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)