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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 microns 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Workers exposed to vermiculite contaminated with fibrous tremolite were surveyed for the presence of respiratory symptoms by questionnaire, and for pneumoconiosis by chest radiograph. Pulmonary function was measured by spirometry and single-breath carbon monoxide diffusing capacity ( DLCOsb ). Fiber exposure indexes, expressed as fiber/ml-yr, were derived for each worker from available industrial hygiene data and work histories. The estimated cumulative exposure for the work force ranged from 0.01 to 39 fiber/ml-yr. Discriminant analysis demonstrated significant correlates with shortness of breath and pleuritic chest pain to cumulative fiber exposure. The radiographic changes were limited to pleural changes and involved 4.4% of the population. Parametric and discriminant analysis demonstrated a significant correlation with radiographic changes and cumulative fiber exposure. There were no correlations between spirometry or DLCOsb and fiber exposure. Exposure to vermiculite contaminated with fibrous tremolite can cause pleural changes in occupationally exposed workers. This is supported by the previously identified 12 cases of benign pleural effusions in this working population and the association of pleural radiographic changes and pleuritic chest symptoms with cumulative fiber exposure. The lack of significant parenchymal radiographic, spirometric, and DLCOsb changes most likely reflects the low cumulative fiber exposure.

Fibrous glass and mineral wool workers exposed to airborne man-made mineral fibers prior to 1964 were identified and followed for deaths caused by respiratory disease. Fiber exposure levels were estimated for each worker. Average fiber concentrations were very low in relation to a National Institute of Occupational Safety and Health recommendation that exposure to man-made mineral fibers less than 3.5 microns in diameter be limited to 3 fibers per cubic centimeter of air. Fibrous glass workers were exposed to about one hundredth and mineral wool workers to about one tenth of that amount. Respiratory cancer death rates were not excessive for the fibrous glass workers, but they were significantly elevated for the mineral wool workers. When respiratory cancer deaths were compared with fiber exposure levels, however, there was in no instance a strong positive correlation. There was a significant excess in nonmalignant respiratory disease deaths (excluding influenza and pneumonia) for fibrous glass workers and for the total cohort. When these nonmalignant respiratory disease deaths were compared with fiber exposure levels, however, there was in no instance a strong positive association. A special study was made of workers exposed to small diameter fibers. Respiratory cancer deaths were not in excess; however, there was an excess in nonmalignant respiratory disease deaths. This study provided no consistent evidence of a respiratory disease hazard related to exposure to man-made mineral fibers among the workers who produce these fibers. Results must be interpreted in relation to the relatively low exposure levels for these workers.