Deposition and clearance of inhaled fibrous minerals in the rat. Studies using radioactive tracer techniques.

The deposition and clearance of various fibrous materials have been investigated in the rat using radioactive tracer techniques. The materials used include the U.I.C.C. standard reference samples and synthetic mineral fibres. Measurements of total and alveolar deposition were correlated with the AMADs of the radioactive dust samples which ranged from 1 to 2.5 micron. Although total deposition increases steeply over this range, alveolar deposition is relatively constant only increasing from about 10 to 13%. Alveolar deposition is lower than in man, but the maximum in alveolar deposition appears to occur at a similar aerodynamic diameter. Half times of alveolar clearance, measured over a period of several months following single inhalation exposures, were in the range 60-90 days and no significant difference was observed between amphibole and chrysotile asbestos. Autoradiographs of lung sections indicate that alveolar deposition is relatively uniform and occurs right up to the periphery of the lung. Over a period of several months the uniform distribution alters to one in which fibres accumulate in foci which are mainly subpleural. These foci act as centres for the development of nodular fibrosis.