CLETHODIM First draft prepared by M. Caris, Bureau of Chemical Safety, Health Canada, Ottawa, Canada Explanation Evaluation for acceptable daily intake Biochemical aspects Absorption, distribution and excretion Biotransformation Toxicological studies Acute toxicity Short-term toxicity Long-term toxicity and carcinogenicity Reproductive toxicity Embryotoxicity and teratogenicity Genotoxicity Special studies Skin and eye irritation and skin sensitization Liver cytochrome induction Studies on metabolites Acute toxicity Short-term toxicity Embryotoxicity and teratogenicity Genotoxicity Observations in humans Comments Toxicological evaluation References Explanation Clethodim is a new, selective cyclohexanedione herbicide which is effective against a wide range of annual and perennial grasses and has little or no activity against broadleaf weeds and sedges. It exerts its activity by inhibiting acetyl coenzyme A carboxylase, an enzyme common to the pathways of biosynthesis of fatty acids and flavonoids. Interference occurs at the acetyl coenzyme A-malonyl coenzyme A transferase site (Rendina & Felts, 1988). Clethodim was considered for the first time by the WHO Expert Group at the 1994 Joint Meeting on Pesticide Residues. Evaluation for acceptable daily intake 1. Biochemical aspects (a) Absorption, distribution and excretion Male and female Crl:CD(SD)BR rats were given single oral doses of [propyl-1-14C]-clethodim at 4.4 or 468 mg/kg bw or unlabelled test material at 4.5 mg/kg bw per day for 14 consecutive days before treatment with a single radiolabelled dose of 4.8 mg/kg bw. Elimination was rapid: 94-98% of the administered dose was excreted within 48 h after treatment. The principal route of excretion was the urine (87-93%), and a smaller percentage (9-17%) of the radioactivity was eliminated in the faeces. The mean amount of radioactivity excreted in expired air as carbon dioxide represented 0.5-1% of the administered dose. Although the elimination patterns were similar in all groups, the rate of elimination was somewhat faster in animals that were administered the single low dose of 4.4 mg/kg bw (98% eliminated within 40 h) than in those given the single high dose of 468 mg/kg bw (98% within 50 h). No differences in elimination rate were seen for animals of either sex administered repeated low doses of clethodim. Seven days after treatment, the total amount of radiolabel recovered from organs and tissues was less than 1% of the administered dose. The highest residual tissue concentrations were found in the adrenals, kidney and liver. There were no significant dose-related or sex-specific differences in tissue distribution, when expressed as a proportion of the dose administered, and there was no evidence of bioaccumulation (Rose et al., 1988a). Groups of 8-10 white Leghorn laying hens were given [cyclohexene-4,6-14C]-clethodim at 0, 2.1 or 51.3 mg/kg bw per day for five consecutive days and were sacrificed about 4 h after the final treatment. Radioanalysis showed that 78% of the low dose and 85% of the high dose of administered radioactivity was excreted in the faeces; 1.9% of the low dose and 4.2% of the high dose were found in the tissues. The radiolabel was distributed in the tissues in the following order of decreasing concentration: gastrointestinal tract > kidney > liver. In eggs, 0.1% of the low dose and 0.3% of the high dose were found; the levels were highest in egg whites, intermediate in shells and lowest in yolks (Lee et al., 1988). A single lactating goat received [propyl-1-14C]-clethodim at 1.16 mg/kg bw per day in alfalfa diet, in three equal daily doses of 14.2 mg for three days and then a single dose of 14.2 mg on the fourth day, for a total of 10 doses. One female goat served as control. The treated goat was sacrificed 4 h after the final dose. Clethodim was rapidly absorbed: the peak blood radiocarbon concentration (0.273 ppm) was achieved within the first hour after the initial dose. The mean amount of radiolabel recovered in the urine represented 56% of the administered dose and that in the faeces, 34%. The total amount of radiolabel found in the milk, blood and tissues represented less than 1% of the amount administered. Milk contained only 0.14%; the peak concentration (0.035 ppm) was attained after the sixth dose. The tissues contained 0.37% and the blood, 0.22% of the dose. The highest residual tissue concentrations were detected in the liver and kidney (Rose et al., 1988b). (b) Biotransformation The proposed metabolic pathways for clethodim in rats are depicted in Figure 1. It is postulated that once clethodim has been absorbed it can be (i) oxidized to clethodim sulfoxide (dominant process), (ii) converted to the S-methyl via a sulfonium cation intermediate, (iii) cleaved at the oxime N-O bond to generate imine or (iv) hydroxylated at the 5 position. In the study described above in which male and female Crl:CD(SD)BR rats were given single oral doses of [propyl-1- 14C]-clethodim or unlabelled material (Rose et al., 1988a), a supplementary group of male rats were given a single oral dose of 450 mg/kg bw radiolabelled compound to ensure a sufficiently large quantity of labelled metabolites. Urine and faeces were collected and analysed for the parent compound and its metabolites. The metabolic profiles of males and females in all dose groups were remarkably similar. Nine urinary metabolites were identified and characterized. The major metabolite was clethodim sulfoxide (representing 65-75% of the administered dose), and smaller amounts were found of the imine sulfoxide (6-13%), the sulfone (1-3%), the 5-hydroxy sulfoxide/sulfone (0.5-1.5%) and the oxazole sulfone (0-5%). The primary faecal metabolites, which accounted for more than 1% of the radiolabel, were identified as clethodim sulfoxide and the imine sulfoxide. Minor (present as < 1% of the dose) urinary and faecal metabolites were the oxazole sulfoxide, the demethyl sulfoxide and the aromatic sulfone. Other minor faecal metabolites were clethodim sulfone, the trione sulfoxide and c-olefins. Parent clethodim accounted for about 1% of the administered dose (Rose et al., 1988a).Two groups of eight white Leghorn laying hens were given daily doses of [cyclohexene-4,6-14C]-clethodim at 2.1 or 51.3 mg/kg bw per day by capsule for five consecutive days. The hens were sacrificed about 4 h after the final dose, and tissues were collected for analysis. Two major metabolites, clethodim sulfone and clethodim sulfoxide, were identified in tissues and eggs. Clethodim sulfone accounted for up to 57% of tissue levels of radiolabel, whereas clethodim sulfoxide accounted for 10-31%. Clethodim sulfoxide was the principal metabolite in egg white (26-82%) and yolk (25-37%); parent clethodim was detected in significantly smaller amounts in both tissues and eggs. The proposed metabolic pathway in chickens was different from and considered to be simpler than that observed in rats and goats, since none of the imine, 5-hydroxy or S-methyl analogues was detected in chickens (Lee et al., 1988). In the study described above in which a lactating goat received [propyl-1-14C]-clethodim (Rose et al., 1988b), hind- and forequarter muscle, peritoneal and subcutaneous fat, liver, kidneys, heart and blood were collected to allow characterization of metabolites. The major urinary metabolite was clethodim sulfoxide, which accounted for 67% of the urinary radiocarbon. Other urinary radiolabelled components were identified as clethodim (3-27%) and the demethyl sulfoxide (12-18%), S-methyl (7-13%), imine sulfoxide (1.5-2.8%), sulfone (1.5-2.2%) and 5-hydroxy sulfoxide (0-3%). In the milk, about half of the radiocarbon could be extracted into organic solvents and occurred in clethodim, clethodim sulfoxide and clethodim demethyl sulfoxide; the other half of the radiocarbon was water soluble and was shown to be 14C-lactose. In blood and tissues, the maximal extractable radiocarbon residues accounted for 77-95% of the radiolabel and were identified as clethodim and the sulfoxide, demethyl sulfoxide, imine sulfoxide, sulfone and 5-hydroxy sulfone. The proposed metabolic pathway in goats was essentially the same as that proposed for rats (Rose et al., 1988b). 2. Toxicological studies (a) Acute toxicity Technical-grade clethodim has been tested for acute toxicity in mice, rats and rabbits. The results are summarized in Table 1. Clethodim was virtually non-toxic after oral or dermal administration to rabbits or after inhalation by rats. Slight to moderate toxicity was observed in mice and rats treated orally, with LD50 levels of 1360-2570 mg/kg bw. Clethodim administered intraperitoneally was moderately toxic to rats, with a combined LD50 for the two sexes of 1117 mg/kg bw. (b) Short-term toxicity Mice Groups of 10 male and 10 female Charles River CD-1 mice were fed diets containing technical-grade clethodim (purity, 83.3%) for four weeks at 100, 250, 625, 1500 or 4000 ppm, equivalent to 0, 15, 38, 94, 225 or 600 mg/kg bw per day. A slight anaemic process was manifested in male mice as a decreased erythrocyte count at > 1500 ppm, decreased haemoglobin at > 625 ppm and lowered haematocrit at 4000 ppm. Increased liver weights, which were correlated microscopically with centrilobular hypertrophy, were observed in males fed 1500 ppm and in animals of each sex treated at the highest dose of 4000 ppm. An increased incidence of focal coagulative necrosis of the liver was recorded in males treated at > 1500 ppm. Treatment appeared to have no effect on survival, clinical signs, body weight or food consumption. The NOAEL was 250 ppm, equivalent to 38 mg/kg bw per day, on the basis of the dose-related decrease in erythroid parameters at dietary levels > 625 ppm (Cox & Slabik, 1986). Rats Technical-grade clethodim (purity, 83.2%) was applied in carboxymethylcellulose and Tween 80 to the skin of groups of six male and six female Crl:CD BR rats at doses corresponding to 0, 10, 100 or 1000 mg/kg bw per day for 6 h/day, five days per week for four weeks, for a total of 21 exposures. A dose-related increase in the occurrence of skin irritation was observed at all dose levels. Clinical signs seen at 1000 mg/kg bw per day were described as anogenital discharge and staining of the fur, alopecia and red nasal discharge. At the highest dose, group mean body weights, corresponding weight gains and feed efficiency values were decreased in males, and increased liver weights were recorded in females. In males, a slight increase was observed in kidney regeneration, which was described as a minimal multifocal lesion. Although this finding was observed only in treated rats, evidence of chronic progressive nephropathy is not uncommon in this strain of rat and was not considered to represent a treatment-related effect. The NOAEL for systemic toxicity under the conditions of this study was thus 100 mg/kg bw per day (Cushman et al., 1987a). Table 1. Acute toxicity of technical-grade clethodim in male and female rodents Species, Route and vehicle LD50 Purity Reference strain (mg/kg bw) (%) Mouse, CD-1 Oral; M: 2570 83.3 Cox & Zoetis, 1986 Tween 80 + CMC F: 2430 (technical) Rat, Crl:CD Oral; M: 1630 83.3 Cushman et al., 1986d (SD)BR Tween 80 + CMC (technical) Rat, Crl:CD Intraperitoneal; M: 1040 NR Cox, 1988 (SD)BR Tween 80 + CMC F: 1200 Rat, Inhalation M&F: 83.3 Griffis et al., 1986 Sprague-Dawley > 3.9 mg/l (technical) Rabbit, New Oral; M: > 2000 and 82.5 Dougherty et al., 1989 Zealand Tween 80 + CMC < 5000 (technical) white F: > 5000 Rabbit, New Dermal M&F: > 5000 83.3 Cushman et al., 1987b Zealand (technical) white NR, not reported; Tween 80, 0.5% polyoxyethylenesorbitan monooleate; CMC, carboxymethylcellulose In a preliminary five-week study, groups of 10 male and 10 female Crl:CD(SD)BR rats were treated with technical-grade clethodim (purity, 83.4%) at dietary levels of 0, 5, 200, 1000, 4000 or 8000 ppm, equal to 0.3, 13, 66, 261 or 515 mg/kg bw per day for males and 0.3, 14, 71, 291 or 554 mg/kg bw per day for females. Treatment-related effects were decreased body-weight gain and food consumption (particularly during the first week of the study) in animals of each sex at 4000 and 8000 ppm; increased liver weights at > 4000 ppm; and slight to mild centrilobular hypertrophy in males at 1000 ppm and in animals of each sex at 4000 and 8000 ppm. Dose-related, statistically significant decreases in haemoglobin concentration were noted in males at > 1000 ppm and in haematocrit in males at > 4000 ppm. Raised cholesterol concentrations were recorded in males receiving 8000 ppm, and raised serum uric acid levels were seen in females given > 4000 ppm. Treatment had no effect on survival, clinical signs or urinary parameters. The NOAEL in this study was 200 ppm, equal to 13 mg/kg bw per day, on the basis of decreases in erythroid parameters and centrilobular hypertrophy of the liver at 1000 ppm and more (Cisson & Eisenlord, 1986). Technical-grade clethodim (purity, 84%) was administered to groups of 12 male and 12 female Crl:CD(SD)BR rats for 13 weeks at dietary levels of 0, 50, 500, 2500 or 5000 ppm, equal to 2, 25, 134 or 280 mg/kg bw per day for males and 3, 30, 160 or 340 mg/kg bw per day for females. In order to study the reversibility of potential treatment-related effects, an additional 12 rats of each sex were assigned to the groups receiving 0, 2500 and 5000 ppm and were kept for a six-week recovery period after the end of treatment with clethodim. Significantly decreased body weights and weight gains were recorded in males treated with 2500 ppm and in animals of each sex treated with 5000 ppm. Decreased mean food consumption was noted in both males and females at 5000 ppm. Significantly ( p < 0.05) increased concentrations of cholesterol, total protein and globulin recorded in males fed 5000 ppm were within the normal control range of variability. Increased liver weights and increased incidence and severity of centrilobular hypertrophy of the liver were noted in males and females fed 2500 and 5000 ppm. A slightly increased incidence of renal focal regeneration was seen in males treated at > 2500 ppm. The pathologist did not consider this finding to be related to treatment; rather, these lesions were regarded as typical of the earliest minimal stage of spontaneous chronic progressive nephropathy. Treatment did not affect survival, clinical signs, ophthalmoscopic or haematological parameters or the results of urinalysis. No treatment-related effects were seen after the six-week recovery period. The NOAEL was 500 ppm, equal to 25 mg/kg bw per day, as determined by an increased incidence of hepatic centrilobular hypertrophy and decreased body-weight gain in animals of each sex treated at 2500 ppm and above (Dougherty et al., 1987). Dogs Groups of four male and four female beagle dogs received gelatin capsules containing technical-grade clethodim (purity, 83.3%) orally at 0, 1, 25, 75 or 125 mg/kg bw per day for 13 weeks. Treatment affected blood chemistry in females, which had increased cholesterol levels at 75 mg/kg bw per day and above and increased alkaline phosphatase activity at 125 mg/kg bw per day. An increased globulin concentration, with a concomitant decrease in the albumin:globulin ratio, was noted in males treated at 125 mg/kg bw per day. Significantly ( p < 0.05) increased total leukocyte counts were seen in males and decreased activated partial thromboplastin time was seen in females after one month at 75 and 125 mg/kg bw per day. As no similar differences from control values were seen, however, after two or three months of treatment, and the only differences seen were in one sex, the significance of these findings is doubtful. Increased liver weights were recorded in males and females fed 75 or 125 mg/kg bw per day. Slight increases in the severity of cytoplasmic vesiculation and vacuolation of the centrilobular hepatocytes were seen in animals of each sex treated at 125 mg/kg bw per day. Treatment did not affect survival, clinical signs, ophthalmoscopic parameters, body weight or food consumption. The NOAEL was 25 mg/kg bw per day on the basis of elevated cholesterol levels and increased liver weights at 75 mg/kg bw per day and above (Daly & Knezevich, 1987). In a one-year study, groups of six male and six female beagle dogs were administered technical-grade clethodim (purity, 83.3%) in gelatin capsules at doses of 0, 1, 75 or 200-300 mg/kg bw per day. In the absence of any signs of overt toxicity, the high dose of 200 mg/kg bw per day was increased after seven weeks of treatment to 300 mg/kg bw per day. Significant effects on haematological parameters were seen, expressed as increased platelet and leukocyte counts in females at 75 mg/kg bw per day and in males and females at 300 mg/kg bw per day. At 300 mg/kg bw per day, erythroid parameters (erythrocyte, haemoglobin and haematocrit values) were decreased in animals of each sex, and reticulocyte and segmented neutrophil counts were increased in females. Treatment-related effects on blood chemistry were seen as increased levels of cholesterol, triglycerides, alkaline phosphatase and alanine aminotransferase in males and females at 300 mg/kg bw per day. Decreased serum glucose concentrations were noted in both males and females at the high dose and in females treated at 75 mg/kg bw per day. Increased liver weights were recorded in animals of each sex at 75 and 300 mg/kg bw per day. Significantly ( p < 0.05) increased thyroid weights seen in males at 300 mg/kg bw per day were not correlated with any microscopic changes. Histopathological alterations in animals of each sex treated at 300 mg/kg bw per day included hepatocellular enlargement, increased granular pigment (which was not associated with bile, iron or acid-fast lipofuscin) and slight hypercellularity of the bone marrow; the last finding was also observed in one male and one female at 75 mg/kg bw per day. The significance of a slightly increased incidence of pigment (not otherwise characterized) in the spleen of females receiving 75 or 300 mg/kg bw per day was uncertain. Treatment did not affect survival, clinical signs, ophthalmoscopic parameters, body weight, food consumption or the results of urinalysis. The NOAEL was 1 mg/kg bw per day on the basis of treatment-related effects on haematological and blood chemical parameters, increased liver weight and hypercellularity of the bone marrow at 75 mg/kg bw per day and above (Cox & Zoetis, 1988a). (c) Long-term toxicity and carcinogenicity Mice Technical-grade clethodim (purity, 83.3%) was administered in the diet to groups of 60 male and 60 female Crl:CD-1 (ICR)BR mice for 78 weeks at 0, 20, 200, 1000 or 2000-3000 ppm, equivalent to 3, 30, 150 or 300-450 mg/kg bw per day. The high dose was increased to 3000 ppm after 15 weeks of treatment, when haematological assessment did not show the significant decrease in erythrocyte parameters seen in the four-week preliminary study. Ten mice of each sex were sacrificed after 52 weeks of treatment in each group for interim assessment. A significant ( p < 0.05) trend to decreased survival was noted among males and females fed 3000 ppm, with survival at 78 weeks of 58, 66, 60, 52 and 32% males and 67, 84, 80, 59 and 48% females, respectively. The predominant cause of death at this dose was increased incidence and severity of systemic amyloidosis. Decreased erythrocyte counts were recorded in animals of each sex at 3000 ppm, with concomitant decreases in haemoglobin and haematocrit values in males. After 52 weeks of treatment, increased liver weights and centrilobular hypertrophy of the liver were observed in males at 1000 ppm and in males and females at 3000 ppm. Increased pigment, described as morphologically compatible with haemosiderin and bile, was noted in males at 3000 ppm. After 78 weeks of treatment, the hepatic changes included increased liver weights in females at 3000 ppm, centrilobular hypertrophy and increased pigment in both males and females at 1000 and 3000 ppm and bile-duct hyperplasia in males at > 1000 ppm. An increased incidence of multifocal, amphophilic alveolar lung macrophages was also observed in animals of each sex treated at > 1000 ppm. No significant effect was seen on body weight, food consumption or clinical signs. The NOAEL was 200 ppm, equivalent to 30 mg/kg bw per day, on the basis of hepatic changes, notably centrilobular hypertrophy, increased pigment and bile-duct hyperplasia, and an increased incidence of alveolar macrophages in the lungs of mice treated at 1000 ppm and above. There was no evidence that clethodim has carcinogenic potential (Cox & Zoetis, 1988b). Rats Groups of 65 male and 65 female Crl:CD (SD)BR rats were administered technical-grade clethodim (purity, 83%) in the diet at levels of 0, 5, 20, 500 or 2500 ppm, equal to 0.2, 0.6, 16 or 86 mg/kg bw per day for males and 0.2, 0.7, 21 or 110 mg/kg bw per day for females, for two years. Ten rats of each sex in each group were sacrificed after one year. After two years, 47, 49, 46, 50 and 33% of males and 55, 58, 51, 40 and 49% of females were still alive in the five dose groups, respectively. Treatment did not affect cause or time of death, clinical signs, ophthalmoscopic or haematological parameters or the results of clinical chemistry or urinalysis. Body-weight gain and food consumption were significantly decreased in animals of each sex during the first year of treatment with 2500 ppm. Food intake, calculated relative to body weight, was slightly greater in males and females at 2500 ppm than in the other treated groups. At interim sacrifice after one year, increased liver weights and slight to mild centrilobular hypertrophy were noted in rats of each sex fed 2500 ppm. Increased liver weights seen in females at 500 ppm were not correlated with any microscopically discernible change. At terminal sacrifice, liver weights of females at 2500 ppm were increased; males had no significant increase in liver weight, and no treatment-related centrilobular hypertrophy was seen in animals of either sex. Females treated at 2500 ppm had a slightly greater (12%) incidence of binucleated cells in the liver than the controls (2%), but the effect was of uncertain toxicological significance. Clethodim at dietary levels up to 3000 ppm showed no evidence of carcinogenic potential. The NOAEL was 500 ppm, equal to 16 mg/kg bw per day, on the basis of decreased body-weight gain, decreased food intake, increased liver weight and associated centrilobular hypertrophy at 2500 ppm (Dougherty et al., 1988a). (d) Reproductive toxicity Rats In a preliminary study, groups of eight male and eight female Crl:CD(SD)BR rats were fed technical-grade clethodim (purity, 83.3%) at dietary levels of 0, 500, 2000 or 5000 ppm, equivalent to 25, 100 or 250 mg/kg bw per day, for one week before and during mating. Males were sacrificed after mating, whereas females were treated throughout gestation and up to day 7 of the lactation period for a single litter. Parental animals of each sex that received 5000 ppm had decreased body-weight gain and food intake ( p < 0.05, only in males). Mean pup weights and corresponding weight gains were decreased at all dietary levels. No adverse effects on reproductive parameters were evident at the highest dose (McKensie, 1986). In a two-generation (one litter per generation) study, groups of 30 male and 30 female Crl:COBS CD(SD) rats were treated with technical-grade clethodim (purity, 83%) at dietary levels of 0, 5, 20, 500 or 2500 ppm, equal to 0.1, 1.4, 39 or 190 mg/kg bw per day for males and 0.2, 1.8, 45 or 220 mg/kg bw per day for females. Mean body weight was decreased at 2500 ppm in both males and females of the F1 generation and in males of the F0 generation. Occasional significant ( p < 0.05) decreases in food consumption were recorded in F1 males and females treated with 2500 ppm. Treatment had no effect on parental survival, clinical signs, organ weights or histopathological manifestations; there were no adverse effects on reproductive indices (mating, fertility, pregnancy and gestation); and there was no effect on litter size, sex ratio, pup weight or pup viability. A significant ( p < 0.05) increase in the number of stillborn pups was observed in the litters of F1 dams treated at 2500 ppm; however, this finding was not considered to be related to treatment, since the value was within the historical control range, and no similar increase was seen in the subsequent F2 litter. The NOAEL for parental systemic toxicity was 500 ppm, equal to 39 mg/kg bw per day, on the basis of decreased body weights and food consumption at 2500 ppm. The NOAEL for adverse effects on reproduction in the F0 and F1 generations was 2500 ppm, the highest dietary level tested, equal to 190 mg/kg bw per day (Tellone et al., 1987). (e) Embryotoxicity and teratogenicity Rats In a preliminary range-finding study, groups of 10 mated female Crl:CD(SD) rats were given technical-grade clethodim (purity, 82.6%) in Tween 80 and carboxymethylcellulose by gavage at 0, 50, 150, 300 or 500 mg/kg bw per day during days 6-15 of gestation. The day on which evidence of mating was observed was designated day 0 of gestation. Clinical signs of toxicity were an increased incidence of excessive salivation in females at 300 and 500 mg/kg bw per day, and slightly decreased body-weight gain, decreased mean number of uterine implantations and decreased mean fetal body weights at 500 mg/kg bw per day. External examination of the fetuses failed to reveal any gross findings related to treatment (Schroeder & Daly, 1986). Groups of 25 mated female Crl:CD(COBS) rats were treated with technical-grade clethodim (purity, 82.6%) in Tween 80 and carboxymethylcellulose daily by gavage at 0, 10, 100, 350 or 700 mg/kg bw per day during days 6-15 of gestation. The day on which evidence of mating was observed was designated day 0 of gestation. Treatment with clethodim at 350 mg/kg bw per day and more decreased maternal body weight. Toxicity was manifested at 700 mg/kg bw per day as increased mortality (20%), decreased food intake and clinical signs of poor physical condition, including red nasal discharge, chromodacryorrhoea and staining of the anogenital region. Excessive salivation was observed in females treated at 350 and 700 mg/kg bw per day. Significantly decreased fetal weights and increased incidences of fetuses with skeletal variations or at least one ossification variation were recorded at 350 mg/kg bw per day and more. The skeletal variations were apparent as definite delays in ossification and were identified by incompletely or unossified vertebral elements (thoracic, sacral, caudal) and unossified fifth and/or sixth sternebrae. Treatment at the highest dose, 700 mg/kg bw per day, induced a significant increase in the number of fetuses (8/221; 3.6%) and litters (6/18; 33.2%) with external malformations, comprising primarily an increased incidence (seven fetuses in six litters) of tail defects characterized by short, filamentous or absent tails. An imperforated anus was recorded in two fetuses in two litters at this dose. Visceral malformations (exencephaly, defects of the lung, aortic arch and large intestine, absence of kidneys, bladder or ureter) were observed in four fetuses in three litters of dams exposed to 700 mg/kg bw per day but not in concurrent or historical controls (5032 fetuses in 806 litters; 38 studies). Three of the four fetuses with visceral malformations also had external malformations. The NOAEL for maternal and developmental toxicity was 100 mg/kg bw per day. The NOAEL for teratogenicity was 350 mg/kg bw per day on the basis of an increased incidence of malformations, particularly tail defects, observed at the maternally toxic and lethal dose of 700 mg/kg bw per day (Schroeder & Daly, 1987). Rabbits In a range-finding study, groups of eight artificially inseminated female New Zealand white Hra: specific-pathogen-free rabbits were treated by gavage with clethodim (purity, 83.3%) in Tween 80 and carboxymethylcellulose at 0, 50, 150, 300 or 500 mg/kg bw per day on days 7-19 of gestation. The day of insemination was designated day 0 of gestation. Maternal toxicity was seen at all doses as decreased body-weight gain and food consumption. An increased incidence of alopecia was recorded at 150 mg/kg bw per day and more. Dried faeces and gastrointestinal lesions (hairball and/or ulceration of the gastric mucosa) were observed at doses of 300 mg/kg bw per day and more. In the groups given 300 and 500 mg/kg bw per day, two of seven pregnant rabbits died, apparently due to concomitant weight loss, decreased food intake, gastrointestinal lesions and/or abortion. In the group given 500 mg/kg bw per day, four of seven rabbits aborted, and one rabbit delivered prematurely. Data on litters of dams given 500 mg/kg bw per day could not effectively be evaluated, as only one female survived to term; dams given 300 mg/kg bw per day had an increased incidence of resorption and decreased litter weights when compared with the controls (Dearlove et al., 1986). Groups of 20 artificially inseminated female New Zealand white Hra specific-pathogen-free rabbits were administered technical-grade clethodim (purity, 83.3%) in Tween 80 and sodium carboxymethylcellulose by gavage at doses of 0, 25, 100 or 300 mg/kg bw per day on days 7-19 of gestation. The day of insemination was designated day 0 of gestation. Mean body weights, corresponding weight gains and food consumption were decreased in dams given 100 or 300 mg/kg bw per day. An increased incidence of dried faeces was also noted at 100 mg/kg bw per day and more; the presence of a red substance on the cage pans of the dams at 300 mg/kg bw per day was considered to be related to gastrointestinal and/or rectal irritation. Treatment had no adverse effect on survival, the abortion rate, pre- or post-implantation loss, the number of live fetuses, fetal weight or the fetal sex ratio. A slight increase in the incidence of minor skeletal alterations, comprising angulation of one or both hyoid alae, irregular ossification of the skull and nasal passages, was observed at 300 mg/kg bw per day; however, in the absence of a clear dose-response relationship, no direct correlation with treatment could be concluded. Clethodim was not teratogenic at doses up to 300 mg/kg bw per day. The NOAEL for maternal toxicity was 25 mg/kg bw per day, and that for developmental toxicity was 300 mg/kg bw per day (Dearlove et al., 1987). (f) Genotoxicity The results of assays for mutagenicity of technical-grade clethodim are presented in Table 2. The compound did not induce gene mutation in bacteria in vitro. Clethodim of unknown purity (Putnam, 1986a) induced chromosomal aberrations in Chinese hamster ovary cells in the absence of exogenous metabolic activation, but a purified preparation did not (Putnam, 1986b). Clethodim at doses sufficiently high to cause acute lethality did not induce micronuclei in bone-marrow cells of rats treated in vivo, and it did not induce unscheduled DNA synthesis in hepatocytes of mice treated in vivo. (g) Special studies (i) Skin and eye irritation and skin sensitization Technical-grade clethodim (purity, 83.2%) was applied at a dose of 0.5 ml under occluded conditions to two intact and two abraded sites on the shorn backs of each of 12 female New Zealand white rabbits for 4 h. Slight erythema, observed immediately after dosing, was followed 24-72 h later by slight-to-severe erythema and slight-to-moderate oedema. General clearance was seen by 14 days. The primary irritation score was 0.7. The test material was considered to be slightly irritating to rabbit skin (Cushman et al., 1986b). Undiluted technical-grade clethodim (purity, 83.3%) was instilled at a dose of 0.1 ml into the conjunctival sac of one eye of each of nine male New Zealand white rabbits, the other eye serving as a control. The eyes of three of the nine rabbits were rinsed after a 30-sec exposure. No corneal opacity or iritis was observed. In the six rabbits with unrinsed eyes, conjunctival irritation was moderate to severe 1 h after dosing and slight to moderate 24 h after dosing; all eyes were clear after 72 h. In the rinsed eyes, conjunctival irritation was moderate at 1 h and slight at 24 h; all eyes were clear at 48 h. The test material was considered to be mildly irritating to the rabbit eye (Cushman et al., 1986a). Table 2. Genotoxicity of technical-grade clethodim End-point Test system Concentration Purity (%) Resultsa Reference In vitro Reverse mutation S. typhimurium TA98, 0.1-10 mg/plate 83.3 Negativea Carver et al., 100, 1535, 1537 (technical) 1986b E. coli WP2 uvrA S. typhimurium TA98, 0.1-10 mg/plate 83.3 Negativea Carver et al., 100, 1535, 1537 (technical) 1986a Reverse mutation S. typhimurium TA98, 0, 0.1, 0.33, 1.0, 91.1 Negativea Machado et al., 100, 1535, 1537 3.33, 10 mg/plate (technical) 1990 E. coli WP2 uvrA Chromosomal Chinese hamster 0.03, 0.1, 0.3, 1.0 µl/ml NR Negativeb Putnam, 1986a aberration ovary CHO-K1 0.6, 0.8, 1.0, 1.2 µl/ml Positivec at CCI 61 cells 1.0, 1.2 µl/ml Chromosomal Chinese hamster 0.03, 0.1, 0.3, 1.0 µl/ml 96.1 Negativea Putnam, 1986b aberration ovary CHO-K1 0.6, 0.8, 1.0, 1.2 µl/ml (purified) CCI 61 cells In vivo Chromosomal Male and female 0, 150, 500, 1500 83.3 Negative Putnam, 1987 aberration Sprague- mg/kg bw, (technical) Dawley rats single oral dose Unscheduled Male B6C3F1 0, 100, 1000, 5000 83.3 Negative Mirsalis & DNA synthesis mice mg/kg bw, gavage (technical) Steinmetz, 1986 NR, not reported a In the presence and absence of metabolic activation b In the presence of metabolic activation c In the absence of metabolic activation Technical-grade clethodim (purity, 83.4%) did not appear to sensitize the skin of male Hartley albino guinea-pigs when tested by the modified Buehler test (Cushman et al., 1986c). (ii) Liver cytochrome induction Groups of eight male Crl:CD BR rats were treated by gavage with technical-grade clethodim (purity, 83.8%) in carboxymethylcellulose and Tween 80 at 0 or 250 mg/kg bw per day for 21 consecutive days. Liver samples taken at sacrifice were assayed for cytochrome P450 activity. Treatment did not affect survival, clinical signs or body weight. The weights of the livers of animals of each sex were significantly increased (20-23%), and enlarged livers were observed upon gross examination of two treated animals. Although the mean cytochrome P450 and hepatic protein contents were significantly greater in treated animals than controls, the mean concentrations of hepatic cytochrome P450 per milligram of protein or per gram of liver were not significantly increased. These results may reflect increased liver weight and do not provide evidence that clethodim induces liver cytochrome P450 (Beatty et al., 1989). 3. Studies on metabolites The imine sulfone and the 5-hydroxy sulfone of clethodim occurred in larger amounts in plants than in rats (Rose et al., 1988a). Ancillary studies on these metabolites are summarized in Table 3. (a) Acute toxicity Five female Crl:CD(SD)BR rats were given a single oral dose of 1.4 g/kg bw of the imine sulfone of clethodim. One animal had decreased motor activity 4 h after dosing and was dead the next day (Dougherty et al., 1988b). Groups of five female Crl:CD (SD)BR rats received the 5-hydroxy sulfone of clethodim or technical-grade clethodim as a single oral dose of 1.4 g/kg bw. There were no clinical signs of toxicity, and all animals treated with the 5-hydroxy sulfone survived the 14-day observation period after dosing. All five rats treated with clethodim showed overt signs of toxicity, noted as salivation, decreased motor activity, collapse, hyperactivity, tremors, diarrhoea, dehydration and nasal, ocular, oral and anogenital discharge, and all died within three days of dosing (Dougherty et al., 1988c). (b) Short-term toxicity The imine sulfone of clethodim was administered daily in the diet to groups of 10 male and 10 female Crl:CD (SD)BR rats at 0, 100, 1000 or 8000 ppm, equal to 6.7, 71 or 600 mg/kg bw per day, for five weeks. Body weight and food consumption were significantly decreased during the first week of treatment in males given 8000 ppm. Other effects observed only at 8000 ppm were increased serum cholesterol levels in animals of each sex, increased reticulocyte counts in males and increased liver weights in males and females in the absence of related histopathological alterations. Treatment did not affect survival, clinical signs or ophthalmoscopic parameters. The NOAEL was 1000 ppm, equal to 71 mg/kg bw per day (Beatty et al., 1988a). Groups of 10 male and 10 female Crl:CD (SD)BR rats were fed the 5-hydroxy sulfone of clethodim daily at dietary concentrations of 0, 100, 1000 or 8000 ppm, equal to 5.9, 68 or 590 mg/kg bw per day, for five weeks. No signs of toxicity were seen at any dose. On the basis of the absence of any effects on survival, clinical signs, body weight, food consumption, haematological, blood chemical or histopathological changes, or organ weights, the NOAEL was greater than 8000 ppm, equal to 590 mg/kg bw per day (Beatty et al., 1988b). Table 3. Effects of clethodim and its imine sulfone and 5-hydroxy sulfone Study Clethodim Imine sulfone 5-Hydroxy sulfone Acute toxicity; 3/5 deaths (Cushman et al., 1986d) 1/5 deaths 0/5 deaths female rat; 5/5 deaths (Dougherty et al., 1988c) (Dougherty et al., 1988b) (Dougherty et al., 1.4 g/kg bw 1988bc) Five-week dietary; Decreased body weight and Decreased body weight and No treatment-related male & female rats food intake, slight anaemia, food intake, increased effects; NOAEL, increased liver weights, liver weights, cholesterol > 588mg/kg bw per day liver hypertrophy at 4000 and and reticulocytes at 8000 (Beatty et al., 1988b) 8000 ppm; anaemia, liver ppm. NOAEL, 71 mg/kg bw per hypertrophy at 1000 ppm day (Beatty et al., 1988a) NOAEL, 13 mg/kg bw per day (Cisson & Eisenlord, 1986) Teratogenicity; rats Maternal and fetal toxicity Maternal toxicity at 100 Clinical signs and at 350 and 700 mg/kg bw per and 700 mg/kg bw per day; slightly decreased day; NOAEL, 100 mg/kg bw fetal effects at 700 mg/kg fetal body weights at per day. Increased incidence bw per day 700 mg/kg bw per day of tail malformations at NOAEL, 10 mg/kg bw NOAEL, 100 mg/kg 700 mg/kg bw per day per day (Hoberman & per day (Hoberman & (Schroeder & Daly, 1987) Christian, 1988a) Christian, 1988b) Microbial gene Negative Negative Negative mutation (Carver et al., 1986a,b) (Carver et al., 1988) (Carver eta[., 1987) Chromosomal Positive in absence of Negative Negative aberration, metabolic activation (Putnam, 1988a) (Putnam, 1988b) CHO cells (Putnam, 1986a) (c) Embryotoxicity and teratogenicity Groups of 10 pregnant female Crl:CD (SD)BR rats were treated by gavage with the imine sulfone of clethodim in Tween 80 and carboxymethylcellulose at doses of 0, 10, 100 or 700 mg/kg bw per day during days 6-15 of gestation. Maternal toxicity was seen at the high dose of 700 mg/kg bw per day, manifested as excessive salivation and decreased body weight and food consumption. Significant decreases in maternal body weight were also recorded at 100 mg/kg bw per day. At 700 mg/kg bw per day, fetal weights were decreased, and there were increased incidences of fetuses and litters with cervical ribs and delayed sternal ossification. The NOAEL for maternal toxicity was 10 mg/kg bw per day on the basis of reduced body weights at 100 mg/kg bw per day and more. An increased incidence of fetal variations at the maternally toxic dose of 700 mg/kg bw per day resulted in an NOAEL of 100 mg/kg bw per day for developmental toxicity (Hoberman & Christian, 1988a). Groups of 10 pregnant female Crl:CD (SD)BR rats were administered the 5-hydroxy sulfone of clethodim in carboxymethylcellulose and Tween 80 by gavage at 0, 10, 100 or 700 mg/kg bw per day on days 6-15 of gestation. At 700 mg/kg bw per day, one female showed excessive salivation and two females had rales; a slight decrease in fetal body weights in this group, although not statistically significant, was possibly related to treatment. No teratogenicity was seen at any dose. The NOAEL for maternal and fetal toxicity was 100 mg/kg bw per day (Hoberman & Christian, 1988b). (d) Genotoxicity Neither the imine sulfone nor the 5-hydroxy sulfone of clethodim induced gene mutation in Salmonella typhimurium TA98, TA100, TA1535 or TA1537 or in Escherichia coli WP2 uvrA in the presence or absence of metabolic activation. Neither metabolite induced chromosomal aberrations in Chinese hamster ovary cells. 4. Observations in humans No information was available. Comments Clethodim was readily absorbed by rats after oral administration. Excretion was rapid and occurred predominantly via the urine, with lesser amounts eliminated in the faeces and as carbon dioxide. There were no significant dose-related or sex-specific differences in elimination pattern or tissue distribution, and there was no evidence of bioaccumulation. The dominant metabolic pathway proposed for clethodim in rats is oxidation to clethodim sulfoxide. Other postulated pathways are cleavage of the N-O bond to form the imine, conversion of the S-ethyl group to S-methyl, formation of the oxazole, and hydroxylation at the 5 position. The urinary metabolites identified were the sulfoxides and sulfones of clethodim and 5-hydroxy clethodim, the sulfoxides of the imine and S-methyl clethodim and the sulfone of the oxazole. Clethodim had slight to moderate acute oral toxicity in the rat and mouse. WHO has not classified clethodim with regard to toxic hazard. The primary effect of treatment with clethodim after short- and long-term dietary exposure in the mouse, rat and dog was on the liver. Hepatic effects were manifest as increased liver weights and centrilobular hypertrophy. A study in rats administered clethodim at 250 mg/kg bw per day did not provide evidence for liver cytochrome P450 induction. In a four-week study in mice given dietary concentrations of 0, 100, 250, 625, 1500 or 4000 ppm, the NOAEL was 250 ppm, equivalent to 38 mg/kg bw per day on the basis of evidence of slight anaemia at 625 ppm and above. In a 78-week study of toxicity and carcinogenicity in which mice received dietary levels of 0, 20, 200, 1000 or 2000-3000 ppm, the NOAEL was 200 ppm, equivalent to 30 mg/kg bw per day, on the basis of hepatic effects and an increased incidence of alveolar lung macrophages at 1000 ppm and above. In a five-week study in which rats received dietary levels of 0, 5, 200, 1000, 4000 or 8000 ppm, the NOAEL was 200 ppm, equal to 13 mg/kg bw per day, on the basis of liver hypertrophy and evidence of slight anaemia at 1000 ppm and above. A 13-week study at dietary concentrations of 0, 50, 500, 2500 or 5000 ppm and a two-year feeding study at dietary levels of 0, 5, 20, 500 or 2500 ppm in rats revealed an NOAEL of 500 ppm, equal to 25 mg/kg bw per day in the first study and equal to 16 mg/kg bw per day in the second. The NOAEL was based on decreased body weights and liver hypertrophy at dietary levels of 2500 ppm and above. In dogs, 13-week oral administration of capsules of clethodim at doses of 0, 1, 25, 75 or 125 mg/kg bw per day resulted in an NOAEL of 25 mg/kg bw per day, on the basis of increased liver weight and cholesterol levels at 75 mg/kg bw per day and above. In a one-year study at doses of 0, 1, 75 or 200-300 mg/kg bw per day, the NOAEL was 1 mg/kg bw per day on the basis of treatment-related effects on the liver at 75 mg/kg bw per day and above. Clethodim was not carcinogenic when fed to mice or rats at dietary levels of up to 2500 ppm. A two-generation study of reproductive toxicity in rats treated with clethodim at dietary levels of 0, 5, 20, 500 or 2500 ppm did not reveal any adverse effects on reproduction. The NOAEL was 500 ppm, equal to 39 mg/kg bw per day, on the basis of decreased parental body weights and food consumption at 2500 ppm. Studies of teratogenicity were conducted with clethodim in rats at doses of 0, 10, 100, 350 or 700 mg/kg bw per day and in rabbits at 0, 25, 100 or 300 mg/kg bw per day. In rats, the NOAEL for maternal toxicity was 100 mg/kg bw per day. Fetal toxicity was observed at the maternally toxic doses of 350 and 700 mg/kg bw per day. An increased incidence of malformations, specifically tail defects (short, filamentous or absent tails), was observed at the maternally toxic and lethal high dose of 700 mg/kg bw per day. In rabbits, maternal toxicity was observed at 100 and 300 mg/kg bw per day, resulting in an NOAEL of 25 mg/kg bw per day. There were no adverse effects on the rabbit fetus and no evidence of teratogenic potential at doses up to 300 mg/kg bw per day. Clethodim was adequately tested for genotoxicity in a series of assays in vivo and in vitro. The Meeting concluded that clethodim was not genotoxic. Although the imine sulfone and 5-hydroxy sulfone metabolites of clethodim have been reported to occur in higher amounts in plants than in animals, neither of the metabolites was more toxic than the parent, clethodim, in studies of acute or short-term toxicity and teratogenicity. There was similarly no evidence of genotoxic potential. An ADI was established on the basis of the NOAEL of 1 mg/kg bw per day from the one-year study in dogs and a safety factor of 100. Toxicological evaluation Levels that cause no toxic effect Mouse: 200 ppm, equivalent to 30 mg/kg bw per day (78-week study of toxicity and carcinogenicity) Rat: 500 ppm, equal to 16 mg/kg bw per day (two-year study of toxicity and carcinogenicity) Rabbit: 25 mg/kg bw per day (study of teratogenicity) Dog: 1 mg/kg bw per day (one-year study of toxicity) Estimate of acceptable daily intake for humans 0-0.01 mg/kg bw Studies that would provide information useful for continued evaluation of the compound Observations in humans References Beatty, P.W., Bagos, A.D., Richter, W.R. & Wong, Z.A. (1988a) Five-week oral toxicity study in rats with RE-47719 (SX-1800). Project No. 2949. Unpublished report dated 15 November 1988 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Beatty, P.W., Bagos, A.C., Richter, W.R. & Wong, Z.A. (1988b) Five-week oral toxicity study in rats with RE-51228 (SX-1803). Project No. 2950. Unpublished report dated 15 November 1988 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Beatty, P.W., Brorby, G.P. & Wong, Z.A. (1989) The potential of RE-45601 Technical (SX-1688) to induce cytochrome P-450 following 21-day oral administration in male rats. Project No. 2784. Unpublished report dated 16 November 1989 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Carver, J.H., Machado, M.L. & Richter, W.R. (1986a) Microbial/mammalian microsome mutagenicity plate incorporation assay with RE-45601 Technical (83% purity, SC-1688). Project No. SOCAL 2505. Unpublished report dated 13 January 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Carver, J.H., Machado, M.L. & Richter, W.R. (1986b) Microbial/mammalian microsome mutagenicity plate incorporation assay with RE-45601 Technical (83% purity, SC-1688). Project No. CEHC 2555. Unpublished report dated 28 April 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Carver, J.H., Machado, M.L. & Richter, W.R. (1987) Microbial/mammalian microsome mutagenicity plate incorporation assay with RE-51228. Project No. 2856. Unpublished report dated 7 December 1987 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Carver, J.H., Machado, M.L. & Richter, W.R. (1988) Microbial/mammalian microsome mutagenicity plate incorporation assay with RE-47719. Project No. 2948. Unpublished report dated 19 October 1988 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cisson, C.M. & Eisenlord, G.H. (1986) Five-week pilot feeding study in rats with RE-45601 Technical (SX-1653). Project No. SOCAL 2457. Unpublished report dated 7 October 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cox, R.H. (1988) Acute intraperitoneal toxicity study in rats with Chevron RE-45601 Technical (SX-1688). Project No. 2107-151. Unpublished revised report dated 6 April 1988 from Hazelton Laboratories America Inc., Vienna, VA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cox, R.H. & Slabik, C.M. (1986) Four-week subchronic oral toxicity study in mice with Chevron RE-45601 Technical. Project No. 2107-140. Unpublished report dated 21 July 1986 from Hazelton Laboratories America Inc., Vienna, VA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cox, R.H. & Zoetis, T. (1986) Acute oral toxicity study in mice with Chevron RE-45601 Technical. Project No. 2107-143. Unpublished report dated 16 September 1986 from Hazelton Laboratories America Inc., Vienna, VA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cox, R.H. & Zoetis, T. (1988b) One-year oral toxicity study in dogs with Chevron RE-45601 Technical (SX-1688). Project No. 2107-153. Unpublished report dated 28 October 1988 from Hazelton Laboratories America Inc., Vienna, VA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cox, R.H. & Zoetis, T. (1988b) Chronic oral oncogenicity study in mice with Chevron RE-45601 Technical (SX-1688). Project No. 2107-145. Unpublished report dated 25 October 1988 from Hazelton Laboratories America Inc., Vienna, VA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cushman, J.R., Thompson, J.D. & Wong, Z.A. (1986a) The acute eye irritation potential of RE-45601 Technical (SX-1688). Project No. CEHC 2511. Unpublished report dated 1 October 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cushman, J.R., Korenaga, G.L. & Wong, Z.A. (1986b) The four-hour skin irritation potential of RE-45601 Technical (SX-1688). Project No. CEHC 2512. Unpublished report dated 18 December 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cushman, J.R., Cooper, P.N. & Wong, Z.A. (1986c) Modified Buehler Test for the skin sensitization potential of RE-45601 Technical (SX-1688). Project No. CEHC 2514. Unpublished report dated 15 December 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cushman, J.R., Easter, M.D. & Wong, Z.A. (1986d) The acute oral toxicity of RE-45601 Technical (SX-1688) in adult male and female rats. Project No. SOCAL 2498. Unpublished report dated 27 June 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cushman, J.R., Hedgecock, J.H. & Wong, Z.A. (1987a) Four-week repeated dose dermal toxicity study in rats with RE-45601 Technical (SX-1688). Project No. CEHC 2552. Unpublished report dated 20 November 1987 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Cushman, J.R., Korenaga, G.L. & Wong, Z.A. (1987b) The acute dermal toxicity of RE-45601 Technical (SX-1688) in adult male and female rabbits. Project No. CEHC 2510. Unpublished report dated 7 January 1987 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Daly, I.W. & Knezevich, A.L. (1987) Ninety-day subchronic oral toxicity study in dogs with Chevron RE-45601 Technical. Project No. 85-2999. Unpublished report dated 26 February 1987 from Bio/dynamics Inc., East Millstone, NJ, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Dearlove, G.E., Hoberman, A.M. & Christian, M.S. (1986) Pilot teratology study in rabbits with Chevron RE-45601 Technical. Project No. 303-007P. Unpublished report dated 15 July 1986 from Argus Research Laboratories Inc., Horsham, PA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Dearlove, G.E., Hoberman, A.M. & Christian, M.S. (1987) Teratology study in rabbits with Chevron RE-45601 Technical. Project No. 303-007. Unpublished report dated 30 January 1987 from Argus Research Laboratories Inc., Horsham, PA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Dougherty, K.K., Eisenlord, G.H., Low, S.S. & Wong, Z.A. (1987) 13-Week oral toxicity study in rats with RE-45601 Technical (SX-1688). Project No. SOCAL 2501. Unpublished report dated 13 February 1987 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Dougherty, K.K., Eisenlord, G.H. & Wong, Z.A. (1988a) Combined chronic toxicity/oncogenicity study in rats with RE-45601 Technical (SX-1688). Project No. SOCAL 2500. Unpublished report dated 1 November 1988 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Dougherty, K.K., Duncan, R.A. & Wong, Z.A. (1988b) The comparative acute oral toxicity of RE-47719 (SX-1800) and RE-45601 (SX-1688) in adult female rats. Project No. 2952. Unpublished report dated 21 October 1988 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Dougherty, K.K., Duncan, R.A. & Wong, Z.A. (1988c) The comparative acute oral toxicity of RE-51228 (SX-1796) and RE-45601 (SX-1688) in adult female rats. Project No. 2951. Unpublished report dated 21 October 1988 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Dougherty, K.K., Waid, L.J. & Wong, Z.A. (1989) The acute oral toxicity of RE-45601 Technical (SX-1688) in adult male and female rabbits. Project No. CEHC 2992. Unpublished report dated 21 June 1989 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Griffis, L.C., Bruce, E.D. & Wong, Z.A. (1986) The acute inhalation toxicity of RE-45601 Technical (SX-1688) in rats. Project No. CEHC 2513. Unpublished report dated 7 November 1986 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Hoberman, A.M. & Christian, M.S. (1988a) Oral teratogenicity and developmental toxicity screen in rats with RE-47719. Project No. 303-012. Unpublished report dated 8 November 1988 from Argus Research Laboratories Inc., Horsham, PA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Hoberman, A.M. & Christian, M.S. (1988b) Oral teratogenicity and developmental toxicity screen in rats with RE-51228. Project No. 303-010. Unpublished report dated 8 November 1988 from Argus Research Laboratories Inc., Horsham, PA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Lee, S.G., Maier, K.M., Tamichi, E.H. & Tucker, B.V. (1988) [Ring-4,6-14C] clethodim: A radiocarbon metabolism study in laying hens. Project No. MEF-0089. Unpublished report dated 30 December 1988 from Chevron Chemical Company, Ortho Agricultural Chemicals Division, Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Machado, M.L., Lubeck, S.G. & Wilkenfeld, R.M. (1990) Microbial/microsome reverse mutation plate incorporation assay with RE-45601 Technical (SX-1845). Project No. CEHC 3146. Unpublished report dated 20 August 1990 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. McKensie, K.M. (1986) Pilot rat reproduction study with Chevron RE-45601 Technical. Project No. 6183-102. Unpublished report dated 16 December 1986 from Hazelton Laboratories America Inc., Madison, WI, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Mirsalis, J.C. & Steinmetz, K.L. (1986) In vivo--in vitro hepatocyte DNA repair assay: in vitro evaluation of unscheduled DNA synthesis (UDS) following oral administration of Chevron RE-45601 Technical to B6C3F1 Mice. Project No. LSC-1960. Unpublished report dated August 1986 from SRI International, Meno Park, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Putnam, D.L. (1986a) Chromosome aberrations in Chinese hamster ovary (CHO) cells with Chevron RE-45601 Technical. Project No. T4529.337. Unpublished report dated August 1986 from Microbiological Associates Inc., Bethesda, MD, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Putnam, D.L. (1986b) Chromosome aberrations in Chinese hamster ovary (CHO) cells with purified Chevron RE-45601. Project No. T429.337. Unpublished report dated 15 December 1986 from Microbiological Associates Inc., Bethesda, MD, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Putnam, D.L. (1987) Cytogenetics assay in bone marrow cells of rats following acute oral exposure to RE-45601 Technical. Project No. T5172.105. Unpublished report dated 25 February 1987 from Microbiological Associates Inc., Bethesda, MD, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Putnam, D.L. (1988a) Chromosome aberrations in Chinese hamster ovary (CHO) cells: RE-47719. Project No. T8226.337003. Unpublished report dated 10 November 1988 from Microbiological Associates Inc., Bethesda, MD, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Putnam, D.L. (1988b) Chromosome aberrations in Chinese hamster ovary (CHO) cells: RE-51228. Project No. T8227.337003. Unpublished report dated 10 November 1988 from Microbiological Associates Inc., Bethesda, MD, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Rendina, A.R. & Felts, J.M. (1988) Cyclohexanedione herbicides are selective and potent inhibitors of acetyl-CoA carboxylase from grasses. Plant Physiol., 86, 983-986. Rose, A.F., Griffis, L.C., Suzuki, J.P., Bruce, E.D., Primer, R.L., Wong, Z.A. & Tucker, B.V. (1988a) The in vivo metabolism of [propyl-1-14C] clethodim in rats. Project No. MEF-0086/CEHC 2515. Unpublished report dated 22 December 1988 from Chevron Chemical Co., Ortho Agricultural Chemicals Division, Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Rose, A.F., Suzuki, J.P., Primer, R.L. & Tucker, B.V. (1988b) The in vivo metabolism of [propyl-1-14C] clethodim in a lactating goat. Project No. MEF-0038. Unpublished report dated 29 December 1988 from Chevron Chemical Co., Ortho Agricultural Chemicals Division, Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Schroeder, R.E. & Daly, I.W. (1986) A pilot teratology study in rats with Chevron RE-45601 Technical. Project No. 85-3032. Unpublished report dated 8 September 1986 from Bio/dynamics Inc., East Millstone, NJ, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Schroeder, R.E. & Daly, I.W. (1987) Teratology study in rats with Chevron RE-45601 Technical. Project No. 86-3042. Unpublished report dated 20 July 1987 from Bio/dynamics Inc., East Millstone, NJ, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA. Tellone, C.I., Hardy, L.M. & Richter, W.R. (1987) Two-generation (one litter) reproduction study in rats with RE-45601 Technical. Project No. CEHC 2596. Unpublished report dated 27 August 1987 from Chevron Environmental Health Center Inc., Richmond, CA, USA. Submitted to WHO by Tomen Pacific Agro Co., San Francisco, CA, USA.
See Also: Toxicological Abbreviations