Bromochloroacetic acid is a water disinfection by-product. Bromochloroacetic acid was nominated to the National Toxicology Program by the United States Environmental Protection Agency for toxicity and carcinogenicity studies in rats and mice because of widespread human exposure and because a related dihaloacetate, dichloroacetate, was found to be carcinogenic to the liver of rats and mice. Drinking water was selected as the route of exposure to mimic human exposure to this chemical. Male and female F344/N rats and B6C3F1 mice were exposed to bromochloroacetic acid (greater than 95% pure) in drinking water for 2 weeks, 3 months, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and peripheral blood erythrocytes of exposed mice.
Two-week study in rats
Groups of five male and five female rats were exposed to drinking water containing 0, 62.5, 125, 250, 500, or 1,000 mg/L bromochloroacetic acid for 2 weeks (equivalent to average daily doses of approximately 9, 18, 35, 75, or 140 mg bromochloroacetic acid/kg body weight to males and 8, 17, 35, 70, or 130 mg/kg to females). All rats survived to the end of the study. Mean body weights of exposed males and females were similar to those of the controls. Water consumption by exposed and control groups was similar. Right kidney weights of 1,000 mg/L males were significantly increased. No exposure-related gross or histopathologic lesions were observed.
Two-week study in mice
Groups of five male and five female mice were exposed to drinking water containing 0, 62.5, 125, 250, 500, or 1,000 mg/L bromochloroacetic acid for 2 weeks (equivalent to average daily doses of approximately 10, 20, 40, 80, or 170 mg/kg to males and 9, 17, 40, 75, or 155 mg/kg to females). All mice survived to the end of the study. Mean body weights of 250 mg/L males were significantly greater than those of the controls. Water consumption by exposed and control groups was similar. No gross or histopathologic lesions related to exposure to bromochloroacetic acid were observed.
Three-month study in rats
Groups of 10 male and 10 female rats were exposed to drinking water containing 0, 62.5, 125, 250, 500, or 1,000 mg/L bromochloroacetic acid for 3 months (equivalent to average daily doses of approximately 5, 10, 20, 40, or 75 mg/kg to males and 5, 10, 20, 40, or 85 mg/kg to females). All rats survived to the end of the study. Mean body weights of exposed male and female rats were similar to those of the controls. Water consumption by exposed and control groups was similar. Liver weights of 500 and 1,000 mg/L males and females and kidney weights of 1,000 mg/L males were significantly increased. In the liver, there were significantly increased incidences of cytoplasmic vacuolization in 1,000 mg/L males and females.
Three-month study in mice
Groups of 10 male and 10 female mice were exposed to drinking water containing 0, 62.5, 125, 250, 500, or 1,000 mg/L bromochloroacetic acid for 3 months (equivalent to average daily doses of approximately 8, 16, 32, 65, or 125 mg/kg to males and 8, 17, 35, 70, or 140 mg/kg to females). All mice survived to the end of the study. Mean body weight gains of females exposed to 250 mg/L or greater were significantly decreased. Water consumption by exposed and control groups was similar. Liver weights of 1,000 mg/L males and all exposed groups of females were significantly increased. All males and females exposed to 500 or 1,000 mg/L had periportal cytoplasmic vacuolization. In the spleen, there were increased incidences of hematopoietic cell proliferation in 62.5, 125, and 250 mg/L males and 125 and 1,000 mg/L females.
Two-year study in rats
Groups of 50 male and 50 female rats were exposed to drinking water containing 0, 250, 500, or 1,000 mg/L bromochloroacetic acid for 2 years (equivalent to average daily doses of approximately 10, 20, or 40 mg/kg to males and 13, 25, or 50 mg/kg to females). Survival of exposed rats was similar to that of the control groups. Mean body weights of 500 mg/L males were 8% less than the control group after week 81, and those of 1,000 mg/L males were 10% less than the control group after week 69. Mean body weights of 1,000 mg/L females were 10% less than the control group after week 85. Water consumption by exposed and control groups was similar.
The incidences of malignant mesothelioma in all exposed groups of male rats exceeded the historical control ranges, and the incidence in the 500 mg/L group was significantly increased. Positive trends in the incidences of adenoma of the large intestine (colon or rectum) occurred in male and female rats, and the incidence in 1,000 mg/L females was significantly increased. Although the incidences of mammary gland fibroadenoma were not significantly increased in exposed female rats, the incidences of multiple fibroadenomas of the mammary gland were increased in 500 and 1,000 mg/L females. The incidence of pancreatic islet adenoma was significantly increased in 500 mg/L males. The incidences of hepatocellular adenoma occurred with a positive trend in females; the incidences in 500 mg/L males and 1,000 mg/L males and females exceeded the historical control ranges.
In the liver, the incidences of eosinophilic focus in 500 mg/L females and 1,000 mg/L males and females and of mixed cell focus in 1,000 mg/L females were significantly increased. In the lung, the incidence of alveolar epithelium hyperplasia was significantly increased in 1,000 mg/L females.
Two-year study in mice
Groups of 50 male and 50 female mice were exposed to drinking water containing 0, 250, 500, or 1,000 mg/L bromochloroacetic acid for 2 years (equivalent to average daily doses of approximately 25, 50, or 90 mg/kg to males and 15, 30, or 60 mg/kg to females). Survival of 1,000 mg/L males was significantly less than that of the control group. Mean body weights of 1,000 mg/L males were 12% less than the control group after week 97, and those of 1,000 mg/L females were 8% less than the control group after week 21. Water consumption by exposed and control groups was similar.
The incidences of hepatocellular adenoma in 250 and 500 mg/L males and all exposed groups of females, hepatocellular carcinoma in 500 and 1,000 mg/L males and 500 mg/L females, hepatocellular adenoma or carcinoma (combined) in all exposed groups of males and females, and hepatoblastoma in all exposed groups of males were significantly increased. The incidences of hepatocyte cytoplasmic vacuolization in all exposed groups, eosinophilic focus in 500 and 1,000 mg/L females, and centrilobular necrosis in 1,000 mg/L males were significantly increased.
The incidences of hematopoietic cell proliferation of the spleen were significantly increased in 500 and 1,000 mg/L males, and the incidence of bone marrow hyperplasia was significantly increased in 1,000 mg/L males.
Genetic toxicology
In two different bacterial mutagenicity assays, bromochloroacetic acid was positive in Salmonella typhimurium strain TA100, in tests conducted with and without exogenous metabolic activation enzymes (S9); no mutagenicity was detected in strain TA98 or in Escherichia coli WP2 uvrA/pKM101, with or without S9. No significant increases in the frequency of micronucleated erythrocytes were observed in blood samples of male or female mice exposed to bromochloroacetic acid for 3 months in drinking water, indicating no induction of chromosomal damage in proerythrocytes under these conditions in mice.
Conclusions
Under the conditions of these 2-year studies there was clear evidence of carcinogenic activity of bromochloroacetic acid in male F344/N rats based on increased incidences of malignant mesotheliomas and adenomas of the large intestine. There was clear evidence of carcinogenic activity of bromochloroacetic acid in female F344/N rats based on increased incidences of adenomas of the large intestine; increased incidences of multiple fibroadenomas of the mammary gland in female rats were also considered to be exposure related. Increased incidences of pancreatic islet adenomas in male rats and of hepatocellular adenomas in male and female rats may have been related to bromochloroacetic acid exposure. There was clear evidence of carcinogenic activity of bromochloroacetic acid in male and female B6C3F1 mice based on increased incidences of hepatocellular neoplasms and hepatoblastoma (males only).
Exposure to bromochloroacetic acid for 2 years resulted in increased incidences of nonneoplastic lesions in the liver of male rats, liver and lung of female rats, and liver of male and female mice.