About 24 per cent of total inhaled Ru106O2 was deposited in lungs of mice. Lung retention of deposited Ru106 was studied with a whole-body monitor. Radiochemical assay of tissues from mice killed at intervals up to 70 weeks after exposure confirmed retention in pulmonary tissues. Of three exponential components of the lung clearance curve the longest biological half life was 230 days for about 2 per cent of the total lung deposition. Translocation to other tissues was also observed. Several tissues including ovaries and adrenal glands attained greater concentrations, though smaller quantities, than the lungs. The total dose to lung over the 70-week period was estimated to be 4600 rads per µc of total Ru106 deposited. An MPC(air) for Ru106O2 of 1.3 × 10−8 µc per cm3 air for a 40-hr week was derived by assuming lung to be the critical organ and by extrapolating the data from mouse to man on the basis of differences in weight alone, ignoring differences in anatomy and physiology.
©1961Health Physics Society