ISOTOPIC AND ELEMENTAL COMPOSITION OF PLUTONIUM/AMERICIUM OXIDES INFLUENCE PULMONARY AND EXTRA-PULMONARY DISTRIBUTION AFTER INHALATION IN RATS

Abstract

The biodistribution of plutonium and americium has been studied in a rat model after inhalation of two PuO₂ powders in lungs and extra-pulmonary organs from 3 d to 3 mo. The main difference between the two powders was the content of americium (approximately 46% and 4.5% of total alpha activity). The PuO₂ with a higher proportion of americium shows an accelerated transfer of activity from lungs to blood as compared to PuO₂ with the lower americium content, illustrated by increased urinary excretion and higher bone and liver actinide retention. The total alpha activity measured reflects mostly the americium biological behavior. The activity contained in epithelial lining fluid, recovered in the acellular phase of broncho-alveolar lavages, mainly contains americium, whereas plutonium remains trapped in macrophages. Epithelial lining fluid could represent a transitional pulmonary compartment prior to translocation of actinides to the blood and subsequent deposition in extra-pulmonary retention organs. In addition, differential behaviors of plutonium and americium are also observed between the PuO₂ powders with a higher dissolution rate for both plutonium and americium being obtained for the PuO₂ with the highest americium content. Our results indicate that the biological behavior of plutonium and americium after translocation into blood differ two-fold: (1) for the two actinides for the same PuO₂ aerosol, and (2) for the same actinide from the two different aerosols. These results highlight the importance of considering the specific behavior of each contaminant after accidental pulmonary intake when assessing extra-pulmonary deposits from the level of activity excreted in urine or for therapeutic strategy decisions.