Mortality in a Chinese chrysotile miner cohort

Background Few data were available to address cause-specific mortality in asbestos miners in China. This study observed a cohort of workers from the largest chrysotile asbestos mine to evaluate the association between asbestos exposure and cause-specific mortality. Methods The cohort consisting of 1,539 male workers was observed from 1981 to 2006. Information on occupational and smoking history and vital status was obtained through personnel records and individual contact. Causes and dates of deaths were verified from hospitals. Workers were divided into two groups: miners and millers (miner group) and control group (not direct exposed). Recent asbestos dust measurements in the workplaces showed that the concentrations ranged from 12 to 197 mg/m 3 . Amphibole contamination was very low. Cox proportional hazard models with competing risks were fit to estimate hazard ratios for cause-specific mortality associated with asbestos exposure (miners vs. controls). In addition, standardized mortality ratios (SMRs) were calculated based on national mortality rates. Results All mortality rates of selected causes, particularly lung cancer, were substantially higher in the miner group than in the controls. SMRs of lung cancer and nonmalignant respiratory diseases in the miners were 4.71 (95% CI, 3.57, 6.21) and 3.53 (2.78, 4.48), respectively. The controls had similar mortality rates of all causes, lung cancer, all cancers as national rates, but a higher mortality from respiratory diseases. Asbestos exposure was related to a 4.6-fold mortality risk for lung cancer and over threefold risk for all cancers and respiratory diseases, while smoking and age were adjusted. The highest SMR of lung cancer was observed in miners who smoked. Conclusion The results suggested excessive cause-specific mortality, in particular from lung cancer and respiratory diseases, in the cohort, which was associated with exposure to chrysotile asbestos.