Comparison of methods of estimation of lifetime cancer risk due to chronic exposure to transuranics.

The cancer risk due to chronic transuranic intakes is properly calculated using an integration over multiple years of intake of the annual effective dose rates arising each year following an intake multiplied by age-dependent risk functions for the year during which the dose is actually received. Approximate computations of risk involving sums of the products of committed effective dose and the age-dependent risk functions for each year of intake indicate the appropriateness of the committed effective dose as a surrogate quantity for risk when applied to different circumstances. The assumptions that all dose is received at the time of intake with committed effective dose and that risk is uniform over a range of ages both lead to a misuse of the available age-dependent risk functions and thus contribute to a divergence from the true risk associated with an intake over multiple years. Comparison of the correctly integrated risk functions with the approximations gives insights into how the current committed effective dose models used for regulatory purposes are not necessarily indicative of the risk for chronic intakes of radionuclides with long biological and radiological half-lives. A summary and comparison of such computations for transuranic intakes was prepared for the ingestion of water and the inhalation of different particle sizes by both males and females. Risk results for committed effective dose consistently overestimated risks by approximately 100% for all transuranics for ingestion models and approximately 75% for all transuranics for Type M inhalation models considering age-dependent risk models. For constant risk as a function of age, the committed effective dose integration underestimated the actual risk situation by nearly 60% for ingestion and 50% for Type M inhalation during the first 20 y.