Use of animal studies for assessing intakes of inhaled actinide-bearing dusts

This paper reviews the methodology used in the execution and interpretation of animal studies (mostly conducted at NRPB) designed to provide guidance on limits of intake and the effectiveness of chest monitoring for persons exposed to various uranium, plutonium, americium, and thorium bearing dusts. The lung retention and transportability characteristics of the actinides in humans have been predicted by combining the absorption rates into blood calculated from the animal studies with particle transport rates from the alveolar region of the human lung. This approach is compatible with the application of the new ICRP respiratory tract model. The results of the animal experiments demonstrate the diversity of the absorption rates for the different chemical forms of the actinides and their disparity from the default values proposed by ICRP for Type F, M, and S compounds in the absence of specific data. The predicted lung retention kinetics of the actinides in humans provide the basis for assessing the validity of chest monitoring; for this purpose the most recent ICRP values for doses per unit intake and deposition in the alveolar region of the lungs have been taken into account. The results show that for some dusts, the data on be interpreted with confidence, while for others the method is impracticable or has considerable uncertainty. Overall, the results support the ICRP recommendation that material specific information is to be preferred for setting limits on intake and interpreting monitoring data. The paper concludes with suggestions for further work.