn, H. L. and Hensehler, D. (1969) The ability of phosphorylated
    cholinesterases to be reactivated by obidoxime chloride (Toxogonin)
    in vivo. Arch. Toxikol. 24: 147-63

    Katague, D. B. (1966) Determination of fenthion residues in milk by
    electron-capture gas chromatography. Chemagro Corp., Research
    Department, Report No. 17, 887

    Keith, J. O, and Mulla, M. S. (1966) Relative toxicity of five
    organo-phosphorus mosquito larvicides to mallard ducks. J. Wildlife
    Management 30: 553-63

    Kimmerle, G. (1960) Re: Active substance S1752. Unpublished report
    submitted by Farbenfabriken Bayer A.G.

    Kimmerle, G. (1961) Subchronische oral versuche bei ratten mit
    S-1752-Wirkstoff. Unpublished report submitted by Farbenfabriken Bayer

    Kimmerle, G. (1963) Product BH6 and S1752 Poisoning. Unpublished
    report submitted by Farbenfabriken Bayer A.G.

    Kimmerle, G. (1965a) Nourotoxic studies with Bayer 29493. Unpublished
    report submitted by Farbenfabriken Bayer A.G.

    Kimmerle, G. (1965b) Neurotoxische untersuch-ungen mit
    S-1752-Werkstoff. Unpublished report submitted by Farbenfabriken Bayer

    Kimmerle, G. (1966) Langdavernde Inhalatronsversuche bei hunden mit
    dem Baytex-Werkstoff (S-1752)

    Kimmerle, G. (1967a) Abhangigkeit der akuten oralen toxizitat bei
    ratten vom losungsmittel. Unpublished report submitted by
    Farbenfabriken Bayer A.G.

    Kimmerle, G. (1967b) Potenzierung von DDVP und S-1752. Unpublished
    report submitted by Farbenfabriken Bayer A.G.

    Klimmer, O. R. (1963) Toxicological testing of Bayer 29493.
    Unpublished report submitted by Farbenfabriken Bayer A.G.

    Knowles, C. O. and Arthur, B. W. (1966) Metabolism of and residues
    associated with dermal and intramuscular application of radiolabelled
    fenthion to dairy cows. J. econ. Entomol. 59: 1346-52

    Krause, Ch. and Kirchhoff, J. (1969) Organophosphatrückstande auf
    Marktproben von Obst und Gemüse sowie auf Getreideerzeugnissen
    Nachrichtenbl. Deut. Pflanzenschutzdienstes (Braunschweig), 21:

    Leuck, D. B. and Bowman, M. C. (1968) Residues of fenthion and five of
    its metabolites their persistence on corn and grass forage, J. econ.
    Entomol. 61: 1594-1597

    Lorke, D. and Kimmerle, G. (1969) The action of reactivators in
    phosphoric acid ester poisoning. Arch. Pharmakol. 263: 237-8

    Loser, E. (1969) Generation versuche an Ration. Unpublished report
    submitted by Farbenfabriken Bayer A.G.

    McGrath, H. B. (1969) Toxicity of Bayer 29493 in calves. Unpublished
    report submitted by Farbenfabriken Bayer A.G

    Metcalf, R. L., Fukuto, T. R. and Winton, M. Y. (1963) Chemical and
    biological behaviour of fenthion residues. Bull. Wld Hlth Org. 29:

    Möllhoff, E. (1970) Determination of trichlorfon and fenthion residues
    in animals of different species, Pestic. Sci. 2: 179-181

    Nelson, D. L. (1967) The acute oral toxicity of three phenolic
    compounds to adult female rats. Unpublished report submitted by
    Farbenfabriken Bayer A.G.

    Niessen, H., Tietz, H. and Frehse, H. (1962a) Papier
    chromatographische Trennung aromatischer
    Phosphorsäure-ester-Insektizide. J. Chromatog. 9: 111-113

    Niessen, H., Tietz, H. and Frehse, H. (1962b) On the occurrence of
    biologically active metabolites of the active ingredient S-1752 after
    application of Lebaycid(R) Pflanzenschutz-Nachr. Bayer 15: 125-147

    Olson, T. J. (1966) The determination of the stability of fenthion and
    its oxygen analog sulfon in frozen cattle tissues. Chemagro Corp.,
    Research Department, Report No. 19, 289,

    Olson, T. J. (1967a) Determination of residues of fenthion in soil by
    thermionic emission gas chromatography. Chemagro Corp., Research
    Department, Report No. 20, 324.

    Olson, T. J. (1967b) Determination of residues of fenthion in rice
    grain by thermionic emission gas chromatography. Chemagro Corp.,
    Research Department, Report No. 20, 417 (revised 21 October, 1968)

    Olson, T. J. (1967c) A study of the possible interference of other
    pesticides with the analytical method for fenthion in rice. Chemagro
    Corp., Research Department, Report No. 20, 595

    Olson, T. J. (1968) Determination of fenthion in eggs and milk by
    thermionic emission gas chromatography. Chemagro Corp., Research
    Department, Report No. 22, 933

    Pickering, E. N. (1966) Organic phosphate insecticide poisoning. Can.
    J. Med. Tech., p. 174

    Pigatti, A., Pigatti, P., Orlando, A., Suplicy, F. O., Sampaio, A. S.
    and Rigitano, O. (1967) Persistência de residuos de fenthion am
    pêssego, ameixa e maca. Arq. Inst. Biol. (S. Paulo) 34: 275-284

    Sherman, M. and Ross, E. (1961) Acute and subacute toxicity of
    insecticides to chicks. Toxicol Appl. Pharmacol. 3, 512-33

    Shillam, K. W. G., Medd, R. K., Roberts, N. L. and Burrows, I. E.
    (1971) Residual levels of fenthion in raw and pasteurized milk. Report
    of Huntington Research Centre 4225/71/383

    Shimamoto, K. and Hattori, K. (1969) Chronic feeding of Baytex
    (O, O-dimethyl-o-(4-methylmercapto-3-methyl) phenyl-thiophosphate) in
    rats. Acta Med. Univ. Kioto, 40: 163-71

    Shipp, E. (1970) Fenthion residues in milk. Report of the Entomology
    School, University of New South Wales

    Spicer, E. J. F. (1971) Pathology Report of Bay 29493. Generation
    study in rats. Unpublished report submitted by Farbenfabriken Bayer

    Taylor, A. (1963) Observations on human exposure to the
    organophosphorus insecticide fenthion in Nigeria. Bull. Wld Hlth Org.,
    29: 213-18

    Thornton, J. S. (1967) Determination of fenthion residues in animal
    tissues by thermionic emission flame gas chromatography. Chemagro
    Corp., Research Department, Report No. 20 420 (revised 21 October,

    Tomizawa, Ch., Fukuda, H., Masuda, T. and Miyahara, Y. (1962) Fate of
    O,o-dimethyl O-(3-methyl-4-methylmercaptophenyl) thiophosphate sprayed
    on tea and cabbage leaves. Japan. J. appl. Entomol. Zool., 6:

    von Clarmann, M. and Geldmacher-von Mallinckrodt, M. (1966) A
    successfully treated case of acute oral poisoning by fenthion and its
    demonstration in the gastric contents and urine. Arch. Toxik., 22:

    Wendel, L. E. and Bull, D. L. (1970) Systemic activity and metabolism
    of dimethyl p-(methylthio) phenyl phosphate in cotton. J. Agr. Food
    Chem., 18: 420-424

    See Also:
       Toxicological Abbreviations
       Fenthion (ICSC)
       Fenthion (WHO Pesticide Residues Series 5)
       Fenthion (Pesticide residues in food: 1977 evaluations)
       Fenthion (Pesticide residues in food: 1978 evaluations)
       Fenthion (Pesticide residues in food: 1979 evaluations)
       Fenthion (Pesticide residues in food: 1980 evaluations)
       Fenthion (Pesticide residues in food: 1983 evaluations)
       Fenthion (Pesticide residues in food: 1995 evaluations Part II Toxicological & Environmental)
       Fenthion (Pesticide residues in food: 1995 evaluations Part II Toxicological & Environmental)
       Fenthion (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental)