FAO Meeting Report No. PL/1965/10/1 WHO/Food Add./27.65 EVALUATION OF THE TOXICITY OF PESTICIDE RESIDUES IN FOOD The content of this document is the result of the deliberations of the Joint Meeting of the FAO Committee on Pesticides in Agriculture and the WHO Expert Committee on Pesticide Residues, which met in Rome, 15-22 March 19651 Food and Agriculture Organization of the United Nations World Health Organization 1965 1 Report of the second joint meeting of the FAO Committee on Pesticides in Agriculture and the WHO Expert Committee on Pesticide Residues, FAO Meeting Report No. PL/1965/10; WHO/Food Add./26.65 AZINPHOS-METHYL Chemical name O,O-dimethyl-S-(4-oxo-1,2,3,-benzotriazin-3, (4H)-yl-methyl)-phosphoro-dithioate; [S-(3,4-dihydro-4-oxobenzo-[-d] (1,2,3) triazin-3-yl-methyl]-dimethyl phosphoro-thiolothionate. Synonyms Guthion, Gusathion Empirical formula C10H12O3N3PS2 Structural formulaBIOLOGICAL DATA Biochemical aspects Azinphos-methyl is activated to gutoxon, a highly potent cholinesterase inhibitor. The molar I50 in rat brain is 2.99 × 10-8 (Schrader, 1963). Acute toxicity Animal Route LD50 mg/kg References body-weight Rat Oral 11-25 DuBois et al., 1957; Gaines, 1960 Rat Intraperitoneal 5-11.6 DuBois et al., 1957 Mouse Oral 8.0* Sato, 1959 Guinea-pig Oral 80.0 Dubois et al., 1957 Guinea-pig Intraperitoneal 40.0 DuBois et al., 1957 * Given as azinphos-methyl emulsion. Short-term studies Rat. The addition of azinphos-methyl to the diet of groups, each 10 young male and 10 young female rats, at levels of 2, 5 and 20 ppm did not markedly alter the growth-rate over 60 days. The body-weight of the male rats fed 20 ppm was about 4% less than that of the controls. In the rats fed 2 and 5 ppm for 120 days, cholinesterase activity was unaffected, but at 20 ppm there was inhibition in the brain (10%) and in serum and erythrocytes (about 30%). After 120 days no appreciable changes in the gross and microscopic appearance of brain, heart, liver, spleen, adrenals, stomach, intestines, skeletal muscle and bone marrow were found. There was no evidence of demyelination in the nervous system (DuBois, 1956). When weanling male rats were fed diets containing 50 and 100 ppm of azinphos-methyl for 16 weeks, approximately half of each group died. All animals receiving azinphos-methyl in the diet showed marked cholinergic effects, including diarrhoea, salivation, lacrimation, muscular tremors and fasciculations. These symptoms were most marked during the first month on the diets. The rats fed 50 ppm of azinphos-methyl weighed about 10% less and the rats fed 10 ppm, 18% less than rats fed a normal diet. The cholinesterase activity of the serum, brain, erythrocytes and submaxillary glands of rats fed 50 and 100 ppm was markedly inhibited. The inhibition was most marked in the erythrocytes and brain and the animals did not fully recover from these effects during a 3-week period on a normal diet. Both gross and microscopic examination failed to indicate any evidence of testicular atrophy due to the presence of the high levels of azinphos-methyl in the diet (Doull et al., 1951). Dog. Groups of 2 dogs, 1 male and 1 female, given 5, 10, 20 and 50 ppm of azinphos-methyl did not show any loss of weight nor any symptoms of azinphos-methyl poisoning during a 12-week period. At dietary levels of 5, 10 and 20 ppm there was no significant decrease but at 50 ppm there was a 25% decrease in serum cholinesterase activity at the end of the 12-week period. The erythrocyte cholinesterase of the 1 male and 1 female dog began to be inhibited at 10 ppm in the diet (DuBois, 1957). Long-term studies No data available. Comments on experimental studies reported Satisfactory studies have been carried out in rats but in the studies in dogs only a very small number of animals was used. EVALUATION Level causing no significant toxicological effect in rat 5 ppm in the diet, equivalent to 0.25 mg/kg body-weight per day. Estimate of acceptable daily intake for man 0-0.0025 mg/kg body-weight per day. Further work desirable Chemical composition and toxicity of the residues. Observations on the effect in man. Reproduction studies in the rat. REFERENCES Doull, J., Amido, P. & DuBois, K. P. (1951) Unpublished report, 5 June DuBois, K. P. (1956) University of Chicago. Unpublished final report, 3 May DuBois, K. P. (1957) University of Chicago. Unpublished final report, 1 June DuBois, K. P., Thursh, D. R. & Murphy, S. D. (1957) J. Pharmacol. exp. Ther., 119, 208 Gaines, Th. B. (1960) Toxicol. Appl. Pharmacol., 2, 88 Sato, J. (1959) Kumamoto med. J., 12, 312 (from Chemical Abstracts, 1960, 54, 21473) Schrader, G. (1963) Die Entwicklung neuer insektizider Phosphorsäure-Ester, Verlag Chemie Weinheim
See Also: Toxicological Abbreviations Azinphos-methyl (ICSC) Azinphos-methyl (FAO/PL:1968/M/9/1) Azinphos-methyl (WHO Pesticide Residues Series 2) Azinphos-methyl (WHO Pesticide Residues Series 3) Azinphos-methyl (WHO Pesticide Residues Series 4) Azinphos-methyl (Pesticide residues in food: 1991 evaluations Part II Toxicology)