Mesothelioma and the fiber type in three American asbestos factories - preliminary report.

Preliminary findings are reported from three cohort studies in two asbestos factories (A and B) where chrysotile only was processed and a third (C) where chrysotile, amosite, and crocidolite were used. A total of 10,763 men and 3,118 women has been studied, of whom 97% and 89%, respectively, have been traced and 36% and 16% have died. Death certificates have so far been obtained and coded for 89% of the deaths. The standardized mortality ratios (SMRs) for persons employed less than a year varied greatly between plants. For men employed at least 1 a, an SMR of 129 for all causes and one of 285 for respiratory cancer were found in the chrysotile textile plant (A). The experience of respiratory cancer in this textile plant appears much worse in relation to fiber exposure levels than that observed in chrysotile mines and mills. Other findings in the three plants await clarification by analyses of exposure-response relationships. Among 2,341 deaths from the two chrysotile factories there has been one mesothelioma (0.4 per 1,000); among 1,429 deaths at factory C, which used mixed fibers, there have been 18 (12.6 per 1,000). This finding supports much other evidence that amphiboles are mainly responsible for mesothelioma, whereas chrysotile has little or no mesothelioma-producing potential.