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 public hospital 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 of silica dust exposure (PDE), free silica content, and total dust and respirable dust concentrations. The qualitative risk of silicosis was 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-exposed male and female miners (log-rank test χ21=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, free silica 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 silica dust. Comprehensive qualitative risk assessment showed noncoal miners had a medium risk of silicosis, and the risks caused by total silica dust and respirable silica dust exposure were high and medium, respectively. When predicting H and I over the next 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 dust concentrations, median I10, I20, and I30 would be 6.8%, 27.7%, and 57.4%, respectively. These findings showed that miners in nonmetal, 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 suffer high-level exposure to silica dust and a medium-level risk of silicosis. Data of both total silica dust and respirable silica dust are vital for occupational health risk assessment in order to devise effective control measures to reduce noncoal mine silica dust levels, improve miners' working environment, and reduce the risk of silicosis.

Investigation of critical factors influencing the underestimation of hearing loss predicted by the ISO 1999 predicting model.

OBJECTIVE: To analyze factors influencing the underestimation of noise-induced permanent threshold shift (NIPTS) among manufacturing workers, providing baseline data for revising noise exposure standard. DESIGN: A cross-sectional study was designed with 2702 noise-exposed workers from 35 enterprises from 10 industries. Personal noise exposure level(LAeq,8h) and noise kurtosis level were determined by a noise dosimeter. Questionnaires and hearing loss tests were performed for each subject. The predicted NIPTS was calculated using the ISO 1999:2013 model for each participant, and the actual measured NIPTS was corrected for age and sex. The factors influencing the underestimation of NIPTS were investigated. RESULTS: The predicted NIPTS at each test frequency (0.5, 1, 2, 3, 4, or 6kHz) and mean NIPTS at 2, 3, 4, and 6kHz (NIPTS2346) using the ISO 1999:2013 model were significantly lower than their corresponding measured NIPTS, respectively (P < 0.001). The ISO model significantly underestimated the NIPTS2346 by 12.36 dB HL. The multiple linear regression analysis showed that noise exposure level, exposure duration, age, and kurtosis could affect the degree of underestimation of NIPTS2346. The generalized additive model (GAM) with (penalized) spline components showed nonlinear relationships between critical factors (age, exposure duration, noise level, and kurtosis) and the underestimated NIPTS2346.The underestimated NIPTS2346 decreased with an increase in exposure duration (especially over ten years). There was no apparent trend in the underestimated NIPTS2346 with age. The underestimated NIPTS2346 decreased with the increased noise level [especially > 90 dB(A)]. The underestimated NIPTS2346 increased with an increase in noise kurtosis after adjusting for the noise exposure level and exposure duration and ultimately exhibiting a linear regression relationship. CONCLUSIONS: The ISO 1999 predicting model significantly underestimated the noise-induced hearing loss among manufacturing workers. The degree of underestimation became more significant at the noise exposure condition of fewer than ten years, less than 90 dB(A), and higher kurtosis levels. It is necessary to apply kurtosis to adjust the underestimation of hearing loss and consider the applying condition of noise energy metrics when using the ISO predicting model.

[Effects of noise exposure level on the relationship between SNPs of SOD1 and the susceptibility to noise-induced hearing loss (NIHL)].

OBJECTIVE: To explore the effects of noise exposure level and cumulative noise exposure (CNE) on the relationship between rs2070424 and rs10432782 SNPs in SOD1 and the susceptibility to noise-induced hearing loss (NIHL). METHODS: A case-control study was performed for investigating the effects of environmental risk factors on the susceptibility to NIHL in 201 sensitive workers and 202 resistant workers.A questionnaire was utilized to investigate the occupational health and to identify the occupational risk factors. The noise exposure levels were detected according to the Chinese standard Measurement of noise in the workplace (GBZ/T 189.8-2007). The peripheral blood samples (5 ml blood for each sample) were from sensitive workers and resistant workers. Genomic DNA was extracted on the basis of the standard procedures of Takara kit. SNPs were detected using standard procedures of TaqMan probe allele identification method. RESULTS: In group exposed to 85 - 92 dB noise (A), the risk of NIHL in the subjects with the AA genotype of rs2070424 was lower than that in the subjects with the GG genotype, OR = 0.37 (95%CI: 0.17∼ 0.80). In group exposed to > 82 dB CNE (A), the AA genotype of rs2070424 is a protective factor of NIHL, as compared with the GG genotype, OR = 0.25 (95%CI: 0.09 ∼ 0.70). In group exposed to 85 - 92 dB noise (A), the risk of NIHL in the subjects with the GG genotype of rs10432782 was compared with the risk of NIHL in the subjects with the TT genotype, OR = 3.17 (95%CI: 1.16 ∼ 6.89). The GT genotype was compared with TT genotype, OR = 2.39 (95%CI: 1.16 ∼ 4.97). In group exposed to 75 ∼ 82 dB CNE (A), the risk of NIHL in the subjects with the GG genotype was compared with the risk of NIHL in the subjects with the TT genotype, OR = 2.35 (95%CI: 0.96 ∼ 5.72), P = 0.06. The GG genotype may bea risk factor of NIHJ. CONCLUSION: The noise exposure level and CNE may influence the relationship between rs2070424, rs10432782 SNPs in SOD1 and noise-induced hearing loss.

[Association between SNPs in SOD1 and noise-induced hearing loss in Chinese Han population].

OBJECTIVE: To observe the association between SNPs in SOD1 (rs1041740, rs2070424, rs10432782 and rs4998557) and noise-induced hearing loss in Chinese Han population. METHODS: A case-control study was used to study the effects of environmental risk factors on the susceptibility to noise induced hearing loss (NIHL) in 201 sensitive workers and 202 resistant workers. A questionnaire was designed to carry out an investigation, and an occupational health survey was used to identify the occupational risk factors. Genomic DNA was extracted from peripheral blood cells using standard procedures of Takara kit, and 5 ml blood was from each subject. SNPs were detected using standard procedures of TaqMan probe allele identification method. RESULTS: In SOD1 gene, the A allele of rs2070424 was a protective factor of NIHL, compared with the G allele (OR = 0.67, 95%CI: 0.50 approximately 0.88). The risk with NIHL in subjects with AA genotype was significantly lower than that in subjects with GG genotype (OR = 0.48, 95%CI: 0.26 approximately 0.79). After adjusting the confusion factors, OR was 0.44 and 95%CI was 0.25 approximately 0.78. CONCLUSION: In Chinese Han population, the SNP of rs2070424 in SOD1 may be associated with the susceptibility to NIHL.

[Mechanism study of adaptive response in high background radiation area of Yangjiang in China].

OBJECTIVE: To study the adaptive response mechanisms in high background radiation area (HBRA) among Yangjiang local people through gene and protein expression of receptor for advanced glycation end products (RAGE) and S100A6 in peripheral blood and sputum in inhabitants of HBRA. METHODS: A total of 53 male inhabitants were selected from HBRA in Yangjiang as the exposure group, while 53 male inhabitants were selected from Enping (control area, CA)as the control group. The content of RAGE and S100A6 gene and protein were detected by RT-PCR and Western blotting assay. Thermo luminescent dosemeter(TLD) assay was used to measure the outside dose and estimate the effective dose. RESULTS: The effective dose in CA and HBRA was respectively 1.95 mSv and 6.24 mSv, which was 3 fold difference. Compared with CA, RAGE and S100A6 expression were significantly reduced in both gene and protein level in HBRA. The relative median mRNA expression of RAGE and S100A6 in peripheral blood were respectively 0.28, 1.06 and 0.16, 0.79 in CA and HBRA group, there was significance (with analysis Z values of -2.587 and -2.328 respectively, P < 0.05) with Wilcoxon rank test. For the protein of sputum, the relative median expression were respectively 2.98, 2.25 and 0.53, 0.47 with significant difference (with analysis Z values of -2.201 and -2.366 respectively, P < 0.05) by Wilcoxon rank test. CONCLUSION: The low expression of RAGE and S100A6 in HBRA group might be correlated with the adaptive response and the low mortality of cancer in HBRA.

[p16 and MGMT gene methylation in sputum cells of uranium workers].

OBJECTIVE: To study the methylation of O-6-methylguanine-DNA methyltransferase (MGMT) and p16 gene in the sputum cells of radon-exposed population. To provide the experimental base for finding the molecular biomarker of the high risk population of the radon-induced lung cancer. METHODS: 91 radon-exposed workers were divided into 4 groups, high dosage group (> 120 WLM), middle dosage group (between 60 and 120 WLM), low dosage group (between 30 and 60 WLB) and lower dosage group (between 2 and 30 WLM) according to the accumulated exposure dosage of the radon daughters. The abnormal methylation of p16 and MGMT gene in the sputum cells of the population in the four groups was detected with the methylation specific PCR (MSP). RESULTS: There was significantly upward trend for the p16 gene methylation rate (0.00%-20.00%), the MGMT gene methylation rate (0.00%-28.00%) and the total methylation rate (0.00%-40.00%) with the increase of the accumulated exposure dosage of the radon daughters (P < 0.01). CONCLUSION: The methylation of p16 and MGMT gene is related to the accumulate exposure dosage of the radon daughters.