233UO2 and 233UO2(NO3)2 in aqueous suspension have been administered to rats by pulmonary intubation. The 233U associated with the fraction of the 233UO2 less than 4 nm in diameter translocates from lungs to blood at the same rapid rate as 233U from 233UO2(NO3)2. Identical reactions with blood plasma and lung fluid were observed whether the 233U was administered as less than 4 nm 233UO2 particles or 233UO2(NO3)2. It is suggested that oxidation of UO2 to UO3 occurs followed by the formation of uranyl ion. In blood plasma, approximately 50 per cent of the 233U is bound to transferrin, 25 per cent to citrate and 25 per cent on bicarbonate.

The metabolic behavior of 239Pu and 241Am present in three industrial dusts has been studied after their inhalation by the rat. A comparative experiment has also been carried out with a mixture of these actinides, inhaled as their nitrates. The aim of this work was to provide an experimental basis for assessing limits on intake and to establish whether the 239Pu content in the lungs could be interpolated from measurements of 241Am. The results (1) demonstrate the wide differences in the lung retention kinetics of the actinides and in the absolute and relative amounts which translocate to the blood that can occur for industrially produced materials; (2) show that the annual limits on intake (ALI) for the different materials vary between those postulated for class W and Y compounds by the International Commission on Radiological Protection; (3) indicate that, depending on the nature of the dust, acute intakes of 239Pu equivalent to the ALI can be estimated from 241Am chest-monitoring data at times from a few days up to about 3 y after exposure.