Mortality in a Chinese chrysotile miner cohort

Our plain-English summary of Mortality in a Chinese chrysotile miner cohort, by X. Wang, S. Lin, E. Yano, et al (International Archives of Occupational and Environmental Health, 2012).

The study

• Authors: X. Wang, S. Lin, E. Yano, H. Qiu, I.T. Yu, L. Tse, Y. Lan, M. Wang
• Journal: International Archives of Occupational and Environmental Health
• Published: 2012;85(4):405-12
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

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.

In plain English

This cohort study followed 1,539 male workers at China's largest chrysotile mine, in Qinghai Province, from 1981 to 2006. The authors compared 1,080 workers directly engaged in mining, milling, mechanical maintenance and transportation with 459 rear service and administration workers not directly exposed, and compared both groups with national death rates. Dust measured in 2006 ranged from 12 to 197 mg/m3; no tremolite was detected. There were 428 deaths. Against national rates, miners' lung cancer deaths were 4.71 times expected (95% CI 3.57 to 6.21); nonmalignant respiratory disease deaths, 3.53 times (2.78 to 4.48). Adjusted for smoking, age at entry and employment years, miners' lung cancer hazard ratio against controls was 4.61 (1.96 to 10.86). Miners who smoked had the highest lung cancer standardized mortality ratio (SMR) against national rates, 5.45 (4.11 to 7.22). No mesothelioma deaths were recorded. The controls' respiratory disease SMR was also raised, 1.85 (1.15 to 2.96). The authors concluded that lung cancer and nonmalignant respiratory diseases were the most prominent causes of death in directly exposed workers. They noted lacking fibre measurements and detailed smoking data.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cohort study comparing directly exposed miners and millers with an internal control group of workers at the same mine, plus standardized mortality ratios against national mortality rates
• Who was studied: 1,539 male employees alive on 1 January 1981 at the largest chrysotile mine in China (Qinghai Province), followed to 31 December 2006. The miner group of 1,080 covered mining, milling, mechanical maintenance and transportation workers. The control group of 459 covered rear service and administration workers. Female employees were excluded.
• Exposure: Chrysotile asbestos dust from mining and milling. Total dust measured in 2006 ranged from 12 to 197 mg/m3, with an average of 91.3 mg/m3. No tremolite was detected, so any amphibole contamination was below 0.1%.
• Main results:
  • 428 deaths occurred in the whole cohort: 343 among the 1,080 miners and 85 among the 459 controls.
  • Miner group compared with national rates: lung cancer SMR 4.71 (95% CI 3.57, 6.21), based on 50 observed deaths, and nonmalignant respiratory disease SMR 3.53 (95% CI 2.78, 4.48).
  • Control group compared with national rates: rates were close to national levels except for nonmalignant respiratory diseases, SMR 1.85 (95% CI 1.15, 2.96). The control group's lung cancer SMR was 1.20 (0.55, 2.62).
  • Miners compared with controls, adjusted for age at entry, smoking and employment years: lung cancer hazard ratio 4.61 (95% CI 1.96, 10.86). The other hazard ratios were all causes 2.09 (1.64, 2.66), all cancers 3.22 (1.92, 5.41), gastrointestinal cancer 2.96 (1.39, 6.31) and nonmalignant respiratory diseases 3.34 (1.76, 6.33).
  • Lung cancer SMR by smoking status: 5.45 (95% CI 4.11, 7.22) in miners who smoked, 1.79 (0.49, 6.51) in nonsmoking miners, 1.66 (0.71, 3.88) in smoking controls and 1.05 (0.19, 5.96) in nonsmoking controls. The relative asbestos effect was 0.52 (95% CI 0.07, 1.11), which the authors read as an interaction between asbestos and smoking that was more than multiplicative.
  • No mesothelioma deaths were recorded in either group.
  • 87 workers in the miner group (8%) were diagnosed with asbestosis.
• The authors' conclusion: The authors concluded that the most prominent causes of death in workers directly engaged in asbestos mining and milling were lung cancer and nonmalignant respiratory diseases. They described the excess risks as most likely attributable to asbestos exposure.
• Limitations the authors state:
  • Fibre concentration data for the mine's workshops were lacking. Only total dust was measured periodically, which prevented a reliable exposure assessment and exposure-response analysis.
  • Smoking was recorded only as ever-smoker or nonsmoker. Smoking amount and duration were not available.
  • SMRs were calculated from national rates for 1990 and 2004 only, which may have made them inaccurate.
  • The authors could not be certain that the asbestos was entirely free of amphibole.
  • Control workers were likely exposed indirectly to asbestos dust through dust around the offices and living near the mine.
  • The interaction result may not have reached statistical significance because the sample size was inadequate.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Lung cancer.

Medical terms in this study, explained in our Lexicon: Chrysotile, Asbestos Exposure, Amphibole Group, Hazard Ratio, standardized mortality ratio (SMR), Lung Cancer.

Related studies

• Cancer mortality in Chinese chrysotile asbestos miners: exposure-response relationships — X. Wang, E. Yano, et al. (2013)
• Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort — S. Lin, X. Wang, et al. (2014)
• Cause-specific mortality in relation to chrysotile-asbestos exposure in a Chinese cohort — S. Lin, X. Wang, et al. (2012)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• Analysis of mortality in chrysotile asbestos miners in China — L. Du, X. Wang, et al. (2012)

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