Cancer mortality among workers exposed to amphibole-free chrysotile asbestos

The issue of whether exposure to chrysotile asbestos alone, without contami nation from amphibole asbestos, causes lung cancer and mesothelioma was inv estigated in a 25-year longitudinal study (1972-1996) in Chongqin, China. T he study cohort comprised 515 male asbestos plant workers exposed to chryso tile only; the control cohort included 650 non-dust-exposed workers. The re sults of analysis in which the proportional hazards model was used indicate d that mortality due to all causes, all cancers, and lung cancer was relate d to asbestos exposure; the relative risks, adjusted for age and smoking, w ere 2.9, 4.3, and 6.6, respectively. Fiber concentrations in the raw materi al section and the textile section of the plant were 7.6 and 4.5 fibers/ml, respectively Because of differences between the study and control plants, the authors also compared various sections of the asbestos plant that had d ifferent levels of dust exposure. The adjusted relative risk of lung cancer was 8.1 for workers exposed to high versus low levels of asbestos. Two cas es of malignant mesothelioma, one pleural and the other peritoneal, were fo und in the asbestos cohort. These results suggest that heavy exposure to pu re chrysotile asbestos alone, with negligible amphibole contamination, can cause lung cancer and malignant mesothelioma in exposed workers.