Long term lung retention studies of 125Sb aerosols in humans

This paper describes the retention of 125Sb oxide aerosols in human lungs based on the data obtained from a group of seven accidental inhalation exposure cases. Long-term follow-up studies for periods of time ranging from 1 to 3 d post intake to 199 to 2,422 d post intake have indicated the biological lung clearance half-time of this material ranging from about 600 to 1,100 d for non-smokers and 1,700 to 3,700 d for smokers. The retention in the lungs after 180 d in all the seven cases is found to be much more than 51% of the estimated initial alveolar deposit, which is consistent with the present ICRP criteria of assignment to the lung absorption Type S. There is little previously reported human data on this radionuclide compound. In these studies reliable information on actual time of intake, the likely type of material, and the amount of retained body/lung activity in initial days after the incident was also available, which adds to the importance of these data. The results of these studies provide a basis for firm classification and suggest that oxides of antimony need to be removed from absorption Type M (earlier class W) where these are presently listed by ICRP and be placed in absorption Type S (earlier class Y). The range of measured retained lung activities after the initial rapid clearance phase (7 d post exposure) was about 3 to 14 kBq, which was sufficient for long-term follow up studies using the whole body counters.