Bromodichloroacetic acid is a haloacetic acid that forms when drinking water supplies containing natural organic matter are disinfected with chlorine-containing oxidizing compounds and when bromide is present in the source water. Bromodichloroacetic acid was nominated for toxicity and carcinogenicity studies by the American Water Works Association Research Foundation and the United States Environmental Protection Agency because of widespread human exposure to this water disinfection by-product and because related dihaloacetic acids were found to be carcinogenic to the liver of rats and mice. Male and female F344/N rats and B6C3F1/N mice were exposed to bromodichloroacetic acid (greater than 97% pure) in drinking water for 2 weeks or 3 months, and male and female F344/NTac rats and B6C3F1/N mice were exposed for 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and mouse peripheral blood erythrocytes.
Two-week study in F344/N rats
Groups of five male and five female rats were exposed to 0, 62.5, 125, 250, 500, or 1,000 mg bromodichloroacetic acid/L drinking water for 16 days (equivalent to average daily doses of approximately 7, 15, 31, 56, or 131 mg bromodichloroacetic acid/kg body weight to males and 8, 15, 30, 58, or 113 mg/kg to females). All rats survived to the end of the study. Mean body weights of exposed groups of male and female rats were similar to those of the controls. Water consumption by exposed and control groups was similar. No organ weight differences were attributed to exposure to bromodichloroacetic acid. No gross or histologic lesions related to bromodichloroacetic acid exposure were observed.
Two-week study in F344/N mice
Groups of five male and five female mice were exposed to 0, 62.5, 125, 250, 500, or 1,000 mg bromodichloroacetic acid/L drinking water for 16 days (equivalent to average daily doses of approximately 10, 20, 41, 84, or 175 mg/kg to males and 11, 16, 40, 78, or 138 mg/kg to females). All mice survived to the end of the study. Mean body weights of exposed groups of male and female mice were similar to those of the controls. Water consumption by exposed and control groups was similar. No gross or histologic lesions related to bromodichloroacetic acid exposure were observed.
Three-month study in F344/N rats
Groups of 10 male and 10 female rats were exposed to 0, 62.5, 125, 250, 500, or 1,000 mg bromodichloroacetic acid/L drinking water for 14 weeks (equivalent to average daily doses of approximately 5, 9, 19, 37, or 72 mg/kg to males and 5, 10, 20, 43, or 69 mg/kg to females). In addition, groups of 10 male and 10 female clinical pathology study rats were exposed to the same concentrations for 4 weeks. All exposed rats survived until the end of the study. Mean body weights of 1,000 mg/L females were significantly less than those of the controls. Kidney weights of 1,000 mg/L females were significantly greater than those of the controls. Male rats exposed to 1,000 mg/L exhibited decreased left testis weights and sperm motility, suggesting a potential for bromodichloroacetic acid to be a reproductive toxicant in male rats. No chemical-related histologic lesions were noted.
Three-month study in F344/N mice
Groups of 10 male and 10 female mice were exposed to 0, 62.5, 125, 250, 500, or 1,000 mg bromodichloroacetic acid/L drinking water for 14 weeks (equivalent to average daily doses of approximately 7, 15, 30, 59, or 123 mg/kg to males and 9, 17, 36, 70, or 129 mg/kg to females). All mice survived to the end of the study. Mean body weights of exposed groups were similar to those of controls. Water consumption by exposed and control groups was generally similar. The absolute and relative liver weights of 500 and 1,000 mg/L males were significantly greater than those of controls, and the absolute kidney weight of 1,000 mg/L males was significantly less than that of controls. In the liver of females exposed to 1,000 mg/L, the incidence of glycogen depletion (minimal) was significantly greater than the control incidence.
Two-year study in F344/NTac rats
Groups of 66 male and 66 female rats were exposed to 0, 250, 500, or 1,000 mg bromodichloroacetic acid/L drinking water for up to 104 weeks (equivalent to average daily doses of approximately 11, 21, or 43 mg/kg to males and 13, 28, or 57 mg/kg to females). Eight male and eight female rats from each group were removed at 6 and 13 months for interim evaluations.
Survival of 500 and 1,000 mg/L females was significantly less than that of the controls. The mean body weights of 1,000 mg/L males were approximately 10% less than those of controls after week 89, and those of 1,000 mg/L females were less after week 13. Water consumption by 1,000 mg/L males was less than that by controls throughout the study; in 1,000 mg/L females, water consumption was less during the first year of the study but similar to control values during the second year. At the 6-month interim evaluation, relative liver weights of 500 and 1,000 mg/L females were significantly greater than those of the controls.
In females, the incidences of mammary gland fibroadenoma and fibroadenoma or carcinoma (combined) in all exposed groups were significantly greater than the control incidences, as was the incidence of carcinoma at 1,000 mg/L. The incidence of hyperplasia of the mammary gland in 1,000 mg/L females was significantly increased. Two males in the 250 mg/L group, three males in the 500 mg/L group, and one male in the 1,000 mg/L group had mammary gland fibroadenomas. No fibroadenomas were observed in the control males.
At the 13-month evaluation, the incidence of malignant mesothelioma of the testis in the 1,000 mg/L group was significantly increased. In all organs at 2 years, the incidences of malignant mesothelioma in males occurred with a positive trend and were significantly increased in all exposed groups.
The incidences of keratoacanthoma and of basal cell adenoma or carcinoma (combined) of the skin in males occurred with positive trends, and the 1,000 mg/L group incidences were significantly greater than the control incidences. The combined incidence of squamous cell papilloma, keratoacanthoma, sebaceous gland adenoma, basal cell adenoma, basal cell carcinoma, or squamous cell carcinoma in 1,000 mg/L males was significantly increased. The incidence of subcutaneous fibroma was significantly increased in 1,000 mg/L males.
The incidences of adenoma of the large intestine (cecum, colon, rectum) were slightly increased in 500 and 1,000 mg/L males.
Incidences of glioma, oligodendroglioma, and benign granular cell tumor of the meninges occurred in the brain of male rats in the original evaluation, but the differences between the exposed group incidences and the control group incidences were not statistically significant. An extended evaluation of additional brain sections, up to nine per animal, was conducted; one additional control male had a glioma and one additional 500 mg/L male had an oligodendroglioma. While there was no statistically significant increase in the incidences of glioma or oligodendroglioma (combined), these neoplasms have not been observed in historical controls.
One male in the control group and three each in the 500 and 1,000 mg/L groups had squamous cell papillomas or squamous cell carcinomas of the oral cavity (oral mucosa or tongue).
In the bone marrow, the incidences of angiectasis in all exposed groups of males and females and hyperplasia in all exposed groups of females and in 1,000 mg/L males were significantly increased when compared to the control group incidences.
At 2 years, the incidence of eosinophilic focus in the liver of 1,000 mg/L males and 500 and 1,000 mg/L females were significantly increased. Also, there were significantly increased incidences of hepatic hematopoietic cell proliferation in 500 and 1,000 mg/L females.
In the spleen of females, significantly increased incidences of hematopoietic cell proliferation were observed in the 500 and 1,000 mg/L groups.
Two-year study in F344/NTac mice
Groups of 66 male and 66 female mice were exposed to 0, 250, 500, or 1,000 mg bromodichloroacetic acid/L drinking water for up to 105 weeks (equivalent to average daily doses of approximately 23, 52, or 108 mg/kg to males and 17, 34, or 68 mg/kg to females). Seven or eight male and eight female mice from each group were removed at 6 and 14 months for interim evaluations.
Survival of 500 and 1,000 mg/L males was significantly decreased. The most common cause of early deaths in 500 mg/L males and 1,000 mg/L males and females appeared to be liver neoplasms. Compared to those of controls, mean body weights were over 10% less in 500 mg/L males after week 73, in 1,000 mg/L males after week 57, in 250 and 500 mg/L females after week 89, and in 1,000 mg/L females after week 73. Water consumption by all exposed groups of males and by 250 and 500 mg/L females was generally greater than that by controls during the second year of the study. At the 6-month interim evaluation, left and right kidney weights of 1,000 mg/L males were significantly less than those of the controls.
At the 14-month evaluation, exposure concentration-related increased incidences of atypical focus of cellular alteration of the liver were noted in all exposed groups of male and female mice, and the incidences in 1,000 mg/L males and females were significantly increased. A single case of hepatoblastoma was noted in a 1,000 mg/L male.
At 2 years, the incidences of hepatocellular adenoma in all exposed groups of females, hepatocellular carcinoma in all exposed groups of males and in 500 and 1,000 mg/L females, and hepatoblastoma in all exposed groups of males and in 1,000 mg/L females were significantly increased compared to those in the control groups. The incidences of multiple hepatocellular carcinoma and multiple hepatoblastoma in males and females and multiple hepatocellular adenoma in females were generally increased in an exposure concentration-related manner. When combined, the incidences of hepatocellular adenoma, hepatocellular carcinoma, or hepatoblastoma were significantly increased in 250 and 1,000 mg/L males and in all exposed groups of females.
In the liver, the incidences of eosinophilic focus in exposed females and atypical focus of cellular alteration (i.e., eosinophilic cell focus and mixed cell focus) in exposed groups of males and females (except 250 mg/L) were significantly greater than those in the controls.
In the Harderian gland of males, the incidences of adenoma and adenoma or carcinoma (combined) in the 500 and 1,000 mg/L groups were significantly greater than those in the controls.
The incidences of atrophy of the testis increased with increasing exposure concentration, and the increases in the 500 and 1,000 mg/L groups were significant. In the epididymis, the incidences of atrophy in all exposed groups, hypospermia in the 1,000 mg/L group, and epithelium degeneration in the 500 and 1,000 mg/L groups were significantly increased.
Genetic toxicology
Bromodichloroacetic acid was tested in two independent bacterial gene mutation assays. In the first assay, conducted with an uncharacterized sample of bromodichloroacetic acid, the compound was judged to be weakly positive based on responses seen in S. typhimurium strain TA97 in the presence of rat or hamster S9 metabolic activation enzymes; an equivocal response was obtained in TA97 in the absence of S9, and no mutagenic activity was seen in strains TA98, TA100, or TA1535. In the second assay, conducted with the same well-characterized lot of bromodichloroacetic acid that was used in the 2-year bioassays, positive responses were seen in S. typhimurium strains TA97, TA98, and TA100 and the E. coli strain WP2 uvrA/pkM101 in the absence of S9. With rat S9, equivocal responses were seen with the three S. typhimurium tester strains, and a positive response was observed in the E. coli strain. In vivo, no significant increases in the frequencies of micronucleated normochromatic erythrocytes or the percent of polychromatic erythrocytes (reticulocytes) were observed in blood samples from male or female B6C3F1/N mice administered bromodichloroacetic acid in drinking water for 3 months.
Conclusions
Under the conditions of these 2-year studies, there was clear evidence of carcinogenic activity (see a summary of the Peer Review Panel comments and the public discussion on this Technical Report in Appendix P) of bromodichloroacetic acid in male F344/NTac rats based on increased incidences of malignant mesothelioma and the combined incidences of epithelial tumors of the skin. Occurrences of subcutaneous fibromas were also related to exposure to bromodichloroacetic acid. Occurrences of glioma or oligodendroglioma (combined) of the brain, squamous cell papilloma and squamous cell carcinoma of the oral cavity (oral mucosa or tongue), adenoma of the large intestine, and fibroadenoma of the mammary gland may have been related to exposure to bromodichloroacetic acid. There was clear evidence of carcinogenic activity of bromodichloroacetic acid in female F344/NTac rats based on increased incidences of fibroadenoma and carcinoma of the mammary gland. The occurrences of glioma or oligodendroglioma (combined) of the brain may have been related to bromodichloroacetic acid exposure. There was clear evidence of carcinogenic activity of bromodichloroacetic acid in male B6C3F1/N mice based on increased incidences of hepatocellular carcinoma and hepatoblastoma and increased incidences of adenoma or carcinoma (combined) of the Harderian gland. There was clear evidence of carcinogenic activity of bromodichloroacetic acid in female B6C3F1/N mice based on increased incidences of hepatocellular adenoma, hepatocellular carcinoma, and hepatoblastoma.
Exposure to bromodichloroacetic acid for 2 years resulted in increased incidences of nonneoplastic lesions in the bone marrow and liver of male and female rats, spleen of female rats, liver of male and female mice, and testis and epididymis of male mice.
National Toxicology Program (NTP). 2015. NTP technical report on the toxicology studies of bromodichloroacetic acid (CASRN 71133-14-7) in F344/N rats and B6C3F1/N mice and toxicology and carcinogenesis studies of bromodichloroacetic acid in F344/NTac rats and B6C3F1/N mice (drinking water studies). Research Triangle Park, NC: National Toxicology Program. Technical Report 583. https://doi.org/10.22427/NTP-TR-583