5-Chloro-o-toluidine, an aromatic amine and dye intermediate, was selected for bioassay by the National Cancer Institute because of the high incidence of bladder cancer observed among dye manufacturing industry workers.
A bioassay for the possible carcinogenicity of 5-chloro-o-toluidine was conducted using Fisher 344 rats and B6C3F1 mice. 5-Chloro-o-toluidine was administered in the feed, at either of two concentrations, to groups of 50 male and 50 female animals of each species. Twenty animals of each sex and species were placed on test as controls. The high and low dietary concentrations of 5-chloro-o-toluidine were 5,000 and 2,500 ppm for rats and 4,000 and 2,000 ppm for mice. The compound was administered in the diet for 78 weeks, followed by an observation period of 26 weeks for rats and 13 weeks for mice.
There were significant positive associations between the concentrations of 5-chloro-o-toluidine administered and mortality among male and female mice, but not among rats of either sex. Adequate numbers of animals in all groups survived sufficiently long to be at risk from late-developing tumors. Distinct mean body weight depression was apparent when dosed female rats and dosed mice of both sexes were compared to their controls, indicating that the concentrations administered to these animals in this bioassay may have approximated the maximum tolerated concentrations. Since no mean body weight depression, relative to controls, no significantly accelerated mortality, and no signs of toxicity other than fatty metamorphosis of the liver were associated with administration of 5-chloro-o-toluidine to male rats, it is possible that these animals may have been able to tolerate a higher dietary concentration of the compound.
There was a significant positive association between the concentration of 5-chloro-o-toluidine administered to male rats and the incidence of adrenal pheochromocytomas in these animals; however, neither of the Fisher comparisons was significant. None of the other statistical tests fortumors at any site in male and female rats indicated a significant positive association between dosage and incidence.
In mice of both sexes there were significant positive associations between concentration administered and the incidence of hemangiosarcomas. In addition, the high dose to control Fisher exact comparisons for both sexes were significant. The Cochran-Armitage tests were also significant and positive for the incidences of hepatocellular carcinomas in both sexes of mice. For males and females the high dose to control Fisher exact comparisons were significant, and for females the low dose to control comparison was also significant.
Under the conditions of this bioassay, 5-chloro-o-toluidine was carcinogenic to B6C3F1 mice, inducing hemangiosarcomas and hepatocellular carcinomas in both males and females. There was no conclusive evidence of the carcinogenicity of the compound in Fisher 344 rats.