Pulmonary retention of neutron-activated coal dust.

Coal dust aerosols with cesium-134 and scandium-46 labels were studied in dogs and rats following brief inhalation exposures by external measurement of gamma photons in the 0.6 to 0.8 and 0.9 to 1.1 MeV regions, respectively. Ancillary in vitro studies of the leaching characteristics of the two radionuclides from coal were made and control studies utilizing the "free" radionuclides were undertaken for each of the investigations with radioactive coal dust. The biological data strongly infer that coal dust retention in canine lungs is extremely protracted with a biological half-life no shorter than approximately 4.3 yr and probably much longer. The biological model which was formulated and analyzed to obtain this finding is discussed along with its limitations.