USE OF ANIMAL STUDIES FOR ASSESSING INTAKES OF INHALED ACTINIDE-BEARING DUSTS

This paper reviews the methodology used in the execution and interpret ation of animal studies (mostly conducted at NRPB) designed to provide guidance on limits of intake and the effectiveness of chest monitorin g for persons exposed to various uranium, plutonium, americium, and th orium bearing dusts. The lung retention and transportability character istics of the actinides in humans have been predicted by combining the absorption rates into blood calculated from the animal studies with p article transport rates from the alveolar region of the human lung. Th is approach is compatible with the application of the new ICRP respira tory tract model. The results of the animal experiments demonstrate th e diversity of the absorption rates for the different chemical forms o f the actinides and their disparity from the default values proposed b y ICRP for Type F, M, and S compounds in the absence of specific data. The predicted lung retention kinetics of the actinides in humans prov ide the basis for assessing the validity of chest monitoring; for this purpose the most recent ICRP values for doses per unit intake and dep osition in the alveolar region of the lungs have been taken into accou nt. The results show that for some dusts, the data on be interpreted w ith confidence, while for others the method is impracticable or has co nsiderable uncertainty. Overall, the results support the ICRP recommen dation that material specific information is to be preferred for setti ng limits on intake and interpreting monitoring data. The paper conclu des with suggestions for further work.