title: Toxicology and Carcinogenesis Studies of Bromoethane (Ethyl Bromide) (CAS No. 74-96-4) in F344/N Rats and B6C3F1 Mice (Inhalation Studies).
abstract: Bromoethane is an alkylating agent used primarily as a chemical intermediate in various organic syntheses. In toxicology and carcinogenesis studies, groups of F344/N rats and B6C3F1 mice of each sex received whole-body exposure to bromoethane (greater than 98% pure) once for 4 hours or for 6 hours per day, 5 days per week, for 14 days, 14 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Chinese hamster ovary (CHO) cells. Single-Exposure, Fourteen-Day, and Fourteen-Week Studies: Single-exposure inhalation studies were conducted in rats and mice at target concentrations of 625, 1,250, 2,500, 5,000, or 10,000 ppm bromoethane. All rats exposed to 10,000 ppm bromoethane and 3/5 female rats exposed to 5,000 ppm died before the end of the single-exposure studies. All mice exposed to 5,000 or 10,000 ppm bromoethane and 2/5 female mice exposed to 1,250 ppm died before the end of the studies. Fourteen-day inhalation studies were conducted in rats and mice at target concentrations of 0, 250, 500, 1,000, 2,000, or 4,000 ppm bromoethane. All rats and mice exposed to 2,000 or 4,000 ppm died before the end of the 14-day studies. Final mean body weights of exposed and control rats were similar. Fourteen-week inhalation studies were conducted in rats and mice at target concentrations of 0, 100, 200, 400, 800, or 1,600 ppm bromoethane. Four of 10 male and 2/10 female rats exposed to 1,600 ppm died before the end of the 14-week studies. The final mean body weights of rats exposed to 1,600 ppm were lower than the initial mean body weights. Compound-related lesions observed in rats at 1,600 ppm, but not at lower concentrations, included minimal atrophy of the thigh muscle, minimal-to-moderate multifocal mineralization in the cerebellum of the brain, minimal-to-severe hemosiderosis of the spleen, marked atrophy of the testis, and minimal-to- mild atrophy of the uterus. The effects in the testis and uterus are probably due to chemical-related loss in body weight during the studies. In mice, compound-related deaths included 3/10 male and 1/10 female mice exposed to 1,600 ppm, 1/9 males exposed to 800 ppm, and 1/10 males exposed to 400 ppm. The final mean body weights of male and female mice exposed to 1,600 ppm were about 15% lower than those of controls. Compound-related effects included atrophy of the uterus and involution of the ovary in females exposed to 1,600 ppm bromoethane. Based on these results, 2-year studies were conducted by exposing groups of 49 or 50 rats or mice of each sex to bromoethane at 0, 100, 200, or 400 ppm, 6 hours per day, 5 days per week. Body Weight and Survival in the Two-Year Studies: Mean body weights of exposed and control rats were generally similar throughout the studies. No significant differences in survival were observed between any groups of male rats (control, 17/49; 100 ppm, 26/50; 200 ppm, 27/50; 400 ppm, 21/50); survival of the 100-ppm group of female rats was greater than that of controls (19/50; 29/50; 24/49; 23/50), and the number of control and 400-ppm male rats and control female rats surviving to the end of the studies was low. Mean body weights of the 400-ppm group of male mice were up to 9% lower than those of controls throughout the study. Mean body weights of the 400-ppm group of female mice were generally 6%-16% lower than those of controls after week 29. No differences in survival were observed between any group of male mice (35/50; 37/50; 30/50; 34/50). The survival of the 400-ppm group of female mice was lower than that of controls at the end of the study (36/50; 37/50; 37/49; 23/49). Nonneoplastic and Neoplastic Effects in the Two-Year Studies: The incidences of pheochromocytomas or malignant pheochromocytomas (combined) of the adrenal medulla were increased in exposed male rats (control, 8/40; 100 ppm, 23/45; 200 ppm, 18/46; 400 ppm, 21/46). Granular cell neoplasms of the brain were seen in exposed male rats but not in controls (0/49; 3/50; 1/50; 1/50). A glioma, an astrocytoma, or an oligodendroglioma was seen in 3/50 male rats exposed to 100 p in 3/50 male rats exposed to 100 ppm. Gliomas were not observed in control female rats, but they occurred in exposed female rats with a significant positive trend (0/50; 1/50; 1/48; 3/50). The historical incidence of granular cell tumors in male F344/N rat chamber controls at the study laboratory is 0/297. The incidences of gliomas in the exposed female groups were not significantly greater than that in the controls and were within the historical incidence range for glial cell neoplasms for untreated controls in NTP studies (mean: 23/1,969, 1&percnt;; range: 0/50-3/50), but they exceeded the historical incidence range for chamber controls at the study laboratory (mean: 1/297, 0.3&percnt;; range: 0/50-1/50). Alveolar epithelial hyperplasia was increased in rats exposed to 400 ppm bromoethane (male: 3/48; 7/49; 7/48; 18/48; female: 5/50; 4/48; 5/47; 10/49). Alveolar/bronchiolar adenomas or carcinomas (combined) were seen in four male rats exposed to 200 ppm and in one exposed to 400 ppm. Alveolar/bronchiolar adenomas were observed in 3/49 female rats at 400 ppm but not at lower concentrations or in controls. The incidences in exposed male and female rats were not significantly greater than those in controls; however, the historical incidence in rat chamber controls for alveolar/bronchiolar adenomas or carcinomas (combined) at the study laboratory is 6/299 (2&percnt;) for males and 4/297 (1.3&percnt;) for females. The incidences of epithelial hyperplasia and squamous metaplasia of the nasal cavity were increased in rats exposed to 400 ppm. The incidence of suppurative inflammation of the nasal cavity was increased in exposed male rats, and the incidences of suppurative inflammation of the larynx and metaplasia of the olfactory sensory epithelium were increased in exposed male and female rats. An adenoma of the nose was seen in one 400-ppm male rat and in one 400-ppm female mouse. Suppurative inflammation and dilatation of the salivary gland ducts were observed at increased incidences in the 200- and 400-ppm groups of female rats. Animals were found to be positive for rat coronavirus/sialodacryoadenitis virus antibodies. The incidence of mammary gland neoplasms was significantly lower in female rats at 400 ppm than in controls (18/50; 15/50; 10/48; 7/50). Adenomas (0/50; 1/50; 1/47; 6/48), adenocarcinomas (0/50; 2/50; 3/47; 19/48), and squamous cell carcinomas (0/50; 1/50; 1/47; 3/48) of the uterus occurred in exposed female mice and not in control mice. The incidence of alveolar/bronchiolar neoplasms was greater in male mice at 400 ppm than in controls (adenomas or carcinomas, combined: 7/50; 6/50; 12/50; 15/50). Acute/chronic inflammation of the lung was observed at increased incidences in female mice at 200 and 400 ppm. Genetic Toxicology: Bromoethane, tested in a closed environment of a desiccator, was mutagenic in S. typhimurium strain TA100 with and without exogenous metabolic activation; it was not mutagenic in strain TA98. In cultured CHO cells, bromoethane induced sister chromatid exchanges (SCEs) but not chromosomal aberrations in both the presence and absence of exogenous metabolic activation. Conclusions: Under the conditions of these 2-year inhalation studies, there was some evidence of carcinogenic activity of bromoethane for male F344/N rats, as indicated by increased incidences of pheochromocytomas of the adrenal gland; neoplasms of the brain and lung may also have been related to exposure to bromoethane. For female F344/N rats, there was equivocal evidence of carcinogenic activity, as indicated by marginally increased incidences of neoplasms of the brain and lung. For male B6C3F1 mice, there was equivocal evidence of carcinogenic activity, based on marginally increased incidences of neoplasms of the lung. There was clear evidence of carcinogenic activity for female B6C3F1 mice, as indicated by neoplasms of the uterus. Synonyms: monobromoethane; bromic ether; hydrobromic ether