Bromodichloromethane (99% pure), one of several trihalomethanes commonly formed after chlorination of water, was selected for study because no carcinogenicity data were available for this compound and because chloroform, a related trihalomethane, had been found to cause tumors in rodents. The general population might be exposed to bromodichloromethane in drinking water supplies, in swimming pools, and in a variety of food substances.
Single-administration, 14-day, 13-week, and 2-year studies were conducted in F344/N rats and B6C3F1 mice. The chemical was administered by gavage in corn oil because human exposure is primarily oral. Additional studies were performed to evaluate the potential for genetic damage in bacteria and mammalian cells.
Results of the short-term studies
In the single-administration studies, the chemical was administered at doses of 150-2,500 mg/kg per day. All rats and female mice at 1,250 and 2,500 mg/kg and all male mice at 600, 1,250, and 2,500 mg/kg died; 2/5 male rats, 1/5 female rats, and 2/5 female mice at 600 mg/kg died; all animals at lower dose levels survived.
In the 14-day studies, rats received doses of 38-600 mg/kg, and mice received doses of 19-300 mg/kg per day. One female rat at 38 mg/kg and one female rat at 600 mg/kg died. Weight loss or decreased weight gain was seen at 300 and 600 mg/kg in male and female rats. All male mice at 150 and 300 mg/kg died, and one female mouse at 300 mg/kg died; no weight effects were observed in surviving mice. Dose-related necropsy findings included reddened renal medullae in male rats at 600 mg/kg and in male mice at 150 and 300 mg/kg. Clinical signs seen in high dose groups after dosing were hyperactivity in rats and lethargy in mice.
In the 13-week studies, male and female rats received doses of 19-300 mg/kg per day, male mice received doses of 6.25-100 mg/kg per day, and female mice received doses of 25-400 mg/kg per day. Five of 10 male rats and 2/10 female rats at 300 mg/kg died. None of the mice died. Final body weights of male and female rats at 150 and 300 mg/kg were lower than those of vehicle controls (45%-88% of vehicle control weights); final body weights of male mice at 100 mg/kg and female mice at 400 mg/kg were 92% and 94% of those of the vehicle controls. Centrilobular degeneration in the liver and degeneration and necrosis of the kidney were seen in male rats at 300 mg/kg; centrilobular degeneration was seen in female rats at 300 mg/kg; degeneration andnecrosis of the kidney were seen in male mice at 100 mg/kg, and centrilobular degeneration of the liver was seen in female mice at 200 and 400 mg/kg.
Survival and body weight
Final survival of dosed rats was comparable to that of vehicle controls (male: vehicle control, 28/50; low dose, 36/50; high dose, 28/50; female: 34/50; 27/50; 41/50). Mean body weights of high dose male and female rats were decreased during the last 1.5 years of the study; final mean body weights of high dose male and female rats were 88% and 79% of the vehicle control mean weights. Final mean body weights of low dose male and female rats were comparable to those of the vehicle controls.
Final survival of dosed male mice was comparable to that of the vehicle controls (34/50; 32/50; 42/50). At week 84, survival of female mice was greater than 50% in all dose groups. After week 84, survival of dosed and vehicle control female mice was reduced (final survival: 26/50; 13/50; 15/50), and this decreased survival was associated with ovarian abscesses (8/50; 19/47; 18/49). The final mean body weight of high dose male mice was 95% that of the vehicle controls; the final mean body weight of low dose male mice was comparable to that of the vehicle controls. Mean body weights of the high dose female mice were decreased during the last 1.5 years of the study; the final mean body weight was 75% that of the vehicle controls. The final mean body weight of the low dose female mice was 91% that of the vehicle controls.
Compound-related nonneoplastic lesions included cytomegaly and tubular cell hyperplasia of the kidney and necrosis and fatty metamorphosis of the liver in male rats; eosinophilic cytoplasmic change, clear cell change, focal cellular change, and fatty metamorphosis of the liver and tubular cell hyperplasia of the kidney in female rats; fatty metamorphosisof the liver, renal cytomegaly, and follicular cell hyperplasia of the thyroid gland in male mice; and follicular cell hyperplasia of the thyroid gland in female mice.
Bromodichloromethane caused compound-related increases in the incidences of neoplasms of the large intestine and kidney in male and female rats, the kidney in male mice, and the liver in female mice, as shown in the table (see page 5 of the Technical Report). The neoplasms of the large intestine and kidney are uncommon tumors in F344/N rats and B6C3F1 mice.
Administration of bromodichloromethane was also associated with a decrease in the tumors of the adrenal glands in male rats, the pituitary and mammary glands in female rats, and the pituitary gland in female mice.
An audit of the experimental data was conducted for the 2-year toxicology and carcinogenesis studies of bromodichloromethane. No discrepancies were found that influenced the final interpretations of the results of these studies.
Under the conditions of these 2-year gavage studies, there was clear evidence of carcinogenic activity for male and female F344/N rats and B6C3F1 mice as shown by increased incidences of tubular cell adenomas and adenocarcinomas in the kidney and adenocarcinomas and adenomatous polyps in the large intestine in male and female rats, increased incidences of tubular cell adenomas and adenocarcinomas in the kidney of male mice, and increased incidences of hepatocellular adenomas and carcinomas in female mice.