NTP Technical Report on the Toxicity Studies of 1,1,2,2-Tetrachloroethane (CAS No. 79-34-5) Administered in Microcapsules in Feed to F344/N Rats and B6C3F1 Mice
1,1,2,2-Tetrachloroethane is a solvent that was used in soil sterilization and as an ingredient in herbicides, insecticides, paints, varnishes, metal cleaners, and degreasers. Its production in the United States as an end-product ceased in the early 1990s. 1,1,2,2-Tetrachloroethane is currently used only as a chemical intermediate in the production of other chemicals. It was nominated for study because it was widely used and because it is found in hazardous waste sites and in surface water and groundwater. F344/N rats and B6C3F1 mice were administered 1,1,2,2-tetrachloroethane (at least 99% pure) in microcapsules in the feed for 15 days or 14 weeks. Animals were evaluated for clinical pathology, reproductive system effects, and histopathology. Genetic toxicity studies were conducted in vitro in Salmonella typhimurium, L5178Y mouse lymphoma cells, and Chinese hamster ovary cells and in vivo in Drosophila melanogaster and mouse peripheral blood erythrocytes.
In the 15-day studies, groups of five male and five female rats and mice were fed diets containing 3,325, 6,650, 13,300, 26,600, or 53,200 ppm microencapsulated 1,1,2,2-tetrachloroethane. Additional groups of five male and five female rats and mice served as untreated controls, receiving feed without microcapsules, or as vehicle controls, receiving feed with empty microcapsules. Exposure concentrations of 3,325, 6,650, and 13,300 ppm resulted in average daily doses of 300, 400, and 500 mg 1,1,2,2-tetrachloroethane per kilogram body weight to male and female rats. All rats and mice exposed to 53,200 ppm, all rats and male mice exposed to 26,600 ppm, and two male mice exposed to 13,300 ppm died or were killed moribund before the end of the studies. The mean body weights of all exposed groups of rats and mice with survivors were significantly less than those of the vehicle controls, and all of these groups except 3,325 ppm male rats and female mice lost weight during the studies. Clinical findings included thinness and ruffled fur in rats and mice; 53,200 ppm rats and 26,600 and 53,200 ppm male mice were lethargic, while male mice in the lower exposure groups and exposed female mice (except the 53,200 ppm group) were hyperactive. Thymus weights of rats exposed to 6,650 or 13,300 ppm and all exposed groups of female mice were significantly less than those of the vehicle controls. Liver weights of male rats in the 13,300 ppm group were also significantly less than those of the vehicle controls.
At necropsy, thin carcasses were noted in all exposed groups of male rats, in female rats exposed to 13,300 ppm or greater, in male mice exposed to 6,650 or 13,300 ppm, and in female mice exposed to 13,300 or 26,600 ppm. In rats, hepatodiaphragmatic nodules were noted grossly in one untreated control female, one female exposed to 6,650 ppm, one male and one female exposed to 13,300 ppm, and two males and one female exposed to 26,600 ppm; mild or moderate centrilobular degeneration was observed microscopically in the exposed rats with liver nodules. Pale or mottled livers were noted in all groups of exposed male and female mice and correlated microscopically with hepatocellular degeneration; the severity of hepatocellular degeneration increased with increasing exposure concentration.
In the 14-week studies, groups of 10 male and 10 female rats were fed 268, 589, 1,180, 2,300, or 4,600 ppm microencapsulated 1,1,2,2-tetrachloroethane, and groups of 10 male and 10 female mice received 589, 1,120, 2,300, 4,550, or 9,100 ppm, which resulted in average daily doses of 20 to 320 mg/kg for male and female rats, 100 to 1,360 mg/kg for male mice, and 80 to 1,400 mg/kg for female mice. Additional groups of 10 male and 10 female rats and mice served as untreated and vehicle controls. Groups of 10 male and 10 female special study rats designated for hematology and clinical chemistry analyses on study days 5 and 21 received the same exposure concentrations as the core study rats. All core study animals survived to the end of the studies. The mean body weights of male and female rats exposed to 1,180 ppm or greater and male and female mice exposed to 2,300 ppm or greater were generally significantly less than those of the vehicle controls. Male and female rats in the 4,600 ppm groups lost weight during the study. Clinical findings of toxicity included thinness and pallor in all rats in the 2,300 and 4,600 ppm groups and thinness in mice exposed to 2,300 ppm or greater. Results of the functional observation battery indicated no exposurerelated findings of neurotoxicity in rats or mice.
Results of the hematology and clinical chemistry analyses indicated that exposure of rats and mice to 1,1,2,2-tetrachloroethane induced a hepatic effect, as demonstrated by increases in serum alanine aminotransferase, sorbitol dehydrogenase, alkaline phosphatase, and 5 -nucleotidase activities and total bile acid concentrations. Decreases in serum concentrations of total protein and cholesterol could also have been related to a liver effect or may have been related to the nutritional status of the animals. There was evidence indicating an effect on the circulating erythroid mass, characterized by a minimal to mild microcytic nonresponsive anemia, in exposed rats. Minimal decreases in platelet and lymphocyte counts also occurred in exposed rats.
The thymus weights of female rats exposed to 4,600 ppm were significantly less than those of the vehicle controls. The liver weights of male and female rats increased with increasing exposure concentration up to 1,180 ppm; at higher exposure concentrations, absolute liver weights decreased along with decreasing body weights, although relative liver weights remained increased. The liver weights of male mice in the 1,120 and 2,300 ppm groups and females in all exposed groups were significantly greater than those of the untreated and vehicle controls. Kidney weights of male mice exposed to 2,300 ppm or greater were significantly less than those of the vehicle controls.
Thin carcasses, pale livers, and/or liver foci were noted grossly in exposed male and female rats and mice in the 14-week studies; additionally, exposed male rats had small testes and seminal vesicles and exposed female rats had small or thin uteri. Pale kidneys were observed in one male mouse in each of the 4,550 and 9,100 ppm groups. Microscopic lesions of minimal to moderate average severity were observed in the liver of exposed male and female rats, and splenic lesions were observed in male and female rats administered 1,180 ppm or greater. Male and female rats in the 4,600 ppm groups and females in the 2,300 ppm group also had atrophy of the bone metaphysis and bone marrow, prostate gland, preputial gland, seminal vesicle, testicular germinal epithelium, uterus, and clitoral gland. The incidence of cytoplasmic alteration of the ovarian interstitial cells was significantly increased in female rats in the 4,600 ppm group.
Liver hepatocyte hypertrophy and necrosis, focal pigmentation, and bile duct hyperplasia were observed in exposed male and female mice in the 14-week study. Males also had increased incidences of preputial gland atrophy.
Results of reproductive tissue evaluations in the 14-week studies indicated decreased left cauda epididymis, left epididymis, and left testis (mice) weights and epididymal spermatozoal motility in exposed male rats and mice relative to the vehicle controls. Female rats in the 2,300 ppm group spent more time in diestrus and less time in proestrus, estrus, and metestrus than did vehicle control females. The estrous cycle of female mice in the 9,100 ppm group was longer than that of the vehicle controls.
1,1,2,2-Tetrachloroethane was negative for induction of mutations in S. typhimurium strains TA97, TA98, TA100, TA1535, and TA1537 with and without S9 metabolic activation. It did not induce trifluorothymidine resistance in L5178Y mouse lymphoma cells with or without S9. In cytogenetic tests with cultured Chinese hamster ovary cells, 1,1,2,2-tetrachloroethane induced sister chromatid exchanges but not chromosomal aberrations in the presence and the absence of S9. No increases in the frequencies of sex-linked recessive lethal mutations were observed in germ cells of male D. melanogaster administered 1,1,2,2-tetrachloroethane via feeding or injection. Positive results were obtained in the in vivo peripheral blood micronucleus test in mice in the 14-week feed study; significant increases in the frequencies of micronucleated normochromatic erythrocytes were observed in males and females.
Synonyms: Acetylene tetrachloride; 1,1-dichloro-2,2-dichloroethane; sym-tetrachloroethane; TCE; 1,1,2,2-TCE; tetrachloroethane
Trade names: Acetosol, Bonoform, Boroform, Cellon
Report Date: March 2004