Comparative epidemiology of men exposed to asbestos and man-made mineral fibers

Comparative analyses are presented of selected studies of long-term reactions to occupational exposures to asbestos and man-made mineral fibers (MMMF), with emphasis on studies with dose-response information and long enough period of follow-up to observe lung cancer excess, if it occurred. Uniform dose estimates based on average number of fibers per milliliter were derived and tabulated with the corresponding standard mortality (or morbidity) ratio (SMR), crude probability for each unfavorable outcome, and the likelihood that at least as many deaths would have occurred as a result of the expected numbers under Poisson assumptions. A dose-response relationship was said to have been indicated when the crude probability increased monotonically with dose and/or the Poisson probability decreased and reached a value of less than 0.05. Some arbitrary assumptions had to be made in estimation of the dose, and they may need to be corrected. Gravimetric dose estimates may have given different results. Studies selected for analysis included Quebec asbestos miners and asbestos cement workers exposed to asbestos, and pooled U.S. and European studies of MMMF workers, as well as a sample of cigarette-smoking fiberglass workers whose X-ray films were evaluated for fine nodular or irregular opacities. The lowest dose capable of showing either a statistically significant excess (single point criterion--SP) or the median dose in an apparent dose-response relationship with cause of death or radiological results is tabulated. Radiological changes show a dose-response relationship for all types, with a median dose for asbestos of 2.8 fibers/ml. For fiberglass workers, the median dose of electron-microscopically detected fibers was two orders of magnitude less. For asbestos SP, exposures of 1.4 to 22 fibers/ml were associated with increased lung cancer, while for mineral wool, the minimal level with significant SP increase in lung cancer was an order of magnitude less. Based on fiber or particle counts, man-made mineral fibers appear to be more potent than asbestos with regard to chronic pulmonary disease.