FIBER BURDEN AND PATTERNS OF ASBESTOS-RELATED DISEASE IN WORKERS WITHHEAVY MIXED AMOSITE AND CHRYSOTILE EXPOSURE

To attempt to determine the mineralogic factors that relate to the app earance of specific types of asbestos-related disease in workers with heavy mixed exposure to amphiboles and chrysotile, we analyzed the pul monary asbestos fiber burden in a series of 144 shipyard workers and i nsulators from the Pacific Northwest. Amosite was found in all lungs, and tremolite and chrysotile in most lungs, but the vast majority of f ibers were amosite. Tremolite and chrysotile concentrations were signi ficantly correlated, indicating that the tremolite originated from chr ysotile products, but no correlation was found between tremolite or ch rysotile concentration and amosite concentration. Time since last expo sure was correlated with decreasing amosite concentration and the calc ulated clearance half time was about 20 yr. In a multiple regression a nalysis that accounted for the presence of more than one disease in ma ny subjects, a high concentration of amosite fibers was correlated wit h the presence of airway fibrosis and asbestosis, whereas subjects wit h mesothelioma, lung cancer, pleural plaques, or no asbestos-related d isease had about the same, much lower, amosite concentration. No relat ionship was found between the concentration of chrysotile or tremolite and any disease. Analysis of fiber size measures (length, width, aspe ct ratio, surface, mass) showed that pleural plaques were strongly ass ociated with high aspect ratio amosite fibers and suggested that mesot heliomas were associated with low aspect ratio amosite fibers. We conc lude that, in this population, the major residual fiber is amosite, an d only amosite concentrations correlate with the presence of specific diseases, raising questions about the role of chrysotile in disease in duction. There are distinct differences in the relationship of fiber b urden and disease comparing workers with heavy amosite exposure to chr ysotile miners and millers; in particular, mesothelioma appears at muc h lower amosite burdens than does asbestosis, in contrast to the situa tion previously reported for chrysotile-induced mesothelioma. Amosite clearance from the lung is extremely slow, requiring decades. Except f or pleural plaques, the association of fiber size and disease remains uncertain.