NSRL for Phenylhydrazine and Phenylhydrazine Hydrochloride

The cancer potencies of phenylhydrazine and phenylhydrazine hydrochloride were estimated from dose-response data from three data sets: lung tumors among male and female mice (combined) exposed orally to phenylhydrazine hydrochloride (Clayson et al., 1966) and blood vessel tumors among male and female mice exposed orally to phenylhydrazine hydrochloride (Toth and Shimizu, 1976). Studies of phenylhydrazine were of poor quality and were not used to derive potency estimates. The cancer potency estimate corresponds to the upper 95 percent confidence bound on the linear term of the multistage model fit to cancer dose-response data in animals. The potency derivation takes into account body size differences between humans and experimental animals. The Proposition 65 “no significant risk level” (NSRL) is defined in regulation as the daily intake level posing a 10 lifetime risk of cancer. Cancer potency for phenylhydrazine hydrochloride was taken as the geometric mean of potencies derived from each data set analyzed. The cancer potency estimate obtained from studies of phenylhydrazine hydrochloride was used as the basis for the phenylhydrazine cancer potency by adjusting for differences in molecular weight. Cancer potency estimates and the corresponding NSRLs are given in Table 1.