ASBESTOS FIBERS AND PLEURAL PLAQUES IN A GENERAL AUTOPSY POPULATION

Abstract

It has been claimed that symmetric lower zone pleural or diaphragmatic plaques are markers of asbestos exposure in asbestos workers and the general population. Total pulmonary asbestos burden was analyzed for 29 patients selected because pleural plaques were found at autopsy, and the results were compared with values obtained for 25 patients who had no occupational asbestos exposure. The average number of asbestos bodies in the plaque groups was 1732/g wet lung, and in the control group, 42/g wet lung. Uncoated asbestos fibers were extracted from lung and counted, measured and identified by morphologic examination, electron diffraction, and energy-dispersive X-ray spectroscopy. The total number of fibes/g wet lung in the plaque group (114 .times. 103) was similar to that in the control group (99 .times. 103), as was the number of chrysotile fibers (51 .times. 103 vs. 68 .times. 103) and noncommercial amphiboles (13 .times. 103 vs. 29 .times. 103). The plaque patients had a marked increase in the number of the commercially used high aspect ratio amphiboles, amosite and crocidolite (50 .times. 103 vs. 1 .times. 103). A retrospective history of fairly certain asbestos exposure was obtained for 16 plaque patients, and such a history correlated strongly with increased numbers of commercial amphiboles in lung. In this general autopsy population, 2 subgroups of patients were present. About 1/2 of the patients had developed pleural plaques as a result of asbestos exposure, while the etiology of the plaques in the other 1/2 was unclear. The presence of pleural plaques correlated with a modest (50-fold) increase in numbers of long high-aspect ratio commercial amphiboles in lung tissue, but did not correlate with numbers of chrysotile fibers, noncommercial amphiboles or the total number of asbestos fibers. Asbestos-induced lesions were related to a complex set of mineralogic parameters and not to mere numbers of fibers in the lung.