PESTICIDE RESIDUES IN FOOD - 1984 Sponsored jointly by FAO and WHO EVALUATIONS 1984 The monographs 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, 24 September - 3 October 1984 Food and Agriculture Organization of the United Nations Rome 1985 DEMETON-S-METHYL-SULPHOXIDE (Oxydemeton-Methyl) EVALUATION FOR ACCEPTABLE DAILY INTAKE BIOCHEMICAL ASPECTS Absorption, Distribution and Excretion Single 5 mg/kg doses of purified oxydemeton-methyl were orally administered to fasted male Wistar rats. Levels of oxydemeton-methyl and its sulfone, demeton-S-methyl sulfone, were determined in blood and selected organs at intervals up to 24 hours. Zero to 24 hour urine and faeces samples were also analyzed for the two compounds. Thin layer chromatography was used to separate the two compounds in extracts of blood and organs. All quantitative analyses were performed by gas liquid chromatography. Oxydemeton-methyl was rapidly absorbed. Distribution in the body organs peaked at 30 minutes and then decreased to non-detectable levels within 24 hours. In assayed organs, sulfone residues were generally 20-40 percent of oxydemeton-methyl residues. Approximately 45 percent of the administered dose was recovered in urine within 24 hours and was present almost entirely as unchanged parent. Very little parent or its sulfone was recovered in faeces. Blood levels of oxydemeton-methyl and its sulfone correlated well with blood cholinesterase activity determinations which decreased rapidly to a minimum at two hours and then gradually recovered (Oyama Takase, 1977). Absorption, distribution and excretion of radioactivity were assayed in male Sprague-Dawley rats given single oral doses of 0.1, 0.5, 5 or 10 mg/kg or intravenous doses of 0.5 or 1 mg/kg of 14C-oxydemeton methyl. Additional female rats were given a single oral dose of 0.5 mg/kg. The test material was very rapidly and nearly completely absorbed following oral administration. Approximately 50 percent of the administered radioactivity was excreted within three hours and 90 percent within nine hours following an oral dose of 0.5 or 5 mg/kg. Within 48 hours, radioactivity excreted in the urine accounts for 98-99 percent of the administered dose. Faeces accounted for 0.6-1.2 percent and expired air for less than 0.1 percent. Radioactivity remaining in the body was about 60 percent of the administered dose at two hours (about 40 percent having been already excreted at that time), 1.3 percent at 24 hours, 0.4 percent at 48 hours and about 0.1 percent at 10 days. Total recovered radioactivity in experiments averaged 91-101 percent. Recovery percentages in excreta were largely independent of dose level, route of administration and sex of the animal. Rates of elimination were dose proportional. In a separate experiment in which 0.5 mg/kg of 14C-oxydemeton methyl was intraduodenally administered to male rats with bile duct fistulas, only 3.5 percent of the administered radioactivity was excreted in the bile within 24 hours. Blood levels of radioactivity peaked about one hour following oral administration of 5 mg/kg of the test material. From zero to six hours following administration, the blood half-life was calculated to be about 1.5 hours, from six to 214 hours to be about five hours and after 24 hours to be considerably longer. Nearly all the radioactivity in blood after 24 hours was accounted for by a high retention in erythrocytes which had considerably higher levels of radioactivity than other organs and tissues for up to ten days. Serum levels after 24 hours were quite low compared to erythrocytes and at ten days were negligible. Distribution of radioactivity in various body organs and tissues was relatively uniform at two hours. Radioactivity did not concentrate in fat tissue or in the reticuloendothelial system (liver, spleen, bone marrow). By days 2-3 post-administration, radioactivity was nearly undetectable in the majority of organs and tissues except for blood and erythrocytes. At day 10, very low levels of radioactivity were still present in these two tissues and the adrenal gland. In a separate experiment, whole body autoradiography confirmed previous findings regarding distribution of radioactivity in body tissues, but also indicated some localized accumulation of radioactivity in the pineal gland, thyroid and in some glands of the genital tract (Cowper's gland, seminal vescicle, accessory genital gland) (Weber, Patzschke and Wegner, 1978). Biotransformation Rat urine samples from the experiments performed by Weber, Patzschke and Wegner in 1978, were collected and subjected to thin layer chromatographic and radioactivity counting methods designed to identify and quantitate the parent compound and metabolites. Zero to eight hour and eight to 24 hour samples were collected from male rats given a single oral dose of 10 mg/kg of 14C-oxydemeton methyl and zero to 24 hour samples from male rats given a single oral dose of 5 mg/kg. About 92 percent of the administered radioactivity was recovered in the urine within eight hours. The routes of metabolism of oxydemeton-methyl (demeton-S-methyl sulfoxide) included oxidation of the side chain sulfoxide group to form the corresponding sulfone and to a slight extent in some, but not all, rats reduction of the same sulfoxide group to form the corresponding sulfide. The reduction to sulfide was only observed after eight hours post-administration and may have been the result of anaerobic microbiological activity in individual animals. Three corresponding O-demethylated metabolites for the sulfoxide, sulfone and sulfide moieties were also identified in the urine as were two additional metabolites, presumably resulting from cleavage of the O-methyl-phosphoric ester group and subsequent methylation and sulfoxidation steps. Approximately 97-99 percent of the radioactivity in zero to 24 hour urine samples, equivalent to about 95 percent of the administered oral dose of 5 mg/kg, was identified and quantitated as follows: demeton-S-methyl sulfoxide (unchanged parent compound), 65 percent; demeton-S-methyl sulfone, 6 percent; O-demethyl-demeton-S-methyl sulfoxide, 6 percent; O-demethyl-demeton-S-methyl sulfone, 4 percent; O-demethyl-demeton- S-methyl, <2 percent; methyl sulfinyl-2-ethyl sulfinyl ethane, 6 percent; and methyl sulfinyl-2-ethyl sulfonyl ethane, 10 percent. Treatment of urine with glucuronidase or sulfatase did not indicate the presence of any glucuronide or sulfate conjugates (Ecker, 1978; Ecker and Colln, 1983). TOXICOLOGICAL STUDIES Special Study on Eye and Skin Irritation R 2170 (oxydemeton-methyl, purity 94.7 percent) was applied in standard tests for irritation to the skin or eyes of New Zealand White rabbits. No erythema or edema was observed at intact or abraded skin sites of six rabbits for up to 72 hours. The primary irritation score was zero. Slight conjunctival reddening for up to 24 hours and slight conjunctival swelling at 1 hour were observed in the eyes of five rabbits exposed for five minutes to the test material. Nearly identical readings were also made for the eyes of three rabbits exposed for 24 hours. All other readings in all rabbits were zero for up to seven days (Thyssen, 1981). Short-Term Studies Rabbit New Zealand White rabbits were given dermal applications of R 2170 (oxydemeton-methyl, purity 94.7 percent) five times per week for three weeks. Each group consisted of six male and six female shorn rabbits, three of each sex with intact skin sites and three with abraded skin sites. Each exposure was six hours in duration. The initial dosage levels of 0 (control), 2 and 20 mg/kg/day were reduced to 0 (control), 0.5 and 5.0 mg/kg/day after two exposures because signs of cholinergic poisoning, consisting of slight muscular tremors lasting about 3.5 hours, were observed in treated animals. General appearance and behaviour were recorded daily. Body weights were determined weekly. Erythema and edema at sites of application were scored after each exposure. Laboratory tests consisting of basic haematology, clinical chemistries and urinalyses were performed at the start and termination of the study. Plasma and erythrocyte cholinesterase activity determinations were performed at the start of the study, after the tenth exposure and at termination of the study. Brain cholinesterase activity was also determined. Gross necropsies were performed on all animals at 24 to 48 hours after the last exposure. Organ weights for heart, lung, liver, spleen, kidney, adrenals, testes, ovaries and thyroid were recorded. Histopathological examination of the above organs and epididymis, uterus and treated and untreated skin from all control and high-dosage level animals was performed. One high-dosage female rabbit died during the study due to a fractured spine. Other than signs of cholinergic poisoning on the second day of exposure, appearance and behaviour of all rabbits was normal. Mean body weights of treated male and female animals were comparable to respective control weights and remained relatively constant during the study. Transient slight erythema and regularly observed slight edema were observed at application sites due to abrading, but were not increased in animals treated with oxydemeton- methyl. Haematology, clinical chemistry and urinalysis tests were negative. Plasma cholinesterase activity was unaffected. Erythrocyte cholinesterase activity was decreased in male and female, intact and abraded, high-dosage level animals at termination of the study. Brain cholinesterase activity was also decreased in intact and abraded high-dosage female animals at termination of the study. No effects related to the test material were observed at necropsy. Small differences in organ weights and organ/body weight ratios were probably not biologically meaningful. Histopathological examinations did not indicate any alterations attributable to the test material. The cholinesterase NOEL for this study is 0.5 mg/kg/day (Mihail and Nash, 1982). Dog Oxydemeton-methyl (R 2170) was administered to four groups of pure bred Beagle dogs at dosage levels of 0 (tap water control), 0.025, 0.25 and 2.5 mg/kg/day for 12 months. Each group consisted of six male and six female dogs that were 21 to 25 weeks old at the initiation of dosing. The test material, which was 51.1 percent pure, was dissolved in tap water and administered by gavage. The individually-housed dogs were fed one to three hours following intubation. The test material was administered by stomach tube because it was found to be unstable in feed but stable in tap water for at least eight days. Daily observations were made for appearance, behaviour and signs of toxicity. Food consumption and water intake were estimated. Weekly body weights were recorded. Clinical examinations for general state of health, including nutritional state, body temperatures and pulse rates were performed at regular intervals throughout the study as were neurological (i.e. reflexes) and ophthalmoscopic examinations. Laboratory tests, consisting of extensive haematological, clinical chemistry and urinalysis examinations, were performed at -2, 3, 6, 13, 26, 39 and 52 weeks. Cholinesterase activities were assayed in plasma and erythrocytes at -2, -1, 3, 6, 13, 26, 39 and 52 weeks and in brain tissue (bulbus olfactorius) as termination of the study. Gross necropsies were performed on all dogs. Organ weights were determined for brain, heart, testes, ovaries, liver, lung, spleen, adrenals, kidneys, pancreas, prostate, thyroid and thymus (the last organ in male dogs only). A full set of 37 organs and tissues was excised and fixed for each dog but, with the exception of a very few tissues from the low- and mid-dosage groups only the histopathological results for control and high-dosage animals were presented in the study report. One female dog in the mid-dosage level group was sacrificed in week eight due to a severely declining state of health. Pathological examination of this animal indicated suppurative bronchitis and/or pneumonia caused its moribund condition and its death was not attributed treatment with oxydemeton-methyl. Normal appearance and behaviour were observed in all other dogs at all times. No signs of toxicity, including typical signs of cholinergic poisoning, were observed in any of the animals at any time. Food consumption and water intake of treated dogs were comparable to that of control dogs. Clinical, neurological and ophthalmoscopic examinations were uniformly negative for pathological findings attributable to the test material. Mean body weights for all male and female treatment groups were comparable to the respective male and female control groups throughout the entire study. Mean body weights at week -1 for male dogs were 8.5, 8.2, 8.5 and 8.2 kg and for female dogs were 7.3, 7.6, 7.8 and 7.7 kg for the control, low-, mid- and high-dosage groups respectively. At 52 weeks, mean body weights for male dogs were 13.3, 13.4, 14.3 and 12.8 kg and for female dogs were 11.6, 11.7, 12.2 and 11.9 kg for the control, low-, mid- and high-dosage levels respectively. Total mean body weight gains during the entire study for male dogs were 4.8, 5.2, 5.8 and 4.6 kg and for female dogs were 4.3, 4.1, 4.4 and 4.2 kg for control, low-, mid-and high-dosage groups respectively. Results of haematological, clinical chemistry and urinalysis examinations indicated no treatment-induced alterations in any of the male or female treatment groups when compared to the respective male and female control groups. Mean plasma cholinesterase activities in male and female mid- and high-dosage groups were decreased below respective concurrent control group activities at every sampling time during the entire period of administration of test material i.e. at weeks 3, 6, 13, 26, 39 and 52. The decreased activities were dose-related. Mean percentage decreases over the entire study, compared to concurrent control values of 100 percent, ranged from 15 to 22 percent, and from 6 to 20 percent for male and female dogs respectively in the mid-dosage group. Similarly, mean percentage decreases ranged from 37 t 48 percent and from 40 to 45 percent for male and female dogs respectively in the high-dosage level group. The consistency and dose-relatedness of these determinations indicate a depression of plasma cholinesterase activity due to the test material at the mid-dosage level of 0.25 mg/kg/day and at the high-dosage level of 2.5 mg/kg/day. At the low-dosage level of 0.025 mg/kg/day, there was very little or no depression of plasma cholinesterase activity. Depression of erythrocyte cholinesterase activity due to the test material was also observed at the high-dosage level of 2.5 mg/kg/day. Mean erythrocyte cholinesterase activities in the male and female high-dosage level groups were decreased below concurrent control activities during the entire period of administration of test material. Mean percentage decreases, compared to concurrent control values of 100 percent, ranged from 33 to 45 percent for male dogs and from 41 to 53 percent for female dogs. At the mid-dosage level of 0.25 mg/kg/day, there was no consistent or apparently meaningful inhibition of erythrocyte cholinesterase activity. At the low dosage level of 0.025 mg/kg/day, there was no inhibition of erythrocyte cholinesterase activity. Brain cholinesterase activity was also decreased in the high dosage level group. Mean percentage decreases for brain cholinesterase activity, compared to control values of 100 percent, were 45 percent for male dogs and 47 percent for female dogs in the 2.5 mg/kg/day group. Equivocal decreases of 10 percent and 13 percent were noted for male and female dogs respectively in the 0.25 mg/kg/group. No decrease was observed in the 0.025 mg/kg/day group. Gross necropsies revealed random findings across control and treated groups that were unrelated to the test material. Mean organ weight determinations for male dogs suggested decreased absolute and organ/body weight ratios for heart and thymus in high- and/or mid-dosage level groups. Mean organ/body weight ratios for testes and pancreas were slightly increased in high- and/or mid-dosage level male groups. In female dogs, mean absolute liver and liver/body weight ratios for high- and mid-dosage animals were slightly higher than control values. Mean absolute pancreas weight and kidney/body weight ratios were also slightly increased in high- and mid-dosage level animals. None of these organ weight changes were supported by relevant clinical, laboratory or histopathological findings. Organ weight changes, therefore, could not be directly related to the test material. Histopathological examination of organs/tissues did not indicate any pathological alterations attributable to the test material. The few lesions noted occurred randomly across control and treated groups and were of types often observed in dogs of similar ages. The plasma cholinesterase NOEL for this study is 0.025 mg/kg/day and the erythrocyte and brain NOEL is 0.25 mg/kg/day. No somatic changes due to oxydemeton-methyl were observed at dosage levels up to 2.5 mg/kg/day (Hoffman and Ruhl, 1984). Special studies on Teratogenicity Rat Oxydemeton-methyl was administered orally by gavage to four groups of pregnant rats from gestation day 6 to gestation day 15 at dosage levels of 0 (control), 0.3, 1.0 and 3.0 mg/kg/day. Dosage levels were selected after a range finding study on non-pregnant female rats demonstrated tremors and severely affected body weight gains at a dosage level of 5.0 mg/kg/day, but no apparent toxicity at 2.5 mg/kg/day when administered daily for ten days. Each group consisted of 20 to 23 FB 30 (Long Evans) strain female rats that were 2.5 to 3.5 months old at initiation of the study. The test material, R 2170 (93.5 percent oxydemeton-methyl), was administered in a 0.5 percent aqueous Cremophor EL emulsion at a constant volume of 10 mg/kg/day to all groups. All rats were housed singly and permitted feed and water ad libitum. Dams were examined daily for mortality, appearance and behaviour. Body weights were recorded on gestation days 0, 20, and on all days of administration of the test material. On gestation day 20, foetuses were removed by caesarean section. Numbers of implantations, viable and dead foetuses, stunted foetuses (less than 3 grams) and foetal sex ratios were recorded. Litter weights, mean foetus weights and mean placenta weights were determined. All foetuses were grossly examined for external anomalies. Approximately 30 percent of the foetuses were examined for visceral malformations by a modification of Wilson's technique. The remaining 70 percent were eviscerated and following examination of abdominal and thoracic organs, were cleared, stained with Alizarin Red and examined for skeletal malformations. In a second experiment, oxydemeton-methyl was administered two additional groups of 25 pregnant rats, one group at a dosage level of 0 (control) and the other group at a dosage level of 3.0 mg/kg/day. The rats in this second experiment were treated exactly as in the first experiment. One control and one mid-dosage level rat in the first experiment died of causes unrelated to the test material. In the first experiment three, one and five rats exhibited transient diarrhoea during gestation days 6 to 15 in the low-, mid-and high-dosage groups respectively. In the second experiment, four control and eight treated rats also exhibited transient diarrhoea during the same period. Although this condition was reported as frequently occurring spontaneously, the incidences observed in both experiments at the dosage level of 3.0 mg/kg/day may possibly be related to the test material. In the first experiment, a significantly decreased weight gain (p < 0.05) of about 16 percent was observed in high-, but not in low- or in mid-dosage level rats during gestation days 6 to 15 compared to weight gains in the control rats. In the second experiment, a similar decrease in weight gain was not observed in the treated rats. In neither experiment was a significantly lower weight gain for any treated group observed when determined for the entire gestation period (days 0 to 20). Non-significant slight decreases in weight gain, however, were observed in the high dosage level rats in the first experiment and in the treated rats in the second experiment for gestation days 0 to 20. In the first experiment, 20 litters were examined in each control and oxydemeton-methyl-treated group. In the second experiment, 24 and 23 litters were examined in the control and treated groups respectively. In neither experiment did the test material have any biologically meaningful effect on the number of pregnancies, mean number of implantations, mean number of viable and dead foetuses, mean number of resorbed embryos, sex ratios of foetuses, mean placent weights or mean foetal body weights. Although gross external examinations did not suggest any localized abnormalities due to the test material, statistically significant ( p < 0.05) increased incidences of stunted foetuses (less than 3 grams) were observed at the dosage level of 3.0 mg/kg/day in both experiments. In the first experiment, the number of stunted foetuses/number of foetuses examined was 2/242, 6/257. 2/237 and 10/243 for the control, low-, mid- and high-dosage levels respectively. In units of mean number of stunted foetuses/litter, the calculated values respectively were 0.10, 0.30, 0.10 and 0.50. In the second experiment the number of stunted foetuses/number of foetuses examined was 1/288 and 9/257 for the control and treated groups respectively. In units of mean number of stunted foetuses/litter, the respective values were 0.08 and 0.39. At a dosage level of 3.0 mg/kg/day, an increased incidence of stunted foetuses was causatively related to the test material. [Note - Historical control data for stunted foetuses was presented in Roetz, 1982 for the same strain of rat and from the same testing laboratory. The number of dams with stunted foetuses in each of 30 control groups (1978-1981) with an average of 23 litters per group was as follows: in seven studies, zero dams with stunted foetuses; in ten studies, one dam; in seven studies, two dams; in five studies, three dams; and in one study four dams. In the first experiment of this study, 4/20 dams had stunted foetuses at 3 mg/kg/day and in the second experiment, 6/23 dams had stunted foetuses at 3 mg/kg/day. The incidence in the first experiment is at the extreme upper limit and the incidence in the second experiment exceeds the historical control range for this effect]. In the first experiment, a statistically significant (p < 0.01) increased incidence of hypoplasia of the telencephalon was also observed in the high-dosage group. The number of foetuses with brain hypoplasia/number of foetuses examined, was 2/242, 8/257, 2/237 and 17/243 for the control, low-, mid- and high-dosage levels respectively. In units of mean numbers of foetuses with brain hypoplasia/litter, the calculated values respectively were 0.10, 0.40. 0.10 and 0.85. In the second experiment, the number of foetuses with hypoplasia of the telencephalon in the control group was 0/288 and in the treated group was 3/257. At a dosage level of 3.0 mg/kg/day, an increased incidence of hypoplasia of the telencephalon was causatively related to the test material. Other visceral and skeletal malformations, including delayed ossification of bones and minor skeletal variations, occurred sporadically across all treatment and control groups and were not related to treatment with oxydemeton- methyl. Since increased incidences of stunted foetuses and hypoplasia of the telencephalon were observed only at the dosage level of 3.0 mg/kg/day, the possibility that these effects may be related to maternal toxicity, also observed only at 3.0 mg/kg/day, must be considered. Maternal toxicity reported at this dosage level consisted of slightly increased incidences of transient diarrhoea during gestation days 6 to 15 in both experiments and a significantly decreased body weight gain of about 16 percent during the same period in the first experiment, but not in the second experiment. Significantly decreased weight gains were not observed in the first experiment however, when determined for gestation days 0 to 20. Whether or not these rather minor maternal toxic effects, together with probably decreased cholinesterase activities, were solely responsible for the observed malformations is equivocal (Machemer, 1979). Rabbit Oxydemeton-methyl was administered by gavage to four groups of 17 HCG primed and artificially inseminated female American Dutch rabbits at dosage levels of 0 (distilled water control), 0.1, 0.4 and 1.6 mg/kg/day. Deaths, severe body weight losses and/or poor reproductive performances were observed in a preceding range-finding study at dosage levels of 3 mg/kg/day and higher. The dosage, from a 0.05 percent solution of 50 percent Metasystox-R in distilled water, was administered on gestation days 7 through 19. Body weights, pregnancy rates and daily observations of does were recorded. On gestation day 28, the does were sacrificed, necropsied and the uterine contents were examined. Numbers of corpora lutea, implantations, resorption and pre- and post-implantation losses were determined. Litter sizes, foetal body weights, viability of foetuses and foetal sex ratios were also determined. All foetuses were examined for gross external, visceral and skeletal anomalies. Three does died during the study due to intercurrent respiratory infections, one each in the control, low- and mid-dosage groups. Maternal body weights of oxydemeton-methyl treated does were comparable to control body weights throughout the study. Maternal toxicity, consisting of transient, dose-related loose stools were observed in 8/17 high-dose and 5/17 mid-dose does. At necropsy, several does had pitted kidneys suggestive of nosematosis. Pregnancy rates were 17/17, 15/17, 16/17 and 14/17 for the control, low-, mid- and high-dosage level groups respectively. Four control animals aborted during the study and one high-dose doe was observed to have only resorption sites at necropsy. The number of litters available for examination at termination of the study were 12, 15, 16 and 13 for the control, low-, mid- and high-dosage levels respectively. The mean numbers of resorptions per doe were 0.8, 0.6, 0.8 and 1.6 and the mean percentage post-implantation losses were 18.1 percent, 10.0 percent and 24.4 percent for the control, low-, mid- and high-dosage levels respectively. Although numbers of resorptions and post-implantation losses were slightly increased for the high-dose animals, neither was significantly different from control values. In addition, increased resorptions were not observed in the preceding range-finding study at dosage levels up to 12 mg/kg/day. Numbers of corpora lutea, implantations, pre-implantation losses and litter sizes, late foetal mortality, foetal body weights, foetal viability and foetal sex ratios in the treated groups were comparable to the control group. Among 87 control, 120 low-, 91 mid- and 97 high-dosage level foetuses examined, no grossly visible, visceral or skeletal terata were observed. A few dysmorphogenic variations and anomalies were observed in control and oxydemeton-methyl-treated groups, but these were of types frequently seen in teratology studies, were not dose-related and were not considered to be related to treatment. Abnormal skeletal development, delayed ossification and increased frequency of spontaneously occurring variations were not promoted by the test material. Oxydemeton-methyl, when administered to pregnant rabbits at dosage levels up to 1.6 mg/kg/day did not induce visceral or skeletal terata. In addition, neither embryotoxicity nor foetotoxicity was observed (Clemens and Hartnagel Jr., 1984). Special Study for Carcinogenicity Mice Oxydemeton-methyl was incorporated in feed at concentrations of 0 (control), 10, 30 and 100 ppm and presented ad libitum to groups of SPF CF-1 mice for two years. The test material was R 2170 (Metosystox R) and had a purity of 91.4 to 93.7 percent. Each control and treatment group consisted of 70 male and 70 female singly-housed mice which were about six to eight weeks old at the initiation of dosing. At twelve months, ten male and ten female mice from each group were sacrificed and examined and at 24 months, all surviving mice were similarly sacrificed and examined. General observations for appearance, behaviour, activity, conditions of hair coat, appetite and thirst were made daily. Body weights were recorded weekly for 14 weeks and at three week intervals thereafter. Food consumption was determined for seven-day intervals. Clinical laboratory tests consisting of standard haematological examinations and clinical chemistry determinations were performed on ten male and ten female mice from each group at 12 and 24 months. Urinalyses and cholinesterase activity determinations were not performed. Gross necropsies were performed on all mice that died or were sacrificed due to a moribund condition during the entire study, and on all mice sacrificed at 12 and 24 months. Organ weights for heart, lung, liver, spleen, kidneys and testes were determined. The following organs/tissues from all mice were excised, fixed and histopathologically examined: heart, lung, liver, pancreas, stomach, kidneys, urinary bladder, testes or ovaries, uterus (females), pituitary, thyroid (also parathyroid, if present in section), adrenal, spleen, bone, skeletal muscle, brain and all gross lesions suspected of being tumours. General observations of oxydemeton-methyl-treated mice were comparable to those of control mice. Determinations of mean feed consumption in units of grams of feed/mouse/day, indicated slightly decreased feed intake by mid- and high-dose male mice and by high-dosage level female mice. Calculations of mean intake of test material, in units of mg/kg/day, yielded 2 and 2, 4 and 6, and 16 and 18 mg/kg/day for male and female mice for the low-, mid- and high-dosage levels respectively. Mean body weights for high-dosage level male and female mice decreased about 10 percent during the first week of feeding of test material. Thereafter, high-dosage level male mice had consistently lower body weights throughout the entire study, and particularly after 26 weeks. High-dosage level female mice quickly regained the lost weight and were generally comparable to the female controls for the remainder of the study. Mean body weights of low- and mid-dosage level male and female mice were similar at all times to mean body weights of their respective control groups. The depressed body weights of the high-dosage level male mice were attributed to the test material. Mortalities during the study were equivalent in all test and control groups. The numbers of mice surviving to termination of the study, out of 60 per groups, were 17, 24, 24 and 22 for the male mice and 17, 20, 27 and 24 for the female mice in the control, low-, mid- and high-dosage levels respectively. Haematological examinations did not reveal consistent alterations due to the test material. Similarly, clinical chemistry determinations did not indicate biologically meaningful changes due to the test material. Significantly decreased urea and creatinine levels in treated male and female mice at 24 months were noted, but could not be attributed to toxic effects of the test material. Gross necropsies did not indicate any pathological findings attributed to oxydemeton-methyl. Masses and nodes were oberved in lungs and livers but appeared to be randomly distributed across control and test groups. Organ weights and organ/body weight ratios suggested possibly increased lung weights in high-dosage level male mice and possibly decreased spleen weights in high-dosage level female mice. Histopathologic examination revealed senile nephropathy in the kidneys of most mice and cystic alterations in the ovaries and cystic dilatations of endometrial glands in the uteri of most female mice. Other non-tumorigenic findings were those commonly observed in mice of comparable ages. The most frequently occurring neoplasms were lung and liver tumours, malignant lymphomas in numerous organs and uterine tumours in female mice. These tumour types occurred in control and test groups with about equal incidences. The degree of malignancy, latency period or incidence of any tumour type was not affected by the test material. The somatic NOEL for this study was 30 ppm (Krotlinger, Loser and Kaliner, 1981). Human Exposure A 41 year-old woman, five months pregnant, ingested approximately 12 grams of oxydemeton-methyl. Upon hospital admission 3.5 hours later, characteristic signs of cholinesterase poisoning were observed and blood cholinesterase activity decreased to 10 of normal. Following 14 days of vigorous treatment, the patient was discharged. The last four months of pregnancy were uneventful and a normal child was delivered. Follow-up examinations of the child revealed no abnormalities of any kind (Carrington da Cost, et al, 1982). Special Studies on Mutagenicity For the results of mutagenicity studies on oxydemeton-methyl, see Table 1. Comments Oxydemeton-methyl was rapidly and nearly completely absorbed in rats following oral administration. About 50 percent single doses up to 5 mg/kg was excreted within three hours and 90 percent within nine hours. By 48 hours, only 0.4 percent remained in the body. Some binding to erythrocytes occurred for at least ten days. Excretion was almost entirely via the urine. Compounds identified in the urine were unchanged parent: compound (65 percent), the corresponding sulfone (6 percent), three O-demethylated metabolites (12 percent) and two additional metabolites (16 percent). In a one-year gavage study on dogs, the NOEL for plasma cholinesterase depression was 0.025 mg/kg/day and for erythrocyte and brain was 0.25 mg/kg/day. No other effects attributable to oxydemeton- methyl were observed at dosage levels up to 2.5 mg/kg/day. In a teratology study on rats, significantly increased incidences of stunted foetuses and of hypoplasia of the telencephalon at the highest dosage level of 3.0 mg/kg/day were attributed to treatment with oxydemeton-methyl. Whether or not these effects might be related to rather minor maternal toxic effects also observed at the same dosage level is uncertain. A teratology study in rabbits at dosage levels up to 1.6 mg/kg/day did not demonstrate embryotoxic, foetotoxic or teratogenic effects. A two-year oncogenicity study in mice demonstrated no tumours attributable to treatment with oxydemeton-methyl. In a series of mutagenicity studies, oxydemeton-methyl presented: mixed results in both in vitro and in vivo tests. Toxicity studies using oxydemeton-methyl as the test material have demonstrated in a one-year gavage study on dogs, a NOEL of 0.025 mg/kg b.w. based on depression of plasma cholinesterase activity, in 90-day dietary studies on rats, a NOEL of 1 ppm (equivalent to 0.05 mg/kg b.w.) based on depression of erythrocyte cholinesterase activity, and in a 60-day study on humans, a NOEL of 0.05 mg/kg b.w. based on depression of serum and erythrocyte cholinesterase activity. Considerable concern continues to exist, however,, with respect to liver toxicity observed at low dosage levels in several short-term rat studies on oxydemeton-methyl. Following submission of the final report for a rat chronic feeding study presently in progress, establishment of an ADI will be reconsidered. FURTHER WORK OR INFORMATION BEFORE AN ADI CAN BE ESTABLISHED Required: Submission of the final report for the rat chronic feeding study on oxydemeton-methyl. Desirable: Further observations in humans. REFERENCES Carrington da Costa, R.B., Maul, E.R., Pimentel, J., Goncalves,J.S., 1982 Rebelo, A. and Oliveiria, L.C. A case of Acute Poisoning by Methyl Demeton in a Female 5 Months Pregnant. Arch. Toxicol., Suppl. 5: 200-204. Submitted by Bayer AG to WHO. Clemens, G.R. and Hartnagel Jr., R.E. A Teratology Study in the Rabbit 1984 with Metasystox R. Elkhart, Indiana, Miles Laboratory Inc. Mobay Tox. Report No. 470. Submitted by Bayer AG to WHO. Ecker, W. Biotransformation of (ethylene-1-C14) Demeton-S-methyl 1978 Sulfoxide (C14 - Metasystox-R AI) in the rat. Bayer AG, Institute of Pharmacokinetics. Report No. 7996. Submitted by Bayer AG to WHO. Ecker, W. and Colln, R. Biotransformation of Demeton-S-methyl 1983 Sulfoxide in rats (final report). Bayer AG, Sparte Pharma. PF Report No. 1758, Pharma Report No. 11480 (F). Submitted by Bayer AG to WHO. Herbold, B. R 2170 (Metasystox R active ingredient; Oxydemeton-methyl 1980a Demeton-S-methyl sulfoxide): micronucleus test on mouse to evaluate R 2170 for mutagenic potential. Bayer AG, Institute for Toxicology. Report No. 9275. Submitted by Bayer AG to WHO. Herbold, B. R 2170 (Study No.: R 2170/003): salmonella/microsome test 1980b for detection of point-mutagenic effects. Bayer AG, Institute for Toxicology. Report No. 8847. Submitted by Bayer AG to WHO. Herbold, B. R. 2170 (Study No.: R 2170/002): dominant lethal study on 1980c male mouse to test for mutagenic effects. Bayer AG, Institute for Toxicology. Report No. 8846. Submitted by Bayer AG to WHO. Herbold, B. R 2170 (Demeton-S-methyl sulfoxide; oxydemeton-methyl; 1981 Metasystox R active ingredient): Micronucleus test on mouse to evaluate R 2170 for mutagenic potential. Bayer AG, Institute for Toxicology. Report No. 10019. Submitted by Bayer AG to WHO. Herbold, B. R 2170 (Oxydemeton-methyl; Metasystox R active ingredient 1983 Sister chromatid exchange in the bone marrow of the Chinese hamster in vivo to test for potential DNA damage. Bayer AG, Institute for Toxicology. Report No. 12144. Submitted by Bayer AG to WHO. Hoffman, K. and Ruhl, C. R 2170 (con, non name: oxydemeton-methyl): 1984 Chronic toxicity to dogs on oral administration (12-month stomach tube study). Bayer AG, Institute for Toxicology. Report No. 12734. Submitted by Bayer AG to WHO. Jagannath, D.R. Mutagenicity evaluation of R 2170 in the rec assay and 1980 the reverse mutation induction assay (final report). Litton Bionetics, Inc. Kensington, Md. LBI Project No. 20998, Report No. R 1733. Submitted by Bayer AG to WHO. Krotlinger, F., Loser, E. and Kaliner, G. R 2170 (Metasystox R active 1981 ingredient; Oxydemeton-methyl: Chronic toxicity study on mice (two-year feeding experiment). Bayer AG, Institute for Toxicology. Report No. 10038. Submitted by Bayer AG to WHO. Machemer, L. R 2170 (oxydemeton-methyl; active ingredient of 1979 Metasystox R): evaluation for embryotoxic and teratogenic effects in orally dosed rats. Bayer AG, Institute for Toxicology. Report No. 8436. Submitted by Bayer AG to WHO. Mihail, F. and Nash, G. R 2170 (Oxydemeton-methyl; Metasystox R active 1982 ingredient): subacute cutaneous toxicity study on rabbits. Bayer AG, Institute for Toxicology. Report No. 10799. Submitted by Bayer AG to WHO. Myhr, B.C. Evaluation of R 2170 (oxydemeton-methyl) in the primary rat 1983 hepatocyte unscheduled DNA synthesis assay (final report). Litton Bionetics Inc., Kensington, MD. LBI Project No. 20991, Report No. R 2688. Submitted by Bayer AG to WHO. Oyama, H. and Takase, I. Absorption, distribution and excretion of 1977 metasystox-R (S-(2-ethylsulfinylethyl) dimethyl phosphorothiolate) and its sulfone in male rats. Tokyo. Agricultural Chemical Institute, Nihon Tokushu Noyaku Seizo K.K., Report No. 1072 (RA). Submitted by Bayer AG to WHO. Pandita, T.K. Mutagenic studies on the insecticide Metasystox-R with 1983 different genetic systems. Mutat. Res. 124: 97-102. Submitted by Bayer AG to WHO. Roetz, R. E 158 (Demeton-S-methylsulphon, Metaisosystox-sulphon): 1982 study for embryotoxic effects on the rat after oral administration. Bayer AG, Institute for Toxicology. Report No. 11234. Submitted by Bayer AG to WHO. Thyssen, J. R 2170 (Active Ingredient of Metasystox R): tests for 1981 irritation of the skin and mucosae. Bayer AG, Institute for Toxicology. Submitted by Bayer AG to WHO (Unpublished). Vaidya, V.G. and Patankar, N. Studies on the cytogenetic effects of 1980 Oxydemeton-methyl in the human leukocyte and mouse micro- nucleus test systems. Mutat. Res. 78: 385-387. Submitted by Bayer AG to WHO. Weber, H., Patzschke, K. and Wegner, L.A. [14C]Demeton-S-methyl 1978 sulphoxide (metasystox R active ingredient): Biokinetic studies on rats. Bayer AG, Institute for Pharmacokinetics. Report No. 7473. Submitted by Bayer AG to WHO. Witterland, W.F. Mutagenicity evaluation of R 2170 (C.N. Oxydemeton- 1984 methyl) in the mouse lymphoma forward mutation assay (final report). Litton Bionetics, PE Veenendaal, The Netherlands. Report No. R 2823. Submitted by Bayer AG to WHO.
See Also: Toxicological Abbreviations Demeton-S-Methyl Sulfoxide (FAO Meeting Report PL/1965/10/1)