Chrysotile, tremolite-actinolite and mesothelioma

The average proportional variation of chrysotile, tremolite-actinolite and other asbestos mineral fibers in the results of lung-fiber burden analyses from studies performed by the authors are examined in this paper. These inv estigations include the examination of cohorts from chrysotile-mining and a sbestos-manufacturing industries, as well as asbestos diseases case-control population groups. The proportions of chrysotile and tremolite-actinolite detected in the lung-fiber burdens were found to vary among the study group s, chrysotile ranging from 4.2 to 98.9%, tremolite-actinolite from not dete ctable to 47.7% by number of the fiber burden. The proportion of other comm ercial amphibole fibers ("amosite" and "crocidolite") ranges from not detec table to 46.4%. The proportion of chrysotile in mining cohorts varies from 39.1% for Canadian cases to 98.9% for cases from Zimbabwe, with tremolite-a ctinolite varying from 47.7 to 0.9%. The proportion of tremolite in Canadia n mining cases exceeds the values detected in cases from all other chrysoti le-mining situations. Levels of chrysotile fibers in the lung tissues of ca ses from asbestos-manufacturing and insulation industries where chrysotile had been utilised extensively range from 87.2 to 20.3%, whereas tremolite v aries from 22.5% to non-detectable limits. For cases of asbestos-related di sease, levels of chrysotile fiber in lung tissue range from 29.3 to 4.2%, w hereas tremolite fiber range from 19.1 to 0.2% by number. The matched case- controls in these studies, together with control cases from studies of asbe stos-exposed cohorts, show proportions of chrysotile fibers varying from 95 .6 to 85.3%, and of tremolite, from 2.9 to 0.8%. The amount of tremolite in proportion to chrysotile asbestos fibers detected in the lung tissue of ca ses from the Canadian chrysotile mining industry were found to exceed level s in all other asbestos disease case-studies, occupationally and non-occupa tionally exposed study-groups, generally by a considerable margin, as illus trated by the values of the ratio of the geometric mean values of chrysotil e to tremolite detected in these various studies.