Occupational Exposure to Silica Dust and Silicosis Risk in Chinese Noncoal Mines:Qualitative and Quantitative Risk Assessment

Background: Despite increasing awareness, silica dust-induced silicosis still contributes to the huge disease burden in China.Worryingly, recent silica dust exposure levels and silicosis risk in Chinese noncoal mines remain unclear.Objective: We aimed to determine recent silica dust exposure levels and assess the risk of silicosis in Chinese noncoal mines. Methods: Between May and December 2020, we conducted a retrospective cohort study on 3 noncoal mines and 1 publichospital to establish, using multivariable Cox regression analyses, prediction formulas of the silicosis cumulative hazard ratio(H) and incidence (I) and a cross-sectional study on 155 noncoal mines in 10 Chinese provinces to determine the prevalence ofsilica dust exposure (PDE), free silica content, and total dust and respirable dust concentrations. The qualitative risk of silicosiswas assessed using the International Mining and Metals Commission's risk-rating table and the occupational hazard risk index;the quantitative risk was assessed using prediction formulas. Results: Kaplan-Meier survival analysis revealed significant differences in the silicosis probability between silica dust-exposedmale and female miners (log-rank test chi 21=7.52, P=.01). A total of 126 noncoal mines, with 29,835 miners and 4623 dust samples,were included; 13,037 (43.7%) miners were exposed to silica dust, of which 12,952 (99.3%) were male. The median PDE, freesilica content, total dust concentration, and respirable dust concentration were 61.6%, 27.6%, 1.30 mg/m3, and 0.58 mg/m3,respectively, indicating that miners in nonmetal, nonferrous metal, small, and open-pit mines suffer high-level exposure to silicadust. Comprehensive qualitative risk assessment showed noncoal miners had a medium risk of silicosis, and the risks caused bytotal silica dust and respirable silica dust exposure were high and medium, respectively. When predicting H and I over the nex 10, 20, and 30 years, we assumed that the miner gender was male. Under exposure to current total silica dust concentrations,median I10, I20, and I30 would be 6.8%, 25.1%, and 49.9%, respectively. Under exposure to current respirable silica dustconcentrations, median I10, I20, and I30 would be 6.8%, 27.7%, and 57.4%, respectively. These findings showed that miners innonmetal, nonferrous metal, small, and open-pit mines have a higher I and higher qualitative silicosis risk. Conclusions: Chinese noncoal miners, especially those in nonmetal, nonferrous metal, small, and open-pit mines, still sufferhigh-level exposure to silica dust and a medium-level risk of silicosis. Data of both total silica dust and respirable silica dust arevital for occupational health risk assessment in order to devise effective control measures to reduce noncoal mine silica dustlevels, improve miners'working environment, and reduce the risk of silicosis