The Chinese silica cohort is one of the largest silica cohort with a sample size of about 74,000 employees from 29 Chinese metal mines and pottery factories. Early analysis reveal some uncertainties in the quantification of the association between silica dust exposure and lung cancer deaths due to occupational confounders such as polycyclic aromatic hydrocarbons (potteries and Iron-copper mines), arsenic (tin mines) and radon daughter (iron-copper mines).
In a recent published exposure-response-estimation of this cohort, the authors excluded 54% cohort participants with either low data quality or heavy occupational confounders, and demonstrated a clear exposure-response relationship between silica dust exposure and lung cancer deaths. However, this study finding ist still questioned by some of the scientific communities, since some residual confounders do still exist in a part of the facilities (such as radon daughter in iron mine and polycyclic aromatic hydrocarbons in pottery factories) and may still bias the study results.
In order to evaluate the possible methodological uncertainties in the recent published exposure-response estimation, we repeated the previous analysis by using the sub-cohort of Chinese tungsten miners which are free from any occupational carcinogenic confounders.
This study cohort includes 19007 workers in six tungsten mines with a follow-up period from January 1, 1960 to December 31, 2003. Cumulative silica dust exposure was estimated by linking the work history to the job-exposure matrix. Time-dependent cox proportional hazards model was used for exposure-response analysis.
This present reanalysis does not provide a clear exposure-response relationship between silica dust exposure and lung cancer deaths. Up to date, the Chinese silica cohort still fails to provide a clear evidence to show that exposure to silica causes lung cancer in the absence of occupational confounding factors.
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