Carcinogenicity and chronic toxicity of butyl methacrylate in rats and mice by a two-year inhalation study.

We conducted a two-year inhalation study of butyl methacrylate using F344/DuCrlCrlj rats and B6D2F₁/Crl mice. Rats were exposed to 0, 30, 125 and 500 ppm (v/v) and mice were exposed to 0, 8, 30 and 125 ppm (v/v) using whole-body inhalation chambers. Non-neoplastic lesions developed in the nasal cavities of both rats and mice, but neoplastic lesions were not found. There was also a positive trend in the incidence of large granular lymphocytic (LGL) leukemia in the spleen of male rats. No changes were observed in female rats. Overall, there is some evidence of carcinogenicity in male rats, but there is no evidence of carcinogenicity in female rats. In male mice, there was a positive trend by Peto's test in the incidence of hepatocellular adenomas, and the incidence of hepatocellular adenomas and hepatocellular carcinomas combined was significantly increased compared to the controls by Fisher's exact test in the 30 ppm exposed male group. In female mice, the incidence of hemangiosarcoma in all organs combined showed a positive trend by Peto's test. Therefore, there is some evidence of carcinogenicity in male mice, and there is equivocal evidence of carcinogenicity in female mice.