Biokinetics of ²³⁸Pu oxides: inferences from bioassay data

The bioassay data collected from several workers involved in ²³⁸Pu inhalation incidents have been analysed using the most recent biokinetic models described in the Occupational Intakes of Radionuclides (OIR) series of publications. Although all exposures were thought to be to ²³⁸Pu oxides, the observed urinary excretion patterns differed in different inhalation incidents. The urinary excretion from individuals involved in one of the incidents increased steadily with time, peaking around two to three years before decreasing. This pattern is described in Part 4 of the OIR series using the '²³⁸PuO₂, ceramic' model. This non-monotonic behaviour, explained as being due to fragmentation and dissolution, was not specific to the incident, but observed in other incidents. The urinary excretion data collected from individuals involved in another incident showed dissolution behaviour between Type M and Type S. Finally, the bioassay data from yet another incident showed a pattern that appears to represent behaviour more insoluble than Type S, which is possibly a result of self-heating due to the decay heat from ²³⁸Pu. The urinary excretion patterns and corresponding dose coefficients have been calculated and compared.