Transfer of environmental plutonium and americium across the human gut: a second study

A follow-up to our previous study is described on human gut transfer factors for plutonium and americium in winkles harvested from the shoreline near the British Nuclear Fuels plc Sellafield reprocessing plant. Six male and two female adult volunteers ate single quantities of shellfish; samples of their urine before and after consumption were analysed. As in the previous study, the plutonium and americium excreted were difficult to detect, and counting times of approximately 8 weeks were employed. Results are presented in detail to allow further interpretation, but preliminary assessment has been carried out on the basis of published data for excretion following transfer to blood. The mean and range obtained for the gut transfer for plutonium was 1.3 (0.2-3.2) x 10(-4); for americium the result was 0.8 (0.4-1.7) x 10(-4). Combined with the results of the previous study when interpreted on the same basis, the results were 1.7 (0.2-4.9) x 10(-4) and 0.9 (0.3-2.8) x 10(-4), respectively. No significant evidence was revealed in this study for differences in gut transfer between males and females, nor for seasonal differences, e.g. due to differences in form of incorporation of actinides in shellfish. For realistic assessments of doses due to shellfish consumption near Sellafield, to assess compliance with criteria recommended by the International Commission on Radiological Protection (ICRP), a suitable value for the gut transfer factor of both plutonium and americium might be 2 x 10(-4). A value of 5 x 10(-4) would appear to be cautious.