INTAKE ASSESSMENT OF WORKERS WHO HAVE INHALED PU-238 AEROSOLS

Biokinetic data from published animal studies have indicated that ther e are significant differences in the radiation dose patterns resulting from the inhalation of Pu-238 oxide rather than Pu-239 oxide aerosols . Although less frequent than for Pu-239, several exposures to Pu-238 have been documented in the USA. A Pu-238 biokinetic and dosimetry mod el developed by Mewhinney and Diel, which was based on the results of animal studies, was applied to urinary bioassay data from workers who inhaled Pu-238 aerosols at three different Pu-238 processing facilitie s. Although all the exposures were purportedly to 'Pu-238 ceramic' or Pu-238 oxide particles, the temporal features of the observed urinary excretion patterns differed among the cases from the various facilitie s. For exposures that occurred at Facility 1, urinary excretion patter ns mimicked those observed in the ITRI Pu-238 dog studies, i.e. the Pu -238 in urine began at its lowest levels immediately after exposure, t hen increased gradually by a factor of 100 over the next 200 days; fro m 200 to about 4000 days, the excretion levels remained relatively con stant, followed then by a very slow decline for the remaining 2000 day s of follow-up. In a case from Facility 2, the inhaled Pu aerosol was much more soluble in vivo, and the urinary excretion kinetics could be modelled with solubility characteristics similar to that of a class D Pu aerosol. In the case from Facility 3, limited particle size analys is indicated the presence of at least two different particle sizes, bo th of which were respirable. The urinary excretion pattern was therefo re modelled by assuming that a bimodal sized aerosol was inhaled. Thes e data suggested several novel features that need to be considered whe n dealing with inhalation exposures to high-specific-activity aerosols such as (PuO2)-Pu-238.