Bioassay of 4-Nitro-o-phenylenediamine for Possible Carcinogenicity (CAS No. 99-56-9)

4-Nitro-o-phenylenediamine, a component of both semipermanent and permanent hair dye formulations, was selected for bioassay by the National Cancer Institute because of the high incidence of bladder cancer reported among workers in the dye manufacturing industry. A bioassay for the possible carcinogenicity of 4-nitro-o-phenylenediamine was conducted using Fischer 344 rats and B6C3F1 mice. 4-Nitro-o-phenylenediamine 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 4-nitro-o-phenylenediamine were, respectively, 750 and 375 ppm for rats and 7500 and 3750 ppm for mice. The compound was administered for 103 weeks to rats and for 102 weeks to mice. The period of compound administration was followed by an observation period of 2 weeks for rats and mice. There were no significant positive associations between the concentrations of 4-nitro-o-phenylenediamine administered and mortality in rats or mice of either sex. Adequate numbers of animals in all groups survived sufficiently long to be at risk from late-developing tumors. Distinct dose-related mean body weight depression was observed in mice, indicating that the concentrations of 4-nitro-o-phenylenediamine administered to these animals in this bioassay may have approximated the maximum tolerated concentrations. Since no distinct mean body weightdepression relative to controls, no significantly accelerated mortality, and no other manifestations of chronic toxicity were associated with administration of 4-nitro-o-phenylenediamine to male or female rats, it is possible that these animals may have been able to tolerate a higher dietary concentration. None of the statistical tests for any site in rats or in mice of either sex indicated a significant positive association between compound administration and tumor incidence. Under the conditions of this bioassay, dietary administration of 4-nitro-o-phenylenediamine was not carcinogenic in Fischer 344 rats or B6C3F1 mice. Levels of Evidence of Carcinogenicity: Male Rats: Negative Female Rats: Negative Male Mice: Negative Female Mice: Negative Synonyms: 4-nitro-1,2-benzenediamine; 4-nitro-phenylenediamine; 4-nitro-1,2-diaminobenzene; 1,2-diamino-4-nitrobenzene; 2-amino-4-nitroaniline; 4-NO; 4-NOP; 4-NOPD; 4-N-o-PDA; C.I. 76020