METHIDATHION First draft prepared by M. Caris, Bureau of Chemical Safety Health and Welfare Canada, Ottawa, Canada EXPLANATION Methidathion is a broad-spectrum organophosphate insecticide, whose mode of action is by inhibition of acetylcholinesterase. Methidathion has been previously evaluated by the Joint Meeting in 1972 (Annex I, reference 18) when a Temporary ADI of 0.005 mg/kg bw was allocated and in 1975 (Annex I, reference 24), when an ADI of 0.005 mg/kg bw was allocated. The purpose of the present evaluation was to review additional toxicity data which had been generated in an effort to compliment and update the existing data base on methidathion. The first comprehensive review of methidathion (Annex I, reference 19) indicated that the technical material contained a minimum of 95% pure active ingredient. The purity of the technical material reported in the presently reviewed studies ranged from 92.6-99.95%. In order to facilitate a comprehensive review of the toxicology data on methidathion, relevant summaries from previously published monographs and monograph addenda (Annex I, references 19 and 25) have been included herein. EVALUATION FOR ACCEPTABLE DAILY INTAKE BIOLOGICAL DATA Biochemical aspects Absorption, distribution, and excretion Mice Male and female CFI mice were treated dermally with 14C- radiolabelled methidathion in the carbonyl carbon of the thiadiazole ring in acetone solution or formulated in petroleum hydrocarbon with emulsifier (the ratio of active ingredient to petroleum hydrocarbon to emulsifier was 6:10:1). The actual dermal dose was stated to be 12 mg/kg bw. The test solutions for both sexes were well absorbed through the skin as measured over a 72-h period, with residual radioactivity on the skin in the acetone group of 0.47-0.67% and in the formulated product of 0.35-1.27% of the dose. The highest concentrations of radioactivity were recovered in the expired CO2 (50.85-64.1%) and urine (14.48-23.47%). Radioactivity found in tissues (0.3-0.7%) and blood (0.03-0.21%) was minimal. Total recovery represented 83-94% of the administered dose. The half-lives for the testing solutions on the skin were calculated for the acetone group to be 9.1 and 10.5 h for males and females, and for the formulated group to be 10.4 and 10.9 h for males and females, respectively. Blood and tissue levels appeared to plateau approximately 4 h post-dosing, with tissue levels rarely exceeding 4 ppm (Simoneaux & Marco, 1984). Rats Methidathion, 14C-radiolabelled in the carbonyl carbon of the thiadiazole ring was administered by gavage to groups of 5 male and 5 female Charles River CD rats as a single oral nominal dose of 0.25 or 2.5 mg/kg bw. A third test group was pretreated with unlabelled methidathion for 14 days at the low dose of 0.25 mg/kg bw/day followed by a single oral 14C-radiolabelled dose of methidathion at 0.25 mg/kg bw. Two rats/sex served as vehicle (3% cornstarch suspension with 0.5% polysorbate-80) controls. The total recovered radioactivity accounted for 75.1-92.9% of the administered dose. The data generated from the present study indicate that the principal route of elimination was via the urine, with 30.3-37.1% of the radioactivity excreted at the low dose and from 41.8-57% excreted at the high dose. Residual tissue levels determined 7 days post-dosing, generally accounted for less than 1% of the dose with highest concentrations of radioactivity found in the liver, carcass and bone. Faeces contained only 2.2-2.6% of the administered radioactivity. Radioactivity in respired CO2 was not measured. The half-lives of elimination in the urine of 14C-labelled methidathion ranged from 7.4 to 9.7 h. There were no obvious differences in the distribution patterns when consideration was given to dose levels administered, pretreatment or sex (Szolics & Simoneaux, 1987a). Groups of 2 SD rats/sex were treated orally by gavage with a single dose of 14C-methidathion radiolabelled on the carbonyl group at a dose of 0.295 or 2.949 mg/kg bw (as suspensions in 3% cornstarch suspension containing 0.5% polysorbate-80). Overall radioactive recovery accounted for 99.6-102.5% of the administered dose. The primary route of elimination was via the urine with 54.2- 56.9% of the dose excreted after 96 h. The second highest source of radioactivity was recovered from expired CO2, representing 32.2- 34.4% of the radioactivity at the low dose and from 41.2-43.5% of the administered dose at the higher dose level. Radiolabelled CO2 was detected within 4 h post-dosing at both dose levels ranging from 3.3-7.5% of the dose, suggesting early fragmentation of the thiadiazole ring. Radioactivity in the faeces accounted for 2.9-4.5% and from 8.2-11.6% of the dose for the low- and high dose level, respectively. There were no major differences in elimination patterns with respect to sex (Szolics & Simoneaux, 1987b). Methidathion, 14C-labelled in the methoxy group was administered as a single oral dose to 2 SD rats/sex at a dose of 2.597 mg/kg bw (in a 3% cornstarch suspension containing 0.5% polysorbate-80). Total radioactive recovery represented 93% of the administered dose. The major route of elimination was via the urine, which in males comprised 39.8% and in females, 48.3% of the administered radiolabel. The level of radioactivity in expired volatiles was 33-39.3% of the dose, with recovery as early as 4 h post-dosing. The radioactivity in the faeces (7.6% and 8.3% for M and F, respectively) and carcass (6.3% and 3.9% for M and F, respectively) contributed minimally to the total recovery (Szolics & Simoneaux, 1987c). Methidathion, 14C-radiolabelled in the ring carbon adjacent to the methoxy group was given to SD rats (2/sex/group) by gavage at a single oral dose of 0.25 or 2.52 mg/kg bw (in a 3% cornstarch suspension containing 0.5% polysorbate-80). The principal route of elimination was via the urine, which represented 52.4-69% of the recovered radioactivity. Radioactivity recovered from the faeces ranged from 5.5-7.6% of the dose and from 3.6-6.7% in the carcass. The majority of the excreted urinary and faecal radiolabel was recovered within 24 h of dosing. Expired CO2 accounted for approximately 10% of the administered dose, with maximum recovery at 24 h and detection as early as 4 h post-dosing. The distribution of radioactivity was not significantly affected by dose or sex. Overall recovery of radioactive label was 77.6-91.5% of the administered dose (Szolics & Simoneaux, 1987d). Male and female SD rats were treated dermally with methidathion 14C-labelled in the carbonyl carbon of the thiadiazole ring in acetone solution or formulated in petroleum hydrocarbon with emulsifier (the ratio of active ingredient to petroleum hydrocarbon to emulsifier was 6:10:1). The dermal dose was stated to be equivalent to 12 mg/kg bw. Methidathion was well absorbed through the skin as measured over a 72-h period. Higher percentages of residual radioactivity were found in the skin of both sexes treated with the formulated product (4.5-9.8%) when compared to the acetone group (0.3-1.9%), suggesting slower absorption of the formulated material over the 72-h period. There were no other differences with respect to sex or testing solution. The highest concentrations of radioactivity, in order of magnitude, were recovered in the expired CO2, urine and carcass. Total recovery represented 86-95% of the administered dose. The half-lives for the testing solutions on the skin were calculated for the acetone group to be 16.9 and 15.9 h for males and females, and for the formulated group to be 17.2 and 17.4 h for males and females, respectively. Plasma and tissue levels generally attained plateau levels 48-h post-dosing, with tissue levels rarely exceeding 2 ppm (Marco & Simoneaux, 1982). Hens Methidathion, 14C-radiolabelled at the second carbon adjacent to the methoxy group was administered to a white leghorn chicken in gelatin capsules equivalent to 45.3 ppm for a period of 16 days. Total radiolabel recovered was 92.7%, of which 89.96% was found in the excreta. Expired CO2 comprised 1.7% of the dose, whereas the remainder of the radioactivity was divided among the egg yolk (0.21%), egg white (0.21%), tissues (0.49%) and blood (0.06%). Radioactive levels in the egg were observed to plateau between days 9 and 14 of treatment. Total residual radioactivity accounted for 0.49% of the administered dose. The highest residue levels in the individual tissues were found in the liver (3.85 ppm) and kidney (2.02 ppm) (Szolics & Simoneaux, 1985). Goats A single lactating goat was treated daily with a capsule of methidathion, 14C-labelled in the ring carbonyl group at a level equivalent to 5 ppm in the diet for a period of 10 consecutive days. Total radioactive recovery from all sources was 91.5% of the administered dose. The principal route of elimination was by expired CO2, representing 65.8% of the dose. Urinary and faecal radiolabel accounted for 20.4% and 3.4% of the dose, respectively. The remaining radioactivity was dispersed among the various fractions, rarely exceeding 1% of the total admin-istered dose. Residual levels in body tissues were less than 0.35% of the dose and ranged from 0.02 to 0.15 ppm. Highest levels were found in the liver. Recovery of radioactivity from milk reached plateau levels at 0.11 ppm after 5 days of treatment (Staley et al. 1987). A single lactating goat was treated daily with a capsule of methidathion, 14C-labelled in the ring carbon adjacent to the methoxy group at a level equivalent to 5 ppm in the diet for a period of 10 consecutive days. The majority of the radioactive label was eliminated via the urine, accounting for 18.1% of the administered dose. Expiration by CO2 and elimination via the faeces represented 9.6% and 6.4% of the dose, respectively. Recovery of the remaining radioactivity was distributed in the blood (2.9%), liver (1.2%) and generally less than 1% of the dose was found in each of the samples from milk, perirenal and omental fat, kidney, leg muscle and tenderloin. Total recovery of radioactivity was only 40.1% of the administered dose. It has been postulated that this may be due to a neutral volatile e.g., methane, which could not be trapped in the standard volatile or CO2 trap (Staley & Simoneaux, 1987). Biotransformation Rats The proposed metabolic pathway in animals is depicted in Figure 1 (Szolics & Simoneaux, 1987h). Partitioning of urine collected from rats treated orally with 14C-carbonyl labelled methidathion at 0.295 or 2.949 mg/kg bw (Szolics & Simoneaux, 1987b) indicated that the urine consisted of mainly organic soluble metabolites, which accounted for 79% in male and 66% in female of the total urinary radioactivity. The major metabolite was the sulfide derivative accounting for 44-45% of the radioactivity. The other principal metabolites were the sulfone (14.2 and 8% for males and females, respectively) and the sulfoxide (11.1 and 3.3% for males and females, respectively). The RH compound represented only 2.4% of the urinary radioactivity whereas the parent, methidathion, was present as only 0.7%. The oxygen analog was not identified. The remainder of the total urinary radioactivity (21-34%) was aqueous soluble metabolites. Two of the three chromatographed peaks, displayed elution patterns similar to the cysteine conjugate (2.1%) and desmonomethyl derivative (15.3%) of methidathion (Szolics & Simoneaux, 1987e). The urine of rats treated with 14C-labelled methidathion in the methoxy group at 2.597 mg/kg bw (Szolics & Simoneaux, 1987c) comprised both organic (67-72%) and aqueous (28-33%) soluble metabolites. The major organic metabolites were the sulfoxide (40.5%) and sulfone (23%). The remainder were identified as the RH compound (1%), unchanged parent (0.8% - female only), the sulfide (0.3% - male only) and oxygen analog (0.2% - male only). The aqueous soluble metabolites were characterized as the cysteine conjugate (2.1%) and desmonomethyl derivative (10.5%) of methidathion (Szolics & Simoneaux, 1987f).Metabolites from the urine of rats administered single oral doses of 14C-labelled methidathion in the ring carbon adjacent to the methoxy group at 0.25 or 2.52 mg/kg bw (Szolics & Simoneaux, 1987d) were identified. Organic soluble metabolites represented 61- 63%, whereas aqueous soluble metabolites accounted for 37-39% of the urinary radioactivity. The major organic metabolite was the sulfide (35.4%). Similar amounts of the sulfoxide (8.6%) and the sulfone (8.2%) were detected. The RH compound represented 2.1% of the radioactivity, and the oxygen analog represented 0.6%. No unchanged parent was identified. With respect to the aqueous soluble metabolites, the desmonomethyl derivative of methidathion accounted for 20% (Szolics & Simoneaux, 1987g). Goats The urine of a single lactating goat treated daily by capsule equivalent to a dietary intake level of 5 ppm for 10 days (Staley et al. 1987) was selected for characterization of metabolites. Partitioning data revealed that 84.5% of the urinary radioactivity were aqueous soluble and 5.5% were organic soluble metabolites. The principal aqueous soluble metabolites were the desmonomethyl derivative (59.7%) and cysteine conjugate (10.4%) of methidathion. Chromatography of the organic soluble components reportedly showed that the metabolites in the goat were qualitatively the same as those found in rat urine. The proposed predominant metabolic pathway of methidathion in the goat was 0-demethylation (Szolics & Simoneaux, 1987h). Toxicological studies Acute toxicity studies Acute toxicity studies conducted in both the male and female Tif.RAIf rat (Table 1), reveal that technical methidathion, upon oral administration is highly toxic with LD50 values of 26 to 43.8 mg/kg bw. The acute dermal studies indicate that methidathion is slightly to moderately toxic. Clinical signs of toxicity, upon oral and dermal dosing were generally manifest as curved or ventral body position, dacryorrhea/chromodacryorrhea, diarrhoea, dyspnea, exophthalmus, ruffled fur, sedation, tonic/clonic muscle spasms and trismus. The symptoms were reversible in surviving animals. The acute oral toxicity of methidathion has been investigated in several animal species (Table 2). The results indicate that methidathion is moderately to highly toxic in all species tested with LD50 values ranging from 17 to 200 mg/kg bw. Table 1. Acute toxicity of technical methidathion Species Sex Route Vehicle LD50 Purity Reference (strain) (mg/kg bw) Rat M&F oral CMC, 2% 43.8 ? Bathe (1973a) (Tif. RAIf) Rat M&F oral PEG, 400 26 96.9% Bathe & Sachsse (Tif. RAIf) (1980a) Rat M&F oral PEG, 400 26 92.7% Bathe & Sachsse (Tif. RAIf) (1980b) Rat M&F dermal CMC, 2% 1546 ? Bathe, (1973b) (Tif. RAIf) Rat M&F dermal CMC, 2% 1663 ? Bathe & Sachsse (Tif. RAIf) (1975) Rat M&F dermal CMC, 2% + 297 92.6% Sarasin (1980) (Tif. RAIf) Tween 80, 0.1% Short-term toxicity studies Rats Five groups of ten male rats received by gavage 0, 0.25, 0.83, 2.5 or 8.3 mg methidiathion/kg bw/day five days a week for four weeks. Signs of cholinesterase inhibition occurred during the first week at the 8.3 mg/kg bw/day level, but not later in this or in other groups. Dose-related cholinesterase inhibition occurred in RBC and plasma, the no-effect level being 0.25 mg/kg bw/day. Plasma cholinesterase had returned to normal three days after treatment was stopped, but RBC cholinesterase had not reached normal figures after 21 days (Noakes & Watson, 1964b). Five groups of five male and five female rats received by gavage 0. 2.5, 5, 10 or 20 mg methidathion/kg bw/day six days a week for four weeks. In the 10 and 20 mg/kg bw/day groups, four and nine animals died, respectively. Body-weight gain was depressed in all groups, but no relation to dosage was apparent. There was a slight increase in fat deposition in the liver at 5 mg/kg bw/day and at the highest level this was more marked (Stenger & Roulet, 1963). Groups of 24 male and 24 female rats were fed for 22 weeks on diets containing 0, 1, 4, 16 or 64 ppm methidathion. In a similar study in the same laboratory, groups of 24 male and 24 female rats were fed for 26 weeks on diets supplying 0, 128 or 256 ppm methidathion. The rate of body-weight gain was reduced at 64 ppm and above in females but not in males. Histopathological examination of liver, spleen and kidneys showed a dose-related increase in fat deposition in the liver at doses above 64 ppm in both sexes. No abnormalities in haematological indices or in results of urinalyses were found (Stenger & Roulet, 1965). Table 2. Acute oral toxicity of methidathion1 Species Sex LD50 Reference (mg/kg bw) Mouse F 17 Noakes & Sanderson, 1964 Hamster F 30 Noakes & Sanderson, 1964 Rat M&F 20-81 Slenger, 1964a,b, 1966a,b; Aeppli, 1969a,b; 1970a,b; Noakes & Sanderson, 1964 Rat M 26-65 Slenger, 1964a Noakes & Sanderson, 1964 Guinea-pig F 25 Slenger, 1964a Noakes & Sanderson, 1964 Rabbit M 80 Sachsse, 1971 Dog M&F 200 Noakes & Sanderson, 1964 Chicken F 80 Annex I, 19 1 Formulations calculated as a.i. Groups of 20 male and 20 female rats were fed for six months on diets containing 0, 0.5, 2, 10, 50 or 250 ppm methidathion. At the 250 ppm level weight gain was slightly depressed and clinical signs of cholinesterase inhibition were seen, particularly in females. Plasma cholinesterase was inhibited in the 250 ppm group and erythrocyte cholinesterase in groups receiving 10 ppm and above. Experimental groups were similar to controls with regard to survival, food intake, weights and microscopic appearance of liver, kidneys, spleen and testes and the macroscopic appearance of other organs (Noakes & Watson, 1964a). Rabbits A dermal study was undertaken with groups of 5 New Zeeland rabbits/sex administered methidathion (purity unknown) topically for 6-h daily non-occlusive exposure periods at doses of 0 (vehicle control, PEG 300), 1, 5 or 20 mg/kg bw/day for a period of 22 consecutive days. There were no significant effects of treatment on survival, food consumption, haematology, blood chemistry, cholinesterase activity, organ weights, gross morphologic or histopathological alterations. Based on minimal effects noted as hypoactivity in a single male at 20 mg/kg bw, occasional incidences of soft faeces or diarrhoea in treated males and a slight trend to decreased body-weight gain in the high dose 20 mg/kg bw/day treated males, a conservative NOAEL may be set at 5 mg/kg bw/day (Folinusz et al. 1986). A second dermal study was conducted with groups of New Zeeland HRP:SPF rabbits (4-6 per sex) topically administered methidathion (95% purity) daily for a 6-h occlusive exposure period at doses of 0 (vehicle control, PEG 400), 1, 10, 40 or 80 mg/kg bw for a period of 21 days. Treatment with methidathion resulted in mortality in males at all dose levels (0/5, 2/5, 2/6, 3/5 and 3/5) and in females at 40 mg/kg bw/day and higher (0/5, 0/5, 0/4, 2/5 and 4/5). Clinical signs of toxicity in males treated at dose levels of 1 mg/kg bw/day and higher and in females treated at dose levels of 40 and 80 mg/kg bw/day were manifest as anorexia, ataxia, hunched posture, languid appearance and laboured respiration. Tremors were observed at dose levels of 10 mg/kg bw/day and higher, whereas convulsions were reported in a single high-dose (80 mg/kg bw/day) treated female. Cholinesterase assessments revealed significant depression in the mean plasma (38-86%), RBC (40-80%) and brain (37-88%) cholinesterase values for both sexes at dose levels of 10 mg/kg bw/day and higher. Treatment-related microscopic alterations were evidenced in the liver and gall bladder. Principal findings in the liver were denoted as hepatocytic clearing and congestion at dose levels as low as 1 mg/kg bw/day. Capsular/subcapsular necrosis with acute inflammation was also noted in several of the treated animals. Lesions of the gall bladder were present in both sexes at dose levels of 10 mg/kg bw/day and higher and were attributed to bile reflux due to hyperperistalsis. Subacute inflammation of the myocardium and degeneration of the medial aorta occasionally with mineralization were observed in several of the rabbits dying during the study period. There were no specific effects of treatment on body-weight, food consumption, ophthalmoscopy, haematological and blood biochemical parameters or organ weights. The NOAEL was determined to be 1 mg/kg bw/day by the author (Osheroff, 1987). The results of the present study when interpreted independently, have not unequivocally demonstrated 1 mg/kg bw/day to be a NOAEL. The author has provided valid argument that evaluation of primary toxicity was complicated by the additive effects of stress especially during clinical observations. The occlusive rubber binding used may not only have enhanced the absorption of the test material but in combination with the neck collar, may have increased the stress factor, thus augmenting the toxicity of the test material. In view of the intrinsic variables in the present study design, it is considered appropriate to critically assess the results of the present study in conjunction with those generated from the previously conducted rabbit dermal study, wherein dermal administration of methidathion under non-occlusive means failed to produce effects in rabbits at dose levels as high as 5 mg/kg bw/day (Folinusz et al. 1986). Dogs Four groups of three male and three female beagle dogs received diets containing 0, 4, 16 or 65 ppm methidathion for two years. The animals were starved of diet one day each week and received a double ration on the next day. Administration of methidathion was discontinued from week 16 to 19. Erythrocyte cholinesterase was inhibited in the 64 ppm group, but brain cholinesterase was unaffected by treatment. SGPT was markedly elevated in the 64 and 16 ppm groups and slightly raised in males of the 4 ppm group. During weeks 16 to 19 these levels fell, but only the 4 ppm group returned to normal. SGOT levels were not the same as controls at all treatment levels, but serum alkaline phosphatase was elevated and sulfobromophthalein retention increased in the 16 and 64 ppm groups. The livers of dogs receiving 16 and 64 ppm were pigmented on macroscopic examination. Microscopically, pigmentation could be seen in macrophages and hepatic cells (principally centrilobular) in the 16 and 64 ppm groups, the intensity of deposit being dose-related. The Perl's reaction showed that the pigment did not contain appreciable quantities of iron. The kidneys of the 64 ppm group also showed pigmentation. It was questionable whether the livers of the 4 ppm group contained excess pigment. Control and test groups were indistinguishable regarding behaviour, results of clinical tests including neurological examination, haematological findings, organ weights and macroscopic and microscopic appearance of organs other than those mentioned. An additional two dogs received 64 ppm methidathion in the diet for four weeks. The SGOT was elevated at two and four weeks and at autopsy the livers were dark in colour. Moderate diffuse pigmentation was seen microscopically in the liver of one animal. The plasma enzyme and liver histology changes at 30 days of treatment at 64 ppm were not increased after treatment for two years at this dose. Furthermore, the serum enzyme changes at 16-19 weeks of treatment at 64 ppm were reversible and returned to normal three weeks after cessation of treatment. The NOAEL was 4 ppm (Johnston, 1967). The histological slides of the liver tissue from the original study were re-evaluated and submitted to the 1975 Joint Meeting Annex 1, reference 25). Intrahepatic cholestasis was observed in dogs fed 16 and 64 ppm methidathion. Neither degenerative nor inflammatory changes were associated with this lesion. Pigmentation occurred as bile-plugs in biliary ductules, or as amorphous deposits in Kupffer cells or as lipofuscin in both hepatic and Kupffer cells. Haemolysis was not detected. A minimal degree lipofuscin pigmentation was also observed at 4 ppm and in the control group. Mild irregular fatty changes of the hepatocytes with occasional periportal histiolymphocytic infiltration of the liver were observed in both treated and control animals (Hess, 1975). Methidathion (97% purity) was administered to groups of 4 beagle dogs per sex in the daily feed at dietary levels of 0, 0.5, 4, 45 or 140 ppm equal to 0, 0.02, 0.16, 1.96 or 5.67 mg/kg bw/day, respectively, for a period of 90 days. An additional group of 4 dogs per sex was treated orally by gelatin capsule at a dose level of 0.14 mg/kg bw/day, equal to a daily dietary intake level of 4 ppm, for a similar treatment duration. A NOAEL of 4 ppm was assessed based upon the evidence of cholestasis in all male and female dogs treated at 45 and 140 ppm. Cholestasis was similarly described in a single male dog treated by capsule at 0.14 mg/kg bw/day. Other consequences of treatment evident in both sexes at dietary levels of 45 ppm and higher were discoloration of the liver and markedly enhanced enzyme activity, expressed as increased levels of ALP, SGOT, SGPT, GGT and sorbitol dehydrogenase. RBC cholinesterase activity was significantly (75-88%) inhibited in dogs of both sexes treated at 140 ppm. Brain cholinesterase activity was inhibited (26.8%) in the 140 ppm treated females when compared to the controls. There were no effects of methidathion treatment on serum cholinesterase levels. Clinical signs of tremor and reduced activity post-dosing, observed during the latter part of the study, were exhibited in a single male dog at the high dose level. Reduced activity was also noted in a single male treated at 45 ppm. Other effects of treatment were significantly decreased mean food intake values in the high dose treated males when compared to the control group. There were no treatment-related effects observed with respect to survival, body-weights, ophthalmoscopic examination, haematological parameters, urinalysis or organ weights (Chang & Wyand, 1990). Six groups of 4 beagle dogs/sex were treated with methidathion (96% purity) at dietary levels of 0, 0.5, 2, 4, 40 or 140 ppm, equal to 0, 0.02, 0.07, 0.15, 1.34 or 4.51 mg/kg bw/day, respectively, for a period of 12 months. A NOAEL of 4 ppm was indicated based on treatment-related hepatic effects observed grossly as general discoloration of the liver and characterized histomorphologically as cholestasis and chronic inflammation of the liver in both sexes at dietary levels of 40 ppm and higher. Associated changes in blood biochemical parameters were denoted by elevated ALP, SGOT, SGPT, sorbitol dehydrogenase and bilirubin levels. Other significant clinical changes recorded only in the females were increased GGT and decreased total protein and albumin values. RBC choline-sterase activity was markedly inhibited (76-87%) in both male and females dogs treated with methidathion at 140 ppm. Serum cholinesterase activity was not adversely affected by treatment at any dietary level. Brain cholinesterase activity was significantly depressed (16-27%) in both sexes treated at 140 ppm when compared to the controls. Another effect of treatment was related to decreased food consumption in male dogs treated with methidation at a dietary level of 140 ppm. There were no effects of treatment on survival, clinical signs, body-weights, ophthalmoscopy, haematology, urinalysis, faecal examination or organ weights (Chang and Walberg, 1991). Monkeys Three groups of Rhesus monkeys (approximately equal number of each sex) were administered 0, 0.25 or 1.0 mg methidathion/kg bw/day by stomach tube, 6 days a week for 23 months. Two of each group were autopsied after 12 months. Plasma and erythrocyte cholinesterase activity were inhibited in the 1 mg/kg bw/day group, but not at the lower level. Brain cholinesterase was unaltered by treatment. Growth, results of haemological tests, results of chemical analyses of serum (including SGPT and ALP) and macro- and microscopic examination of tissues were similar in control and test groups (Fabran et al., 1971). Long-term toxicity/carcinogenicity studies Mice A 23-month study was conducted with groups of 50 Charles River CD-1 mice per sex/group fed diets containing methidathion (purity not stated) at levels of 0, 3, 10, 50 or 100 ppm equal to 0.43, 1.42, 6.99 or 13.70 mg/kg bw/day, respectively. An additional 120 mice/sex/group were assigned to the chronic phase of this bioassay. Interim sacrifices of 20 mice/sex/group were scheduled after 3, 6, 12 and 13 months. Animals sacrificed at 13 months were maintained on control diet for one month as recovery animals following 12 months of continuous treatment. The remaining animals (40/sex/group, maximum) were sacrificed after 18 months of treatment. Treatment of mice with methidathion resulted in slightly decreased survival of the 100 ppm treated males when compared to the controls. The only clinical sign remarked upon was discoloration of the urine in the 50 and 100 ppm treated males. Potentially reversible increases in liver enzyme activity were reported in males at 50 ppm and higher and in females at 100 ppm. Significantly decreased but potentially reversible RBC cholinesterase activity values (26-46%) were registered in males at 100 ppm and in females at 50 ppm and higher. Brain cholinesterase activity was markedly inhibited (15-49%) in both sexes at 100 ppm. There were no inhibitory effects of treatment on plasma cholinesterase activity. There were no effects of methidathion treatment noted with respect to body-weights, food and water consumption or ophthalmoscopy. Treatment-related target organ alterations were manifest in the gall bladder and liver at dietary levels of 50 ppm and higher in males and in females at 100 ppm. Microscopic changes were described in the gall bladder as cholecystitis and hyperplasia and, hepatic findings were denoted as bile duct hyperplasia, bile stasis, cholangiofibrosis, chronic hepatitis and hypertrophy. Increased extramedullary haematopoiesis of the spleen, associated with increased spleen weights were observed in the 100 ppm treated males. Treatment of male mice with methidathion resulted in a significantly increased incidence of hepatocellular tumours (adenomas, carcinomas and adenomas/carcinomas combined). 0 3 10 50 100 ppm Adenoma 1/46 9/45 7/47 8/43 21/45 Carcinoma 8/46 6/45 4/47 13/43 17/45 Combined 9/46 15/45 11/47 21/43 38/45 Historical control data (Quest et al. 1990) generated from 14 studies conducted at the same test facility with the same strain of mouse, revealed that the incidences of hepatocellular tumours reported in the present study exceeded the historical control range at dietary levels of 50 ppm and higher. Latency, expressed in terms of time to appearance of first tumour, was not apparently decreased in the treated male groups when compared to the concurrent controls. The incidence of hepatocellular tumours was not increased in female mice treated with methidathion The NOAEL in this study was 10 ppm, equal to 1.4 mg/kg bw/day (Goldenthal, 1986). Rats In order to investigate the long-term toxic effects and possible carcinogenic action of methidathion, four groups of 25 male and 25 female rats each were fed for three weeks on diets containing 0, 2, 8 or 32 ppm and for a further 101 weeks on diets containing 0, 4, 16 or 64 ppm methidathion. The rate of gain in body weight was reduced from week 8 in male animals of the 64 ppm group. After the first year the rates of gain became erratic in all groups, making interpretation of the findings difficult. Female rats on test diets grew at a rate comparable to controls. Erythrocyte cholinesterase was inhibited in the 16 and 64 ppm groups, while plasma cholinesterase showed minimal inhibition at 100 weeks in the 64 ppm group only. Brain cholinesterase was inhibited in the 64 ppm group, with marginal and no reduction in the 16 and 4 ppm groups, respectively. Decreased relative adrenal weights were found in females of the 16 ppm and 64 ppm groups, and decreased ovary weights in the 64 ppm group. The relative kidney weights of males was increased in the 16 and 64 ppm groups. A greater frequency of hepatic degenerative changes was noted in rats fed methidathion in the diet; the high incidence of pulmonary infections in the rats renders this finding of doubtful toxicological significance. The food intake, results of haematological investigations and chemical analysis of serum (including SPGT) and the survival rate were similar in the test groups and in the control group. The incidence of tumours was variable between groups but was low and not dose- related, and no unusual tumours were found. The NOAEL in this study was 4 ppm methidathion in the diet (Johnston, 1967). Groups of 65 Crl:COBS CD(SD) BR rats/sex were treated with methidathion (97.3% purity) at dietary levels of 0, 4, 40 or 100 ppm equal to 0.16, 1.72 or 4.91 mg/kg bw/day, respectively for a period of 104 weeks. For interim sacrifice purposes, an additional 15 rats/sex/group were assigned on study. At 52 weeks, 10 rats/sex/group were sacrificed with the remaining 5 rats/sex/ group sacrificed at week 93 of study. Treatment with methidathion resulted in clinical signs expressed in the 40 and 100 ppm groups as alopecia, chromorhinorrhea, hyperactivity, skin lesions, tremors, hypersensitivity to the touch and fasciculation. Mean body-weights and weight gains were decreased in both sexes at 100 ppm throughout the course of treatment. Body-weight gains were decreased at a dietary level of 40 ppm during the initial few weeks of treatment, with comparable weight gain thereafter. Mean food intake was significantly increased in both sexes treated at dietary levels of 40 ppm and higher, whereas water consumption was decreased at 100 ppm and occasionally at 40 ppm. Treatment-related haematological findings were exhibited at a dietary level of 100 ppm as inverted neutrophil:lymphocyte ratios, reduced RBC parameters and increased platelet counts. Variations in blood biochemical parameters were observed at 40 ppm and higher as decreased total bilirubin, decreased total protein as well as changes in electrolyte levels (decreased potassium and calcium, and increased inorganic phosphorus and chloride). Significant inhibition of RBC (14-38%), serum (22- 66%) and brain (42-74%) cholinesterase activity were determined in both sexes of rats treated at dietary levels of 40 ppm and higher. Notable changes in urinalyses were revealed as decreased volume and increased specific gravity at 40 ppm and higher which correlated well with the reduced fluid intake reported in these groups. Gross necropsy findings showed an increased incidence of skin lesions in the 40 and 100 ppm levels which were associated microscopically with ulceration and/or chronic purulent inflammation. Other pathological alterations were related to an increased incidence in focal accumulations of foamy macrophages in the alveoli of the 100 ppm treated males and females. There were no effects of treatment on survival or ophthalmoscopy. The NOAEL for in-life parameters was determined to be 4 ppm, equal to 0.16 mg/kg bw/day. There was no evidence of methidathion-induced carcinogenic potential (Yau et al., 1986). Reproduction studies Rats In a three-generation study, three groups of 10 male and 20 female rats were fed on a diet containing 0, 2 or 16 ppm methidathion for three weeks, and thereafter on a diet containing 0, 4 or 32 ppm methidathion. Litters from the second mating were used to provide the new generations. The F1b litters did not receive test diets until 26 days and the F2b until 22 days after weaning. F0, Flb and F2b generations received diets for 27-28 weeks during which they produced two litters. The number of young surviving at weaning was reduced in all generations of litters from animals fed 32 ppm methidathion and the mean liver weight of F3b weanlings of this group was slightly increased. Body weights, reproductive capacity and mortality of parents and the number of litters, litter size, mean birth and weaning weights of test groups were comparable to controls. The number of stillbirths and incidence of congenital abnormalities were unaltered by treatment. No histological damage was found in the organs of the F3b animals examined. The NOAEL in this study was 4 ppm methidathion (Lobdell & Johnston, 1966). A two-generation (one litter per generation) reproduction study was conducted with groups of 15 male and 30 female Charles River SD CR1:CD BR rats fed methidathion (purity not specified) at dietary levels of 0, 5, 25 or 50 ppm equal to 0, 0.43, 2.08 or 4.23 mg/kg bw/day, respectively. With respect to reproductive performance, statistically (p < 0.05) reduced mating indices were recorded for the 25 and 50 ppm groups in the F1 generation. Although the mating indices were reduced in these groups (69% and 66%, respectively) relative to the concurrent F1 control group (88%), they were nevertheless not significantly different from those calculated for the F0 generation control (73%) or treated groups (60-65%). The fertility and gestation indices were comparable among groups. Treatment-related effects on maternal animals fed dietary levels of 25 ppm and higher were revealed by clinical signs of toxicity manifest during lactation as slight and/or intermittent tremors. Mean body-weights of F1 50 ppm-treated males were decreased prior to and during the 12-week premating period. Mean body-weights gains were not, however, significantly different from controls. Body- weights of females recorded during lactation of both generations were decreased at 50 ppm when compared to the concurrent control. Decreased ovary weights recorded in females at 25 and 50 ppm were not correlated with histopathological changes. Effects of treatment on progeny were expressed as decreased survival in the 50 ppm group of the F1 generation, decreased body-weights and clinical signs in both generations at 25 and 50 ppm. The clinical signs were suggestive of poor maternal care and were described as weakness/lethargy, coolness to the touch and starving appearance. On the basis of the reported findings, a NOAEL of 5 ppm, equal to 0.43 mg/kg bw/day, was indicated (Salamon, 1987). Special studies on teratogenicity Rats A teratology study was conducted with groups of 25 mated female Crl: COBS CD(SD)BR rats administered methidathion (93.2-96% purity) at 0.25, 1.0 and 2.5 mg/kg bw/day or the control (vehicle, 3% aqueous cornstarch with 0.5% Tween 80) orally by gavage from days 6 to 15 of gestation, inclusive. Confirmation of mating was determined by presence of sperm in the vaginal washing, and this day was designated day 0 of gestation. A NOAEL for maternal toxicity was indicated at 1.0 mg/kg bw/day based on mortality, decreased body- weights, food intake and clinical signs at 2.5 mg/kg bw/day. Clinical signs of toxicity in the high dose (2.5 mg/kg bw/day) group were suggestive of organophosphorus intoxication including, lethargy, tremors, lacrimation, salivation, raspy respiration, exophthalmia, chromodacryorrhea. A NOAEL for embryofetal toxicity was set at the highest dose level tested of 2.5 mg/kg bw/day. There were no significant differences noted with respect to the mean number of implantations, live fetuses or mean number of resorptions on a litter basis. There was similarly no significant variability in the post-implantation loss, fetal sex ratio or in the mean fetal litter weight in the treated groups when compared to the control. Treatment with methidathion failed to uncover any evidence of teratogenic potential (Mainiero et al. 1987). Rabbits Methidathion (purity not specified) was administered orally by gavage at 0 (vehicle control, 3% cornstarch with 0.5% Tween 80), 2, 6 or 12 mg/kg bw/day to groups of 19 artificially inseminated New Zeeland white rabbits on days 7 through 19 of gestation. The day of artificial insemination was designated as day 0 of gestation. Treatment-related clinical signs of toxicity at the high dose (12 mg/kg bw/day) treated animals were manifest as ataxia, tremors, salivation and miosis. In the absence of similar effects in the control or other treated groups, the NOAEL for maternal toxicity was demonstrated to be 6 mg/kg bw/day. There was no evidence of embryofetal developmental toxicity or potential for teratogenicity at any of the dose levels investigated, including the highest dose of 12 mg/kg bw/day (Hummel et al. 1987). Special studies on genotoxicity A battery of mutagenicity assays were conducted with technical methidathion, the results of which are presented in Table 3. The tests performed to evaluate potential for gene mutation in bacteria, DNA damage as well as chromosome aberration were negative. A dominant lethal study in mice was also negative. Positive responses were observed in the in vitro assays with Saccharomyces cerevisiae and in the Chinese hamster test for sister chromatid exchange. In vivo tests conducted to examine the similar endpoints, did not however elicit any evidence of mutagenic potential in mammalian cells. Special studies on delayed neurotoxicity Four adult hens received four subcutaneous injections of 50 mg methidathion/kg body-weight (the maximum tolerated dose) at weekly intervals and they were observed for a further four weeks. The signs of acute poisoning lasted two to three days each time, but birds remained in good condition and no paralysis developed. Neuropathological examinations were not performed (Noakes, 1964). Five groups of ten adult hens were fed diets containing 0, 16, 52 or 160 ppm methidathion or 316 ppm tri-orthocresylphosphate for 45-47 days. No abnormal neurological signs were found in birds fed methidathion, but those on tri-orthocresylphosphate showed leg weakness, lack of balance and ataxia during the final week of treatment. Unequivocal evidence of demyelination of neural tissue was not found in methidathion or tri-orthocresylphosphate-treated animals (Johnston, 1965). The delayed neurotoxic potential of methidathion (purity not specified) was investigated in groups of 10-30 female white leghorn hens. The animals were administered the test material twice, 21 days apart, at 0 (vehicle, CMC 2%), 43.75, 87.5, 175 or 350 mg/kg bw. Animals receiving methidathion at 350 mg/kg bw were pretreated with an intramuscular injection of atropine sulfate, 10 mg/kg bw, one hour prior to treatment. Groups of 3 male and 3 female hens received a single oral dose of the positive control, TOCP at 215, 464, 600, 1000 or 2150 mg/kg bw and were then observed for 21 days post- dosing. A preliminary acute oral study indicated that the LD50 of methidathion in the hen was 175 mg/kg bw. Clinical signs of intoxication were expressed as ataxia, slight tremor, curved or ventral body position and sedation, with subsequent recovery in surviving animals, 8-10 h post-dosing. Histopathological evaluation of the spinal cord and peripheral nerves did not reveal any treatment-related lesions of the nervous system, whereas TOCP toxicity was evidenced as central-peripheral, distally accentuated neuropathy. Treatment with methidathion did not produce any signs of delayed neurotoxicity (Ullmann et al. 1977). Table 3. Genotoxicity of technical methidathion Test Test system Concentration Purity Results References (vehicle) Reverse mutation S. typhimurium 25, 75, 225, 675, 2025 98.4% negative Arni & Muller (1980a) (in vivo) TA98, 100, 1535, 1537 µg/0.1 mL (DMSO) 1., 2. S. typhimurium 25, 75, 225, 675, 2025 93.4% negative Arni & Muller (1980b) TA98, 100, 1535, 1537 µg/0.1 mL (DMSO) 1., 2. S. typhimurium 0, 0.1, 0.5, 1, 5, 10, 50 99.95% negative Satou et al. (1979) TA98, 100, 1535, 1537 mg/mL (DMSO) 1., 2. E. coli B/r WP2 Try- Hcr- S. typhimurium 10, 50, 100, 500, 1000, ? negative Simmon et al. (1977) TA98, 100, 1535, 1537, 5000 µg/plate (DMSO) 1., 2. 1538 Rec assay (in vitro) B. subtilis 5, 25, 100 mg/mL (DMSO) 99.95% negative Satou et al. (1979) H17, M45 Reverse mutation/ S. typhimurium 10, 20, 40 mg/kg bw ? negative Simmon et al. (1977) Host-mediated TA1535, 1538/Male Swiss (single oral doses) (in vivo) Webster mouse (inocculated ip) 5, 10, 20 mg/kg bw negative (5 oral doses) (DMSO) S. typhimurium 0, 5, 10, 20 mg/kg bw 93.4% negative Arni & Muller (1980c) TA98, 100, 1537/ (3 oral doses: 2 h, 1 h male mouse and prior to innoculation) (inocculated iv) (CMC, 0.5%) Table 3 (cont'd) Test Test system Concentration Purity Results References (vehicle) Gene conversion/ S. cerevisiae MP-1 675, 1250, 2500, 5000, 93.4 conversion: Arni & Muller (1981) forward mutation 10000 µg/mL (DMSO) slight (+ ve) (in vivo) mutation: (+ ve) Forward mutation Mouse lymphoma cells - 0, 15 mg/kg bw (3 oral 93.4% negative Strasser & Muller (1980) host-mediated (in L5 178Y/mouse doses post-innoculation) vivo) (DBA/Bom) (CMC) DNA repair Mouse (male CD-1) 5 x 10-7 to 1% (DMSO) ? negative Tong (1982a) (in vivo) hepatocytes Rat (male F344) 5 x 10-9 to 1% (DMSO) ? negative Tong (1982b) hepatocytes Rat hepatocytes 0.128, 0.64, 3.2, 16 97.2% negative Puri & Muller (1982a) µg/mL (DMSO) Rat hepatocytes 1.85, 5.56, 16.67, 50, 100, 96% negative Hertner & Arni (1990) 200 µg/mL (DMSO) Human fibroblasts 1.024, 5.12, 25.6, 128 ? negative Puri & Muller (1982b) µg/mL (DMSO) SCE (in vivo) Chinese hamster 0, 10, 20, 40, 80 µg/mL 99.1% slight (+ ve) Chem et al. (1981) cell line V79 (DMSO) at 40, 80 ug/mL SCE (in vivo) Chinese hamster 0, 17, 34, 68 mg/kg bw 93.4% negative Hool & Muller (1980) (bone marrow) (CMC) Table 3 (cont'd) Test Test system Concentration Purity Results References (vehicle) Chromosome Chinese hamster ovary 43, 75, 87.5, 175, 350 96% negative Strasser & Arni (1990) aberration CCL 61 µg/mL (DMSO) (in vivo) 96.9% negative Hool et al. (1980) Nucleus anomaly Chinese hamster 0, 17, 34, 68 mg/kg bw (in vivo) (bone marrow) (2 oral doses) (CMC) 98.4% negative Fritz (1976) Dominant lethal Mice, NMRI 0, 15, 45 mg/kg bw (CMC) (in vivo) 1. = in the presence of metabolic activation 2. = in the absence of metabolic activation Special studies on irritation and sensitization The eye irritation potential of technical methidathion was investigated in 3 English Silver strain rabbits/sex. Administration of 0.1 grams of methidathion into the conjunctival sac of the left eye (right eye served as control) produced irritating conjunctival reaction in the unwashed eye of a single male rabbit (Sachsse, 1973a). Technical methidathion (as a 50% polyethylene glycol suspension) was applied under occlusive conditions to the shaved backs of male and female English Silver strain rabbits for 24 h. Skin reactions were observed as very slight erythema in one male and moderate to severe erythema in association with slight oedema in one female rabbit (Sachsse, 1973b). The shaved backs of male Hartley albino guinea-pigs were repeatedly treated with technical methidathion as a 10% solution in diethyl ether. There was no evidence of skin sensitization potential (Cannelongo, 1984). Special studies on potentiation The potentiating effects of methidathion (purity not specified) with profenofos (Sachsse & Bathe, 1977b) and methacrifos (Sachsse & Bathe, 1978) were investigated in male and female Tif:RAIf rats by comparing the theoretical LD50 values, based on an assumption of strictly additive toxicity, with that of the experimentally derived LD50 values for the equitoxic mixtures. There was no potentiating effect of methidathion with profenofos, whereas a slight enhancement of acute toxicity was observed with an equitoxic mixture of methidathion and methacrifos. Special studies on promoting activity Male F344 DuCrj strain rats received a single ip injection of the initiator, N-nitrosodiethylamine (DEN) at 200 mg/kg bw. Two weeks thereafter, the rats were treated with methidathion (92.7% purity) at dietary levels of 0, 10, 30, 100 or 300 ppm (equal to 0, 1.0, 2.3, 7.6 or 22.9 mg/kg bw, respectively) or the positive control, 3'-methyl-4-dimethyl amino azobenzene (3'-Me-DAB) at 600 ppm (equal to 33.9 mg/kg bw) for a period of 6 weeks. Three weeks following treatment with DEN, partial hepatectomy was performed on all animals. Histochemical evaluation of 4 liver sections from each animal after 8 weeks on study, revealed a significantly increased number of GGT positive foci per unit area in rats treated with methidathion at 100 and 300 ppm and in the 600 ppm 3'-Me-DAB positive control group. No increases in the number of GGT positive foci were observed in additional groups of rats treated with methidathion at 100 and 300 ppm alone, without previous initiation with DEN. The number of foci in rats treated with methidathion at 30 ppm and lower were not different from the controls (Arai, 1981). A second short-term study of the promoting activity in the rat liver was conducted with groups of male Fischer 344 DuCrj strain rats administered methidathion (98.6% purity) at dietary levels of 0, 35, 46, 59, 77 or 100 ppm (equal to 0, 2.7, 3.5, 4.8, 6.0 or 7.6 mg/kg bw/day, respectively) for a period of 6 weeks. Two weeks prior to feeding with methidathion, the rats were pretreated with a single ip injection of the initiator DEN at 200 mg/kg bw. Partial (two- thirds) hepatectomy was performed three weeks after initiation and the animals were sacrificed after 8 weeks on study. Histochemical analysis unveiled a significant dose-related increase in the number of GGT positive foci in rats treated with methidathion at dietary levels of 59 ppm and higher. The number of GGT positive foci at dietary levels of 46 ppm and lower were comparable to the controls. No increases in the number of GGT positive foci were recorded in an additional group of rats treated with methidathion at 100 ppm alone, without previous initiation with DEN (Daiyu-Kai Institute of Medical Science, 1983). Special studies on therapeutic activity of antidotes The therapeutic potential of antidotes was tested by administering methidathion (purity not specified) orally by gavage to Tif.RAIf rats at the LD80 of 46 mg/kg bw. The therapeutic agents, atropine sulfate alone, toxogonin alone, PAM alone and toxogonin combined with atropine sulfate were then administered intramuscularly after the first appearance of clinical signs of poisoning. A further aspect of therapeutics was investigated, by administering 5 repeated daily oral doses of methidathion at the LD50 (34 mg/kg bw) to rats and then, upon observation of clinical signs, commencing with the respective combination of antidotes. All therapeutic agents were, according to the treatment regimen, effective against the oral LD80 of methidathion. A positive protective effect against repeated LD50 doses of methidathion were observed with atropine and toxogonin. PAM and toxogonin in combination with atropine had minimal protective effect against repeated challenges to methidathion (Sachsse & Bathe, 1977a). Observations in humans One male subject took 4 mg/day (equal to 0.04 mg/kg bw/day) for 17 days, and 8 mg/day (equal to 0.08 mg/kg bw/day) of methidathion for 27 days. No effect was found on RBC and plasma cholinesterase, the thrombocyte count and stability or on the clinical condition of the subject (Payot, 1965). Two groups of eight men received 0.04 or 0.11 mg methidathion/kg bw/day orally in capsules for 6 weeks. Four men received placebo capsules. The treatment with methidathion was without effect on plasma and RBC cholinesterase, SGPT and SGOT and results of urinalyses or on EEG pattern or clinical condition of the subject (Coulston, 1970). A case of massive poisoning was reported to have occurred where a 25-year old man weighing 60 kg ingested a number of mouthfuls of supracide 40 (methidathion, 40% active ingredient). The man was discovered approximately 2 hours after the event, in an unconscious, semi-comatose condition. Upon admission to hospital the patient was treated intravenously with atropine and toxogonin. The cholinesterase activity in the serum was found to be zero a few hours after admission. The patient was discharged after 15 days of hospitalization. The laboratory findings were normal with exception of cholinesterase activity which remained low. Follow-up examination at 2, 5 and 10 months revealed no abnormalities with no evidence of delayed neurotoxicity (Teitelman et al. 1975). A case of attempted suicide occurred in a 50-year old man weighing 67 kg who had ingested approximately 6.2 g or 40 ml of Supracid 20 (methidathion, 15.5% active ingredient). About 1.5 h after the incident, the subject was admitted to hospital suffering from mental confusion, muscle fasciculations, bradycardia, miosis, sweating, salivation and lacrimation. The patient underwent gastric lavage followed by treatment with atropine sulphate and pralidoxime. Six hours after ingestion of methidathion, the incidence of muscle fasciculations increased followed by bronchorrhea and coma. Serum and RBC cholinesterase values, as measured over eight days following poisoning were generally less than 50% of normal values. Cholinesterase values assessed after 45 days were normal. Lymphocytic NTE activity was normal as determined on days 5, 10, 17 and 45 after poisoning. The patient was discharged after 21 days of hospitalization. A follow-up examination after 7 months failed to establish any evidence of delayed polyneuropathy or other neurological abnormality (Zoppellari et al. 1990). COMMENTS Methidathion was extensively absorbed when administered orally to rats. The routes of elimination were via the urine and expired CO2. There were no significant differences in elimination patterns with regard to dose levels administered, pre-treatment or sex. In the rat, the predominant urinary metabolites were the sulfide, sulfoxide, sulfone and desmonomethyl derivative. Negligible quantities of the parent and oxygen analog were detected in the urine. The predominant metabolic pathway of methidathion in the goat was via O-demethylation with the desmonomethyl derivative as the principal urinary metabolite. Cysteine conjugates were identified in each species. Methidathion has a high acute oral toxicity. The World Health Organization has classified methidathion as highly hazardous (WHO, 1992). Methidathion was administered to dogs for 90 days at dietary concentrations of 0, 0.5, 4, 45 or 140 ppm, or 0.14 mg/kg bw/day (equal to 4 ppm) by capsule, and for a period of 12 months at 0, 0.5, 2, 4, 40, or 140 ppm in the diet. In both studies the dietary NOAEL was determined to be 4 ppm, equal to 0.16 mg/kg bw/day, based on liver effects, most notably cholestasis and increased liver enzymatic activity in serum at dietary levels of 40 ppm and above. Cholestasis was observed in a single male dog treated by capsule at 0.14 mg/kg bw/day. Erythrocyte and brain cholinesterase activities were affected only at the highest level of 140 ppm. Long-term dietary treatment of mice with methidathion for 23 months at 0, 3, 10, 50 or 100 ppm revealed an increased incidence of hepatocellular tumours in males at 50 ppm and above, resulting in a NOAEL of 10 ppm, equal to 1.4 mg/kg bw/day. Erythrocyte cholinesterase was inhibited at 50 ppm (equal to 7 mg/kg bw/day) and above, whereas brain cholinesterase activity was affected at 100 ppm (equal to 13.7 mg/kg bw/day). A 104-week long-term toxicity/carcinogenicity study in rats fed methidathion at 0, 4, 40 or 100 ppm indicated a NOAEL of 4 ppm, equal to 0.16 mg/kg bw/day, based on inhibition of erythrocyte and brain cholinesterase activity at 40 ppm and above. Methidathion was not carcinogenic in rats. In a two-generation reproduction study in rats at dietary concentrations of 0, 5, 25 or 50 ppm, the NOAEL was 5 ppm, equal to 0.43 mg/kg bw/day. At 25 ppm, reduced mating indices in the F1 generation and decreased progeny body weights were observed. There were no teratogenic effects observed when methidathion was administered by gavage to rats at doses of 0, 0.25, 1.0, or 2.5 mg/kg bw/day or to rabbits at doses of 0, 2, 6 or 12 mg/kg bw/day. Maternal effects were demonstrated at the highest doses in both the rat and rabbit as clinical signs of toxicity. In the rat, increased mortality as well as decreased body-weights and food consumption were also observed. The NOAELs in the rat and rabbit were determined to be 1 and 6 mg/kg bw/day, respectively. Treatment of hens with methidathion did not produce any clinical or pathological evidence of delayed neurotoxicity. In two reported cases of poisoning with methidathion, each of the male subjects exhibited classic clinical and biochemical signs of organophosphorus intoxication. Both subjects recovered, with no evidence of delayed neurotoxicity uncovered upon follow-up examination. In one of the cases jaundice was reported during the recovery period. Two human volunteer studies failed to reveal any inhibition of erythrocyte or serum cholinesterase activity at doses up to 0.11 mg/kg bw/day. After reviewing the available genotoxicity data, the Meeting concluded that methidathion was not genotoxic. In the dog, the effects on the liver appeared to have occurred at levels lower than the levels causing inhibition of cholinesterase activity, giving a NOAEL of 0.1 mg/kg bw/day. Whether or not there was a relationship to the potential induction of liver effects in man could not be ascertained. The Meeting concluded, after consideration of the hepatocellular tumours found in male mice in the long-term toxicity study, together with the lack of genotoxicity, that methidathion did not present a carcinogenic hazard for humans. The previous ADI, based on a NOAEL in man of 0.11 mg/kg bw/day, was revised. The revised ADI is based on the NOAEL in the dog and a 100-fold safety factor. TOXICOLOGICAL EVALUATION Level causing no toxicological effect Mouse: 10 ppm, equal to 1.4 mg/kg bw/day (23-month study) Rat 4 ppm, equal to 0.16 mg/kg bw/day (104-week study) 5 ppm, equal to 0.43 mg/kg bw/day (reproduction study) Dog: 0.1 mg/kg bw/day (90-day, one-year, and two-year studies) Human: 0.11 mg/kg bw/day. Estimate of acceptable daily intake for humans 0 - 0.001 mg/kg bw Studies which will provide information valuable in the continued evaluation of the compound Further observations in humans REFERENCES Aeppli, L. (1969a) Akute Toxizität, Ratte per os, A 2039 E (0 40 WP). Unveröffentlicht. Geigy, J.R. AG. Aeppli, L. (1969b) Akute Toxizität, Ratte per os, A 3628 E (0 40 WP). Unveröffentlicht. Geigy, J.R. AG. Aeppli, L. (1970a) Akute Toxizität, Ratte per os, A 3628 blaugefärbt. Unveröffentlicht. Geigy, J.R. AG. Aeppli, L. (1970b) Akute Toxizität, Ratte per os, A 3389 C (= 40 ES). Unveröffentlicht. Geigy, J.R. AG. Arai, M. (1981). In vivo short term study on the promoting activity of methidathion (CG-831) (translation). Unpublished report dated October 31, 1981 from Daiyu-Kai Ikagaku Kenkyu-Sho, Japan. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Arni, P. & Muller, D. (1980a). Salmonella/mammalian-microsome mutagenicity test with GS 13005 (Test for mutagenic properties in bacteria). Project No. 79/1556. Unpublished report dated April 17, 1980 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Arni, P. & Muller, D. (1980b). Salmonella/mammalian-microsome mutagenicity test with GS 13005 (Test for mutagenic properties in bacteria). Project No. 801488. Unpublished report dated October 29, 1980 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Arni, P. & Muller, D., 1980c. Intrasanguine host-mediated assay with S. typhimurium with GS 13005 (Test for the demonstration of point mutations in bacteria in vivo). Project No. 801494. Unpublished report dated October 31, 1980 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Arni, P. & Muller, D. (1981). Mutagenicity test on Saccharomyces cerevisiae MP-1 in vitro with GS 13005 (Test for mutagenic properties in yeast cells). Project No. 802030. Unpublished report dated November 5, 1981 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Bathe, R. (1973a). Acute oral LD50 of technical GS 13005 in the rat. Unpublished report dated May 25, 1973 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Bathe, R. (1973b). Acute dermal LD50 of technical GS 13005 in the rat. Project No. Siss 2929. Unpublished report dated October 3, 1973 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba- Geigy Ltd., Basle, Switzerland. Bathe, R. & Sachsse, K. (1975). Acute dermal LD50 in the rat of technical GS 13005. Project No. Siss 4650. Unpublished report dated September 15, 1975 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Bathe, R. & Sachsse, K. (1980a). Acute oral LD50 in the rat of technical GS 13005. Project No. 791668. Unpublished report dated January 9, 1980 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Bathe, R. & Sachsse, K. (1980b). Acute oral LD50 in the rat of technical GS 13005. Project No. 791667. Unpublished report dated January 10, 1980 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Cannelongo, B. (1984). Guinea pig skin sensitization. Supracide technical FL 830958. Project No. 3152-83. Unpublished report dated January 9, 1984 from Stillmeadow, Inc., Houston, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Chang J. and Walberg, J. (1991). One-year dietary study in Beagle dogs. Project No. F00028. Unpublished report dated June 24, 1991 from Ciba-Geigy Corporation, Framington, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Chang, J. & Wyand, S. (1990). 90-day oral toxicity study in Beagle dogs. Project No. F-00023. Unpublished report dated March 21, 1990 from Ciba-Geigy Corporation, Farmington, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Chen, H., Hsueh, J., Sirianni, S., & Huang, C. (1981). Induction of sister-chromatid exchanges and cell cycle delay in cultured mammalian cells treated with eight organophosphorus pesticides. Mutation Research, 88: 307-316. Coulston, F. (1970). Effects on man of small daily doses of GS13005. Unpublished report of Albany Medical College. Submitted to WHO in 1972 and cited in Annex I, 19. Daiyu-Kai Institute of Medical Science (1983). In vivo short-term study on dose-dependence and threshold level of promoting activity of GS13005 in the rat liver. Unpublished report received June 1983 from Daiyu-Kai Institute of Medical Science, Japan. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Fabran, J.E., Golberg, L. and Coulston, F. (1971). Two-year safety evaluation study of GS13005 on Rhesus monkey. Unpublished report of Albany Medical College. Submitted to WHO in 1972, and cited in Annex I, 19. Folinusz, P., Huber, K., Schiavo, D., Hazelette, J., & Green, J. (1986). Methidathion: 21-day dermal toxicity study in rabbits. Project No. 86019. Unpublished report dated August 28, 1986 from Ciba-Geigy Corporation, Summit, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Fritz, H. (1976). Dominant lethal study on GS 13005 technical, mouse (test for cytotoxic or mutagenic effects on male germinal cells). Project No. 327633. Unpublished report dated August 3, 1976, supplemented May 26, 1987, from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Goldenthal, E. (1986). Two-year dietary oncogenicity study in mice. Project No. 382-087. Unpublished report dated March 7, 1986 from International Research and Development Corporation, Mattawan, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Hertner, T. & Arni, P. (1990). Autoradiographic DNA repair test on rat hepatocytes. Project No. 891344. Unpublished report dated February 6, 1990 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Hess, R. (1975) Nature of the liver changes observed in a two-year feeding study in dogs. Unpublished report from the Toxicology/Pathology Dept., Ciba-Geigy. Submitted to WHO by Ciba- Geigy Ltd., Basle, Switzerland. Hool, G., Langauer, M., & Muller, D. (1980). Nucleus anomaly test in somatic interphase nuclei of Chinese hamster. Project No. 800437. Unpublished report dated July 2, 1980, supplemented May 26, 1987, from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba- Geigy Ltd., Basle, Switzerland. Hool, G. & Muller, D. (1980). Sister chromatid exchange study GS 13005 Chinese hamster (test for mutagenic effects of bone marrow cells). Project No. 801489. Unpublished report dated November 4, 1980, supplemented May 26, 1987, from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Hummel, H., Youreneff, M., Giknis, M., Arthur, A. & Yau, E., 1987. Methidathion: a teratology (segment II) study in rabbits. Project No. 86131. Unpublished report dated January 13, 1987 from Ciba-Geigy Corporation, Summit, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Johnston, C.D. (1965) GS 13 005. Demyelination study in the chicken. Report from Woodard Research Corp. (unpublished). Johnston, C.D. (1967). GS 13 005. safety evaluation by two-year feeding studies in rats and dogs. Final report from Woodard Research Corp. (unpublished). Lobdell, B.J. & Johnston, C.D. (1966). GS 13 005. Three-generation reproduction study in the rat. Report from Woodard Research Corp. (unpublished). Mainiero, J., Levy, E., Infurna, R., & Yau, E. (1987). Methidathion technical: a teratology (segment II) study in rats. Project No.: 86172. Unpublished report dated January 15, 1987 from Ciba-Geigy Corporation, Summit, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Marco, G. & Simoneaux, B. (1982). Dermal absorption of thiadiazole- 14C-methidathion by rats. Project No. ABR-81058. Unpublished report dated April 22, 1982 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Noakes, D.N. & Sanderson, D.M. (1964) The toxicology of GS 13 005 and GS12968. Species variation in acute oral tosicity. Report from Chesterford Park Research Station (unpublished). Noakes, D.N. (1964) The toxicology of GS 13 005 and GS 12968. Tests for delayed neurotoxic effects in the hen. Report from Chesterford Park Research Station (unpublished). Noakes, D.N. & Watson, W.A. (1964a) The toxicology of GS 13 005 and GS 12968. Dietary toxicity to the rat: 6-month study. Report from Chesterford Park Research Station (unpublished). Noakes, D.N. & Watson, W.A. (1964b) The toxicology of GS 12 968 (NC 2962) and GS 13 005 (NC 2964). Cumulative oral toxicity to the rat. Report from Chesterford Park Research Station (unpublished). Osheroff, M. (1987). 21-day dermal toxicity study in rabbits with methidathion technical. Project No. 483-254. Unpublished report dated January 15, 1987 from Hazleton Laboratories America, Inc., Vienna, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Payot, H.P., GS13005. Subchionische toxizitat am menschen (Einzel und Selbstversuch). Unveröffentlichter Berict der Geigy J.R., Ag. Submitted to WHO in 1972 and cited in Annex I, 19. Puri E. & Muller D. (1982a). Autoradiographic DNA repair test on rat hepatocytes GS 13005 ( in vitro test for DNA-damaging properties). Project No. 820585. Unpublished report dated October 19, 1982 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Puri E. & Muller D. (1982b). Autoradiographic DNA repair test on human fibroblasts GS 13005 ( in vitro test for DNA-damaging properties). Project No. 820586. Unpublished report dated October 18, 1982 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Quest, J., Copley, M., Hamernik, K., Rinde, E., Fisher, B., Engler, R., Burnam, W. & Fenner-Crisp, P. (1990). Evaluation of the carcinogenic potential of pesticides, 2. Methidathion. Regulatory Toxicology and Pharmacology, 12: 117-126. Sachsse, K. (1971) Acute oral LD50 of technical GS 13 005 in the dog. Report from Ciba-Geigy Ltd (unpublished). Sachsse, K. (1973a). Irritation of technical GS 13005 in the rabbit eye. Project No. Siss 2929. Unpublished report dated June 6, 1973 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba- Geigy Ltd., Basle, Switzerland. Sachsse, K. (1973b). Skin irritation in the rabbit after single application of technical GS 13005. Project No. Siss 2929. Unpublished report dated June 6, 1973 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Sachsse, K. & Bathe, R. (1977a). The therapeutic activity of atropine sulfate, pralidoxim (PAM) and toxogonin with regard to GS 13005 in the rat. Unpublished report dated December 5, 1977 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Sachsse, K. & Bathe, R. (1977b). Potentiation study: CGA 15324 versus 2 insecticides, GS 13005 (methidathion) and G 24480 (diazinon) in the rat. Unpublished report dated February 15, 1977 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba- Geigy Ltd., Basle, Switzerland. Sachsse, K. & Bathe, R., 1978. CGA 20168 versus 6 insecticides, C 177 (DDVP), C 570 (phosphamidon), GS 13005 (methidathion), G 24480 (diazinon), CGA 15324 and malathion. Project No. 404478-Siss 6526. Unpublished report dated June 23, 1978 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Salamon, C. (1987). Two-generation reproduction study in albino rats with methidathion technical. Project No. 450-2125. Unpublished report dated January 15, 1987 from American Biogenic Corporation, Decatur, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Sarasin G. (1980). Acute dermal LD50 in the rat of GS 13005 technical Rohschmelze (=crude melt) (Ex Monthey). Project No. 801726. Unpublished report dated December 17, 1980 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Satou, S., Kimura, Y., Yamamoto, K. & Ichihara, A. (1979). In vitro microbial assays for mutagenicity testing of DMTP (methidathion). Project No. NRI-79-2884. Unpublished report dated August 31, 1979 from Nomura Research Institute, Japan. Submitted to WHO by Ciba- Geigy Ltd., Basle, Switzerland. Simmon, V., Poole, D. Nevell, G., & Skinner, W. (1977). In vitro and in vivo microbiological assays of six Ciba-Geigy chemicals. Project No. LSC-5686. Unpublished report dated March 1977 from Stanford Research Institute, Menlo Park, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Simoneaux, B. & Marco, G. (1984). Dermal absorption of thiadiazole- 14C-methidathion by mice. Project No. ABR-84015. Unpublished report dated April 12, 1984 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Staley, J., Murphy, T., & Simoneaux, B. (1987). Metabolism of 14C (Carbonyl) labelled methidathion in a goat. Project No. ABR-86112. Unpublished report dated February 26, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Stenger, E.G. & Roulet, F. (1963) Subchronische Toxizität, Ratte per os, GS 13005 rein. Unveröffentlichter Bericht der Geigy, J.R. AG. Stenger, E.G. (1964a) Akute Toxizität, Ratte per os, GS 13005 40 WP. Unveröffentlichter Bericht der Geigy, J.R. AG. Stenger, E.G. (1964b) Akute Atoxizität, Ratte per os, GS 13005 40 ES. Unveröffentlichter Bericht der Geigy, J.R. AG. Stenger, E.G. & Roulet, F. (1965) Chronische Toxizität, Ratte, Fütterungsversuche 4-22- Wochen, GS 13 005. Unveröffenlichter Bericht der Geigy, J.R. AG. Stenger, E.G. (1966a) Akute Toxizität, Ratte per os, GS 13 005 40 WP. Unveröffentlichter Bericht der Geigy, J.R. AG. Stenger, E.G. (1966b) Akute Toxizität, Ratte per os, A 2041 C (= 40 ES). Unveröffentlichter Bericht der Geigy, J.R. AG. Staley, J. & Simoneaux, B. (1987). Metabolism of methidathion labelled with 14C on the ring carbon adjacent to the methoxy group in a goat. Project No. ABR-86118. Unpublished report dated March 2, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Strasser, F. & Arni, P. (1990). Chromosome studies on Chinese hamster ovary cell line CCL 61 in vitro. Project No. 891202. Unpublished report dated January 30, 1990 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Strasser, F. & Muller, D. (1980). Point mutation assay with mouse lymphoma cells, host mediated assay with GS 13005 (test for mutagenic properties in mammalian cells). Project No. 801495. Unpublished report dated October 21, 1980 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1985). Partitioning characteristics and 14C distribution in a chicken dosed with 2 -14C-methidathion for 16 days. Project No. ABR-85039. Unpublished report dated July 22, 1985 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987a). Disposition of methidathion in the rat. Project No.: ABR-86122. Unpublished report dated March 6, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987b). The disposition of radioactivity in rats dosed with carbonyl 14C-methidathion. Project No. ABR-86084. Unpublished report dated February 26, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987c). The disposition of radioactivity in rats dosed with methoxy labelled 14C- methidathion. Project No. ABR-86115. Unpublished report dated March 2, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987d). The disposition of radioactivity in rats dosed with 14C-methidathion labelled in the ring carbon adjacent to the methoxy group. Project No. ABR-86095. Unpublished report dated February 26, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987e). Characterization of carbonyl 14C-labelled methidathion metabolites in rat urine. Project No. ABR-86107. Unpublished report dated March 2, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987f). Characterization of methoxy 14C-labelled methidathion metabolites in rat urine. Project No. ABR-86116. Unpublished report dated February 26, 1987 from Ciba- Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987g). Characterization of 14C- methidathion metabolites in rat urine - label 14C adjacent to the methoxy group. Project No. ABR-86114. Unpublished report dated March 2, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Szolics, I. & Simoneaux, B. (1987h). Characterization of 14C- methidathion metabolites in goat urine. Project No. ABR-86113. Unpublished report dated March 3, 1987 from Ciba-Geigy Corporation, Greensboro, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Teitelman, U., Adler, M., Levy, I., & Dikstein, S. (1975). Treatment of massive poisoning by the organophosphate methidathion. Clinical Toxicology, 8(3), 277-282. Tong C. (1982a) The hepatocyte primary culture/DNA repair assay on compound GS 13005 - 008266 using mouse hepatocytes in culture. Project No. M 111881. Unpublished report dated February 10, 1982 from Naylor Dana Institute, Valhalla, USA. Submitted to WHO by Ciba- Geigy Ltd., Basle, Switzerland. Tong C. (1982b) The hepatocyte primary culture/DNA repair assay on compound GS 13005 - 008266 using rat hepatocytes in culture. Project No. M 111881. Unpublished report dated February 10, 1982 from Naylor Dana Institute, Valhalla, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Ullmann, L., Krinke, G., Sachsse, K. & Hess, R. (1977). Acute oral toxicity and neurotoxicity study of technical GS 13005 in the domestic fowl ( Gallus domesticus). Project No. Siss 5927. Unpublished report dated November 8, 1977 from Ciba-Geigy Ltd., Basle, Switzerland. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. 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. Yau, E., McMartin, D., Zaidi, I., & Green, J. (1986). Methidathion: 2-year oral oncogenicity and toxicity study in albino rats. Project No. 86061. Unpublished report dated May 23, 1986 from Ciba-Geigy Corporation, Summit, USA. Submitted to WHO by Ciba-Geigy Ltd., Basle, Switzerland. Zoppellari, R., Targa, L., Tonini, P., & Zatelli, R., 1990. Acute poisoning with methidathion: A case. Human & Experimental Toxicology, 9(6), 415-419.
See Also: Toxicological Abbreviations Methidathion (ICSC) Methidathion (WHO Pesticide Residues Series 2) Methidathion (WHO Pesticide Residues Series 5) Methidathion (Pesticide residues in food: 1979 evaluations) Methidathion (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental)