Benzidine Dihydrochloride: Risk Assessment. LITTLEFIELD, N. A., NELSON, C. J., AND GAYLOR, D. W. (1984).Fundam. Appl. Toxicol. 4, 69–80. Benzidine, recognized as a bladder carcinogen in man and as a liver carcinogen in experimental animals, is the chemical basis of as many as 200 commercial dyes. Physiological processes can metabolize these dyes to release benzidine, thereby creating a potential exposure hazard. To assess this hazard, both sexes of F1hybrid (genetically homogeneous) and monohybrid (genetically heterogeneous) mice from a BALB/c male and C57BL/6 female cross were exposed for their respective lifespans to benzidine dihydrochloride in their drinking water at concentrations of 0, 30, 40, 60, 80, 120, and 160 ppm for males, and 0, 20, 30, 40, 60, 80, and 120 ppm for females. Animals were removed from the study when they were dead or moribund. This study was terminated after 33 months of exposure. Using the endpoint of hepatocellular adenomas and carcinomas, the Armitage Doll multistage model was used to describe the tumor rates in the experimental dose range and to obtain the upper confidence level on tumor rates. Linear interpolation was used between zero dose and the upper confidence level of the lowest experimental dosage for predicting potential low dose tumor rates. Dose-response effects on body weight, survival, and liver neoplasms were noted in both stocks. For each of the endpoints, the females were more susceptible than males and the F1(homogeneous) stock was more susceptible than the monohybrid cross (heterogeneous). The calculated virtually“safe”dose predicted to produce less than one per million F1female mice with a liver tumor is 0.045 ppb. One part per billion of benzidine dihydrochloride in the drinking water of these mice is estimated to produce liver tumors in less than 2.23 mice per 100,000 popul
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