IPCS INCHEM Home


    PESTICIDE RESIDUES IN FOOD - 1982


    Sponsored jointly by FAO and WHO






    EVALUATIONS 1982





    Data and recommendations of the joint meeting
    of the FAO Panel of Experts on Pesticide Residues
    in Food and the Environment and the
    WHO Expert Group on Pesticide Residues
    Rome, 23 November - 2 December 1982

    Food and Agriculture Organization of the United Nations
    Rome 1983


    ACEPHATE

    CH3S  O        O
         \"        "
          P - NH - C - CH3
         /
    CH3O

    Explanation

         Acephate was evaluated by the Joint Meeting in 1976 (FAO/WHO
    1977)1/ and a full ADI was allocated, based on no-effect levels taken
    exclusively from Industrial Bio-Test Laboratories (IBT) data.
    Additional data have become available and are summarized in this
    Monograph Addendum.

    EVALUATION FOR ACCEPTABLE DAILY INTAKE

    BIOCHEMICAL ASPECTS

    Effects on Enzymes and Other Biochemical Parameters

         The anticholinesterase activity of acephate (99.3%), technical
    acephate (93.6%), methamidophos (99.6%), a metabolite of acephate and
    mixtures of acephate and methamidophos in brain and erythrocytes of
    rats and monkeys were determined  in vitro. The I50 values were:

         Based on the data, brain cholinesterase appeared to be
    considerably more sensitive than erythrocyte cholinesterase to
    anticholinesterase activity of acephate (99.3%) in rats. Additionally,
    technical acephate (93.6%) was more potent than acephate (99.3%) as a
    cholinesterase inhibitor, probably owing to contamination of the
    technical material with methamidophos as an impurity. The latter was
    substantially more potent as an anticholinesterase agent than acephate
    (99.3%or 93.6%) (Wong  et al 1979).

    Rat

         Four control and four treated groups of rats (Sprague-Dawley
    derived) comprising 5 males per group were fed technical acephate in
    their diet at 0 or 75 ppm for a maximum of 20 days. One control and
    one treated group were sacrificed on days 6, 11, 15 and 20. Inhibition
    (31-41%) of brain cholinesterase was evident in the treated groups at
    all sampling intervals. Neither plasma cholinesterase nor erythrocyte
    cholinesterase was depressed (<20%) at any time during the 

              

    1/  See Annex 2 for WHO and FAO documentation.

                                                                                                   
                                         I50

                                 Brain cholinesterase       Erythrocyte Cholinesterase

                                 Rat          Monkey        Rat           Monkey
                                                                                               

    Acephate (99.3%)             >1  10-3    1  10-3      9  10-3

    Technical acephate (93.6%)   4.5  10-4   9  10-5      5  10-4      1  10-4

    Methamidophos                5  10-6     3.5  10-6    9  10-7      9  10-6

    Mixture I                    4.5  10-4                 1.0  10-4

    Mixture II                   8.0  10-5                 1.5  10-4

    Mixture III                  8.0  10-5                 9.0  10-5
                                                                                               

         Mixture I:     "Acephate concentration adjusted to 93.6% with
                         1% methamidophos added"

         Mixture II:    "Technical acephate (93.6%) with 2% methamidophos added".

         Mixture III:   "Acephate concentration adjusted to 93.6% with
                        3% methamidophos added".
    
    experiment. In another simultaneously conducted study, 5 control
    groups and 5 treated groups of 10 male rats were given dietary levels
    of technical acephate at 0 or 75 ppm for up to 7 days and then
    sacrificed at different time intervals. Activity of cholinesterase in
    brain was reduced by 34% while that in plasma or erythrocytes was
    reduced by 21-25% on test day 7. No significant depression (<20%) of
    the enzyme in plasma, erythrocytes or brain was observed at any time
    during the recovery period, i.e. 1, 2, 4 and 6 weeks after treatment
    withdrawal (Chevron 1980).

    TOXICOLOGICAL STUDIES

    Special Studies on Teratogenicity

    Rabbit

         A pilot study with groups of 5 artificially inseminated Dutch
    Belted rabbits was undertaken to determine dosage levels of technical
    acephate to be used in a teratology study. Results showed that oral
    doses up to 10 mg/kg body weight/day given on day 6 through day 27,
    inclusive of gestation, induced no mortality or adverse effects on

    body weight. Mortality and toxic signs occurred at 30 mg/kg body
    weight/day, and all rabbits at 100 mg/kg body weight/day died. The 3
    surviving does at 30 mg/kg body weight/day had only viable foetuses
    with no resportions at sacrifice on gestation day 28. However, 2/3
    pregnant does at 10 mg/kg body weight/day and 1/4 pregnant does at
    3 mg/kg body weight/day had only resportions with no viable foetuses
    (Rodwell and Jessup 1980).

         Groups of 16 artificially inseminated Dutch Belted rabbits were
    intubated with an aqueous solution of technical acephate at 0, 1.0,
    3.0 or 10 mg/kg body weight/day on gestation days 6 through 27
    (Day 0 = day of insemination). All surviving does were sacrificed on
    day 28 of gestation and foetuses were removed by caesarean section for
    external, visceral and skeletal examination. No mortality was
    observed. The pregnancy rate was comparable in all groups. Maternal
    body weight during gestation was not adversely affected. Does at both
    3 and 10 mg/kg body weight/day showed a slightly increased incidence
    of nasal discharge. Two of the pregnant does at 10 mg/kg body
    weight/day aborted. Sex ratio (M/F) of foetuses was increased at
    10 mg/kg body weight/day. A slight decrease (not dose-related) in the
    mean number of viable foetuses and total implantations occurred in all
    treated groups. There were no significant differences between control
    and treated groups with respect to early and late resorptions, post-
    implantation loss, mean number of corpora lutea and mean foetal
    weight. Anasarca was detected in 3/66 foetuses (from 1/12 litters) and
    dome-shaped head in an additional foetus from another litter at
    10 mg/kg body weight/day. Neither of these abnormalities was observed
    in concurrent controls, lower dosage groups or in a total of 741
    foetuses from 118 litters that served as historical controls. No
    significant increase in frequency of any other type of malformation
    was observed, although a non-dose-related increase in incidence of
    total (soft tissue and skeletal) malformations was noted in all
    treated groups, as compared to concurrent controls. Such an increase
    was not evident when compared to historical controls. Overall, 3 mg/kg
    body weight appears to be a teratogenic no-effect level (Rodwell
     et al 1980).

    Special Studies on Neurotoxicity

         Twenty-four white Leghorn hens (about 7 months old) were
    intubated with a single dose of 375 mg/kg body weight of acephate
    (98.9% pure) followed immediately by 5 mg/kg body weight of atropine
    intramuscularly. (The oral LD50 of acephate in hens was determined to
    be 360 mg/kg body weight prior to initiation of the neurotoxicity
    study.) Twelve hens, given distilled water only, were used as
    controls. In the treated group, 3 hens died and 2 were sacrificed in
    moribund condition within 5 days of dosing. During the 21-day post-
    exposure period, symptoms of acute poisoning, such as depressed
    spontaneous activity, were seen up to 11 days but no delayed
    neurotoxic symptoms were noted at any time. Histopathological

    evaluation of the sciatic nerve and several sections of the spinal
    cord revealed no morphological changes suggestive of delayed
    neurotoxic activity of acephate. Positive controls, treated orally
    with 500 mg/kg body weight of TOCP, exhibited signs and histological
    changes in the nervous tissue typical of delayed neurotoxicity
    (Hayashizaki  et al undated).

    Special Studies on Eye and Skin Irritation

         One-tenth milliliter (=31.8 mg) of Orthene Specialty Concentrate
    (a formulation containing 97.8% acephate) produced slight conjunctival
    redness, chemosis and discharge at one hour when placed in the eyes of
    New Zealand White rabbits. At this time, slight chemosis was also
    noted in treated eyes that had been rinsed with distilled water. All
    eyes were normal at 24 hours. No corneal opacity or iritis was
    observed at any time during the study (Levy  et al 1979a).

         In a patch test with 6 New Zealand rabbits, 0.5G of Orthene
    Specialty Concentrate induced well-defined erythema in the abraded
    skin of 2 rabbits at 24 hours. Slight erythema was noted in the intact
    skin of an additional rabbit at 48 hours. Treated sites of all 6
    animals were normal by 72 hours (Levy  et al 1979b).

    Acute Toxicity

    Dermal

         No mortality occurred in groups of 6 male rabbits (New Zealand
    White) with clipped trunk skin (3 with intact skin and 3 with abraded
    skin per group) exposed for 24 hours to 5 000 or 10 000 mg/kg body
    weight of technical acephate (97.8%) in physiological saline. The
    LD50 was over 10 000 mg/kg body weight. Toxic signs observed were
    tremors after both dosage levels and diarrhoea after 10 000 mg/kg body
    weight (Rittenhouse and MacGregory 1977).

    Inhalation

         Five male and 5 female rats (Sprague-Dawley derived) were exposed
    in an inhalation chamber for 4 hours to an aerosol of Orthene
    Specialty Concentrate dissolved in distilled water at a calculated
    nominal concentration of 61.7 mg/l air (particle size of aerosol not
    given). There was no mortality. Tremors, ataxia and decreased
    spontaneous activity were observed in all the animals after exposure.
    No toxic signs were evident the following day or during the subsequent
    14-day observation period (Rittenhouse  et al 1979).

    Short-Term Studies

    Rat

         Groups of Sprague-Dawley rats (70 males and 70 females per
    control or treated group) were fed diets containing technical acephate
    at 10 or 50 ppm for 190 days and 138 days, respectively. A high dosage
    group was given 250 ppm for 119 days and then 350 ppm for 71
    subsequent days. The study, originally designed to evaluate chronic
    toxicity and carcinogenic potential of the compound, was terminated
    early after the discovery of an impurity (not identified) in the test
    material. No compound-related findings were noted with respect to
    mortality, physical condition, food consumption or ophthalmoscopic
    observations at 3 months. Growth was depressed in males of the top
    dosage group at week 18 and thereafter. Except for a slight decrease
    in total serum protein and serum albumin in females of all treated
    groups and in males of the top dosage group at 3 months, there were no
    significant differences between control and treated groups in
    haematological and urinalysis parameters. Assay of tissue
    cholinesterase several times over the course of the experiment
    indicated significant inhibition (>20%) of plasma, erythrocyte and
    brain cholinesterase in the top dosage group at most intervals. At
    50 ppm, males exhibited depression (>20%) of brain cholinesterase at
    weeks 7 and 17 and females displayed inhibition (>20%) of plasma
    cholinesterase at weeks 6 and 15 and of brain cholinesterase at week
    17. (Brain cholinesterase at week 17 was reduced in both sexes at
    10 ppm by only about 12%.) Organ weight analysed at terminal sacrifice
    (190 days) revealed a significant increase in absolute weight and
    organ/body weight ratio of thyroid in females of the 10 ppm and top
    dosage groups. Thyroid/body weight ratio was, however, significantly
    elevated in males in the top dosage group. No histopathology data were
    available (Chevron 1979).

    Long-Term Studies

    Rat

         Groups of 75 male and 75 female rats (Sprague-Dawley CD strain;
    45 days old) were fed technical acephate (92.4%) in their diet at 0,
    5, 50 or 700 ppm for 28 months to assess the chronic toxicity and
    carcinogenic potential of the compound. All animals dying during the
    study, those subjected to interim sacrifice (generally 10 males and
    10 females/group at 4 and 12 months, 5 males and 5 females/group at
    22 months) and all terminal survivors were examined grossly.
    Histopathological examination was conducted on a set of over 30
    tissues plus unusual lesions and tissue masses from all control and
    top dosage animals that died or were sacrificed during the study or
    terminally and on gross lesions, tissue masses, eyes and adrenals from
    presumably all animals of 5 and 50 ppm groups.

         Survival was generally good and not adversely affected by
    treatment. Growth was depressed in males at 700 ppm throughout the
    study. Food consumption was consistently increased in both sexes at
    700 ppm throughout the study and at 5.0 ppm and 50 ppm during the
    first 5 weeks and 17 weeks, respectively. A slight, transient increase
    in the frequency of aggressive behaviour and/or increased activity at
    700 ppm in both sexes, especially in the males, was noted during the
    first 6 months of the study. Alopecia was also evident in animals of
    all groups, including the control, but the incidence (not consistently
    dose-dependent) was slightly increased in both sexes at 700 ppm during
    the entire duration of the study and in males of all treated groups
    occasionally. Ophthalmoscopic examination performed 5 times during the
    experiment revealed that a) "focal retinopathy appeared more
    frequently in the high dose rats than in other groups", b) "some
    animals in the mid- and high-dose groups developed a more diffuse
    retinal degeneration, at least one of which was preceded by focal
    retinopathy, and some rats developed posterior subcapsular or complete
    cataracts", and c) "there was a greater incidence of various types of
    cataracts (i.e. complete, focal posterior polar and posterior
    subcapsular cataracts) in treated animals as compared to controls. No
    consistent dose-related differences were apparent. About half of the
    cataracts were unilateral." (Ophthalmological findings in individual
    animals were not included in the report.) Periodic haematological and
    biochemical studies showed occasional variations from controls in
    values of a number of parameters such as haemoglobin, reticulocytes,
    haematocrit, serum potassium and inorganic phosphorous, but these were
    essentially confined only to the top dosage group. Urinalysis
    conducted periodically during the study showed no abnormalities
    associated with the compound. Activity of cholinesterase in
    erythrocyte and plasma, monitored nine times over course of the study,
    was reduced (>20%) at all of the intervals in the top dosage group.
    At 50 ppm there was depression (>20%) of erythrocyte cholinesterase
    in males after 28 months and of both plasma and erythrocyte
    cholinesterase in females after 6 and 7 weeks and after 28 months.
    Erythrocyte cholinesterase was inhibited by 29% and plasma
    cholinesterase was marginally depressed (19.3%) in females even at
    5 ppm after 7 weeks. Brain cholinesterase was inhibited (>20%) at
    both 50 and 700 ppm after 7 and 19 weeks and 12, 22 and 28 months.
    Inhibition of the tissue (brain, plasma and erythrocyte)
    cholinesterase was dose-dependent and of a greater magnitude with
    brain cholinesterase than with plasma or erythrocyte cholinesterase.
    An increase in organ/body weight ratio of several organs, e.g.
    thyroid, lung, liver, kidney, testis, was detected sporadically in
    males of the top dosage group at interim or terminal sacrifice.
    Liver/body weight ratio was elevated with no concomitant
    histopathological changes of the tissue at both 50 and 700 ppm in
    females sacrificed at the conclusion of the study. Based on summary
    histopathology data unsubstantiated with histopathological findings on
    individual animals, there appeared to be an increase in incidence, as
    compared to concurrent controls, of adrenal medullary tumours in males

    of all treated groups. A variety of gross pathological changes and
    other neoplastic and non-neoplastic findings also occurred, which
    probably were not related to treatment.

         The unavailability of data for individual animals (supposedly
    contained in appendices not included in the report) particularly on
    ophthalmologic observations and gross and histopathological findings
    rendered the present evaluation only preliminary in nature. No
    conclusion, therefore, could be made as to the no-effect level or the
    carcinogenic potential of acephate in the rat (Chevron 1981).

    COMMENTS

         Both the  in vitro and  in vivo cholinesterase studies pointed
    to a higher sensitivity in brain cholinesterase than plasma or
    erythrocyte cholinesterase to the anticholinesterase activity of
    acephate. In a rabbit teratology study, 3 mg/kg body weight was
    considered as a teratogenic no-effect level. An acute delayed
    neurotoxicity in hens, while negative, could only be considered as a
    screen. A long-term toxicity/carcinogenic study in rats was available,
    but, due to the absence of individual animal data in the study,
    particularly on gross and histopathological findings and
    ophthalmoscopic observations, a full evaluation of the study could not
    be made.

         Except for a 2-year oral study in dogs and a teratogenicity study
    in rats, all the IBT studies (including a 2-year study in rats and a
    cholinesterase study in volunteers), which were essential to the
    allocation of an ADI, were found to be invalid. Consequently, the
    Meeting considered it necessary to change the ADI to a temporary
    status using an increased safety factor.

    TOXICOLOGICAL EVALUATION

    Level Causing no Toxicological Effect

         Rat: 5 ppm in the diet, equivalent to 0.25 mg/kg bw

         Dog: 30 ppm in the diet, equivalent to 0.75 mg/kg bw

    Estimate of a Temporary Acceptable Daily Intake for Man

         0 - 0.003 mg/kg bw

    FURTHER WORK OR INFORMATION

    Required (by 1984)

    1.   A multigeneration reproduction study.
    2.   An appropriate delayed neurotoxicity study.
    3.   Data for individual animals in the 28-month toxicity/
         carcinogenicity rat study on ophthalmoscopic observations and
         gross and histopathological findings.

    Desirable

         Further studies to elucidate the metabolic fate of acephate,
    preferably in a non-rodent species.

    REFERENCES

    Chevron. Oral toxicity/carcinogenicity study of technical RE-12420
    1979     in rats. Intended duration: 2 years, study terminated at 190
             days. Report from Bio/dynamics Inc., U.S., submitted to the
             World Health Organization by Chevron Chemical Co.
             (Unpublished)

    1980     Recovery from cholinesterase inhibition following dietary
             exposure to Orthene in the rat. Report from Bio/dynamics
             Inc., U.S., submitted to the World Health Organization by
             Chevron Chemical Co. (Unpublished)

    1981     A life-time oral toxicity/carcinogenicity study with
             technical RE-12420 in rats. Final report, from Bio/dynamics
             Inc. U.S., submitted to the World Health Organization by
             Chevron Chemical Co. (Unpublished)

    Hayashizaki, A., Kawai, M. and Sunomata, K. Studies on acute delayed
    undated  neurotoxicity of Orthene. Report from Bozo Research Center,
             Inc., Japan, submitted to the World Health Organization by
             Chevron Chemical Co. (Unpublished)

    Levy, J.E., Wong, Z.A. and MacGregor, J.A. The eye irritation
    1979a    potential of Orthene Speciality Concentrate. Report from
             Chevron Environmental Center, U.S., submitted to the World
             Health Organization by Chevron Chemical Co. (Unpublished)

    Levy, J.E., Wong, Z.A. and MacGregor, J.A. The skin irritation
    1979b    potential of Orthene Specialty Concentrate. Report from
             Chevron Environmental Center, U.S., submitted to the World
             Health Organization by Chevron Chemical Co. (Unpublished)

    Rittenhouse, J.R. and MacGregor, J.A. The acute dermal toxicity of
    1977     Orthene technical. Report from Safety and Health Division,
             Standard Oil Company of California, U.S., submitted to the
             World Health Organization by Chevron Chemical Co.
             (Unpublished)

    Rittenhouse, J.R., Wong, Z.A. and MacGregor, J.A. The acute
    1979     inhalation toxicity of Orthene Specialty Concentrate. Report
             from Chevron Environmental Health Center, U.S., submitted to
             the World Health Organization by Chevron Chemical Co.
             (Unpublished)

    Rodwell, D.E. and Jessup, D.C. Technical RE-12420, pilot teratology
    1980     study in rabbits. Report from International Research and
             Development Corporation, U.S., submitted to the World Health
             Organization by Chevron Chemical Co. (Unpublished)

    Rodwell, D.E. Jones, J.M. and Jessup, D.C. Technical RE 12420
    1980     teratology study in 1980 rabbits. Report from International
             Research and Development Corporation, U.S., submitted to the
             World Health Organization by Chevron Chemical Co.
             (Unpublished)

    Wong, Z.A., Kodama, J.K. and MacGregor, J.A. Characterization of the
    1979      in vitro inhibition of rat and monkey red blood cell and
             brain acryl cholinesterase by acephate, technical acephate
             and methamidophos and their mixtures. Report from Chevron
             Environmental Health Centre, U.S., submitted to the World
             Health Organization by Chevron Chemical Co. (Unpublished)


    See Also:
       Toxicological Abbreviations
       Acephate (ICSC)
       Acephate (Pesticide residues in food: 1976 evaluations)
       Acephate (Pesticide residues in food: 1979 evaluations)
       Acephate (Pesticide residues in food: 1981 evaluations)
       Acephate (Pesticide residues in food: 1984 evaluations)
       Acephate (Pesticide residues in food: 1984 evaluations)
       Acephate (Pesticide residues in food: 1987 evaluations Part II Toxicology)
       Acephate (Pesticide residues in food: 1988 evaluations Part II Toxicology)
       Acephate (Pesticide residues in food: 1990 evaluations Toxicology)
       Acephate (JMPR Evaluations 2002 Part II Toxicological)
       Acephate (JMPR Evaluations 2005 Part II Toxicological)