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    PHORATE

    First draft prepared by
    M. Caris,
    Bureau of Chemical Safety,
    Health Canada, Ottawa, Canada

         Explanation
         Evaluation for acceptable daily intake
              Biochemical aspects
                   Absorption, distribution and excretion
                   Biotransformation
              Toxicological studies
                   Acute toxicity
                   Short-term toxicity
                   Long-term toxicity and carcinogenicity
                   Reproductive toxicity
                   Embryotoxicity and teratogenicity
                   Genotoxicity
                   Special studies
                        Delayed neuropathy
              Studies of metabolites
                   Enzymes and biochemical parameters
                   Acute toxicity
                   Short-term toxicity
              Observations in humans
              Comments
              Toxicological evaluation
         References

    Explanation

         Phorate, an organophosphorus insecticide which inhibits
    cholinesterase, was first reviewed by the Joint Meeting in 1977
    (Annex I, reference 28). A temporary ADI of 0-0.0002 mg/kg bw was
    established in 1982 (Annex I, reference 38). In 1985, after review
    of a study of delayed neurotoxicity in chickens, an ADI of 0-0.0002
    mg/kg bw was established (Annex I, reference 44).

         The purpose of the present evaluation was to review additional
    information on toxicity, submitted to complement and update the
    database. This included a 90-day study in mice treated in the diet,
    14-day and one-year studies of toxicity in dogs treated orally, a
    two-generation study of reproductive toxicity in rats, studies of
    teratogenicity and preliminary range-finding studies in rats and
    rabbits, and studies to determine genotoxicity. In order to
    facilitate a comprehensive review of data on the toxicology of
    phorate, relevant summaries from previously published monographs and
    monograph addenda (Annex I, references 29, 39 and 46) are included
    in this monograph.

    Evaluation for acceptable daily intake

    1.  Biochemical aspects

    (a)  Absorption, distribution and excretion

         Male rats given a single oral dose of 2 mg/kg bw of
    32P-labelled phorate excreted 35% of the administered radiolabel
    in the urine and 3.5% in the faeces within 144 h. Male rats given
    six daily doses of 1 mg/kg bw excreted 12% of the administered
    radiolabel in the urine and 6% in the faeces within seven days.
    Brain, liver and kidney tissues from the latter animals contained
    unidentified and largely unextractable residues (Bowman & Casida,
    1958; Annex I, reference 29).

    (b)  Biotransformation

         The urine of male rats given daily oral doses of 1 mg/kg bw
    contained 17% diethyl phosphoric acid, 80%  O,O-diethyl
    phosphorothioic acid and 3%  O,O-diethyl phosphorodithioic acid.
    After 32P-labelled phorate was incubated with rat liver slice
    preparations, less than 1% of the radiolabelled compound was
    converted to hydrolysis products or unextractable residues. Phorate
    sulfoxide, phorate sulfone, phoratoxon sulfoxide and phoratoxon
    sulfone were formed (Figure 1) (Bowman & Casida, 1958; Annex I,
    reference 29).

    2.  Toxicological studies

    (a)  Acute toxicity

         The acute toxicity of phorate is summarized in Table 1. Phorate
    was extremely toxic to rats when administered by the oral, dermal
    and intravenous routes, with acute LD50 values ranging from 1.1 to
    10 mg/kg bw. Phorate was also severely toxic to rabbits after dermal
    administration and to mice when given either orally or
    intraperitoneally.

    FIGURE 01


    
    Table 1.  Acute toxicity of technical-grade phorate
                                                                                          
    Species   Sex   Route             LD50 (mg/kg bw per day)  Reference
                                      or LC50 (mg/m3)
                                                                                          

    Mouse     NR    Oral              11                       Blinn, 1982
              NR    Intraperitoneal   3                        Blinn, 1982
    Rat       NR    Oral              1.9-10                   Blinn, 1982
              M&F   Oral              M: 2.3; F: 1.1           Gaines, 1969
              M&F   Oral              M: 2.8; F: 1.6           Anon., 1976
              M&F   Oral              M: 3.7; F: 1.4           Newell & Dilley, 1978
              NR    Dermal            3                        Blinn, 1982
              M&F   Dermal            M: 6.2; F: 2.5           Gaines, 1969

              M     Dermal            5.7                      American Cyanamid Co., 1976
              M&F   Dermal            M: 9.3; F: 3.9           Newell & Dilley, 1978

              M&F   Intravenous       M: 2.2; F: 1.2           Newell & Dilley, 1978

              M&F   Inhalation (1 h)  M: 60                    Newell & Dilley, 1978
                                      F: 11                    Newell & Dilley, 1978
    Rabbit    M     Dermal            5.2                      Anon., 1976
                                                                                          

    From Annex I, references 29 and 39; strains not specified
    NR, not reported


    
    (b)  Short-term toxicity

    Mice

         Phorate (purity, 92.1%) was administered to groups of 20 male
    and 20 female Crl:CD-1 (ICR)BR outbred Swiss mice at dietary levels
    of 0, 1, 3 or 6 ppm, equal to 0.18, 0.55 or 1.10 mg/kg bw per day
    for males and 0.23, 0.67 or 1.38 mg/kg bw per day for females, for
    13 weeks. A single male mouse treated at the highest dietary level
    had convulsions on one occasion during the final week of treatment,
    but the relationship of this isolated finding to treatment could not
    be ascertained; no other remarkable clinical signs were reported.
    Treatment had no effect on survival, food consumption or body-weight
    gain. Histopathological examinations were not performed. Plasma,
    erythrocyte and brain cholinesterase activities were measured before
    terminal sacrifice. Plasma cholinesterase activity was significantly
    ( p < 0.05) inhibited in animals of each sex at 3 and 6 ppm and in
    females at 1 ppm. Erythrocyte cholinesterase levels were
    significantly decreased in males and females at the highest dose;
    the inhibition, in relation to values in concurrent controls, was
    50% in males and 61% in females. A slight, non-significant decrease
    in erythrocyte cholinesterase activity (17%) was recorded in females
    at 3 ppm. Brain cholinesterase levels, assayed in both halves of the
    brain, were significantly ( p < 0.05) decreased in animals of each
    sex treated at 3 and 6 ppm, by slightly more than 10% at 3 ppm and
    to about 50% of control values at 6 ppm. Minimal inhibition of
    plasma cholinesterase levels (15%) in females at 1 ppm was not
    considered to represent an adverse effect of treatment, particularly
    in the absence of corresponding decreases in erythrocyte and brain
    cholinesterase levels. The NOAEL was 1 ppm, equal to 0.18 mg/kg bw
    per day, on the basis of significantly reduced brain cholinesterase
    activity at dietary levels of 3 and 6 ppm (Trutter, 1990).

    Rats

         Groups of 50 male and 50 female rats [strain not specified]
    were fed phorate (purity, 92%) in the diet at levels of 0, 0.22,
    0.66, 2 or 6 ppm, equivalent to 0.01, 0.03, 0.1 or 0.3 mg/kg bw per
    day, and groups of 25 male and 25 female rats were fed 12 or 18 ppm,
    equivalent to 0.6 or 0.9 mg/kg bw per day. Treatment continued for
    13 weeks, and cholinesterase activity was monitored each week.
    Occasional episodes of excitability and intermittent tremors were
    noted in females given 6 ppm, and animals of each sex receiving 12
    and 18 ppm showed severe excitability, intermittent tremors and
    ataxia, culminating in death of 50% of animals at 12 ppm and no
    survivors at 18 ppm. Levels of 6 ppm and higher produced significant
    depression of plasma, erythrocyte and brain cholinesterase activity
    in animals of each sex and decreased erythrocyte cholinesterase
    activity in females at 2 ppm. In all groups receiving 6 ppm or less,
    growth, food consumption, survival and liver and kidney weights and
    ratios were within normal limits, and no abnormalities were seen at

    gross necropsy or histological examination. The NOAEL was 2 ppm,
    equivalent to 0.1 mg/kg bw per day, on the basis of inhibition of
    brain cholinesterase activity at 6 ppm and above (Tusing  et al.,
    1956a; Annex I, reference 29).

    Dogs

         Groups of two male and one female mongrel dogs received
    capsules containing 0, 0.01, 0.05, 0.25 or 1.25 mg/kg bw per day of
    phorate (purity, 92%) in corn oil on six days per week for 15 weeks.
    Two males received a single dose of 2.5 mg/kg bw. Plasma and
    erythrocyte cholinesterase activities were monitored weekly; brain
    cholinesterase activity was not measured. At 0.05 mg/kg bw per day,
    plasma enzyme activity was significantly depressed. Erythrocyte
    cholinesterase activity was not affected during the first 12 weeks
    but was depressed slightly (not significantly) during the last three
    weeks of the study. Significant decreases in plasma and erythrocyte
    enzyme activity were observed at 0.25 mg/kg bw per day, and 1.25
    mg/kg bw per day induced total inhibition of plasma cholinesterase
    activity and a significant reduction in erythrocyte cholinesterase
    activity. All of the dogs administered the single dose of 2.5 mg/kg
    bw per day died within 3-4 h; enzyme activity was not determined. No
    signs of systemic toxicity were seen, and haematological, clinical
    chemistry and urine analyses showed no effects in dogs receiving
    0.01 or 0.05 mg/kg bw per day. Histopathological examination
    revealed no consistent findings related to the treatment (Tusing  et
     al., 1956b; Annex I, reference 29).

         Groups of three male and three female beagle dogs were fed
    phorate in the diet at 0, 0.5 or 1.0 ppm, equivalent to 0.012 or
    0.025 mg/kg bw per day, for six weeks. Cholinesterase activity in
    plasma and erythrocytes was determined before and every two weeks
    during the test. Analyses of variance revealed no significant
    difference between the treated and control animals with respect to
    plasma and erythrocyte enzyme activities (Kay & Calandra, 1961;
    Annex I, reference 29).

         In a preliminary range-finding study, groups of two male and
    two female beagle dogs were given capsules containing phorate
    (purity, 92.1%) in corn oil at doses of 0.01, 0.05, 0.10, 0.25 or
    0.50 mg/kg bw per day for 14 days. A control group of three male and
    three female dogs was given capsules containing corn oil. Plasma and
    erythrocyte cholinesterase levels were measured twice before
    treatment, and after 3, 7, 10 and 14 days of treatment; brain
    cholinesterase levels were determined in the cerebellum and cerebrum
    of each dog at sacrifice. Excessive salivation and tremors were seen
    in one female dog given the highest dose, and body-weight gain was
    decreased in comparison with the controls in animals of each sex.
    Slight decreases in total serum protein were recorded in males and
    females at the high dose. Treatment did not affect survival, food
    consumption, haematological parameters or organ weights, and gross

    pathology showed no effects; histopathological examinations were not
    performed. Plasma cholinesterase levels were significantly decreased
    in animals of each sex given 0.10 mg/kg bw per day or more and in
    males given 0.05 mg/kg bw per day, in comparison with values before
    treatment and in control animals, and erythrocyte cholinesterase
    activity was significantly (> 20%) inhibited in both males and
    females at the highest dose of 0.50 mg/kg bw per day. Brain
    cholinesterase activity was inhibited (31-69%) in both males and
    females at 0.10 mg/kg bw per day or more. The NOAEL was 0.05 mg/kg
    bw per day (Piccirillo  et al., 1987).

         Phorate (purity, 92.1%) in corn oil was administered orally by
    capsule to groups of six male and six female beagle dogs at doses of
    0.005, 0.01, 0.05 or 0.25 mg/kg bw per day for one year. Eight male
    and eight female controls received capsules containing only corn
    oil. Plasma and erythrocyte cholinesterase activities were measured
    twice before treatment, at six weeks, at three and six months and at
    sacrifice; brain cholinesterase levels were measured in the cerebrum
    and cerebellum at termination of treatment. Mild tremors were
    observed occasionally in one male and two females during weeks 23-52
    of treatment with the high dose. Mean body weights and overall
    weight gain (26% less than control) were decreased in males at 0.25
    mg/kg bw per day. Ophthalmological examination of all dogs before
    treatment, at six months and at one year showed no treatment-related
    effects. There were no adverse effects on food consumption or
    haematological or urinary parameters. Decreased ( p < 0.05) total
    protein levels were recorded at week 6, at three and six months and
    at termination of treatment in males treated at 0.25 mg/kg bw per
    day. Although the values were reported to be within the range in
    historical controls, no supporting data were provided. As the
    individual levels of total protein in males at the high dose were
    consistently below concurrent values before treatment and in
    controls, the finding appeared to be related to treatment. The
    decreases ( p < 0.05) in total protein values in females and the
    decreased albumin values in males at the high dose were within the
    lower limits of control values. Gross and histopathological
    examination revealed no lesions that could be attributed to
    treatment with phorate. The highest dose induced inhibition of
    erythrocyte (> 20%) and brain cholinesterase activity (43-54%);
    plasma cholinesterase levels were significantly decreased in animals
    of each sex at doses of 0.05 mg/kg bw per day and above. The
    decrease in plasma cholinesterase activity at this dose was not
    considered to be adverse in the absence of correlative inhibition of
    brain and erythrocyte cholinesterase activity and evidence of
    clinical toxicity. The NOAEL was 0.05 mg/kg bw per day on the basis
    of decreased body weight, significant inhibition of erythrocyte and
    brain cholinesterase activity and clinical signs consistent with
    cholinergic toxicity at the high dose of 0.25 mg/kg bw per day
    (Shellenberger & Tegeris, 1987).

    (c)  Long-term toxicity and carcinogenicity

    Mice

         Groups of 50 male and 50 female 41-day-old CD-1 outbred Swiss
    albino mice were fed technical-grade phorate (purity, 85.5%) in the
    diet at 0, 1, 3 or 6 ppm, equivalent to 0.15, 0.45 or 0.9 mg/kg bw
    per day for 18 months. All animals that died or were killed in
    moribund condition during the study or were sacrificed terminally
    were subjected to gross and histopathological examination. Survival
    was not adversely affected: 78-90% of males and 66-74% of females in
    the control and treated groups were still alive at the end of the
    experiment. The growth of females at 6 ppm was retarded almost
    throughout the experiment. All treated animals appeared to eat less
    food during the first three weeks and occasionally thereafter, but
    no consistent dose-response relationship was seen. Some clinical
    signs, such as tremors, hyperactivity and excessive salivation,
    occurred at higher incidence and more frequently in animals at the
    highest dose than in controls. Gross pathological examination showed
    no changes significantly different from those in the controls, and
    microscopic evaluation of a wide range of tissues from each animal
    revealed no alterations related to treatment. There was no
    significant dose-related increase in the incidence of any particular
    type of tumour, of animals with tumours, of animals with malignant
    tumours or of animals with multiple primary tumours. Although the
    incidence of alveolar and bronchiolar adenoma appeared to be
    increased in males at 6 ppm (8/50, compared with 3/50 in controls),
    this effect was not considered to be related to treatment since the
    increase was not statistically significant and this tumour is known
    to occur frequently in CD-1 mice. The NOAEL was 3 ppm, equivalent to
    0.45 mg/kg bw per day, on the basis of decreased body weight and
    clinical signs of toxicity at 6 ppm (Litton Bionetics, 1981a; Annex
    I, reference 39).

    Rats

         Groups of 50 male and 50 female five-week-old Crl:COBS CD(SD)
    BR rats were fed dietary levels of technical-grade phorate (purity,
    84.5%) at 0, 1, 3 or 6 ppm, equal to 0.05, 0.16 or 0.32 mg/kg bw per
    day in males and 0.07, 0.19 or 0.43 mg/kg bw per day in females, for
    24 months. The mortality rate appeared to be increased in females at
    6 ppm, as only 36% survived to the end of the experiment; however,
    more than 60% of animals in all groups, including the controls,
    lived at least 90 weeks. The only clinical sign related to treatment
    was tremors induced by over-dosing (327% of all the intended doses)
    during week 9. Growth was depressed in females at 6 ppm during the
    first 26 weeks and again between weeks 74 and 102. Food consumption
    showed no consistent dose-response pattern. On haematological
    examination, clinical chemistry and urinalysis performed at 6, 12
    and 24 months, the only notable findings were decreased values for
    erythrocyte counts, haemoglobin and haematocrit in females at the

    highest dose at 12 months. Dose-related inhibition (> 20%) of
    plasma cholinesterase activity was noted in males at 6 ppm at 12
    months, in all treated males at 24 months and in females at both 3
    and 6 ppm at all sampling intervals (3, 6, 12 and 24 months).
    Erythrocyte cholinesterase activity was not significantly depressed
    (< 20%) at any time. The activity of brain cholinesterase was
    reduced (> 20%) in males at 6 ppm and in females at 3 ppm or more.
    At sacrifice, females given the highest dose had increased
    organ:body weight ratios with respect to the adrenals, brain, heart,
    liver and spleen. On gross pathological and histopathological
    examination of a variety of tissues, the only effect apparently
    related to treatment was a significant increase in the incidence of
    inflammation and epithelial hyperplasia of the forestomach in
    animals of each sex, but particularly in males, at 6 ppm. The most
    prevalent types of spontaneous tumours were pituitary adenomas in
    animals of each sex and mammary tumours in females. There were no
    significant differences between control and treated groups with
    regard to incidence, type or time of appearance of tumours. The
    marginal no-effect level was 1 ppm, equal to 0.05 mg/kg bw per day
    (Litton Bionetics, 1981b; Annex I, reference 39).

    (d)  Reproductive toxicity

    Mice

         Groups of eight male and 16 female mice (strain not specified)
    were fed phorate (purity unknown) in the diet at levels of 0, 0.6,
    1.5 or 3 ppm, equivalent to 0.09, 0.23 or 0.45 mg/kg bw per day, for
    three generations, with two litters per generation. There were no
    dose-related effects on indices of fertility, gestation, viability
    or lactation during the study, but the lactation index was slightly
    lowered in the group receiving 3 ppm, to below the control value in
    the first mating of the F0 generation, in both matings of the F1
    generation and in the second mating of the F2 generation. Gross
    and microscopic examination of tissues revealed no consistent
    abnormalities related to treatment. The NOAEL was 1.5 ppm,
    equivalent to 0.23 mg/kg bw per day, on the basis of decreased
    lactation indices at 3 ppm (American Cyanamid Co., 1965; Annex I,
    reference 39).

    Rats

         A two-generation study of reproductive toxicity was conducted
    in groups of 25 male and 25 female COBS CD(SD) rats given phorate
    (purity, 92.1%) at dietary levels of 0, 1, 2, 4 or 6 ppm, equal to
    0.09, 0.17, 0.35 or 0.52 mg/kg bw per day in males and 0.10, 0.20,
    0.40 or 0.62 mg/kg bw per day in females, for a minimum of 60 days
    before mating, to produce two consecutive litters (F1a and F1b)
    of the first (F0) parental generation. Groups of 25 males and 25
    females were then selected from the F1b litters to become the
    second-generation (F1) parental animals. Owing to a high incidence

    of mortality during the post-weaning period among F1b pups at 6
    ppm, 30 males and 30 females at this dose were selected as F1
    parents. The second-generation parental animals were treated for a
    minimum of 100 days before mating to produce two consecutive litters
    (F2a and F2b). Animals were exposed continuously to the test
    diets before mating and throughout weaning of the offspring in both
    generations. Cholinesterase levels were determined in plasma,
    erythrocytes and brain from 10 parental F1 rats of each sex in
    each group at terminal sacrifice.

         A treatment-related decrease in body weight and tremors were
    seen at > 4 ppm in parental animals; at 6 ppm, increased
    mortality and clinical signs were seen, manifested as convulsive
    movements and aggressive behaviour. Routine clinical observation of
    the animals revealed an increased incidence of ocular effects at 6
    ppm, described as exophthalmus, 'protrusion of tissue off the
    cornea' and opacities. Subsequent ophthalmological evaluation
    revealed markedly higher incidence and severity of infectious
    sequelae affecting the cornea, anterior uveal tract and posterior
    segment of the eye in rats at this dose. The increased
    susceptibility of rats to ocular disease at the high dose was
    considered to be a secondary effect of treatment with phorate.
    Plasma cholinesterase levels were significantly decreased in females
    at 4 and 6 ppm and in males at 6 ppm. Erythrocyte activity was
    inhibited only slightly (10-11%) in animals of each sex at 6 ppm.
    Inhibition of brain cholinesterase activity was significant in males
    (40%) at 6 ppm and in females at 4 ppm (59%) and 6 ppm (83%). There
    was no significant inhibition of brain cholinesterase activity at
    the lower dietary levels.

         Pup survival during the lactation periods was significantly
    reduced in all litters from both parental generations at 6 ppm and
    in the F2a litter at 4 ppm. The size of both litters from the F1
    generation was slightly decreased at 6 ppm. Mean pup weights were
    decreased in both F1a and F1b litters of animals receiving 4 or
    6 ppm. The mean weights of pups of the F2a litter were decreased
    at 4 ppm (those of the F2b litter were not affected) and in pups
    of both F2a and F2b litters at 6 ppm. Anogenital staining was
    recorded in F1b and F2b pups at 6 ppm but not in control animals
    or in those receiving lower dietary levels. There were no adverse
    effects on mating or fertility indices, pregnancy rate, length of
    gestation, gestation index or sex distribution ratios, and no gross
    morphological alterations or pathological changes were seen in the
    reproductive organs at any of the dietary levels studied. The NOAEL
    was 2 ppm, equal to 0.17 mg/kg bw per day (Schroeder & Daly, 1991).

    (e)  Embryotoxicity and teratogenicity

    Rats

         Groups of 25 mated female Crl:COBS CD (SD)BR rats were given
    technical-grade phorate (purity, 91.7%) by gastric intubaton at 0,
    0.125, 0.25 or 0.5 mg/kg bw per day on gestation days 6-15 and were
    sacrificed on day 20 of gestation. The fetuses were removed for
    gross, skeletal and visceral examination. The pregnancy rate was
    comparable in all groups. During the gestation period, 7/23 pregnant
    dams at 0.5 mg/kg bw per day, none at 0.25 mg/kg bw per day and 1/24
    at 0.125 mg/kg bw per day died. Fetuses at 0.5 mg/kg bw per day had
    an increased frequency of enlarged heart (not otherwise
    characterized). Clinical signs, body weight and food consumption of
    dams during gestation, the number of implantation sites, the number
    of resorptions, the number of dead fetuses, mean live litter size,
    average fetal weight, sex ratio, and gross, skeletal and visceral
    abnormalities of fetuses were not significantly different from those
    in the controls. The NOAEL for teratogenicity was 0.25 mg/kg bw per
    day (Litton Bionetics, 1978; Annex I, reference 39).

         In a preliminary range-finding study, groups of eight mated
    female Crl:CDBRVAF/Plus (SD) rats were administered phorate (purity,
    92.1%) in corn oil by gavage at doses of 0, 0.25, 0.5, 0.7 or 0.9
    mg/kg bw per day on days 6-15 of gestation. The presence of
    spermatozoa or a copulatory plug was considered evidence of mating,
    and the day on which it occurred was considered day 0 of gestation.
    Treatment with doses > 0.5 mg/kg bw per day was lethal to the
    dams, and there were no survivors at these doses after day 12 of
    gestation. Overt clinical signs of toxicity preceding death included
    twitches, tremors, excessive salivation, exophthalmos, ataxia,
    clonic convulsion, and decreased body weight and food intake. Gross
    examination of rats which died revealed enlarged and/or congested
    adrenal glands. The NOAEL was 0.25 mg/kg bw per day for both
    maternal and developmental toxicity (Lochry, 1990a).

         In a study of teratogenicity, groups of 24-25 mated female
    Crl:CDBRVAF/Plus(SD) rats were treated by gavage with phorate
    (purity, 92.1%) in corn oil at doses of 0, 0.1, 0.2, 0.3 or 0.4
    mg/kg bw per day on days 6-15 of gestation. The presence of
    spermatozoa or a copulatory plug was considered evidence of mating,
    and the day on which this occurred was considered day 0 of
    gestation. Six of 25 females at 0.4 mg/kg bw per day that died
    during days 11-16 of gestation had enlarged adrenal glands. No
    deaths were reported at lower doses. Clinical signs of toxicity seen
    at 0.4 mg/kg bw per day were an increased number of rats with
    tremors, excessive salivation, chromodacryorrhoea and rhinorrhoea,
    urine-stained abdominal fur, decreased motor activity, hunched
    posture, impaired righting reflex and laboured breathing. Maternal
    body weights, corresponding weight gains and food consumption and
    fetal body weights were significantly decreased at 0.4 mg/kg bw per

    day when compared with control values. Increased incidences of
    skeletal variations were observed in fetuses and/or litters at this
    dose, which were related to delays in ossification of the
    sternebrae, incompletely and unossified pubes and incompletely
    ossified ischia. The NOAEL for maternal and developmental toxicity
    was 0.3 mg/kg bw per day on the basis of mortality, clinical signs
    of toxicity, and significantly decreased body weights and food
    consumption in the mothers and decreased fetal body weights and
    potentially reversible delays in skeletal ossification at 0.4 mg/kg
    bw per day (Lochry, 1990b).

         Groups of 10 pregnant Sprague-Dawley rats were exposed by nose
    only in an inhalation chamber to aerosols of technical-grade phorate
    (purity, 78-90%) with a count median diameter of 0.57 Ám, generated
    from a 1% solution of phorate in xylene, for 1 h per day on days
    7-14 of gestation at concentrations of 0.15 ▒ 0.04, 0.4 ▒ 0.15 or
    1.94 ▒ 0.48 mg/m3. Three groups of 15 dams were exposed to xylene
    or air or to a restricted diet. (The reason for including the last
    group was not specified.) All dams were sacrificed on day 20 of
    gestation, and fetuses were removed by caesarean section for
    visceral and skeletal examination. Five dams at the highest dose
    died, and toxic signs (tremors, lachrymation and exophthalmus) were
    noted in animals at this level; one of the dead dams had resorbed
    the entire litter. Average percentage fetal mortality was markedly
    increased at this dose. The summary indicated no treatment-related
    effects on the body weight or food consumption of dams during
    gestation and no effects on pregnancy rate, average number of
    implants, average fetal weight, average number of sternal
    ossification centres or the incidence of supernumerary ribs.
    Specific information on the incidence of any gross or soft-tissue
    abnormalities was not provided (Newell & Dilley, 1978; Annex I,
    reference 39).

    Rabbits

         In a preliminary range-finding study, groups of five mated
    female New Zealand white rabbits were administered phorate (purity,
    92.1%) in corn oil by gavage at doses of 0, 0.3, 0.6, 0.9, 1.2 or
    1.5 mg/kg bw per day on days 6-18 of gestation. The day on which
    coitus with two successive males was observed was designated day 0
    of gestation. The incidences of mortality in the six groups were
    reported as 0/5, 1/5, 1/5, 1/5, 2/5 and 4/5, respectively. Mean
    body-weight loss was seen at 1.2 mg/kg bw per day. Only one female
    at the highest dose survived to scheduled sacrifice. Food intake was
    generally decreased in the groups receiving 0.3, 0.6, 0.9 and 1.2
    mg/kg bw per day, although no clear dose-response relationship was
    seen. Increased numbers of resorptions and post-implantation losses
    were reported at doses > 0.6 mg/kg bw per day. Decreased mean
    fetal body weights and shorter crown-rump lengths were noted at 1.2
    mg/kg bw per day. External examination of the fetuses showed no
    treatment-related malformations or alterations. The only significant

    effects observed at the LOAEL of 0.3 mg/kg bw per day were a single
    maternal death and depressed food intake (Schroeder & Daly, 1986).

         Groups of 20 mated female New Zealand white rabbits were given
    phorate (purity, 92.1%) in corn oil by gavage on days 6-18 of
    gestation at doses of 0, 0.15, 0.5, 0.9 or 1.2 mg/kg bw per day. The
    day on which coitus with two successive males was observed was
    designated day 0 of gestation. At 1.2 mg/kg bw per day, 8/20 females
    died during days 14-19 of gestation, one female aborted and another
    female delivered prematurely on day 28 of gestation, so that only
    10/20 dams survived to scheduled sacrifice. The deaths of two
    females at 0.9 and one at 0.5 mg/kg bw per day were also attributed
    to treatment with phorate. Anogenital staining was observed at a
    higher incidence in females treated with the highest dose. Mean body
    weights and corresponding weight gains were decreased at doses >
    0.5 mg/kg bw per day. Food consumption was decreased in females
    treated at 1.2 mg/kg bw per day. Treatment had no effect on
    pre-implantation loss, number of resorptions, number of live
    fetuses, fetal body weight or fetal sex ratio. At 1.2 mg/kg bw per
    day, all three fetuses in a single litter (five of eight
    implantation sites showed early resorptions) had open eyelids,
    curved scapulae, an absent supraorbital process, an irregular margin
    of the frontals and a displaced anterior fontanel. Although these
    anomalies were not observed in the control group, the incidence of
    open eyes was within that of historical controls; curved scapulae
    had not previously been noted, however, in 1852 fetuses from 269
    litters. Ocular and scapular defects were not seen in other fetuses
    from dams treated at this dose and were not recorded in any of the
    fetuses in the preliminary range-finding study. Although the defects
    seen in this single litter may have been a secondary response to the
    maternal toxicity of the high dose, the weight of evidence would
    suggest that the findings were spurious and perhaps genetically
    predicted. There was insufficient evidence to suggest that phorate
    is teratogenic to rabbits. The NOAEL for maternal toxicity was 0.15
    mg/kg bw per day, as determined by a higher incidence of mortality
    and decreased body weights at > 0.5 mg/kg bw per day. In the
    absence of embryo- or fetotoxicity, the NOAEL for developmental
    toxicity was the highest dose, 1.2 mg/kg bw per day (Schroeder &
    Daly, 1987).

    (f)  Genotoxicity

         A battery of assays were performed to test the genotoxicity of
    phorate, the results of which are presented in Table 2. Assays for
    gene mutation, chromosomal aberrations and other cytogenetics
    end-points  in vitro and  in vivo gave negative results. No
    unscheduled DNA synthesis was seen in human fibroblasts, and
    dominant lethal mutations were not induced in male mice.


    
    Table 2.  Results of tests for the genotoxicity of phorate
                                                                                                            
    End-point       Test system         Concentration            Purity     Results     Reference
                                        of phorate               (%)
                                                                                                            
    In vitro
    Reverse         S. typhimurium      Up to 1000 mg/plate      Technical  Negativea   Simmon et al., 1977b
    mutation        TA100, 1535, 1537,  grade
                    1538; E. coli WP2
    Reverse         E. coli p3478,      1 mg (on filter disc)    Technical  Negativec   Simmon et al., 1977b
    mutation        W3110; B. subtilis  per plate                grade

    Reverse         Chinese hamster     30, 40, 50, 80, 100      92.1       Negativec   Thilager & Kumarop,
    mutation        ovary cells, hprt   nl/ml                                           1985
                    locus               5, 10, 12, 14, 16, 18,              Negatived
                                        20 nl/ml
    Mitotic         S. cerevisiae D3    5% w/v for 4-h           Technical  Negativea   Simmon et al., 1977b
    recombination                       incubation before        grade
                                        plating
    Unscheduled     Human fibroblasts   Up to 1 x 10-3           Technical  Negativea   Simmon et al., 1977b
    DNA synthesis   WI-38                                        grade

    In vivo
    Chromosomal     Male and female     M: 0 (corn oil), 0.25,   92.1       Negative    Ivett & Myhr, 1986
    aberration      Sprague-Dawley      1.25, 2.5 mg/kg bw
                    rats, killed after  per day; F: 0, 0.13,
                    6, 18, 30 h         0.63, 1.25 mg/kg bw
                                        per day
    Dominant        Male mice           0, 5, 10, 20 mg/kg bw    Technical  Negative    Simmon et al., 1977b
    lethal                              per day in diet for      grade
    mutation                            7 weeks, weekly
                                        matings for 8 weeks
                                                                                                            

    a In the presence and absence of metabolic activation
    b From Annex 1, reference 46
    c In the absence of metabolic activation
    d In the presence of metabolic activation


    
    (g)  Special studies

    Delayed neuropathy in chickens

         Groups of six adult hens were fed 0 or 40 ppm phorate (purity
    unspecified), equivalent to 5 mg/kg bw per day, in the diet for four
    weeks. A third group received 4000 ppm tri- ortho-tolyl phosphate
    as a positive control. Each hen was anaesthetized and immediately
    perfused with buffered formalin, and sections of brain, lower
    thoracic cord and each sciatic nerve were prepared for microscopic
    examination. Tri- ortho-tolyl phosphate induced myelin loss in each
    hen, but phorate had no adverse effects on nerve fibres or the
    myelin sheath (Levinskas  et al., 1965; Annex I, reference 29).

         Phorate (purity, 89.5%) dissolved in corn oil was administered
    by gavage to fasted white Leghorn hens (22-23-months old). The
    LD50 by a single oral dose was 14.2 mg/kg bw. Fifty fasted hens
    were then given an intramuscular injection of 10 mg/kg bw of
    atropine sulfate and 1 h later given a single oral dose of 14.2
    mg/kg bw phorate. An additional 15 fasted, atropinized hens were
    given corn oil only, and 15 hens that did not receive atropine were
    given tri- ortho-tolyl phosphate at 500 mg/kg bw as a positive
    control. All surviving hens in the test and vehicle control groups
    received the same doses 21 days later, except that atropine sulfate
    was administered at 30 mg/kg bw. All hens were observed daily for
    mortality, clinical signs and evidence of neurotoxic reactions. Body
    weights and food consumption were recorded every three days. All
    hens that died during the study and all hens that were killed at
    termination of the study at 42 days were subjected to gross
    necropsy. Those killed at the end of the study were perfused with
    10% neutralized formalin, and brains, vertebral columns (with spinal
    cord  in situ) and the entire right and left sciatic nerves were
    excised and fixed. Microscopic slides of neural tissue were prepared
    by taking a sagittal section of the entire brain (corpus striatum,
    cerebellum, pons), longitudinal and cross-sections of the cervical,
    thoracic and lumbrosacral levels of the spinal cord and both
    sagittal and longitudinal sections of the right and left sciatic
    nerves. Sections were stained with haematoxylin and eosin, and
    replicate sections were stained with luxol fast blue. Tissues from
    10 hens in each group were examined histologically.

         None of the 15 hens fed corn oil died during the 42-day study,
    and all 15 hens given tri- ortho-tolyl phosphate were killed  in
     extremis on day 16 of the study after clinical signs of
    neuropathy, first observed on day 11, became progressively more
    severe. These signs included generalized weakness, ataxia and
    paralysis of the legs and wings. Of the 50 hens treated with
    phorate, 27 died within 24 h of the first dose and 13 more within 24
    h of the second dose. Ten hens survived to termination of the study.
    Vehicle control and phorate-treated hens had slight generalized
    weakness of the limbs, lasting about 2 h, shortly after each

    treatment with atropine sulfate; treated hens had slightly more
    severe reactions and, in addition, slight to moderate ataxia for up
    to 2 h after treatment with phorate. No clinical signs of delayed
    neuropathy were observed, however, in any vehicle-control or test
    birds. In comparison with vehicle controls, the mean body-weight
    gains of tested hens were greater at 0-21 days and smaller at 21-42
    days, and the mean feed consumption of test hens was smaller at 0-21
    days and greater at 21-42 days. No effects attributable to phorate
    were seen at gross necropsy.

         Histological examination of neural tissues from
    positive-control hens revealed treatment-related lesions involving
    the brain, spinal cord and/or sciatic nerves in all 10 birds.
    Generally mild to moderate axonal degeneration was observed in the
    brains of 4/10 hens, in the spinal cords of 10/10 hens and in the
    sciatic nerves of 10/10. In addition, demyelination was observed in
    the spinal cords and in the sciatic nerves of 7/10 hens;
    Schwann-cell hyperplasia was also observed in the sciatic nerves of
    3/10 hens. These lesions were compatible with a delayed neurotoxic
    response induced by tri- ortho-tolyl phosphate. Minimal to mild
    focal axonal degeneration of the sciatic nerves was noted in 3/10
    hens treated with phorate; no axonal degeneration was seen in
    vehicle-control hens. The axonal degeneration observed in the
    treated birds was associated with interstitial infiltration of
    lymphoid cells, which was also observed in other test and
    vehicle-control hens. This syndrome, which was distinctly different
    from that observed in the positive-control hens, was ascribed to
    lesions of a naturally occurring disease (Marek's disease) and was
    considered not to be related to treatment with phorate. Treatment
    did not induce clinical or histopathological signs indicative of
    acute delayed neuropathy (Fletcher, 1984; Annex I, reference 46).

    3.  Studies on metabolites

    (a)  Enzymes and biochemical parameters

         The metabolites of phorate that inhibit cholinesterase are
    phorate sulfoxide and sulfone and the oxygen analogue phoratoxon and
    its sulfoxide and sulfone. The negative logarithms of the molar
    concentrations of these compounds that induce 50% inhibition of
    erythrocyte cholinesterase are as follows: phorate, 3.17; phorate
    sulfoxide, 3.35; phorate sulfone, 5.00; phoratoxon, 5.87; phoratoxon
    sulfoxide, 6.76; and phoratoxon sulfone, 7.02 (Annex I, reference
    29).

    (b)  Acute toxicity

         The acute toxicity of metabolites of phorate was studied in
    rats and mice; the results are shown in Table 3. Both the parent
    compound and the metabolites are extremely acutely toxic.

        Table 3.  Acute toxicity of phorate and its metabolites
                                                                                               
    Compound                 LD50 in rats (mg/kg bw per day)    LD50 in mice (mg/kg bw per day)
                                                                                               
                             Oral            Intraperitoneal    Oral            Intraperitoneal
                                                                                               

    Phorate                  1.9-10          3                  11              3
    Phorate sulfoxide        2-4             11                 7               1
    Phorate sulfone          1.8-2.0         27                 9               2
    Phoratoxon               0.6-0.8         -                  -               -
    Phoratoxon sulfoxide     1.4-1.6         1                  3               0.02
    Phoratoxon sulfone       0.6-0.8         1.8                5               0.4
                                                                                               
    From Blinn, 1982; Annex I, reference 39
        (c) Short-term toxicity

    Rats

         Groups of 35 male and 35 female rats (strain not specified)
    were fed phorate sulfoxide (purity, 92%) at dietary levels of 0.32,
    0.8 or 2 ppm, equivalent to 0.02, 0.04 or 0.1 mg/kg bw per day, for
    90 days. Fifty males and 50 females served as controls. Brain,
    erythrocyte and plasma cholinesterase activities were determined
    twice a week. A significant ( p < 0.05) depression of erythrocyte
    and brain cholinesterase activity was seen in females at 2 ppm; the
    decrease in plasma cholinesterase activity at this dose was less
    consistent and was considered to be borderline. Borderline
    depression of erythrocyte enzyme activity was seen at 0.8 ppm. At
    0.32 ppm, all values were within acceptable statistical limits for
    animals of each sex. No effects were observed on other

    haematological parameters, organ weights or ratios, and no
    consistent histopathological effect was noted that could be
    attributed to feeding 2 ppm or less of phorate sulfoxide (Levinskas
     et al., 1968; Annex I, reference 29).

         Groups of 30 male and 30 female Charles River CD strain rats
    (50 male and 50 female controls), 51 days of age, were fed phorate
    sulfone (purity, 92%; containing 6% unchanged phorate and about 2%
    phorate sulfoxide) in the diet at 0, 0.32, 0.8 or 2 ppm, equivalent
    to 0.02, 0.04 or 0.1 mg/kg bw per day, for 90 days. None of the
    animals died before the end of the experiment, and there were no
    treatment-related changes in appearance or behaviour. Weight gain
    and increased food consumption were seen in males fed 0.8 or 2 ppm.
    Assay of tissue cholinesterase activity five times during the course
    of the experiment showed inhibition (> 20%) of erythrocyte
    cholinesterase at 2 ppm in animals of each sex at most time
    intervals. Plasma cholinesterase activity was reduced by 23-27% in
    males at 2 ppm after one, three and five weeks and by 25-72% in
    females at 2 ppm after all sampling intervals; plasma cholinesterase
    was also inhibited (39%) in females at 0.8 ppm after one and three
    weeks. The activity of brain cholinesterase was reduced (> 20%)
    only in females at 2 ppm after three, five and eight weeks. Control
    and treated groups did not differ significantly with regard to
    values for haematocrit, haemoglobin and total leukocyte count at the
    end of the experiment. No treatment-related effects were observed on
    the absolute weights of kidneys or liver, and no gross pathological
    changes were seen. Histopathological evaluation of a variety of
    tissues from five males and five females in the control and
    highest-dose groups revealed no morphological alterations
    attributable to treatment. The NOAEL was 0.32 ppm, equivalent to
    0.02 mg/kg bw per day (Hutchison  et al., 1978; Annex I, reference
    39).

    4.  Observations in humans

         No relevant information was available.

    Comments

         The limited data available indicate that phorate given orally
    to rats is not readily eliminated, with less than 40% of the
    administered radioactivity recovered within six days after
    treatment. Urinary metabolites were identified as  O,O-diethyl
     O-hydrogen phosphoro-thioate, diethyl hydrogen phosphorate and
     O,O-diethyl  O-hydrogen phosphorodithioate.

         Phorate was severely acutely toxic in mice, rats and rabbits
    after administration by various routes. WHO (1992) has classified
    phorate as extremely hazardous.

         In a 13-week study of the toxicity study of dietary levels of
    0, 1, 3 and 6 ppm phorate in mice, the NOAEL was 1 ppm, equal to
    0.18 mg/kg bw per day, on the basis of inhibition of brain
    cholinesterase activity at dietary levels of 3 ppm and above.

         In rats that received phorate in the diet at 0, 0.22, 0.66, 2,
    6, 12 or 18 ppm for 13 weeks, the NOAEL was 2 ppm, equivalent to 0.1
    mg/kg bw per day, on the basis of inhibition of brain cholinesterase
    activity. At 6 ppm, cholinesterase inhibition was associated with
    tremors and hyperexcitability and at 12 and 18 ppm, with death.

         In a one-year study of toxicity in dogs, phorate was
    administered orally in capsules at doses of 0, 0.005, 0.01, 0.05 or
    0.25 mg/kg bw per day. The NOAEL was 0.05 mg/kg bw per day, as
    determined by decreased body weights, significant inhibition of
    erythrocyte and brain cholinesterase activity and clinical signs
    consistent with cholinergic toxicity at 0.25 mg/kg bw per day. A
    preliminary 14-day range-finding study, a six-week study of dietary
    administration and a 15-week study in which phorate was given orally
    in capsules supported the findings reported in the one-year study.

         Mice and rats were treated with phorate at dietary levels of 0,
    1, 3 or 6 ppm for 18 and 24 months, respectively. In mice, the NOAEL
    was 3 ppm, equivalent to 0.45 mg/kg bw per day, on the basis of
    decreased body weights and increased incidences of tremors,
    hyperactivity and excessive salivation at 6 ppm. Cholinesterase
    activity was not measured in this study. In the study of toxicity
    and carcinogenicity in rats, the NOAEL was 1 ppm, equal to 0.05
    mg/kg bw per day, on the basis of significant inhibition of brain
    cholinesterase at 3 ppm and above. There was no apparent effect on
    erythrocyte cholinesterase activity. Phorate was not carcinogenic
    when fed to mice or rats at dietary levels of up to 6 ppm.

         A two-generation study of reproductive toxicity in rats given
    phorate at dietary levels of 0, 1, 2, 4 or 6 ppm showed no adverse
    effects on reproductive parameters. The NOAEL was 2 ppm, equal to
    0.17 mg/kg bw per day, on the basis of decreased brain
    cholinesterase activity, tremors, decreased parental and pup body

    weights and decreased pup survival at 4 ppm and above. In a
    three-generation study of reproductive toxicity in mice fed dietary
    levels of 0, 0.6, 1.5 or 3 ppm, the NOAEL was 1.5 ppm, equivalent to
    0.23 mg/kg bw per day, on the basis of slightly reduced lactation
    indices at 3 ppm.

         Two studies of teratogenicity were conducted with phorate in
    rats, at dose levels of 0, 0.125, 0.25 or 0.5 mg/kg bw per day and
    0, 0.1, 0.2, 0.3 or 0.4 mg/kg bw per day. The NOAEL for maternal and
    developmental toxicity was 0.3 mg/kg bw per day on the basis of
    severe maternal toxicity culminating in death, decreased fetal body
    weights and delays in fetal skeletal ossification at 0.4 mg/kg bw
    per day. There was no evidence of teratogenic potential at doses as
    high as 0.4 mg/kg bw per day. At the maternally lethal dose of 0.5
    mg/kg bw per day, there was an increased incidence of fetuses with
    enlarged hearts. In rabbits treated with doses of 0, 0.15, 0.5, 0.9
    or 1.2 mg/kg bw per day, maternal mortality and decreased body
    weight were observed at doses of 0.5 mg/kg bw per day and above,
    resulting in an NOAEL of 0.15 mg/kg bw per day. In the absence of
    embryo- and fetotoxicity, the NOAEL for developmental toxicity was
    the highest dose, 1.2 mg/kg bw per day. Phorate was not teratogenic
    to rabbits.

         Phorate has been adequately tested for genotoxicity  in vitro
    and  in vivo in a battery of assays. The Meeting concluded that
    phorate is not genotoxic.

         No clinical or histopathological signs of delayed neuropathy
    were seen in chickens.

         Ninety-day studies of the toxicity of phorate administered in
    the diet were conducted in rats with the cholinesterase-inhibiting
    sulfoxide and sulfone metabolites of phorate. The metabolites of
    phorate were marginally more potent inhibitors of brain
    cholinesterase than phorate in female rats. Brain cholinesterase
    activity was inhibited in animals of each sex after administration
    of phorate at a dietary level of 6 ppm, but no significant
    inhibition was apparent at 2 ppm in either sex. The sulfoxide and
    sulfone metabolites of phorate inhibited brain cholinesterase only
    in females treated at the highest dietary level, 2 ppm. There were
    no significant differences in the erythrocyte cholinesterase
    inhibiting activity of the metabolites and the parent compound,
    phorate.

         An ADI was allocated on the basis of a NOAEL of 0.05 mg/kg bw
    per day in the one-year study of toxicity in dogs and the two-year
    feeding study in rats. The effect noted in both species was
    inhibition of brain cholinesterase activity, which was associated in
    dogs with clinical signs consistent with cholinergic toxicity. A
    safety factor of 100 was applied.

    Toxicological evaluation

    Levels that cause no toxic effect

         Mouse:    1 ppm, equal to 0.18 mg/kg bw per day (13-week study
                   of toxicity)

         Rat:      1 ppm, equal to 0.05 mg/kg bw per day (two-year study
                   of toxicity and carcinogenicity)

         Rabbit:   0.15 mg/kg bw per day (study of teratogenicity)

         Dog:      0.05 mg/kg bw per day (one-year study of toxicity)

    Estimate of acceptable daily intake for humans

         0-0.0005 mg/kg bw

    Studies that would provide information useful for continued
    evaluation of the compound

    1.   Adequate studies on absorption, distribution, excretion and
         metabolism in rats. Studies known to exist may address this
         need, in whole or in part. In order to maintain the ADI, these
         data should be submitted in 1995, in time for review in 1996.

    2.   Observations in humans

    References

    American Cyanamid Co. (1965) Report on Thimet systemic insecticide:
    successive generation studies with mice. Unpublished report from
    Central Medical Department Cyanamid. Submitted to WHO by American
    Cynamid Co., Wayne, NJ, USA.

    American Cyanamid Co. (1976) Thimet soil and systemic insecticide.
    Unpublished technical information from Cyanamid International Corp.
    Submitted to WHO by American Cynamid Co., Wayne, NJ, USA.

    Blinn, R.C. (1982) Personal communication to WHO by American Cynamid
    Co., Wayne, NJ, USA.

    Bowman, J.S. & Casida, J.E. (1958) Further studies on the metabolism
    of Thimet by plants, insects and mammals.  J. Econ. Entomol., 51,
    838-843.

    Fletcher, D.W. (1984) 42-Day neurotoxicity study with phorate in
    mature white leghorn chickens. Unpublished report from Bio-life
    Associates Ltd, BLAL No. 83 DN 103, AC Protocol No. 981-84-114.
    Submitted to WHO by American Cynamid Co., Wayne, NJ, USA.

    Gaines, T.B. (1969) Acute toxicity of pesticides.  Toxicol. Appl.
     Pharmacol., 14, 515-534.

    Hutchison, E.B., Fegle, H.C., McNerney, J.M. & Levinskas, G.J.
    (1978) Thimet(R) systemic insecticide: ninety-day repeated feeding
    to albino rats (CL 18,161). Unpublished report from Central Medical
    Department, American Cyanamid Co., Submitted to WHO by American
    Cynamid Co., Wayne, NJ, USA.

    Ivett, J.L. & Myhr, B.C. (1986) Chromosomal aberrations in vivo in
    mammalian bone marrow cells on AC 35,024. Second amended report,
    Project ID No. 8049, 10947-001. Unpublished report dated 9 January
    1986 from Litton Bionetics, Kensington, MD, USA. Submitted to WHO by
    American Cyanamid Co., Princeton, NJ, USA.

    Kay, J.H. & Calandra, J.C. (1961) Effects of thimet phorate on
    cholinesterase activity in the dog. Unpublished report from
    Industrial Bio-test Lans, Inc. Submitted to WHO by American Cynamid
    Co., Wayne, NJ, USA.

    Levinskas, G.J., Morici, B.S. & Shaffer, C.B. (1965) Thimet systemic
    insecticide: demyelination studies in white leghorn hens.
    Unpublished report from Central Medical Department, American
    Cyanamid Co. Submitted to WHO by American Cynamid Co., Wayne, NJ,
    USA.

    Levinskas, G.J., McNerney, J.M. & Fegluy, H.C. (1968) Report on
    sulfoxide of Thimet systemic insecticide: ninety-day repeated

    feeding to albino rats. Unpublished report from Central Medical
    Department, American Cyanamid Co. Submitted to WHO by American
    Cynamid Co., Wayne, NJ, USA.

    Litton Bionetics (1978) Teratology study in rats; Thimet(R)
    phorate. Final unpublished report from Litton Bionetics, Inc.
    Unpublished report from Central Medical Department, American
    Cyanamid Co. Submitted to WHO by American Cynamid Co., Wayne, NJ,
    USA.

    Litton Bionetics (1981a) 18-Month chronic toxicity and potential
    carcinogenicity study in mice. Phorate. Final unpublished report
    from Central Medical Department, American Cyanamid Co. Submitted to
    WHO by American Cynamid Co., Wayne, NJ, USA.

    Litton Bionetics (1981b) 24-Month chronic toxicity and potential
    carcinogenicity study in mice. Phorate. Final unpublished report
    from Central Medical Department, American Cyanamid Co. Submitted to
    WHO by American Cynamid Co., Wayne, NJ, USA.

    Lochry, E.A. (1990a) An oral developmental toxicity (embryo-fetal
    toxicity/teratogenicity) pilot study with AC 35,024 in rats. Final
    report, Project ID No. 101P-012. Unpublished report dated 19 June
    1990 from Argus Research Laboratories Inc., Horsham, PA, USA.
    Submitted to WHO by American Cyanamid Co., Princeton, NJ, USA.

    Lochry, E.A. (1990b) An oral developmental toxicity (embryo-fetal
    toxicity/teratogenicity) definitive study with AC 35,024 in rats.
    Final report, Project ID No. 101-012. Unpublished report dated 23
    October 1990 from Argus Research Laboratories Inc., Horsham, PA,
    USA. Submitted to WHO by American Cyanamid Co., Princeton, NJ, USA.

    Newell, G.W. & Dilley, J.V. (1978) Teratology and acute toxicology
    of selected chemical pesticides administered by inhalation. US
    Environmental Protection Agency Report No. 600/1-78-003, January
    1978. Submitted to WHO by American Cynamid Co., Wayne, NJ, USA.

    Piccirillo, V.J., Shellenberger, T.E. & Dauvin, E. M. (1987) 14-Day
    range-finding oral toxicity study in the dog with AC 35,024. Revised
    final report No. 85013. Unpublished report dated 11 February 1987
    from Tegeris Laboratories Inc., Princeton, NJ, USA. Submitted to WHO
    by American Cyanamid Co., Princeton, NJ, USA.

    Schroeder, R.E. & Daly, I.W. (1986) A range-finding teratology study
    with phorate in rabbits. Final report, project No. 86-3038.
    Unpublished report dated 5 August 1986 from Bio/dynamics Inc., East
    Millstone, NJ, USA. Submitted to WHO by American Cyanamid Co.,
    Princeton, NJ, USA.

    Schroeder, R.E. & Daly, I.W. (1987) A teratology study with phorate
    in rabbits. Final report, project No. 86-3039. Unpublished report

    dated 6 April 1987 from Bio/dynamics Inc., East Millstone, NJ, USA.
    Submitted to WHO by American Cyanamid Co., Princeton, NJ, USA.

    Schroeder, R.E. & Daly, I.W. (1991) A two-generation (two litters)
    reproduction study with AC 35,024 to rats. Final report, Project ID
    No. 88-3350. Unpublished report dated 23 September 1991 from
    Bio/dynamics Inc., East Millstone, NJ, USA. Submitted to WHO by
    American Cyanamid Co., Princeton, NJ, USA.

    Shellenberger, T.E. & Tegeris, A.S. (1987) One-year oral toxicity
    study in purebred beagle dogs with AC 35,024. Final report No.
    85015. Unpublished report dated 20 February 1987 from Tegeris
    Laboratories Inc., Laurel, MD, USA. Submitted to WHO by American
    Cyanamid Co., Princeton, NJ, USA.

    Simmon, V.F., Mitchell, A.D. & Jorgenson, T.A. (1987) Evaluation of
    selected pesticides as chemical mutagens in  in vitro and  in vivo
    studies. Unpublished report from Stanford Research Institute, SRI
    Report No. LSU-3493, for the US Environmental Protection Agency, EPA
    Report No. EPA-600/1-77-028. Submitted to WHO by American Cynamid
    Co., Wayne, NJ, USA.

    Thilagar, A. & Kumarop, V. (1985) Test for chemical induction of
    gene mutation at the  hgrpt locus in cultured Chinese hamster ovary
    (CHO) cells with and without metabolic activation. Final report,
    Study No. 980-85-133. Unpublished report dated 8 August 1985 from
    Sitek Research Laboratories, Rockville, MD, USA. Submitted to WHO by
    American Cyanamid Co., Princeton, NJ, USA.

    Trutter, J.A. (1990) 13-Week dietary toxicity study in albino mice
    with AC 35,024. Final report, Project ID No. 362-201. Unpublished
    report dated 16 May 1990 from Hazleton Laboratories America Inc.,
    Vienna, VA, USA. Submitted to WHO by American Cyanamid Co.,
    Princeton, NJ, USA.

    Tusing, T.W., Kindzin, W., Hanzal, R. & Howard, J. (1956a) Repeated
    oral administration (dogs). Experimental insecticide 3911, 92%.
    Unpublished report from Hazleton Labs, Inc. Submitted to WHO by
    Submitted to WHO by American Cynamid Co., Wayne, NJ, USA.

    Tusing, T.W., Paynter, O.E., Kindzin, M., Hanzal, R. & Howard, J.
    (1956b) Subacute feeding study--experimental insecticide 3911, 92%.
    Unpublished report from Hazleton Labs, Inc. Submitted to WHO by
    Submitted to WHO by American Cynamid Co., Wayne, NJ, USA.

    WHO (1992) The WHO recommended classification of pesticides by
    hazard and guidelines to classification 1992-1993 (WHO/PCS/92.14).
    Available from the International Programme on Chemical Safety, World
    Health Organization, Geneva, Switzerland.


    See Also:
       Toxicological Abbreviations
       Phorate (ICSC)
       Phorate (Pesticide residues in food: 1977 evaluations)
       Phorate (Pesticide residues in food: 1982 evaluations)
       Phorate (Pesticide residues in food: 1984 evaluations)
       Phorate (Pesticide residues in food: 1985 evaluations Part II Toxicology)
       Phorate (Pesticide residues in food: 1996 evaluations Part II Toxicological)