INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY WORLD HEALTH ORGANIZATION TOXICOLOGICAL EVALUATION OF CERTAIN VETERINARY DRUG RESIDUES IN FOOD WHO FOOD ADDITIVES SERIES 45 Prepared by the Fifty-fourth meeting of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) World Health Organization, Geneva, 2000 DICYCLANIL First draft prepared by M.E.J. Pronk and G.J. Schefferlie Centre for Substances and Risk Assessment, National Institute of Public Health and the Environment, Bilthoven, The Netherlands Explanation Biological data Biochemical aspects Absorption, distribution, and excretion Biotransformation Toxicological studies Acute toxicity Short-term studies of toxicity Long-term studies of toxicity and carcinogenicity Genotoxicity Reproductive toxicity Multigeneration studies Developmental toxicity Special studies: Pharmacological effects Comments Evaluation References 1. EXPLANATION Dicyclanil is a pyrimidine-derived regulator of insect growth used for topical treatment of sheep to prevent larval infestation by the blowfly (Lucilia cuprina). It is used as a pour-on formulation containing 5% (w/v) of the drug. Data were provided on the use of dicyclanil applied as a pour-on formulation to sheep at a maximum dose of 0.1 g/kg bw. Dicyclanil has not previously been evaluated by the Committee. The chemical name of dicyclanil (CAS No. 112636-83-6) is 4,6-diamino-2-cyclopropylamino-pyrimidine-5-carbonitrile. The purity of the technical-grade material used in the pivotal studies of toxicity and pharmacology was 94.3%, unless otherwise stated. 2. BIOLOGICAL DATA 2.1 Biochemical aspects 2.1.1 Absorption, distribution, and excretion Five groups of three male Han Wistar rats received a single dose of 50 mg/kg bw technical-grade dicyclanil in polyethylene glycol 200:ethanol (5:3 v/v) by oral gavage. Blood samples were taken from one group each at 2, 4, 8, 16, and 24 h after administration. The maximum concentration of dicyclanil in plasma, approximately 20 µg/ml, was found in the animals sampled at 8 h. The concentration in plasma from animals sampled at 24 h ranged from 1.6 to 3.6 µg/ml. The study was of unconventional design, without GLP or quality assurance certification. The pharmacokinetics of dicyclanil could not be calculated (Dubach-Powell, 1996). [2-14C]Pyrimidyl-labelled dicyclanil (purity, 98%) in polyethylene glycol 200: ethanol (5:3 v/v) was administered to Tif:RAIf (SPF) rats by oral gavage for 7 consecutive days at a dose of 0.5 or 20 mg/kg bw per day. Urine and faeces were collected throughout treatment, until the time of death. Three rats of each sex per dose were killed 24 and 72 h after the last dose, and abdominal fat, kidneys, liver, skeletal muscle, plasma, whole blood, gastrointestinal tract with contents, and the residual carcass were taken for analysis. All samples were analysed for radiolabel by liquid scintillation counting. The study was certified for compliance with GLP and quality assurance. On the basis of the radiolabel in urine and tissues, absorption from the gastrointestinal tract represented 80-85% of the administered dose. Within 24 h after the last dose, 93-96% of the total dose had been excreted, predominantly via the urine (79-83%) and to a lesser extent via the faeces (6-12%). During the following 48 h, only an additional 2-3% was excreted, indicating rapid elimination of the absorbed material. The concentration of radiolabel in tissues 24 h after the final dose of 0.5 mg/kg bw was < 4 µg/kg as dicyclanil equivalents, except in liver (270 µg/kg), blood (170 µg/kg), kidneys (37 µg/kg), and residual carcass (23 µg/kg). At 72 h, these concentrations had declined to 40-80% of their values at 24 h, except in blood, where the levels declined very slowly. The radiolabel in blood was associated with erythrocytes. The concentrations of residues in tissue were proportional to the dose. No differences were observed between males and females (Hassler, 1994). 2.1.2 Biotransformation In the study of Hassler (1994) described above, the metabolites in urine, faeces, and tissues were characterized by thin-layer chromatography and those in urine and faeces also by high-performance liquid chromatography. Further investigations on the same samples included solid-phase extraction, high-voltage electrophoresis, and nuclear magnetic resonance, infrared, and mass spectroscopy. This study was certified for compliance with GLP and quality assurance (Thanei, 1996a). The metabolic pattern in urine, faeces, and selected tissues constituted up to 12 metabolite fractions and was essentially independent of dose and sex. One major fraction, representing 48-54% of the total dose, dominated the urinary metabolite pattern and was identified as N-(4,6-diamino-5-cyano-pyrimidin-2-yl)propionamide. The parent compound was also found in urine, where it accounted for 2-7% of the total dose. Other identified urinary metabolites were 2,4,6-triaminopyrimidin-5-carbonitrile (9-10%), 3-(4,6-diamino-5-cyanopyrimidin-2-ylamino)propionic acid (4-10%), and 2-(4,6-diamino-5-cyanopyrimidin-2-ylamino)-3-hydroxypropionic acid (1-3%). All these metabolites were also identified in faeces, but at markedly lower concentrations, each fraction representing < 3% of the total dose. The parent compound accounted for approximately 1% of the total dose in faeces. Besides polar metabolites, 2,4,6-triaminopyrimidin-5-carbonitrile was the major metabolite in liver and kidneys, with smaller amounts of parent compound and probably N-(4,6-diamino-5-cyanopyrimidin-2-yl)propionamide. A similar but quantitatively different metabolic pattern was observed in muscle and fat, which contained more nonpolar metabolites (most pronounced in fat) (Hassler, 1994; Thanei, 1996a). Biotransformation of dicyclanil in rats is limited to the cyclopropyl ring, while the cyano group is metabolically stable. Biotransformation in rats involves oxidative opening of the cyclopropyl ring at various positions, followed by further oxidation and cleavage of the cyclopropyl- N-bond (i.e. dealkylation). Most of the metabolites are the result of more than one transformation. The metabolic pathways of dicyclanil in sheep treated topically are essentially the same as those in rats (Phillips, 1996; Thanei, 1996b; Löffler, 1998). The proposed metabolic pathway of dicyclanil in rats and sheep is given in Figure 1. 2.2 Toxicological studies 2.2.1 Acute toxicity In studies with technical-grade dicyclanil in distilled water containing 0.5% carboxymethylcellulose in 0.1% aqueous polysorbate 80 in male and female Tif:RAIf (SPF) rats, one study that followed OECD test guideline 401 with GLP and quality assurance certification showed an LD50 value after oral administration of 560 mg/kg bw in males and of approximately 500 mg/kg bw in females. Common signs of toxicity observed were piloerection, hunched posture, and dyspnoea. All animals had reduced locomotor activity, with ataxia in some males. At necropsy, involuted testes were found in two males that had received 200 mg/kg bw dicyclanil (Hartmann, 1992a). In a study that followed OECD test guideline 402 with GLP and quality assurance certification, the LD50 after dermal application was > 2000 mg/kg bw in both males and females. The only signs of toxicity observed were piloerection and hunched posture (Hartmann, 1992b). In a study that followed OECD test guideline 403 with GLP and quality assurance certification, rats of the same strain were exposed by nose only to a dicyclanil aerosol for 4 h (minimal mean aerodynamic diameter, 0.9-2.5 µm). The LC50 after exposure by inhalation was 3400 mg/m3 for males and 3000 mg/m3 for females. The toxic signs observed were piloerection, hunched posture, dyspnoea, and reduced locomotor activity. Spotted lungs were found in animals exposed to higher doses of dicyclanil, and abdominal distention was found in males that survived the high dose (Hartmann, 1993). In all studies, the surviving animals recovered within 2-12 days.Three male New Zealand white rabbits (Chbb:NZW) received a semi-occlusive topical application of 0.5 g of technical-grade dicyclanil moistened with distilled water containing 0.5% carboxymethylcellulose in 0.1% aqueous polysorbate 80 to their shaved flanks. The study followed OECD test guideline 404, with GLP and quality assurance certification. Only very slight erythema was observed 1 ( n = 3) to 24 h ( n = 1) after removal of the patch (Hagemann, 1992a). In a study that followed OECD test guideline 405 with GLP and quality assurance certification, three female New Zealand white rabbits (Chbb:NZW) received an instillation of 0.1 ml (84 mg) of technical-grade dicyclanil into the conjunctival sac of one eye. The other eye served as control. The cornea appeared to be unaffected by treatment; one animal showed an affected iris 1 h after instillation but recovered within 24 h. Slight chemosis of the conjunctiva was observed in two animals 1 h after instillation, but they recovered within 24 h. Redness of the conjunctiva was seen in all animals, although at different grades (score 1 or 2), and recovery to normal occurred within 1-7 days (Hagemann, 1992b). In 10 male and 10 female Pirbright white Tif:DHP guinea-pigs submitted to an optimization test that followed OECD test guideline 406 with GLP and quality assurance certification, no significant skin sensitization (1/20 positive) was observed after epidermal challenge with 20% technical-grade dicyclanil in vaseline, this being a subirritant dose. When the skin barrier was intentionally bypassed, i.e. by intradermal challenge with a 0.1% solution of technical-grade dicyclanil in 10% propylene glycol, 13 of 20 treated animals showed positive reactions versus 3 of 20 animals given the vehicle ( p < 0.01) (Hagemann, 1993). 2.2.2 Short-term studies of toxicity Rats In a 28-day range-finding study, groups of five male and five female Tif:RAIf (SPF) rats received technical-grade dicyclanil (purity, > 98%) in the diet at a concentration of 0, 100, 500, or 2000 mg/kg of diet, equal to average achieved intakes of 0, 9.5, 50, and 150 mg/kg bw per day for males and 0, 9.4, 49, and 160 mg/kg bw per day for females. The study followed OECD test guideline 407 (adapted to the objectives of a range-finding study) without GLP or quality assurance certification. No treatment-related deaths occurred. Piloerection was observed in animals of each sex at the highest dose during the second half of the study. Dose-dependent reductions in food consumption, body-weight gain, and final body weight were noted in all treated groups. These were particularly marked in males at the high dose. Water consumption was reduced in females at 500 and 2000 mg/kg of diet. Increased incidences of anisocytosis and polychromasia of erythrocytes and a slightly lower (not statistically significant) leukocyte count were noted in males at the high dose. In both males and females at this dose, higher plasma concentrations of urea and cholesterol and increased activities of aspartate aminotransferase (twofold) and alanine aminotransferase (five- to sevenfold) were noted. Hypoglycaemia and lower plasma total bilirubin concentrations were also observed in these animals, although the changes were not statistically significant in females. Males at the high dose also had slightly lower plasma globulin and calcium concentrations, while females at this dose had an increased plasma phosphate concentration. Consistent with the reduced body weights of all treated animals, the absolute weights of a number of organs were decreased, whereas the relative weights of a number of other organs were increased. The only notable changes in organ weights which could be considered to be treatment-related effects were reductions in the absolute and relative weights of the prostate in males at the intermediate and high doses and of the adrenals in females at the low and intermediate doses. No macroscopic changes were found, apart from emaciation at the high dose. Histopathologically, reduced spermatogenesis in the testes was seen in 1/5 males at 500 mg/kg of diet and 5/5 males at 2000 mg/kg of diet, accompanied by accumulation of cellular debris in the epididymal duct in all those at the high dose. These animals also showed immaturity of the prostate. In 1/5 females at 500 mg/kg of diet and in 4/5 females at 2000 mg/kg of diet, polyovular ovarian follicles, as indicated by hypercellularity, were seen (Bachmann, 1991). In a 3-month study of toxicity, groups of 10 male and 10 female Tif:RAIf (SPF) rats received technical-grade dicyclanil in the diet at a concentration of 0, 5, 25, 125, or 500 mg/kg of diet, equal to average achieved intakes of 0, 0.31, 1.6, 8.0, and 33 mg/kg bw per day for males and 0, 0.31, 1.7, 8.4, and 34 mg/kg bw per day for females. Ten additional animals of each sex in the control and high-dose groups were kept for a 4-week recovery period. The study followed OECD test guideline 408, with GLP and quality assurance certification. No treatment-related deaths or clinical signs were observed. Slight reductions in body-weight gain and food consumption were observed in animals of each sex at the high dose and in males at 125 mg/kg of diet. Owing to a compensatory increase in food intake during the recovery period, the body weights of animals at the high dose were comparable to those of the controls by the end of the recovery period. Chemical analysis of blood revealed slightly lower plasma glucose concentrations in males and females at 125 and 500 mg/kg of diet at the end of the treatment period, but this was reversed within the recovery period. Higher organ:body weight ratios were observed for kidneys, brain, and testis in males at the high dose and for liver and brain in females at this dose, these changes being reversible within the 4-week recovery period. Although the relative epididymidal weights were increased in males at doses > 25 mg/kg of diet, this was considered not to be toxicologically significant because the absolute epididymidal weights were not different from those of controls and there were no abnormal histopathological findings. No treatment-related ophthalmological or haematological changes were observed, and no gross or microscopic alterations were observed. One female at the high dose that was alllowed to recover had a mammary tumour, which was considered to be of spontaneous origin. On the basis of the reduction in body-weight gain, the NOEL was 25 mg/kg of diet, equal to 1.6 mg/kg bw per day (Bachmann, 1993). In a study that followed OECD test guideline 410 with GLP and quality assurance certification, groups of five male and five female Tif:RAIf (SPF) rats received dermal applications of technical-grade dicyclanil at a dose of 0, 5, 30, 300, or 1000 mg/kg bw per day, 6 h/day on 5 days per week for 4 weeks. Dicyclanil was dissolved in water containing 0.5% carboxymethylcellulose and 0.1% polysorbate 80 and was applied under an occlusive dressing to a clipped dorsal area of the skin. At the end of each application period, the site was washed with lukewarm water. None of the animals died and no treatment-related clinical signs were observed. Apart from a few incidental findings, no signs of local skin irritation were seen. Male rats at 300 and 1000 mg/kg bw per day showed dose-dependently decreased body weights and body-weight gain and slightly lower food consumption. The plasma concentrations of sodium and calcium were slightly reduced in these animals. Females at the high dose showed increased absolute and relative liver weights. A similar effect was observed in females at 300 mg/kg bw per day but did not reach statistical significance. The absolute, but not the relative, weight of the brain of females was increased at doses > 30 mg/kg bw per day, without histopathological findings. No treatment-related effects were noted on gross examination. Microscopic examination showed hepatocyte hypertrophy in males at 1000 mg/kg bw per day and in females at 300 and 1000 mg/kg bw per day. The NOEL was 30 mg/kg bw per day, on the basis of decreased body-weight gain and changes in the liver (Marty, 1995). Dogs In a 28-day range-finding study, groups of two male and two female beagles were given technical-grade dicyclanil (purity, > 98%) in the diet at a concentration of 0, 200, 1000, or 2500 mg/kg of diet, equal to average achieved intakes of 0, 5.6, 31, and 66 mg/kg bw per day for males and 0, 6.2, 30, and 50 mg/kg bw per day for females. The study followed OECD test guideline 409 (adapted to the objectives of a range-finding study) without GLP (except for the pathology report) or quality assurance certification. No treatment-related deaths occurred. The clinical signs included body tremors (in animals of each sex at 2500 mg/kg of diet), vomiting (in animals of each sex at 2500 mg/kg of diet and in one male at 1000 mg/kg of diet), dyspnoea and slight apathy (in males at 2500 mg/kg of diet). Animals at the high dose lost weight and had reduced food consumption, and females at 1000 mg/kg of diet also showed a slight reduction in food consumption. The reduction in food consumption did not appear to be due to unpalatability. One male and one female at the high dose showed a prolonged prothrombin time, and the other male at the high dose had a slightly increased number of blood platelets. Alanine aminotransferase activity was markedly increased and alkaline phosphatase activity slightly increased in one male at the high dose and in one female at the intermediate and one at the high dose; aspartate aminotransferase activity was also increased in the female at the high dose. Very slight decreases were observed in plasma potassium concentrations in males at the intermediate and high doses, in plasma glucose concentration in females at the high dose, and in the plasma concentrations of urea, creatinine, and total bilirubin in males and females at the high dose. Urinary analysis revealed an increased incidence of proteinuria in males at the high dose and females at the intermediate and high doses. The absolute and relative weights of the testis and thymus were markedly decreased and those of the heart slightly decreased at 2500 mg/kg of diet. In animals of each sex at 1000 and 2500 mg/kg of diet, the absolute and relative weights of the adrenal and kidney were increased, but without any histopathological changes. Microscopic examination revealed hepatic toxicity in one female at 1000 mg/kg of diet and in all animals at 2500 mg/kg of diet. The toxicity included focal or single-cell necrosis, inflammatory-cell foci, and a brown granular pigment in macrophages. One female at the intermediate dose also had mild bile-duct hyperplasia, and one male at the high dose had periportal hepatocyte enlargement. The testes of males at this dose showed degeneration characterized by reduced numbers of tailed spermatids and increased numbers of multinucleated or giant cells. Mild thymic atrophy was noted in animals of each sex at the highest dose. The heart of one male at this dose was mottled and showed inflammation, fibrosis, and haemorrhage. Tubular basophilia or dilatation was present in the kidneys of all animals at the high dose, two at the intermediate dose, and one at the low dose, but not in controls. This lesion is of minimal toxicological significance (Altmann, 1991). Groups of four male and four female beagles received technical-grade dicyclanil in the diet at a concentration of 0, 20, 100, 500, or 1500 mg/kg of diet for 3 months, equal to average achieved intakes of 0, 0.61, 2.7, 14, and 42 mg/kg bw per day for males and 0, 0.71, 3.5, 17, and 42 mg/kg bw per day for females. The study followed OECD test guideline 409, with GLP and quality assurance certification. One male at the high dose was found dead at week 11 after general deterioration in clinical condition accompanied by tonic-clonic spasms. Post-mortem examination did not reveal the cause of death. Animals at the high dose started to show clinical signs from week 9-11, including slight ataxia, unnaturally raised tails, and frequent shaking. In addition, vomitus and traces of blood in the faeces were observed. Ophthalmoscopic examinations revealed no treatment-related changes. Animals at the high dose lost weight (males only) or had reduced body-weight gain with reduced food intake. A very slight reduction in food intake was also observed transiently in some animals at 500 mg/kg of diet. Slightly reduced haemoglobin concentrations and haematocrit values, associated with minor microcytosis and hypochromasia of erythrocytes, were recorded in animals at the high dose. Increased plasma cholesterol and phospholipid concentrations were observed in animals at doses > 100 mg/kg of diet. Plasma albumin concentrations were slightly decreased in males and females at 1500 mg/kg of diet and in females at 500 mg/kg of diet. Decreased plasma calcium, potassium, urea, creatinine, and total bilirubin concentrations were found in animals at the high dose. Urinary analysis revealed no treatment-related effects. The mean absolute and relative liver weights were increased in animals at the highest dose and in females also at 20, 100 (not statistically significant), and 500 mg/kg of diet (not dose-related). The absolute and relative adrenal weights were also slightly increased at the high dose. The absolute and relative weights of the thymus (males), testis, and spleen (both sexes) were decreased in animals at the high dose. The kidney weights were increased in males (relative) and females (absolute and relative) at 1500 mg/kg of diet. Macroscopic examination showed no treatment-related effects. Microscopy of the liver showed minimal to moderate focal or multifocal subcapsular inflammation with fibrosis in 2/4 males and 3/4 females at the high dose. Enlarged hepatocytes, diagnosed as cellular oedema, were observed in the centrilobular and midzonal region of 3/4 females at 20, 100, and 500 mg/kg of diet and in 1/4 males and all females at 1500 mg/kg of diet. No morphological signs of hepatocellular damage were apparent. Minimal atrophy of the white pulp of the spleen was observed in 3/4 males at 500 and 1500 mg/kg of diet and in all females at 1500 mg/kg of diet. Thymic atrophy was found in 3/4 males at 500 mg/kg of diet and in all males at 1500 mg/kg of diet. Minimal atrophy of the lymphatic tissue of the mesenteric lymph node was observed in 3/4 males at the high dose, and minimal to marked atrophy of the glandular tissue of the prostate was detected in 3/4 males at 100 mg/kg of diet, 1/4 at 500 mg/kg of diet, and 4/4 at 1500 mg/kg of diet. Examination of the testes revealed minimal tubular atrophy in 3/4 males at the high dose, associated with a marked reduction in spermatogenesis in all males of this group. A dose-related increase in the frequency of inflammatory changes associated with epithelial hyperplasia was found in the urinary bladders of females at 100, 500, and 1500 mg/kg of diet (Altmann, 1993). The Committee noted that hepatocyte oedema without hepatocellular damage is not of toxicological significance. Hence, the NOEL was 20 mg/kg of diet, equal to 0.61 mg/kg bw per day, on the basis of increased plasma cholesterol concentrations and histopathological findings in the prostate and urinary bladder. In a 1-year study of toxicity, groups of four male and four female beagles received technical-grade dicyclanil in the diet at a concentration of 0, 5, 25, 150, or 750 mg/kg of diet, equal to average achieved intakes of 0, 0.16, 0.71, 4.4, and 23 mg/kg bw per day for males and 0, 0.15, 0.77, 5.1, and 23 mg/kg bw per day for females. Two additional animals per sex in the control and high-dose groups were maintained for a 4-week recovery period. The observations included deaths, clinical signs, body weight, food consumption, ocular, neurological, haematological, clinical chemical, and urinary parameters, and macroscopic and microscopic end-points. The study followed OECD test guideline 452, with GLP and quality assurance certification. One female at the high dose was found dead on day 13, with no previous abnormal clinical signs. One male at the high dose was killed on study day 32 after vomiting, showing marked apathy, lying in a lateral position, and weight loss correlated to reduced food intake. Vomiting was observed in females at the high dose, and the body-weight gain (in two animals) and food consumption of females at the high dose were slightly reduced. Ocular and neurological examinations revealed no treatment-related effects, nor were there any changes in haematological or urinary parameters. Throughout the treatment period, the plasma cholesterol concentrations were increased in animals of each sex at 750 mg/kg of diet (not statistically significant in females) and in males at 150 mg/kg of diet; in males, the change was not reversed after the 4-week recovery period. Males at the high dose showed slightly lower plasma calcium concentrations. Both males and females at the high dose had reduced plasma concentrations of bilirubin and urea and reduced alkaline phosphatase activity. The changes in blood chemistry were partially reversed during the recovery period. The absolute and relative liver weights were increased in animals at 750 mg/kg of diet, but only the change in absolute weight in males was statistically significant. The absolute (statistically significant) and relative weights of the heart were decreased in females at the high dose. The weight changes were reversed by the end of the 4-week recovery period. The macroscopic and microscopic findings were confined to the two animals at the high dose that died before the scheduled kill. The macroscopic findings consisted of a scar in the liver and pale kidneys in the male and a mass and haemorrhagic content in the abdominal cavity of the female. Histopathologically, both animals showed marked diffuse liver necrosis and kidney lesions (more severe in the male). The male also showed testicular and prostatic atrophy, and the female had a thrombus in a peritoneal blood vessel. The two animals suffered from acute, severe liver failure and resulting cardiocirculatory disturbances, and the male also showed stress due to weight loss. Their condition was very different from that of the other treated dogs in this study, and comparable acute, severe liver toxicity was not seen in the 28-day and 3-month studies in dogs treated with doses up to 2500 and 1500 mg/kg of diet, respectively. The lesions seen in the two animals are considered to be incidental findings. On the basis of increased plasma cholesterol concentrations in males, the NOEL was 25 mg/kg of diet, equal to 0.71 mg/kg bw per day (Altmann, 1995). 2.2.3 Long-term studies of toxicity and carcinogenicity Mice In an 18-month study of carcinogenicity, groups of 60 male and 60 female Tif:MAGf (SPF) mice were given diets containing technical-grade dicyclanil at a concentration of 0, 10, 100, 500, or 1500 mg/kg of diet, equal to average achieved intakes of 0, 1.1, 12, 59, and 210 mg/kg bw per day for males and 0, 1.1, 12, 65, and 200 mg/kg bw per day for females. Ten animals per sex from each group were assigned for evaluation of haematological parameters. The study followed OECD test guideline 451 with GLP and quality assurance certification, but histopathological examination of the animals at the high dose (i.e. the group that was killed before study termination, see below) was limited to the liver and lungs. Clinical signs were observed only in males at the highest dose, which injured themselves through vigorous scratching. A higher mortality rate was noted among males at the high dose and to a lesser extent in females at this dose. The self-inflicted injuries and poor health of the animals at the high dose led to a decision to terminate all surviving animals in this group during weeks 58-59. Doses < 500 mg/kg of diet did not affect survival. The body weights of males and females at 1500 mg/kg of diet were reduced, with an approximately 50% reduction in body-weight gain, and those of females at 500 mg/kg of diet were reduced with a 30% reduction in body-weight gain. As food intake was not affected, higher food consumption ratios were noted in animals of each sex at 1500 mg/kg of diet and in females at 500 mg/kg of diet. Haematological parameters were not affected by treatment. The absolute and relative weights of the liver were increased in animals of each sex at 500 mg/kg of diet (for males after adjustment for three control outliers). In females at 500 mg/kg of diet, the relative weights of the kidney, brain, and adrenals were increased, while the absolute weights of these organs were not changed. The treatment-related macroscopic findings included enlarged livers (characterized histopathologically as hepatocellular hypertrophy) in males at 500 mg/kg of diet and in both sexes at 1500 mg/kg of diet, and masses and/or nodules of the liver in females at 500 and 1500 mg/kg of diet. Treatment-related microscopic findings were observed in the liver, olfactory epithelium, adrenal gland, and bone marrow. Kupffer cell pigmentation (mainly haemosiderin) and hepatocellular necrosis were observed in males at > 100 mg/kg of diet. Increased numbers of hepatocellular mitotic figures and multinucleated hepatocytes were seen in the livers of males at the high dose, and the frequency of foci of cellular change was increased in animals of each sex at the highest dose. The incidence of heptocellular adenomas was higher in females at 500 and 1500 mg/kg of diet (9/53 and 5/60, respectively) than in controls (0/52). In addition, the incidence of hepatocellular carcinomas was increased in females at the highest dose (6/60 versus 0 in all other groups). Pigmentation of the olfactory epithelium was observed at increasing incidence and severity in animals of each sex at 100 and 500 mg/kg of diet, and males at these doses showed an increased incidence of inflammatory cell infiltration (cell type not specified) in the underlying Bowman's glands. At 500 mg/kg of diet, both males and females also showed increased incidences of pigmentation of the adrenal glands, recorded as ceroid (i.e. a partly oxidized form of lipofuscin) deposition, and of hypercellularity of the bone marrow. Treatment with dicyclanil did not affect the number of animals with malignant lymphomas. It was noted, however, that females at 500 mg/kg of diet had more sites that appeared to be infiltrated by malignant lymphoma cells than did controls or animals at other doses (Bachmann, 1996a). The Committee noted that the doses at which the liver adenomas and carcinomas occurred exceeded the maximum tolerated dose for females, and that there were signs of hepatocellular proliferation in these animals which might have been involved in the hepatic carcinogenesis observed. Pigmentation of the olfactory epithelium was also observed in a long-term study in rats (Bachmann, 1996b; see below) and was further investigated in a separate study (Weber, 1998; see below). As the Committee considered the effects on the olfactory epithelium to be of no biological significance (see below), the NOEL in this study in mice was 10 mg/kg of diet, equal to 1.1 mg/kg bw per day, on the basis of effects on the liver. Rats In a 2-year study of carcinogenicity and toxicity, groups of 80 Tif:RAIf (SPF) rats of each sex were given technical-grade dicyclanil in the diet at a concentration of 0, 5, 25, 125, or 500 mg/kg of diet, equal to average achieved intakes of 0, 0.19, 0.97, 4.8, and 22 mg/kg bw per day for males and 0, 0.23, 1.2, 6.0, and 26 mg/kg bw per day for females. Haematological, clinical chemical, and urinary analyses were performed during weeks 13, 26, 52, 78, and 105 on 20, 10, and 10 animals of each sex per group, respectively. After 1 year, 10 animals of each sex per group were killed. The study followed OECD test guideline 453, with GLP and quality assurance certification. Treatment with dicyclanil did not affect the incidence of clinical signs or survival. Decreased food consumption was noted in males and females at the highest dose. The body weights of males and females at 500 mg/kg of diet were reduced (with an approximately 25% reduction in body-weight gain), as were the body weights of animals at 125 mg/kg of diet (with a reduction in body-weight gain of < 10%). Slight but statistically significant red blood cell dyscrasia and a reduced number of monocytes were observed in males at the high dose when compared with controls, but the changes were generally inconsistent over time, not dose-related, and within the range of historical controls and are therefore regarded as toxicologically insignificant. Increased concentrations of inorganic phosphate were observed in males and females at the high dose throughout the study, although the increase was not statistically significant in females. Males at 125 mg/kg of diet also had increased inorganic phosphate concentrations, but these reached statistical significance only in weeks 78 and 105. Lower concentrations of triglycerides were recorded for males at 500 mg/kg of diet, although statistical significance was achieved only in weeks 13 and 26. Urinary parameters were not affected. As a result of the lower terminal body weights, almost all of the relative organ weights were increased in males and females at the highest dose, especially of the kidney, liver, and epididymides. The absolute epididymal weights were also increased in males at the high dose at 105 weeks. Males at 125 mg/kg of diet also had increased relative liver weights, although these were within historical control values. An increased incidence of liver cysts was observed in females at the high dose, characterized primarily as unilocular or multilocular biliary cysts on microscopic examination. In males at the high dose, an increased incidence of masses and nodules in the exocrine pancreas was noted, which were characterized histopathologically as foci or areas of hyperplasia. Aside from the histopathological findings in the pancreas and liver, the only other treatment-related histopathological finding was an increased incidence of pigmentation of the olfactory epithelium in males at > 25 mg/kg of diet and in females at > 125 mg/kg of diet, the effects seen at 125 and 500 mg/kg of diet being more severe than at lower doses. Dicyclanil did not affect the tumour incidence in this study (Bachmann, 1996b). Weber (1998) studied the histological nature and causes of the pigmentation of the olfactory epithelium, using material from male rats in the 2-year study (controls and rats given 500 mg/kg of diet) and the 3-month study (controls and rats given 500 mg/kg of diet; Bachmann, 1993). Material from male control rats of the same strain in five other long-term studies was included to provide more reference material. Minimal to moderate pigmentation was found in controls from the long-term studies with dicyclanil and other compounds, but not in controls from the 3-month study. Treatment with 500 mg/kg of diet resulted in increased pigmentation, which was minimal after 3 months and moderate to marked after 12 and 24 months, the degree of pigmentation at the later times being similar. Staining indicated that the pigment consisted mainly of oxidized lipofuscins and was located in the olfactory epithelium and the underlying lamina propria. The pigment appeared to be located in secondary lysosomes. Further investigations by high-resolution microscopy indicated that the supporting cells and secretory cells of Bowman glands were affected by the pigmentation. Neuronal olfactory perikarya, nerve bundles of the olfactory nerve in the olfactory mucosa, and the olfactory bulbs (in the brain) were free of pigment accumulation. Apart from the pigmentation, no other treatment-related morphological changes in the olfactory mucosa were found. According to the author, the clinical signs in the 2-year study gave no indication of a disturbed olfactory sense due to dicyclanil treatment. In addition, the presence of mucopolysaccharides in the Bowman glands indicated normal functioning of the olfactory mucosa in the dicyclanil-treated rats. The author concluded that the increased pigmentation of the olfactory epithelium in male rats after treatment with dicyclanil results from accumulation of lipofuscin in the cytoplasm of supporting cells and secretory cells of the Bowman glands and is an enhancement of a natural age-related process. In the absence of other morphological changes in the olfactory mucosa, the author considered the pigmentation not to be detrimental to the structure or function of the olfactory mucosa and, therefore, is not to be regarded as adverse (Weber, 1998). Recognizing that the effects on the olfactory epithelium were an enhancement of a natural age-related process, the Committee noted that dicyclanil had no effect on survival, behaviour, or general well-being. As there were no other morphological changes in the olfactory mucosa, the Committee concluded that the effect was of no biological significance. Therefore, the NOEL in the 2-year study in rats was 125 mg/kg of diet, equal to 22 mg/kg bw per day, on the basis of changes in body weight and histopathological changes in the liver and pancreas. 2.2.4 Genotoxicity The results of studies for genotoxicity with technical-grade dicyclanil are summarized in Table 1. The studies were of conventional design, with GLP and quality assurance certification, except for the study of Ogorek & Arni (1987). 2.2.5 Reproductive toxicity (a) Multigeneration study Rats In a two-generation study of reproductive toxicity with two litters per generation, groups of 30 male and 30 female Tif:RAIf (SPF) rats received diets containing technical-grade dicyclanil at a concentration of 0, 5, 30, 200, or 500 mg/kg of diet from 10 weeks before the first mating until necropsy at the end of the lactation period. Dams were allowed to litter and suckle their pups naturally. When possible, the F1a litters were culled to four pups of each sex per litter at day 4 post partum. After weaning, a number of F1a pups were selected to be the F1 parents, and the remaining F1a pups were necropsied. The F0 parents were then mated a second time, and the resulting litters (F1b) were again culled to four pups of each sex per litter. After weaning, both the F1b pups and the F0 parents were necropsied. The same procedure was followed for the F1 parents in order to produce F2a and F2b generations. The observations included clinical signs, deaths, body weight, food consumption, reproductive parameters, pup survival and development, macroscopic appearance at necropsy, and, for parents in the control and high-dose groups, histological appearance of the reproductive and target organs. The study followed OECD test guideline 416, with GLP and quality assurance certification. Effects in F0 parents: The F0 parents showed no treatment-related deaths or clinical signs and no effects on male or female mating or fertility indices, on maternal gestation or parturition indices, or on the duration of gestation. In the premating period, males and females showed decreased body-weight gain and food intake at 500 mg/kg of diet and, marginally, at 200 mg/kg of diet. During both gestation periods, the overall body-weight gain of females in all treated groups was similar to that of controls, while in both lactation periods the overall body-weight gain of females was increased at 500 mg/kg of diet and, marginally, at 200 mg/kg of diet. Gross examination and histology revealed no treatment-related effects. Secondary to the reduced body weights, the relative weights of most organs were increased in males and females at 500 mg/kg of diet. At this dose, the absolute weights of the heart and liver of males were decreased. Table 1. Results of assays for genotoxicity with dicyclanil End-point Test object Concentration Result Reference In vitro Reverse S. typhimurium 20-5000 µg/plate Negativea Ogorek & Arni mutation TA1537, TA98, (1987) TA100 Reverse S. typhimurium 313-5000 µg/plate Negativeb Hertner (1992) mutation TA1535, TA1537, TA98, TA100, E. coli WP2 uvrA Gene mutation V79 Chinese 12.4-400 µg/ml Negative Geleick (1992) hamster lung cells, - S9c hprt locus 24.7-667 µg/ml + S9d,e Chromosomal Chinese hamster 20.8-83.4 µg/ml Negative Hertner (1993a) aberration ovary cells -S9c 166.75-667 µg/ml +S9d,e Unscheduled Primary rat 6.2-670 µg/mle Negative Hertner (1993c) DNA synthesis hepatocytes In vivo Micronucleus Mouse bone 47-188 mg/kg bw; Negativef Hertner (1993b) formation marrow once by oral gavage a With and without rat liver S9 fraction; results of cytotoxicity test not given, precipitation not reported b With and without rat liver S9 fraction; precipitation at 5000 µg/plate c Cytotoxic at the highest concentration d Slightly cytotoxic at the highest concentration e The highest concentration represents the limit of solubility in dimethyl sulfoxide. f At all doses and all times, the ratio of polychromatic to normochromatic erythrocytes did not deviate from that in controls; clinical signs of toxicity (including reduced locomotor activity, unkempt fur, ataxia, piloerection, and diarrhoea) were observed at the highest dose tested; doses > 312.5 mg/kg bw resulted in death. Effects in F1 pups: At all doses and both matings, no treatment-related effects were seen in the F1 offspring in terms of sex ratio, clinical signs, litter size, the development of physical landmarks (surface righting and eye opening), or macroscopic findings at necropsy. A slight increase in the pup mortality rate was observed on days 0-4 post partum at 500 mg/kg of diet (F1a) and at 30 and 200 mg/kg of diet (F1b). This was considered not to be treatment-related because it could be attributed to two (F1a) or three (F1b) litters and no dose-response relationship was found. At 500 mg/kg of diet, the weights of F1a pups were lower than those of controls at birth and on days 14 and 21 post partum, owing to reduced weight gain from day 4 post partum onwards. The weights of F1b pups at the high dose were similar to those of controls from birth through to day 14 post partum. Thereafter, the weight gain decreased, resulting in lower pup weights on day 21 post partum. Effects in F1 parents: In the F1 parents, no treatment-related deaths or clinical signs and no effects on male or female mating or fertility indices, on maternal gestation or parturition indices, or on the duration of gestation were observed. The body weights of the F1 parents at the high dose were lower than those of controls throughout the study. Although the body weights of males at 200 mg/kg of diet were reduced during the final part of the study, the overall body-weight gain of these animals was not different from that of controls. During both gestation periods, the overall body-weight gain of all treated females was slightly lower than that of controls, while in both lactation periods the overall body-weight gain of females was increased at 500 mg/kg of diet and, marginally, at 200 mg/kg of diet. The absolute weights of most organs of males at the high dose were decreased, with the exception of those of the testis and brain. In females at the high dose, only the absolute weights of the heart, liver, and kidney were decreased. At 200 mg/kg of diet, the absolute weight of the liver was decreased in animals of each sex. In contrast, secondary to the reduced body weights of these two groups, the relative weights of most organs were increased, attaining statistical significance for most organs at 500 mg/kg of diet and for brain (both sexes), kidneys (males only), and testis at 200 mg/kg of diet. Gross examination and histology revealed no treatment-related effects. Effects in F2 pups: At all doses and both matings, no treatment-related effects were noted in the F2 offspring in terms of sex ratio, mortality rate, clinical signs, litter size, the development of physical landmarks (surface righting and eye opening), or macroscopic findings at necropsy. The only treatment-related effect observed was reduced weight gain in F2a and F2b pups at the highest dose from day 4 post partum onwards, resulting in significantly lower pup weights on days 14 and 21 post partum. The NOEL for parental toxicity was 30 mg/kg of diet, equal to 2 mg/kg bw per day, on the basis of changes in body weight. The NOEL for reproductive toxicity was 500 mg/kg of diet, equal to 24 mg/kg bw per day, the highest dose tested. The NOEL for pup toxicity was 200 mg/kg of diet, equal to 21 mg/kg bw per day, on the basis of reduced body-weight gain (Khalil, 1995). (b) Developmental toxicity Rats In a range-finding study, groups of eight pregnant Tif:RAIf (SPF) rats received technical-grade dicyclanil (purity, > 98%) in 3% aqueous corn starch by oral gavage at a dose of 0, 75, or 150 mg/kg bw per day on days 6-15 of gestation. On day 21 of gestation, the dams were killed and necropsied, and the fetuses were weighed, sexed, and examined for external abnormalities. Two dams at the high dose were killed in moribund condition. The clinical signs in these animals and in a third animal at the high dose included piloerection, salivation, dyspnoea, and hypotonia. Maternal body-weight gain and gravid uterine weights were dose-dependently decreased in all treated animals, but food consumption was dose-dependently decreased only during the first week of treatment. Post-implantation loss was dose-dependently increased by treatment, owing to early resorptions. Three dams at the high dose resorbed their entire litters. The number of viable fetuses and fetal body weights were dose-dependently reduced. Three fetuses at the high dose showed generalized oedema (FitzGerald, 1990a). In the main study, groups of 24 pregnant Tif:RAIf (SPF) rats received technical-grade dicyclanil in an aqueous solution of 0.5% sodium carboxy-methylcellulose by oral gavage at a dose of 0, 1, 5, 25, or 75 mg/kg bw per day on days 6-15 of gestation. On gestation day 21, the dams were killed and necropsied, and the fetuses were weighed, sexed, and examined for external, visceral, and skeletal abnormalities. The study was of conventional design, with GLP and quality assurance certification. There were no deaths and no treatment-related clinical signs of toxicity. Maternal body weight, body-weight gain, and food consumption as well as net body-weight change and carcass weight at necropsy were reduced at the highest dose. A marginal decrease in these parameters was also observed at 25 mg/kg bw per day. One animal at 75 mg/kg bw per day had total, early resorptions and showed haemorrhagic fluid in the uterus at necropsy. In animals at 75 mg/kg bw per day, the gravid uterine weight was reduced; the number of early postimplantation losses was slightly increased and the number of fetuses per litter was slightly lower, but without statistical significance. Effects on the fetuses were observed only at the highest dose. These included reduced fetal weight, a slight increase in the frequency of renal pelvic dilatation, and a number of mainly sternebral defects and variations due to poor or absent ossification. There was no evidence of teratogenicity. The NOEL for maternal toxicity was 5 mg/kg bw per day, on the basis of a reduction in body-weight gain. The NOEL for developmental toxicity was 25 mg/kg bw per day, on the basis of reduced fetal weight, increased renal pelvic dilatation, and increased skeletal anomalies and variations consistent with a slight delay in skeletal maturation (FitzGerald, 1993a). Rabbits In a range-finding study, groups of eight pregnant Russian rabbits (strain unspecified) received technical-grade dicyclanil (purity, > 98%) in 3% aqueous corn starch by oral gavage at a daily dose of 0, 20, or 40 mg/kg bw on days 7-19 of gestation. On day 29 of gestation, the dams were killed and necropsied, and the fetuses were weighed, sexed, and examined for external abnormalities. No treatment-related deaths or clinical signs were observed. During treatment, the body-weight gain and food consumption of dams at the high dose were considerably reduced. The gravid uterine weights were not affected by treatment. The rate of pre-implantation loss was slightly reduced and that of postimplantation loss slightly increased at 40 mg/kg bw per day, which resulted in a comparable number of fetuses to controls. The body weights of female fetuses were slightly reduced at this dose. There were no remarkable external fetal changes (FitzGerald, 1990b). In the main study, groups of 19 pregnant Russian Chbb:HM rabbits received technical-grade dicyclanil in an aqueous solution of 0.5% sodium carboxy-methylcellulose by oral gavage at a daily dose of 0, 1, 3, 10, or 30 mg/kg bw on days 7-19 of gestation. On gestation day 29, the dams were killed and necropsied, and the fetuses were weighed, sexed, and examined for external, visceral, and skeletal abnormalities. The study was of conventional design, with GLP and quality assurance certification. No deaths or treatment-related clinical signs of toxicity were observed. Maternal body weight, body-weight gain, and food consumption and the carcass weight at necropsy were reduced at 30 mg/kg bw per day. Maternal body-weight gain was also reduced at 10 mg/kg bw per day. Necropsy of the dams revealed no treatment-related effects, and reproductive function was not affected. The body weights of fetuses at the highest dose were reduced, and the fetuses showed skeletal variations indicative of a slight delay in ossification. There was no evidence of teratogenicity. The NOEL for maternal toxicity was 3 mg/kg bw per day on the basis of reduced body-weight gain. The NOEL for developmental toxicity was 10 mg/kg bw per day on the basis of reduced fetal weight and increased skeletal variations consistent with delayed ossification (FitzGerald, 1993b). 2.2.6 Special studies: Pharmacological effects The effects of dicyclanil on the central nervous system (centrally controlled behaviour, body temperature, locomotor activity, hypnotic potentiation, motor coordination), the peripheral nervous system, the autonomic nervous system and smooth muscles, the cardiovascular and respiratory systems, and the gastrointestinal tract were investigated in mice, rats, and guinea-pigs in vivo and in vitro. The effect of dicyclanil on sperm morphology and motility was also examined. All of the studies followed the Japanese Guidelines for the Registration of Pharmaceuticals (General Pharmacology), with GLP and quality assurance certification. In vivo, technical-grade dicyclanil in polyethylene glycol 200:ethanol (5:3 v/v) was administered orally by gavage at a single dose of 0, 1, 10, 50, or 100 mg/kg bw to male NMRI mice or male Han Wistar rats. Doses < 100 mg/kg bw had no effect on the body temperature of rats (Pfister & Gisin, 1996a), on the hexobarbitone-induced sleeping time in mice (Pfister & Gisin, 1996b), or on gastrointestinal motility in mice (Pfister & Gisin, 1996c). In the modified Irwin test for general behavioural changes, treatment of mice with dicyclanil at 100 mg/kg bw slightly inhibited both exploratory activity and the startle response. The changes were most evident 6 h after treatment, with complete recovery of the startle response by 8 h and of exploratory activity by 24 h after treatment. Mice treated with 1 or 10 mg/kg bw showed normal behaviour (Pfister & Gisin, 1996d). After treatment with the vehicle, reduced locomotor activity (static, mobile, and rearing activity and mobile and active times) was seen in control mice over 24 h, being most pronounced during the first 8 h. These parameters were less markedly reduced after treatment with dicyclanil at 1 (not statistically significant) or 10 mg/kg bw. Opposite effects were induced by dicyclanil at 100 mg/kg bw, when the reduction in static activity was more pronounced than in controls while changes in the other parameters were comparable. All of the effects were fully reversed by 24 h after dosing (Pfister & Hussherr, 1996a). Motor coordination in mice, as assessed by recording the time the animals could retain their balance on a rotating rod, was inhibited at 100 mg/kg bw but not at 1 or 10 mg/kg bw. The effect was significant 4 h after dosing but had completely disappeared by 24 h (Pfister & Hussherr, 1996b). Treatment of rats with 100 mg/kg bw (the only dose tested) resulted in slight increases throughout the observation period (6-8 h after dosing) in heart rate (statistically significant) and tidal and minute lung volume (statistically significant only when compared with values for vehicle-treated animals, which generally had lower values than untreated animals). The blood pressure, electrocardiogram, and respiratory rate remained unchanged (Pfister & Nordmann, 1996). Treatment of rats with 50 mg/kg bw (the only dose tested) had no effect on sperm motility, concentration, or morphology. Minor, statistically nonsignificant increases in abnormal sperm morphology 6 weeks after dosing (sperm with head only and with abnormally shaped hooks) were completely reversed by 12 weeks after dosing (Pfister & Gisin, 1996e. In vitro, a concentration of 0, 0.1, 0.3, 1, or 3 mmol/L of technical-grade dicyclanil in dimethyl sulfoxide had no significant effect on directly induced contractions of skeletal muscle or on contractions induced indirectly by phrenic nerve stimulation in the isolated phrenic nerve-diaphragm preparation from rats. The authors concluded that dicylanil has no effect on the skeletal neuromuscular junction (Pfister & Hussherr, 1996c). When dicyclanil was tested on ileum isolated from guinea-pigs, dose-dependent antagonistic activity against the smooth muscle contractions induced by histamine and acetylcholine and against the nonspecific smooth muscle contractions induced by barium chloride was observed at concentrations > 0.3, 1, and > 0.3 mmol/L, respectively. All of the effects were fully and rapidly reversible. Dicyclanil was considered to be only a weak antagonist (Pfister & Gisin, 1996f). 3. COMMENTS The Committee considered the results of studies on the pharmacokinetics, metabolism, acute, short-term and long-term toxicity, carcinogenicity, genotoxicity, reproductive toxicity, and pharmacology of dicyclanil. All of the pivotal studies were carried out according to appropriate standards for study protocol and conduct. After repeated oral administration of radiolabelled dicyclanil to rats, the radiolabel was rapidly and almost completely absorbed and was rapidly distributed to the major organs and tissues. Elimination was rapid (> 93% of the total dose within 24 h) and was virtually complete within 3 days. The major route of elimination was the urine (79-83% of the total dose within 24 h), while the faecal route was of minor importance (6-12% of the total dose within 24 h). Biotransformation in the rat involves oxidative opening of the cyclopropyl ring at various positions, followed by further oxidation and cleavage of the cyclopropyl-N bond (i.e. dealkylation). The metabolic pathways of dicyclanil in sheep treated topically are essentially the same as those in rats. After oral administration of dicyclanil to rats, the LD50 values were 560 mg/kg bw in males and approximately 500 mg/kg bw in females. Dicyclanil is moderately hazardous when given as a single oral dose. In a three-month study of toxicity, rats received dicyclanil in the diet at a concentration of 0, 5, 25, 125, or 500 mg/kg of diet. Male rats at 125 and 500 mg/kg of diet showed decreased food consumption and body-weight gain and slightly decreased plasma glucose concentrations. The weights of the kidneys, brain, and testis relative to that of the body were increased in males at 500 mg/kg of diet, and females at this dose showed decreased food consumption, body-weight gain, and plasma glucose concentrations and increased relative weights of the liver and brain; plasma glucose concentrations were also reduced in females at 125 mg/kg of diet. The NOEL was 25 mg/kg of diet, equal to 1.6 mg/kg bw per day, on the basis of the reduction in body-weight gain. In a 3-month study of toxicity, dogs received dicyclanil in the diet at a concentration of 0, 20, 100, 500, or 1500 mg/kg of diet. Clinical signs consisting mainly of neurotoxicity, decreased food consumption and body-weight gain, and changes in clinical chemistry and erythrocyte parameters were observed mainly at the highest dose. Plasma cholesterol and phospholipid concentrations were increased in animals at concentrations of 100 mg/kg of diet and above. The weights of the spleen (males and females), thymus (males only), and testis were decreased at 1500 mg/kg of diet. Atrophy of the spleen in males and females and atrophy of the thymus, mesenteric lymph node, testis, and prostate in males were observed at concentrations of 100 mg/kg of diet and above. The weights of the liver, adrenals, and kidneys were increased in animals at the highest dose; in females, the liver weights were also increased at lower doses. Inflammatory changes were seen in the urinary bladder of females at concentrations of 100 mg/kg of diet and above and in the livers of males and females at 1500 mg/kg of diet. Hepatocyte oedema was observed in females at all doses, but hepatocellular damage was not seen at any dose in either sex. The Committee noted that hepatocyte oedema without hepatocellular damage is not of toxicological significance. Hence, the NOEL was 20 mg/kg of diet, equal to 0.61 mg/kg bw per day, on the basis of increased plasma cholesterol concentrations and histopathological findings in the prostate and urinary bladder. In a 1-year study, dogs received dicyclanil in the diet at a concentration of 0, 5, 25, 150, or 750 mg/kg of diet. Males showed slightly decreased plasma calcium concentrations and increased absolute and relative liver weights at 750 mg/kg of diet. Plasma cholesterol concentrations were increased in males at 150 and 750 mg/kg of diet, and this change was not reversed after a 4-week recovery period. Females receiving the highest dose vomited and had slightly reduced food consumption and body-weight gain, slightly increased plasma cholesterol concentrations, increased absolute and relative liver weights, and decreased absolute and relative heart weights. Macroscopic and microscopic findings consisting of liver necrosis, tubular lesions in the kidneys, testicular and prostatic atrophy, and vascular thrombus, were found in one male and one female at the highest dose that died before their scheduled sacrifice. These animals suffered from acute, severe liver failure and resulting cardiovascular disturbances and stress due to weight loss. Comparable acute, severe liver toxicity was not observed in the 3-month study of toxicity in dogs given feed containing dicyclanil at concentrations up to 1500 mg/kg of diet. The findings in the two animals were therefore considered to be incidental. The NOEL was 25 mg/kg of diet, equal to 0.71 mg/kg bw per day, on the basis of increased plasma cholesterol concentrations in male dogs. The Committee noted that this NOEL is supported by the NOEL in the 3-month study of toxicity in dogs. It also noted that the histopathological findings observed in the 3-month study were not seen in the 1-year study among animals that lived until the time of scheduled sacrifice. In a study of carcinogenicity, mice received diets containing dicyclanil at a concentration of 0, 10, 100, 500, or 1500 mg/kg of diet for 18 months. The animals at the highest dose were killed during weeks 58-59 because of self-inflicted injuries and poor health. On the basis of significant reductions in body-weight gain, the concentrations of 500 and 1500 mg/kg of diet in females and 1500 mg/kg of diet in males were considered to exceed the maximum tolerated dose. The liver was the main target organ in both male and female mice. The effects included Kupffer cell pigmentation (with haemosiderin) and hepatocellular necrosis in males at doses of 100 mg/kg of diet and higher, increased incidences of hepatocellular adenomas in females at 500 and 1500 mg/kg of diet, and hepatocellular carcinomas in females at 1500 mg/kg of diet. The Committee noted that these liver tumours were observed only at doses that exceeded the maximum tolerated dose and that there were signs of hepatocellular proliferation in these animals which might have been involved in the hepatic carcinogenesis observed. Pigmentation of the olfactory epithelium (with oxidized lipofuscins) was observed in animals of each sex at 100 and 500 mg/kg of diet; in the males, this effect was accompanied by an increased incidence of inflammatory cell infiltration in the underlying Bowman glands. Males and females at 500 mg/kg of diet also showed pigmentation of the adrenal glands (with partly oxidized lipofuscins) and hypercellularity of the bone marrow. As the Committee considered the effects on the olfactory epithelium to be of no biological significance, the NOEL was 10 mg/kg of diet, equal to 1.1 mg/kg bw per day, on the basis of the effects on the liver. In a 2-year study of carcinogenicity and toxicity, rats received diets containing dicyclanil at a concentration of 0, 5, 25, 125, or 500 mg/kg of diet. In animals at the highest dose, food consumption and body-weight gain were decreased, and the relative weights of almost all organs were increased as a result. Treatment-related histopathological alterations were observed in the exocrine pancreas (hyperplasia) in males at the highest dose, in the liver (biliary cysts) in females at the highest dose, and in the olfactory epithelium (pigmentation resulting from accumulation of oxidized lipofuscins) in males at doses of 25 mg/kg of diet and above and in females at doses of 125 mg/kg of diet and above. Although the latter represents enhancement of a naturally occurring age-related process, treatment had no effect on survival, behaviour, or general well-being, and there were no other morphological changes in the olfactory mucosa. Therefore, the Committee concluded that the effect on the olfactory epithelium was of no biological significance. Dicyclanil did not affect the incidence of tumours. The NOEL was 125 mg/kg of diet, equal to 22 mg/kg bw per day, on the basis of changes in body weight and histopathological changes in the liver and pancreas. Dicyclanil has been tested in vitro for its ability to induce reverse mutation in Salmonella typhimurium and Escherichia coli, gene mutation in Chinese hamster lung cells, chromosomal aberrations in Chinese hamster ovary cells, and unscheduled DNA synthesis in primary rat hepatocytes. It has been tested in vivo for its ability to induce micronuclei in bone-marrow cells of mice treated orally. The results of all of these tests were negative. On the basis of these data, the Committee concluded that dicyclanil is not genotoxic. Dicyclanil increased the incidence of liver tumours in female mice. However, as these tumours occurred in only one tissue of animals of one sex and one species at doses that were above the maximum tolerated dose, and dicyclanil is not genotoxic, the Committee concluded that dicyclanil does not represent a carcinogenic risk for humans. In a two-generation study of reproductive toxicity, with two litters per generation, rats were given dicyclanil in the diet at a concentration of 0, 5, 30, 200, or 500 mg/kg of diet. Treatment reduced the body-weight gain of the parental animals at the highest dose and, marginally, at 200 mg/kg of diet. Secondary to this effect, dicyclanil increased the relative weights of most organs in animals at the highest dose and of the brain (males and females), kidneys (males only), and testis at 200 mg/kg of diet. Reproductive parameters were not affected. The only effect of dicyclanil on pups was to reduce their weight gain from day 4 post partum onwards. The NOEL for parental toxicity was 30 mg/kg of diet, equal to 2 mg/kg bw per day, on the basis of changes in body weight. The NOEL for reproductive toxicity was 500 mg/kg of diet, equal to 24 mg/kg bw per day, the highest dose tested. The NOEL for toxicity to the pups was 200 mg/kg of diet, equal to 21 mg/kg bw per day, on the basis of reduced body-weight gain. In a study of developmental toxicity in rats given dicyclanil at a dose of 0, 1, 5, 25, or 75 mg/kg bw per day orally on days 6-15 of gestation, the highest dose was toxic to the dams, as seen by reductions in body-weight gain, food consumption, and the weight of the gravid uterus. Marginal reductions in body-weight gain and food consumption were also observed at 25 mg/kg bw per day. The effects on the fetuses, observed only at the highest dose, were reduced fetal weight, a slightly increased incidence of renal pelvic dilatation, and a number of mainly sternebral defects and variations due to poor or absent ossification. There was no evidence of teratogenicity. The NOEL for maternal toxicity was 5 mg/kg bw per day on the basis of the reduction in body-weight gain. The NOEL for developmental toxicity was 25 mg/kg bw per day on the basis of reduced fetal weight, increased renal pelvic dilatation, increased skeletal anomalies, and variations consistent with a slight delay in skeletal maturation. In a study of developmental toxicity in rabbits given dicyclanil at a dose of 0, 1, 3, 10, or 30 mg/kg bw per day orally on days 7-19 of gestation, dams at 30 mg/kg bw per day had reduced food consumption and those at 10 and 30 mg/kg bw per day showed reduced body-weight gain. The fetuses of dams at the highest dose had lower body weights than controls and an increased incidence of skeletal variations indicative of a slight delay in ossification. There was no evidence of teratogenicity. The NOEL for maternal toxicity was 3 mg/kg bw per day on the basis of reduced body-weight gain. The NOEL for developmental toxicity was 10 mg/kg bw per day on the basis of reduced fetal weight and skeletal variations consistent with delayed ossification. In pharmacological tests in vitro, dicyclanil at doses up to 3 mmol/L had no effect on the skeletal neuromuscular junction. At concentrations of 0.3 mmol/L and higher, it had slightly antagonistic effects on smooth muscle contractions induced by agonists. In mice and rats given a single oral dose of 0, 1, 10, 50, or 100 mg/kg bw, the highest dose affected general behaviour, locomotor activity, motor coordination, heart rate, and tidal and minute lung volume. Locomotor activity was also affected at 10 mg/kg bw and, very slightly, at 1 mg/kg bw. The treatment had no effect on body temperature, hypnotic potentiation, gastrointestinal motility, blood pressure, heart beat, or respiratory rate. 4. EVALUATION The Committee established an ADI of 0-7 mg/kg bw, on the basis of the NOEL of 0.71 mg/kg bw per day for increased plasma cholesterol concentrations in the 1-year study of toxicity in dogs and a safety factor of 100. As is its usual practice, the Committee rounded the value of the ADI to one significant figure. 5. REFERENCES Altmann, B. (1991) CGA 183893 tech. 28-Day range finding toxicity study in beagle dogs. Unpublished report (test no. 901202) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Altmann, B. (1993) CGA 183893 tech. 3-Month subchronic dietary toxicity study in beagle dogs. Unpublished report (test no. 922813) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Altmann, B. (1995) CGA 183893 tech. 12-Month chronic dietary toxicity study in beagle dogs. Unpublished report (test no. 922814) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Bachmann, M. (1991) CGA 183893 tech. 28-Days range finding study in rats (administration in food). Unpublished report (test no. 901201) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Bachmann, M. (1993) CGA 183893 tech. 3-Month oral toxicity study in rats (administration in food). Unpublished report (test no. 922810) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Bachmann, M. (1996a) CGA 183893 tech. 18-Month oncogenicity study in mice. Unpublished report (test no. 922815) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Bachmann, M. (1996b) CGA 183893 tech. 24-Month carcinogenicity and chronic toxicity study in rats. Unpublished report (test no. 922816) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Dubach-Powell, J.R. (1996) Pharmacokinetic study of CGA 183893 tech. in the rat. Unpublished letter report (RCC project no. 615295/Ciba project no. 952803) from Research & Consulting Company, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. FitzGerald, R.E. (1990a) Preliminary oral toxicity study with CGA 183893 technical in pregnant rats (Dose range-finding study). Unpublished report (test no. 901211) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. FitzGerald, R.E. (1990b) Preliminary toxicity study in pregnant rabbits with CGA 183893 technical (oral administration) (Dose rangefinding study). Unpublished report (test no. 901212) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. FitzGerald, R.E. (1993a) CGA 183893 technical: Rat oral teratogenicity. Unpublished report (study no. 922821) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. FitzGerald, R.E. (1993b) CGA 183893 technical: Rabbit oral teratogenicity. Unpublished report (study no. 922822) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Geleick, D. (1992) CGA 183893 tech. Gene mutation test with Chinese hamster cells V79 (OECD conform) in vitro. Unpublished report (test no. 922827) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hagemann, C. (1992a) CGA 183893 tech. Acute dermal irritation/corrosion study in the rabbit. Unpublished report (test no. 922803) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hagemann, C. (1992b) CGA 183893 tech. Acute eye irritation/corrosion study in the rabbit. Unpublished report (test no. 922802). CibaGeigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hagemann, C. (1993) CGA 183893 tech. Skin sensitization test in the guinea pig optimisation test. Unpubished report (test no. 922805) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hartmann, H.R. (1992a) CGA 183893 tech. Acute oral toxicity in the rat. Unpublished report (test no. 922801) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hartmann, H.R. (1992b) CGA 183893 tech. Acute dermal toxicity in the rat. Unpublished report (test no. 922804) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hartmann, H.R. (1993) CGA 183893 tech. Acute inhalation toxicity in the rat. Unpublished report (test no. 922806) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hassler, S. (1994) Absorption, distribution and elimination of [2-14C]pyrimidyl CGA 183893 in the rat after multiple oral administration. Unpublished report (report no. 7/94; project no. 012AM01) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hertner, T. (1992) CGA 183893 tech. Salmonella and Escherichia/liver-microsome test. Unpublished report (test no. 922825) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hertner, T. (1993a) CGA 183893 tech. Cytogenetic test on Chinese hamster cells in vitro (EC conform). Unpublished report (test no. 922826) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hertner, T. (1993b) CGA 183893 tech. Autoradiographic DNA repair test on rat hepatocytes (OECD conform) in vitro. Unpublished report (test no. 922824) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Hertner, T. (1993c) CGA 183893 tech. Micronucleus test, mouse (OECD conform). Unpublished report (test no. 922823) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Khalil, S. (1995) CGA 183893 technical: Rat dietary two-generation reproduction study. Unpublished report (study no. 922818) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Löffler, A. (1998) The nature of residues in tissues of sheep after single topical pour-on administration of [pyrimidine-2-14C]CGA 183893. Unpublished report (study no. 012AM04) from Novartis Crop Protection AG, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Marty, J.H. (1995) CGA 183893 tech. 28-Day repeated dose dermal toxicity study in the rat. Unpublished report (test no. 922807) from Ciba-Geigy Ltd, Stein, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Ogorek, B. & Arni, P. (1987) Salmonella mutagenicity test with three strains with CGA 183893 (Test for mutagenic properties in bacteria). Unpublished report (experiment no. 871051) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Gisin, M.(1996a) General pharmacology of CGA 183893 tech. Effect on the body temperature in the rat. Unpublished report (project no. RCC 615317/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Gisin, M. (1996b) General pharmacology of CGA 183893 tech. Effect on the sleeping time induced by hexobarbitone in the mouse. Unpublished report (project no. RCC 615330/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Gisin, M. (1996c) General pharmacology of CGA 183893 tech. Effect on the intestinal motility (charcoal propulsion) in the mouse. Unpublished report (project no. RCC 615385/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Gisin, M. (1996d) General pharmacology of CGA 183893 tech. Modified Irwin screen test in the mouse. Unpublished report (project no. RCC 615306/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Gisin, M. (1996e) General pharmacology of CGA 183893 tech. Effect on sperm motility, concentration and morphology in the rat. Unpublished report (project no. RCC 615407/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Gisin, M. (1996f) General pharmacology of CGA 183893 tech. Effect on the isolated ileum of the guinea pig. Unpublished report (project no. RCC 615363/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Hussherr, D. (1996a) General pharmacology of CGA 183893 tech. Effect on the locomotor activity in the mouse. Unpublished report (project no. RCC 615328/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Hussherr, D. (1996b) General pharmacology of CGA 183893 tech. Effect on motor co-ordination (rotarod) in the mouse. Unpublished report (project no. RCC 615341/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Hussherr, D. (1996c) General pharmacology of CGA 183893 tech. Effect on the isolated phrenic nerve-diaphragm preparation of the rat. Unpublished report (project no. RCC 615352/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Pfister, T. & Nordmann, A. (1996) General pharmacology of CGA 183893 tech. Effect on the cardiovascular and respiratory systems in the rat. Unpublished report (project no. RCC 615374/CG 952803) from Research & Consulting Company, Ltd, Itingen, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Phillips, M. (1996) [Pyrimidine-2-14C]-CGA 183893. Nature of metabolites in the excreta and tissues of sheep following single pour-on administration. Unpublished report (No. 14072; project no. 158665) from Inveresk Research, Tranent, Scotland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Thanei, P. (1996a) The metabolism of [2-14C]pyrimidyl CGA 183893 in the rat. Unpublished report (No.7/96; project no. 012AM02) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Thanei, P. (1996b) The nature of metabolites in tissues and excreta of sheep after single topical administration of [2-14C]pyrimidyl CGA 183893. Unpublished report (No. 9/96; project no. 012AM03) from Ciba-Geigy Ltd, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland. Weber, E. (1998) CGA 183893 tech. Pigmentation of the olfactory mucosa observed after dietary administration to rats. Unpublished report (report no. CB 98/05) from Novartis Crop Protection AG, Basel, Switzerland. Submitted to WHO by Novartis Animal Health Inc., Basel, Switzerland.
See Also: Toxicological Abbreviations DICYCLANIL (JECFA Evaluation)