TUMORS OF THE BLADDER, KIDNEY, AND INTESTINE OF F344 RATS AND LIVER OF B6C3F(1) MICE ADMINISTERED O-NITROANISOLE IN FEED

o-Nitroanisole, a mutagenic intermediate used in the manufacture of az o dyes, was administered in feed for 2 years at concentrations of 0, 2 22, 666, or 2000 ppm to groups of 60 male and 60 female F344 rats. No significant increase in neoplasms occurred in these groups of rats. Ad ditional (stop exposure) groups of 60 male and 60 female F344 rats rec eived diets containing 0, 6000, or 18,000 ppm for 27 weeks followed by maintenance on control diets for up to an additional 77 weeks. Surviv al of the stop exposure groups was reduced because of the development of chemical related neoplasms of the urinary bladder. After 13, 28, 40 , and 65 weeks on study, 10 rats per group were necropsied and evaluat ed for the presence of chemical associated lesions. Hyperplasia of the epithelium of the urinary bladder was significantly increased at all interim evaluations. A transitional cell carcinoma was observed at the 13-week evaluation in one male rat that received 18,000 ppm and there after transitional cell neoplasms of the bladder were present in male and female rats at each interim evaluation. Adenomatous polyps of the large intestine were significantly increased in groups that received 6 000 or 18,000 ppm. In addition carcinomas of the large intestine were present in four males and two females that received 18,000 ppm. Hyperp lasia of the transitional epithelium of the renal pelvis was significa ntly increased in groups of rats that received 6000 or 18,000 ppm and transitional cell papillomas were observed in three males and one fema le that received 18,000 ppm. Transitional cell carcinomas of the kidne y occurred in one male that received 6000 ppm and six males and one fe male that received 18,000. Groups of 60 male and 60 female B6C3F(1) mi ce received dietary concentrations of 0, 666, 2000, or 6000 ppm o-nitr oanisole for 2 years. No stop exposure study was conducted with mice. The only neoplastic response observed in mice was in the liver of male s; hepatocellular adenomas or carcinomas were increased in groups of m ale mice that received 2000 or 6000 ppm. No increase in neoplasms asso ciated with chemical exposure occurred in female mice. (C) 1996 Societ y of Toxicology