FIBER BURDEN AND PATTERNS OF ASBESTOS-RELATED DISEASE IN CHRYSOTILE MINERS AND MILLERS

To examine how fiber type, fiber concentration, and fiber size correlate with the presence of asbestos-related disease in workers with heavy chrysotile exposure, we used analytic electron microscopy to determine the fiber content of the lungs of 94 long-term chrysotile miners and millers from the region of Thetford Mines, Quebec. Mesothelioma, airway fibrosis, and asbestosis were strongly associated with a high tremolite fiber concentration, whereas pleural plaques and carcinoma of the lung showed no relationship to tremolite burden. Similar patterns were seen for chrysotile concentration, but further analysis suggested that the apparent effect of chrysotile probably was due to the high correlation (r = 0.70) between chrysotile and tremolite concentration rather than to an independent effect of chrysotile. Increased tremolite-chrysotile ratio was marginally associated with the presence of pleural plaques but not with any other disease. Very high correlations (r > 0.90) between the concentrations of fibers longer or shorter than 8 mum prevented assessment of the effects of long compared with short fibers. Pleural plaques were very strongly associated with higher mean tremolite fiber aspect ratios, but no differences in mean fiber size (length, width, aspect ratio, surface area, and mass) were seen for any other disease. Total fiber size measures (total fiber length/g and others) showed differences similar to fiber concentration for mesothelioma, airways fibrosis, and asbestosis, but no one measure was clearly better than another or better than fiber concentration. We conclude that, in this population of heavily exposed chrysotile miners and millers, the presence of airways fibrosis and asbestosis and, probably, mesothelioma reflects high tremolite burden. Whether chrysotile fibers themselves play a role in disease induction remains uncertain. Mean fiber size appears to be of importance only in the genesis of pleural plaques. Carcinoma of the lung is not significantly associated with any mineralogic measure.