Intrathoracic distribution and transport of aerosolized silica in the rat.

Short-term exposure of rats to aerosols of the silicon dioxide, cristobalite, leads to pulmonary inflammation persisting several months. Clearance of particles occurs during the first two weeks after cessation of exposure, after which there is little additional clearance in the whole lung. In the present studies, quantitation of silica in lung compartments at selected times following exposure indicated movement of particles between the alveolar space and the lung tissue per se, with increased alveolar silica content associated with decreased silica content in the tissue compartment. Further, changes in the silica content in the alveolar compartment were generally associated with fluctuations in the alveolar macrophage population. Silica accumulated linearly in the mediastinal lymph nodes and thymus for several months after cessation of exposure, while negligible amounts were found in kidney, spleen, liver, and blood. A compartmental model was used to describe the distribution and translocation kinetics of the inhaled silica in the lung and extrapulmonary tissues.