Toxicology and Carcinogenesis Studies of Hexachloroethane(CAS No. 67-72-1) in F344/N Rats (Gavage Studies)
Chemical Formula: C2Cl6
Hexachloroethane is used in organic synthesis as a retarding agent infermentation, as a camphor substitute in nitrocellulose, in pyrotechnics andsmoke devices, in explosives, and as a solvent. In previous long-termgavage studies with B6C3F1 mice and Osbourne-Mendelrats (78 weeks of exposure followed by 12-34weeks of observation), hexachloroethane caused increased incidences ofhepatocellular carcinomas in mice. However, survival of low and high doseratswas reduced compared with that of vehicle controls, and the effects on ratswere inconclusive. Therefore, additional toxicology and carcinogenesisstudieswere conducted in F344/N rats by administering hexachloroethane(approximately99% pure) in corn oil by gavage to groups of males and females for 16 days,13weeks, or 2 years. Genetic toxicology studies were conducted inSalmonellatyphimurium and in Chinese hamster ovary (CHO) cells. Urinalysis wasperformed in conjunction with the 13-weekstudies.
In the 16-daystudies (dose range, 187-3,000 mg/kg), all rats that received 1,500 or 3,000mg/kg and 1/5 males and 2/5 females that received 750 mg/kg died before theendof the studies. Final mean body weights of rats that received 750 mg/kg were25% lower than that of vehicle controls for males and 37% lower for females.Compound-related clinical signs seen at 750 mg/kg or more includeddyspnea,ataxia, prostration, and excessive lacrimation. Other compound-relatedeffects included hyaline droplet formation in the tubular epithelial cells inall dosed males and tubular cell regeneration and granular casts in the tubulesat the corticomedullary junction in the kidney in males receiving 187 and 375mg/kg.
In the 13-weekstudies (dose range, 47-750 mg/kg), 5/10 male rats and 2/10 female rats thatreceived 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 ofvehiclecontrols. Compound-related clinical signs for both sexes includedhyperactivity at doses of 94 mg/kg or higher and convulsions at doses of 375or750 mg/kg. The relative weights of liver, heart, and kidney were increased forexposed males and females. Kidney lesions were seen in all dosed malegroups,and the severity increased with dose. Papillary necrosis and tubular cellnecrosis and degeneration in the kidney and hemorrhagic necrosis in theurinarybladder were observed in the five male rats that received 750 mg/kg and diedbefore the end of the studies; at all lower doses, hyaline droplets, tubularregeneration, and granular casts were present in the kidney. Nochemical-related kidney lesions were observed in females. Foci ofhepatocellular necrosis were observed in several male and female rats atdosesof 188 mg/kg or higher.
Dose selection for the 2-yearstudies was based primarily on the lesions of the kidney in males and of theliver in females. Studies were conducted by administering hexachloroethaneincorn oil by gavage at 0, 10, or 20 mg/kg body weight, 5 days per week, togroups of 50 male rats. Groups of 50 female rats were administered 0, 80, or160 mg/kg on the same schedule.
Body Weight and Survival in the Two-YearStudies:
Mean body weights of high dose rats were slightly (5%-9%)lower than those of vehicle controls toward the end of the studies. Nosignificant 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 in the Two-YearStudies:
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 tubulehyperplasiawas 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 hyalinedroplet nephropathy that is associated with an accumulation ofliver-generateda2µ-globulinin the cytoplasm of tubular epithelial cells. The severity of nephropathy wasincreased in high dose male rats (moderate vs. mild), and the incidences andseverity 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 renaltubulewere also increased in the high dose male group. One of the carcinomas inthehigh dose group metastasized to the lung. No compound-relatedneoplasms were observed in females.
The incidence of pheochromocytomas of the adrenal gland in low dose maleratswas significantly greater than that in vehicle controls (15/50; 28/50; 21/49),and the incidences for both dosed groups were greater than the meanhistoricalcontrol incidence (28% ± 11%).
Hexachloroethane was not mutagenic in S.typhimuriumstrains TA98, TA100, TA1535, or TA1537 when tested with and withoutexogenousmetabolic activation. In CHO cells, hexachloroethane did notinduce chromosomalaberrations with or with out metabolic activation but did produce sisterchromatid exchanges in the presence of exogenous metabolic activation.
The data, documents, and pathology materials from the 2-yearstudies of hexachloroethane have been audited. The audit findings show thattheconduct of the studies is documented adequately and support the data andresults given in this Technical Report.
Under the conditions of these 2-yeargavage studies, there was clear evidence of carcinogenic activity ofhexachloroethane for male F344/N rats, based on the increased incidences ofrenal neoplasms. The marginally increased incidences ofpheochromocytomas ofthe adrenal gland may have been related to hexachloroethane administrationtomale rats. There was no evidence of carcinogenic activity ofhexachloroethane for female F344/N rats administered 80 or 160 mg/kg bygavagefor 103 weeks.
The severity of nephropathy and incidences of linear mineralization of therenal papillae and hyperplasia of the transitional epithelium of the renalpelvis were increased in dosed male rats. The incidences and severity ofnephropathy were increased in dosed female rats.
Synonyms: carbon hexachloride; ethane hexachloride; hexachlorethane;hexachloroethylene; 1,1,1,2,2,2-hexachloroethane; perchloroethane
Trade Names: Avlothane; Distokal; Distopan; Distopin; Egitol; Falkitol;Fasciolin; Mottenhexe; Phenohep
Note: Hexachloroethane was previously tested in Osborne-Mendel rats andB6C3F1mice by gavage (See TR-68, reported 1978).
Report Date: August 1989