2,4-Dimethoxyaniline hydrochloride, the hydrochloride salt of the dye intermediate 2,4-dimethoxyaniline, was selected for bioassay by the National Cancer Institute because of the increased incidence of bladder cancer among dye manufacturing industry workers. Aromatic amines are one of several classes of chemicals thought to contribute to the increased cancer risk in this industry.
A bioassay for the possible carcinogenicity of 2,4-dimethoxyaniline HCl was conducted using Fischer 344 rats and B6C3F1 mice. 2,4-Dimethoxyaniline HCl 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 2,4-dimethoxyaniline HCl were, respectively, 3,000 and 1,500 ppm for rats and 5,000 and 2,500 ppm for mice. The compound was administered in the diet for 104 weeks to rats and 103 weeks to mice, followed by a 1-week observation period for both species.
There were no significant positive associations between the concentrations of 2,4-dimethoxyaniline HCl 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. Dose-related mean body weight depression was observed for females of both species, indicating that the concentrations of 2,4-dimethoxyaniline HCl administered to these groups may have approximated the maximum tolerated concentrations. Compound-related mean body weight depression was only slight for male rats and was apparent in male mice only until week 50; however follicular-cell hyperplasias and cystic follicles of the thyroid were observed in dosed male mice, suggesting that the concentrations the male mice received may have approximated the maximum tolerated concentrations. Since no distinct mean body weight depression in relation to controls, no significant accelerated mortality, and no other signs of toxicity were associated with administration of 2,4-dimethoxyaniline HCl to male rats, it is possible that these animals may have been able to tolerate a higher dietary concentration.
There was a significant positive trend between concentration of the test chemical and the incidence of a combination of hepatocellular carcinomas and adenomas in male mice and an increase in the combination of these lesions in female mice. However, no statistically significant differences in tumor incidence at any site were observed when dosed rats and mice were compared to their respective controls.
Under the conditions of this bioassay there was no convincing evidence for the carcinogenicity of 2,4-dimethoxyaniline HCl in Fischer 344 rats or B6C3F1 mice.