No Significant Risk Levels (nsrls) for the Proposition 65 Carcinogens Lead and Lead Compounds (oral)

This document provides a basis for the estimation of cancer risk from exposure to lead. Carcinogenic potencies were estimated from oral studies of the carcinogenicity of lead compounds. These estimated potencies were based upon the administered doses of lead; in some cases, it was necessary to calculate lead dose based upon the lead content of the administered compounds. The uncertainty associated with the estimation of cancer risk from exposure to specific forms of lead is recognized. Based on the findings from the administration of different lead compounds by different routes to experimental animals, it is clear that the lead component of these compounds is responsible for renal carcinogenicity. In the absence of clear evidence to the contrary, it will be assumed that the lead content of lead compounds is responsible for the carcinogenicity of these compounds. No animal studies of inhalation exposures to lead compounds were identified, and OEHHA did not examine the potential applicability of the oral carcinogenicity studies for lead to the estimation of inhalation potency. Pharmacokinetic adjustments to address route differences were not explored. Thus, estimates of cancer potency by the inhalation route and the corresponding NSRLs were not developed. Uncertainty also exists regarding the relationship of chemical form to cancer potency, particularly with respect to the influence of form on oral absorption. Absorption data are not available for all lead compounds for which there is potential human exposure, and physicochemical properties (such as water solubility) have not proven to be reliable predictors of absorption. Since the estimation of risk in this assessment is based upon studies conducted with relatively highly absorbed lead compounds, the cancer potencies derived here are expected to be larger (on lead bases) than those for lead compounds which are less well absorbed.