title: Bioassay of 4-chloro-o-phenylenediamine for possible carcinogenicity.
abstract: A bioassay for the possible carcinogenicity of technical-grade 4-chloro-o-phenylenediamine was conducted using Fischer 344 rats and B6C3F1 mice. 4-Chloro-o-phenylenediamine was administered in the feed, at either of two concentrations, to groups of 49 or 50 male and 50 female animals of each species. For male and female rats, the high and low time-weighted average dietary concentrations of 4-chloro-o-phenylenediamine were 1.0 and 0.5 percent, respectively. For male and female mice, the high and low time-weighted average dietary concentrations were 1.4 and 0.7 percent, respectively. After a 78-week period of chemical administration, observation of the rats continued for up to an additional 28 weeks and observation of the mice continued for up to an additional 18 weeks. Fifty animals of each species and sex were placed on test as controls for the chronic bioassay. There was a statistically significant positive association between increased dosage and accelerated mortality in female rats and male mice; however, survival among all groups was adequate for meaningful statistical analysis of late-developing tumors. In male and female rats receiving the test chemical, a significantly increased incidence of neoplasms of the urinary bladder occurred. Neoplastic nodules in the liver and tumors of the forestomach may also have been related to administration of the chemical. A significantly increased incidence of hepatocellular carcinomas occurred in chemically treated male and female mice. It is concluded that under the conditions of this bioassay 4-chloro-o-phenylenediamine was carcinogenic in Fischer 344 rats and B6C3F1 mice, inducing tumors of the urinary bladder and forestomach in both sexes of rats and hepatocellular carcinomas in both sexes of mice.