LUNG RETENTION OF PU FOLLOWING INHALATION OF PUO2 IN RATS MEASURED USING A WHOLE-BODY COUNTER

A lung retention function on the amount of PuO2 in rats was determined . Five rats were exposed to polydisperse aerosols of PuO2 having a siz e of 0.47 mu m activity median aerodynamic diameter. The initial lung burden was between 1990 Bq and 2960 Bq. Instead of serial-sacrifice st udy, in vivo counting of low energy L X-rays with thin NaI(Tl) scintil lation detectors was used to follow the lung retention of Pu at variou s intervals up to 468 days after inhalation. The calibration of this c ounting system was made by measuring lung activity of rats sacrificed for other experimental purposes. It was confirmed that the potential s kin contamination and the Pu translocated to the other organs was not counted at the present counting geometry. Our results showed that 77% of PuO2 deposited deep in the lung was cleared with a half-time of 53 days, whereas the residual 23% stayed there for a longer period (a hal f-time of 795 days).