Hexachloroethane is used in organic synthesis as a retarding agent in fermentation, as a camphor substitute in nitrocellulose, in pyrotechnics and smoke devices, in explosives, and as a solvent. In previous long-term gavage studies with B6C3F1 mice and Osbourne-Mendel rats (78 weeks of exposure followed by 12-34 weeks of observation), hexachloroethane caused increased incidences of hepatocellular carcinomas in mice. However, survival of low and high dose rats was reduced compared with that of vehicle controls, and the effects on rats were inconclusive. Therefore, additional toxicology and carcinogenesis studies were conducted in F344/N rats by administering hexachloroethane(approximately 99% pure) in corn oil by gavage to groups of males and females for 16 days,13 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and in Chinese hamster ovary (CHO) cells. Urinalysis was performed in conjunction with the 13-week studies.
Sixteen-day studies
In the 16-day studies (dose range, 187-3,000 mg/kg), all rats that received 1,500 or 3,000 mg/kg and 1/5 males and 2/5 females that received 750 mg/kg died before the end of the studies. Final mean body weights of rats that received 750 mg/kg were 25% lower than that of vehicle controls for males and 37% lower for females. Compound-related clinical signs seen at 750 mg/kg or more included dyspnea, ataxia, prostration, and excessive lacrimation. Other compound-related effects included hyaline droplet formation in the tubular epithelial cells in all dosed males and tubular cell regeneration and granular casts in the tubules at the corticomedullary junction in the kidney in males receiving 187 and 375mg/kg.
Thirteen-week studies
In the 13-week studies (dose range, 47-750 mg/kg), 5/10 male rats and 2/10 female rats that received 750 mg/kg died before the end of the studies. The final mean bodyweight of male rats that received 750 mg/kg was 19% lower than that of vehicle controls. Compound-related clinical signs for both sexes included hyperactivity at doses of 94 mg/kg or higher and convulsions at doses of 375 or 750 mg/kg. The relative weights of liver, heart, and kidney were increased for exposed males and females. Kidney lesions were seen in all dosed male groups, and the severity increased with dose. Papillary necrosis and tubular cell necrosis and degeneration in the kidney and hemorrhagic necrosis in the urinary bladder were observed in the five male rats that received 750 mg/kg and died before the end of the studies; at all lower doses, hyaline droplets, tubular regeneration, and granular casts were present in the kidney. No chemical-related kidney lesions were observed in females. Foci of hepatocellular necrosis were observed in several male and female rats at doses of 188 mg/kg or higher.
Dose selection for the 2-year studies was based primarily on the lesions of the kidney in males and of the liver in females. Studies were conducted by administering hexachloroethane in corn oil by gavage at 0, 10, or 20 mg/kg body weight, 5 days per week, to groups of 50 male rats. Groups of 50 female rats were administered 0, 80, or 160 mg/kg on the same schedule.
Two-year studies
Body weight and survival
Mean body weights of high dose rats were slightly (5%-9%) lower than those of vehicle controls toward the end of the studies. No significant differences in survival were observed between any groups of rats (male: vehicle control, 31/50; 10 mg/kg, 29/50; 20 mg/kg, 26/50; female: vehicle control, 32/50; 80 mg/kg, 27/50; 160 mg/kg, 32/50).
Nonneoplastic and neoplastic effects
Incidences of kidney mineralization (vehicle control, 2/50; low dose,15/50; high dose, 32/50) and hyperplasia of the pelvic transitional epithelium(0/50; 7/50; 7/50) were increased in dosed male rats. Renal tubule hyperplasia was observed at an increased incidence in high dose male rats (2/50; 4/50;11/50). These lesions have been described as characteristic of the hyaline droplet nephropathy that is associated with an accumulation of liver-generated a2µ-globulin in the cytoplasm of tubular epithelial cells. The severity of nephropathy was increased in high dose male rats (moderate vs. mild), and the incidences and severity of nephropathy were increased in dosed females (22/50; 42/50;45/50). The incidences of adenomas (1/50; 2/50; 4/50), carcinomas (0/50; 0/50; 3/50), and adenomas or carcinomas (combined) (1/50; 2/50; 7/50) of the renal tubule were also increased in the high dose male group. One of the carcinomas in the high dose group metastasized to the lung. No compound-related neoplasms were observed in females.
The incidence of pheochromocytomas of the adrenal gland in low dose male rats was significantly greater than that in vehicle controls (15/50; 28/50; 21/49),and the incidences for both dosed groups were greater than the mean historical control incidence (28% ± 11%).
Genetic toxicology
Hexachloroethane was not mutagenic in S.typhimurium strains TA98, TA100, TA1535, or TA1537 when tested with and without exogenous metabolic activation. In CHO cells, hexachloroethane did not induce chromosomal aberrations with or without metabolic activation but did produce sister chromatid exchanges in the presence of exogenous metabolic activation.
Data audit
The data, documents, and pathology materials from the 2-year studies of hexachloroethane have been audited. The audit findings show that the conduct of the studies is documented adequately and support the data and results given in this Technical Report.
Conclusions
Under the conditions of these 2-year gavage studies, there was clear evidence of carcinogenic activity of hexachloroethane for male F344/N rats, based on the increased incidences of renal neoplasms. The marginally increased incidences of pheochromocytomas of the adrenal gland may have been related to hexachloroethane administration to male rats. There was no evidence of carcinogenic activity of hexachloroethane for female F344/N rats administered 80 or 160 mg/kg by gavage for 103 weeks.
The severity of nephropathy and incidences of linear mineralization of the renal papillae and hyperplasia of the transitional epithelium of the renal pelvis were increased in dosed male rats. The incidences and severity of nephropathy were increased in dosed female rats.
4-Vinyl-1-cyclohexene diepoxide is used a chemical intermediate and as a reactive diluent for diepoxides and epoxy resins. Toxicology and carcinogenesis studies were conducted by administering 4-vinyl-1-cyclohexene diepoxide (97% pure) in acetone by dermal application to individually housed F344/N rats and B6C3F1 mice for 14 days, 13 weeks, 15 months, and 2 years. Additional studies included evaluation of immune function after a 5-day dermal exposure and evaluation of the oral toxicity of 4-vinyl-1-cyclohexene diepoxide in 16-day and 13-week corn oil gavage studies. Genetic toxicology studies were conducted in Salmonella typhimurium, mouse L5178Y lymphoma cells, and Chinese hamster ovary (CHO) cells.
Fourteen-day dermal studies
In the 14-day studies, all rats that received 924 mg/kg or higher (equivalent to 139 mg/rat or higher for males and 112 mg/rat of higher for females) died before the end of the studies. Final mean body weights were lower than those of vehicle controls in males receiving 68 mg/rat and in females receiving 57 mg/rat. Excoriations on the skin at the application site were observed in the groups receiving 57 mg/rat or more. Males receiving 139 mg/rat and females receiving 112 mg/rat had congestion and/or hypoplasia of the bone marrow; most had acute nephrosis. Skin lesions, including epidermal necrosis and ulceration, epidermal hyperplasia, and hyperkeratosis, were found in the 139 and 112 mg/rat group; similar lesions of lesser severity were seen in the two lowest dose groups of each sex.
All mice that received 1,787 mg/kg (equivalent to 43/mouse for males and 37 mg/mouse for females) and 3/5 male mice and 5/5 female mice that received 889 mg/kg (equivalent to 19-21 mg/mouse) died before the end of the 14-day dermal studies. Final mean body weights of exposed and vehicle control mice were generally similar. Lesions of the skin at the site of application were seen in 4/5 males and 4/5 females receiving 5 mg/mouse and all mice receiving 10 and 21 (males) or 19 (females) mg/mouse and included epidermal and sebaceous gland hyperplasia, hyperkeratosis, and ulceration.
Thirteen-week studies
In the 13-week dermal studies, all rats survived to the end of the studies (doses up to 60 mg/rat). The final mean body weights of the 60 mg/rat groups were 9%-14% lower than those of the vehicle controls. Compound-related clinical signs in the 60 mg/rat groups observed during the second half of the studies included redness, scabs, and ulceration at the application site and burrowing behavior after dermal application. Hyperplasia of the sebaceous glands and acanthosis (hyperplasia) and hyperkeratosis of the squamous epithelium were seen at the site of application.
In mice, no compound-related deaths occurred after applications of up to 10 mg/mouse in 13-week dermal studies, and final mean body weights of exposed and vehicle control mice were similar. Relative liver and kidney weights increased with dose. Compound-related lesions of the skin included sebaceous gland hyperplasia and acanthosis (hyperplasia) and hyperkeratosis of the stratified squamous epithelium at the site of application; ovarian atrophy was also considered to be compound related.
In the 13-week oral studies, the major target organ of toxicity in rats and mice was the forestomach, as indicated by hyperkeratosis and hyperplasia of the stratified squamous epithelium. In female mice, ovarian atrophy was seen in 4-vinyl-1-cyclohexene diepoxide-dosed groups.
Two-year studies were conducted by administering 4-vinyl-1-cyclohexene diepoxide in acetone by dermal application, 5 days per week for 105 weeks to groups of 60 rats of each sex at 0, 15, or 30 mg/animal. Groups of 60 mice of each sex were administered 0, 2.5, 5, or 10 mg/animal on the same schedule for 103 weeks. None of the doses selected had produced ulceration of skin in 13-week studies. Ten animals from each group were killed and examined during month 15 for toxicologic evaluation.
Immune function studies
The immunotoxic effects of 4-vinyl-1-cyclohexene diepoxide were studied in male B6C3F1 mice after a 5-day dermal exposure at doses ranging from 2.5 to 10 mg/mouse per day. 4-Vinyl-1-cyclohexene diepoxide was immunosuppressive at 10 mg/mouse and, to a lesser extent, at 5 mg/mouse, as indicated by a decrease in peripheral lymphocytes and the in vitro lymphoproliferative response to phytohemagglutinin and concanavalin A in the high dose group and suppression of the antibody plaque-forming-cell response in the 5 and 10 mg/mouse groups.
Fifteen-month evaluation
Two of 10 male rats that received 30 mg had a squamous cell carcinoma of the skin at or adjacent to the site of application. Acanthosis was seen in exposed rats (mild severity at 30 mg/rat and minimal severity at 15 mg/rat); hyperkeratosis was observed for rats in the 30 mg/rat groups.
Compound-related nonneoplastic skin lesions in mice included acanthosis, hyperkeratosis, and sebaceous gland hyperplasia/hypertrophy. Squamous cell papillomas and carcinomas were seen in mice that received 5 or 10 mg/mouse; none was seen in vehicle control or low dose groups (papillomas--male: mid dose, 1/10; high dose, 2/10; female: 1/10; 1/10; carcinomas-- male: 2/10; 8/10; female: 2/10; 5/10). One vehicle control and all exposed female mice had atrophy of the ovary. Hyperplasia of the ovarian surface epithelium was seen in 8/10 females receiving 5 mg/mouse and 9/9 females receiving 10 mg/mouse. Two of nine females receiving 10 mg/mouse had granulosa cell tumors of the ovary, and 1/9 females receiving 10 mg/mouse had an ovarian papillary cystadenoma.
Two-year studies
Body weights and survival
In general, the body weights and survival were lower in mid and high dose groups than in vehicle controls. The survival was lower in exposed groups, primarily because of neoplasms (survival at week 105--male rats: vehicle control, 7/50; low dose, 8/50; high dose, 4/50; female rats: 27/50; 23/50; 15/50; male mice: vehicle control, 38/50; low dose, 35/50; mid dose, 4/50; high dose, 0/50; female mice: 30/50; 31/50; 15/50; 0/50). All high dose male mice died by week 83; the 10 surviving high dose female mice were killed during week 85.
Nonneoplastic and neoplastic effects
Acanthosis and sebaceous gland hypertrophy of skin from the scapula or back were observed at substantially increased incidences in exposed male and female rats. Squamous cell papillomas in male rats and squamous cell carcinomas in male and female rats were observed only in exposed rats (squamous cell carcinomas--male: vehicle control, 0/50; low dose, 33/50; high dose, 36/50; female: 0/50; 16/50; 34/50). The incidences of basal cell adenomas or carcinomas (combined) were increased (male: 0/50; 1/50; 6/50; female: 0/50; 3/50; 4/50).
For exposed mice, acanthosis, hyperkeratosis, and necrotizing inflammation of the skin were observed over the scapula or back. Squamous cell carcinomas were found only in exposed mice (male: vehicle control, 0/50; low dose, 14/50; mid dose, 39/50; high dose, 42/50; female: 0/50; 6/50; 37/50; 41/50).
Follicular atrophy and tubular hyperplasia of the ovary in female mice were increased (atrophy: 12/50; 43/49; 47/50; tubular hyperplasia: 5/50; 35/49; 38/49; 34/50). Mid and high dose females had benign or malignant granulosa cell tumors (0/50; 0/49; 7/49; 12/50) and benign mixed tumors (0/50; 0/49; 11/49; 6/50). The combined incidences of luteomas, granulosa cell tumors, benign mixed tumors, or malignant granulosa cell tumors in mid and high dose female mice were increased (1/50; 0/49; 17/49; 18/50).
The incidences of alveolar/bronchiolar adenomas or carcinomas (combined) in exposed female mice were marginally increased (4/50; 9/50; 11/50; 7/50).
Genetic toxicology
4-Vinyl-1-cyclohexene diepoxide was mutagenic in S. typhimurium strains TA98, TA100, and TA1535 with and without exogenous metabolic activation; the compound was equivocally mutagenic in strain TA1537 without S9 but gave a positive response in the presence of activation. 4-Vinyl-1-cyclohexene diepoxide induced resistance to trifluorothymidine in mouse L5178Y/TK cells without exogenous metabolic activation; it was not tested with activation. 4-Vinyl-1-cyclohexene diepoxide induced sister chromatid exchanges and chromosomal aberrations in CHO cells in the presence and absence of exogenous metabolic activation.
Conclusions
Under the conditions of these 2-year dermal studies, there was clear evidence of carcinogenic activity of 4-vinyl-1-cyclohexene diepoxide for male and female F344/N rats, as shown by squamous cell and basal cell neoplasms of the skin. There was clear evidence of carcinogenic activity of 4-vinyl-1-cyclohexene diepoxide for male and female B6C3F1 mice, as shown by squamous cell carcinomas of the skin in males and squamous cell carcinomas of the skin and ovarian neoplasms in females; increased incidences of lung neoplasms in females may also have been related to chemical application.