Pulmonary retention of actinides after dissolution of PuO2aerosols: interest in modelling DTPA decorporation

Abstract

This study estimates in terms of amount and localisation the pulmonary retention of dissociated Pu/Am in the rat for the first week following an inhalation exposure to industrial PuO2 aerosols by combining standard biokinetic methods, quantitative analysis of contact autoradiograph obtained from lung section, and treatments by DTPA performed either in vivo or in vitro. The dissociated actinides mainly involved dissolved forms which are homogeneously distributed within lung parenchyma. Most of these chemical forms appears to come from the fraction (fr ) of radioelements which seems to dissolve before particles phagocytosis mainly by alveolar macrophages. Early pulmonary administration of dry diethylenetriaminepentaacetic acid (DTPA) powder (+2 hours) decorporates ~90% of these actinide forms, whereas, a delayed treatment (+1 week) is far less efficient. By contrast, a similar extraction (~90%) of the dissolved actinides from lung sections of rat untreated by the chelating agent is measured after their incubation in a DTPA solution for both 2 hours and 7 days post-exposure times. These results can be explained by a gradual internalisation of a fraction of the early dissolved actinides (mainly Am) in alveolar cells, but not preferentially in alveolar macrophages, whereas the remaining fraction of dissolved actinides are transferred to blood. From these observations, a new model is proposed to help for interpretation of human bioassay data obtained after internal contamination and DTPA treatments.