Uncertainty Analysis of Doses From Inhalation of Depleted Uranium

Measurements of uranium excreted in urine have been widely used to monitor possible exposures to depleted uranium (DU). This paper describes a comprehensive probabilistic uncertainty analysis of doses determined retrospectively from measurements of DU in urine. Parametric uncertainties in the International Commission on Radiological Protection (ICRP) Human Respiratory Tract Model (HRTM) and ICRP systemic model for uranium were considered in the analysis, together with uncertainties in an alternative model for particle removal from the lungs. Probability distributions were assigned to HRTM parameters based on uncertainties documented in ICRP Publication 66 and elsewhere, including the Capstone study of aerosols produced after DU penetrator impacts. Uncertainties in the uranium systemic model were restricted to transfer rates having the greatest effect on urinary excretion, and hence retrospective dose assessments, over the measurement times considered (10-10⁴ d). The overall uncertainty on dose (the ratio of the upper and lower quantiles, q_0.975/q_0.025) was estimated to be about a factor of 50 at 10 days after intake and about a factor of 10 at 10³-10⁴ d. The dose to the lung dominated the committed effective dose, with the lung absorption parameters, particularly the slow dissolution rate, s_s, dominating the overall uncertainty. The median dose determined from a measurement of 1 ng DU, collected in urine in a 24-h period, varied from 0.1 μSv at 10 d to about 1 mSv at 10⁴ d. Despite the large uncertainties, the upper q_0.975 quantile for the assessed dose was below 1 mSv up to 5,000 d.