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

To examine how fiber type, fiber concentration, and fiber size correla te with the presence of asbestos-related disease in workers with heavy chrysotile exposure, we used analytic electron microscopy to determin e the fiber content of the lungs of 94 long-term chrysotile miners and millers from the region of Thetford Mines, Quebec. Mesothelioma, airw ay fibrosis, and asbestosis were strongly associated with a high tremo lite fiber concentration, whereas pleural plaques and carcinoma of the lung showed no relationship to tremolite burden. Similar patterns wer e seen for chrysotile concentration, but further analysis suggested th at the apparent effect of chrysotile probably was due to the high corr elation (r = 0.70) between chrysotile and tremolite concentration rath er than to an independent effect of chrysotile. Increased tremolite-ch rysotile 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 tremo lite fiber aspect ratios, but no differences in mean fiber size (lengt h, width, aspect ratio, surface area, and mass) were seen for any othe r disease. Total fiber size measures (total fiber length/g and others) showed differences similar to fiber concentration for mesothelioma, a irways 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, mesothelio ma reflects high tremolite burden. Whether chrysotile fibers themselve s play a role in disease induction remains uncertain. Mean fiber size appears to be of importance only in the genesis of pleural plaques. Ca rcinoma of the lung is not significantly associated with any mineralog ic measure.