| Objective:Evidence on the carcinogenicity of coal mine dust in occupational settings is still conflicting.In addition,there is an urgent need for an accessible and comprehensive database with national occupational dust exposure data for the coalmining industry.Therefore,we developed the job-exposure matrix(JEM)of dust exposure for use in estimating occupational dust exposure levels in China for coalmining industry.And then,we applied the predicted dust exposures to a population-based cohort of coal miner in China to assess the hazard effect of occupational dust and explore the other potential occupational risk factors for the coalminers.In addition,we conducted this research to evaluate the mortality risk of lung cancer for coalminers exposed to the occupational dust when compared to population with no or low dust exposure.Methods:In the first section of this study,we developed the job-specific and time-specific DUST-JEM of dust from coal mining industry for short-term exposure estimates and time-weighted average values,respectively,by combining 30470 dust exposure measurements between 1950 and 2019 collected from regulatory health and safety inspections,industry databases,reports,and published literature in China through a mixed-effects model with an empirical Bayes estimation procedure.A time trend incorporated as a b-spline was considered as a fixed-effect term while occupations and jobs were included as random-effect terms.In the second section of this study,the basic demographic information and occupational history of 870 workers from different jobs of a large coal mine company in central China from January 1988 to December 2018 were collected.And then the cumulative dust exposure was calculated by the dust job exposure matrix constructed in the first part of this study.The occupational environmental risk factors of coal miners were identified and assessed by the log-rank test and Cox proportional hazards regression model.The survival outcome and survival years(the time range from diagnosis to death or investigation deadline)of coal workers'pneumoconiosis patients were taken as the dependent variables;while age of onset,the stage of disease at first diagnosis,the year of first diagnosis,the cumulative working years and cumulative dust exposure were taken as independent variables to analyze the influencing factors of prognosis of patients with coal worker's pneumoconiosis.Variables were screened by introduced one by one,and the results of each step of fitting model were tested to obtain the optimal regression analysis model.In addition,this study constructed a nomogram to predict the 24-year survival probability of patients with coal worker's pneumoconiosis by scoring different risk factors.At the same time,the receiver operating characteristic and the area under curve were drawn and calculated to evaluate the predictive ability of nomogram model for the death occurrence events within the 24-year of coal workers'pneumoconiosis patients.In the third section of this study,database of PubMed and Chinese National Knowledge Infrastructure as well as reference lists were searched updated to September18,2020.The enrolled articles should report lung cancer mortality risk for coalminers exposed to occupational dust.Basic information was extracted such as the author and publication year,ethnicity,the type and estimates of outcome and the study design.The checklists from Agency for Healthcare Research and Quality and the Newcastle-Ottawa Scale were used for the assessment of quality and bias risk for cross-sectional studies,cohort studies and case control studies,respectively.The overall relative risks were calculated while Begg and Egger tests and sensitivity analysis were performed to explore potential heterogeneity sources.Meta-regression and subgroup analyses were also conducted to give more detailed information for the correlation between dust exposure and lung cancer mortality.Results:In the first section of this study,Dust exposures were estimated for 23occupations and 45 job categories from 1950 to 2019.For the short-term dust exposure levels,there was a declining trend until around 2014 with an obvious discontinuity and the concentrations were beyond the occupational exposure limits for most different jobs and years(10 mg/m~3);while the time-weighted average concentrations showed a downward trend on the whole,and the concentrations for most jobs were beyond the occupational exposure limit(6 mg/m~3 for 8-h TWA)but decreased below the limit level after the year of 2010.According to the results of the second part,the age of onset,initial diagnosis stage,cumulative working years and cumulative dust exposure can significantly affect the prognosis of patients with coal worker's pneumoconiosis.The age of onset was a risk factor for the prognosis of patients with coal worker's pneumoconiosis.With the increase of the age of onset,the risk of death of patients with coal worker's pneumoconiosis also increased,with hazard ratio(HR)of 1.055(1.044-1.066),P<0.001.Compared with the patients in stage I of coal worker's pneumoconiosis,the patients in stage III of coal worker's pneumoconiosis had a significantly higher risk of death,HR and its 95%CI were 2.836(1.571-5.121);compared with the patients with cumulative working years less than 8.88 years,the prognosis of the patients with cumulative working years more than 8.88 years was worse,the HR was 1.585(1.164-2.158).Compared with those with cumulative dust exposure less than 797.71 mg/m~3,the HR of individuals with cumulative dust exposure more than 797.71 mg/m~3 was 1.405(1.034-1.908),and the difference was statistically significant(P=0.030).In addition,the receiver operating characteristic and the area under curve(0.74)further supported the prognostic characteristics of age of onset,disease stage and diagnostic year in the overall survival of coal workers'pneumoconiosis patients.In the third section of this study,a total of 19 articles with 22 different studies(cross-sectional study,case control study and cohort study)including 8909 observed deaths were enrolled from 1964 to 2017 with a significant heterogeneity(I~2=95%,P<0.001).The pooled relative risk of mortality from lung cancer was 1.16(1.03-1.30)for coalminers.Results of meta-regression analysis indicated that the high heterogeneity among these enrolled studies might be caused by the ethnicity differences(P=0.011).Subgroup analysis also indicated that the pooled estimate for Asian population was 4.94(3.95-6.17)with I~2=39.3%and P=0.192.All these results suggested that exposure to occupational dust would significantly increase the mortality risk of lung cancer,especially for Asian population,which should be measured and controlled more strictly.Conclusions:This DUST-JEM makes it available as a source of data in applications on analysis of exposure trends in occupational epidemiology,assessment of health risks as well as the hazard surveillance and prevention for the coalmining industry.What's more,results of the Cox regression model showed that the higher the cumulative dust exposure,the higher the death risk of coal workers with pneumoconiosis.We should strengthen and improve the occupational health and safety management system,take comprehensive measures for the dust prevention and reduction,and then strengthen occupational health screening,and actively carry out the prevention and control of coal workers'pneumoconiosis and various complications,so as to improve the occupational safety and health of coal mine workers.In addition,the systematic review and meta-analysis provides high-quality evidence that exposure to occupational dust might increase the mortality risk of lung cancer,especially for Asian populations.The magnitude of this effect is of major public health importance in view of the ubiquitous existance of coalmining industry in China and even in the world. |
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