The reliability of dose coefficients for inhalation and ingestion of uranium by members of the public

The best estimate of risk to a population group resulting from internal exposure to a particular radionuclide can be used to assess the reliability of the appropriate International Commission on Radiological Protection (ICRP) dose coefficient (E50) for the specified exposure pathway. An estimate of the uncertainty on the risk is important for reliability decisions. This paper describes the application of parameter uncertainty analysis to quantify uncertainties resulting from internal exposures to uranium (as 238U) by members of the public. The study derives uncertainties in biokinetic model parameter values to calculate the distributions of the effective dose per unit intake using the ICRP Publication 60 formalism. The central values and ranges of the distributions are used to infer the uncertainty on the mean effective dose per unit intake to inform the derivation of uncertainty factors (UF) for the dose coefficients. Here, a UF is a conditional probability statement that the value of the best estimate of risk per unit intake has a 95 % probability of being within a factor, UF, of the nominal risk associated with the appropriate ICRP dose coefficient, E50, with respect to uncertainties in the biokinetic model parameter values. Ingestion: it is assumed that exposure occurs through the ingestion of uranium present in food and water. The results suggest a UF of within 3 for all age groups, with median values close to the ICRP values. Inhalation: it is assumed that environmental exposure to uranium occurs via inhalation of a mixture of chemical forms. The results suggest a UF of around 2 for inhalation of uranium by members of the public, with median values close to the ICRP values. (authors)