Other Cohorts
Among 306 workers in a chrysotile paper manufacturing plant that participated in a study, no cases of mesothelioma, asbestosis, or lung cancer were found among the 67 workers who were followed for 15 to 27 years after asbestos was first used in the plant (Gaensler and Goff, 1988). A 30-year historical cohort mortality study was made of 264 men hired during 1935-1945 providing 7000 person-years of follow-up. They worked in a chrysotile asbestos products factory. Two men died of asbestosis, but no case of mesothelioma was reported (Weiss, 1977). Mesothelioma has not been found in South African chrysotile miners and millers despite decades of producing about 100,000 tons of the mineral per year. The contention of the study's authors was that South African chrysotile is not heavily contaminated by tremolite or other amphiboles (Rees et al., 2001). Of 570 Blackburn workers making chrysotile gas masks, one case of mesothelioma was observed. However, the authors state that this employee worked also at another Blackburn plant that used crocidolite (Acheson et al., 1982).