Lung tissues from workers at the Mayak Production Association were examined to determine the distribution of plutonium (Pu) activity in various lung compartments. Stereological sampling methods and autoradiography were used. Pu particles were identified by microscopic examination of autoradiographs and localised in one of six normal anatomic sites and two sites of fibrosis (parenchymal, non-parenchymal). Particle activity was determined by counting the number of tracks emanating from the particles. Over 50% of the Pu activity was localised in sites of fibrosis, which had significantly higher than average activity for the lung. Over 40% of the activity was in lung parenchyma. Activity in the bronchovascular interstitium was significantly lower than average. These results support the hypothesis that Pu activity is not uniformly distributed in the lung, with long-term retained particles concentrated in scars of the lung. The results may significantly affect estimates of dose from inhaled Pu.
The degree of nonuniform distribution of plutonium in the human lung has not been determined; thus current dosimetric models do not account for nonuniform irradiation. A better scientific basis is needed for assessing the risk of developing radiation-induced disease from inhaled alpha-particle-emitting radionuclides. We measured the distribution of plutonium activity in the lung by autoradiography and related the activity to specific compartments of the lung. The study materials were lung specimens from deceased workers employed by the Mayak Production Association. The approach to analyzing these lung samples used contemporary stereological sampling and analysis techniques together with quantitative alpha-particle autoradiography. For the first time, plutonium distribution has been quantified in the human lung. The distribution of long-term retained plutonium is nonuniform, and a significant portion of plutonium was retained in pulmonary scars. In addition, a large fraction of plutonium was present in the parenchyma, where it was retained much longer than was estimated previously. The sequestration of plutonium particles in scars would greatly reduce the radiation exposure of the critical target cells and tissues for lung cancer. Thus the prolonged retention of plutonium in lung scars may not increase the dose or risk for lung cancer.