What are the Uncertainties Associated with the Risk Assessments?
Unlike most toxicological risk assessments and previous assessment of TACs, most of our conclusions are based on human studies except those for cancer. The uncertainties in the risk assessments for adverse neurodevelopmental effects and increased blood pressure are considered to be much less than those for the cancer endpoint. Four major uncertainties, usually encountered in cancer risk assessments, are those due to (1) animal-to-human extrapolation, (2) high-to-low dose extrapolation, (3) accounting for sensitive members in the human population, and (4) small numbers of subjects. Regarding animal-to-human extrapolation, the cancer effect results from oral exposure studies in animals are extrapolated to derive an inhalation unit risk for humans. For the noncancer endpoints from lead exposure, the data used were obtained in humans so that uncertainty introduced by extrapolation is not an issue. The second concern, the degree of uncertainty introduced by extrapolation from high to low do
