Determining the Biological Variability of Daily Amount of Feces to Estimate Dose Uncertainties Based on Data from Mayak Plutonium Workers

The most effective current methods to estimate internal radiation doses from exposures to plutonium containing compounds are based on measured nuclide activity in excreted urine and feces. Typically, urine measurements are made, but fecal measurements can provide additional information about the nature of the exposures. Interpreting and applying the results requires consideration of uncertainties associated with the measurements and subsequent calculations. There are large variations in the daily activities excreted in urine and feces. These uncertainties are characterized as Type A uncertainties (arising mainly from counting statistics) and Type B uncertainties (arising from a range of other error sources such as variation in excreted volumes or masses). For assessment of plutonium exposures, the overall uncertainties are described as "scattering factors" (SFs) obtained by combining these two types of uncertainty. The purpose of this study was to determine the daily fecal excretion volumes and associated SFs for 924 male and female plutonium workers at the Mayak Production Association, Ozersk, Russia. Excreta were measured during routine plutonium bioassays that were conducted in a clinical setting. Over 90% of the male and 80% of the female workers had lower daily fecal excretion masses than reported by the ICRP for reference man and reference woman. This may be at least partially due to the lower fiber content of the diet. The SFs calculated for individual cases were within the range of 1.0 to 3.0 in 84% of the cases with a geometric mean of 2.3 and range from 1.0 to 23.1. No statistical bias was found between the SF values between male and female workers.