Long-Term Exposure to Silica Dust and Risk of Total and Cause-Specific Mortality in Chinese Workers: A Cohort Study

A retro-prospective cohort study by Weihong Chen and colleagues provides new estimates for the risk of total and cause-specific mortality due to long-term silica dust exposure among Chinese workers

Functional variant of the carboxypeptidase M (CPM) gene may affect silica-related pneumoconiosis susceptibility by its expression: a multistage case-control study.

ObjectivesIn a genome-wide association study, we discovered chromosome 12q15 (defined as rs73329476) as a silica-related pneumoconiosis susceptibility region. However, the causal variants in this region have not yet been reported.MethodsWe systematically screened eight potentially functional single-neucleotide polymorphism (SNPs) in the genes near rs73329476 (carboxypeptidase M (CPM) and cleavage and polyadenylation specific factor 6 (CPSF6)) in a case-control study including 177 cases with silicosis and 204 healthy controls, matched to cases with years of silica dust exposure. We evaluated the associations between these eight SNPs and the development of silicosis. Luciferase reporter gene assays were performed to test the effects of selected SNP on the activity of CPM in the promoter. In addition, a two-stage case-control study was performed to investigate the expression differences of the two genes in peripheral blood leucocytes from a total of 64 cases with silicosis and 64 healthy controls with similar years of silica dust exposure as the cases.ResultsWe found a strong association between the mutant rs12812500 G allele and the susceptibility of silicosis (OR=1.45, 95% CI 1.03 to 2.04, p=0.034), while luciferase reporter gene assays indicated that the mutant G allele of rs12812500 is strongly associated with increased luciferase levels compared with the wild-type C allele (p<0.01). Moreover, the mRNA (peripheral blood leucocytes) expression of the CPM gene was significantly higher in subjects with silicosis compared with healthy controls.ConclusionsThe rs12812500 variant of the CPM gene may increase silicosis susceptibility by affecting the expression of CPM, which may contribute to silicosis susceptibility with biological plausibility

PLoS Med

BackgroundHuman exposure to silica dust is very common in both working and living environments. However, the potential long-term health effects have not been well established across different exposure situations.Methods and FindingsWe studied 74,040 workers who worked at 29 metal mines and pottery factories in China for 1 y or more between January 1, 1960, and December 31, 1974, with follow-up until December 31, 2003 (median follow-up of 33 y). We estimated the cumulative silica dust exposure (CDE) for each worker by linking work history to a job\u2013exposure matrix. We calculated standardized mortality ratios for underlying causes of death based on Chinese national mortality rates. Hazard ratios (HRs) for selected causes of death associated with CDE were estimated using the Cox proportional hazards model. The population attributable risks were estimated based on the prevalence of workers with silica dust exposure and HRs. The number of deaths attributable to silica dust exposure among Chinese workers was then calculated using the population attributable risk and the national mortality rate. We observed 19,516 deaths during 2,306,428 person-years of follow-up. Mortality from all causes was higher among workers exposed to silica dust than among non-exposed workers (993 versus 551 per 100,000 person-years). We observed significant positive exposure\u2013response relationships between CDE (measured in milligrams/cubic meter\u2013years, i.e., the sum of silica dust concentrations multiplied by the years of silica exposure) and mortality from all causes (HR 1.026, 95% confidence interval 1.023\u20131.029), respiratory diseases (1.069, 1.064\u20131.074), respiratory tuberculosis (1.065, 1.059\u20131.071), and cardiovascular disease (1.031, 1.025\u20131.036). Significantly elevated standardized mortality ratios were observed for all causes (1.06, 95% confidence interval 1.01\u20131.11), ischemic heart disease (1.65, 1.35\u20131.99), and pneumoconiosis (11.01, 7.67\u201314.95) among workers exposed to respirable silica concentrations equal to or lower than 0.1 mg/m3. After adjustment for potential confounders, including smoking, silica dust exposure accounted for 15.2% of all deaths in this study. We estimated that 4.2% of deaths (231,104 cases) among Chinese workers were attributable to silica dust exposure. The limitations of this study included a lack of data on dietary patterns and leisure time physical activity, possible underestimation of silica dust exposure for individuals who worked at the mines/factories before 1950, and a small number of deaths (4.3%) where the cause of death was based on oral reports from relatives.ConclusionsLong-term silica dust exposure was associated with substantially increased mortality among Chinese workers. The increased risk was observed not only for deaths due to respiratory diseases and lung cancer, but also for deaths due to cardiovascular disease.Please see later in the article for the Editors' SummaryWalk along most sandy beaches and you will be walking on millions of grains of crystalline silica, one of the commonest minerals on earth and a major ingredient in glass and in ceramic glazes. Silica is also used in the manufacture of building materials, in foundry castings, and for sandblasting, and respirable (breathable) crystalline silica particles are produced during quarrying and mining. Unfortunately, silica dust is not innocuous. Several serious diseases are associated with exposure to this dust, including silicosis (a chronic lung disease characterized by scarring and destruction of lung tissue), lung cancer, and pulmonary tuberculosis (a serious lung infection). Moreover, exposure to silica dust increases the risk of death (mortality). Worryingly, recent reports indicate that in the US and Europe, about 1.7 and 3.0 million people, respectively, are occupationally exposed to silica dust, figures that are dwarfed by the more than 23 million workers who are exposed in China. Occupational silica exposure, therefore, represents an important global public health concern.Why Was This Study Done?Although the lung-related adverse health effects of exposure to silica dust have been extensively studied, silica-related health effects may not be limited to these diseases. For example, could silica dust particles increase the risk of cardiovascular disease (diseases that affect the heart and circulation)? Other environmental particulates, such as the products of internal combustion engines, are associated with an increased risk of cardiovascular disease, but no one knows if the same is true for silica dust particles. Moreover, although it is clear that high levels of exposure to silica dust are dangerous, little is known about the adverse health effects of lower exposure levels. In this cohort study, the researchers examined the effect of long-term exposure to silica dust on the risk of all cause and cause-specific mortality in a large group (cohort) of Chinese workers.What Did the Researchers Do and Find?The researchers estimated the cumulative silica dust exposure for 74,040 workers at 29 metal mines and pottery factories from 1960 to 2003 from individual work histories and more than four million measurements of workplace dust concentrations, and collected health and mortality data for all the workers. Death from all causes was higher among workers exposed to silica dust than among non-exposed workers (993 versus 551 deaths per 100,000 person-years), and there was a positive exposure\u2013response relationship between silica dust exposure and death from all causes, respiratory diseases, respiratory tuberculosis, and cardiovascular disease. For example, the hazard ratio for all cause death was 1.026 for every increase in cumulative silica dust exposure of 1 mg/m3-year; a hazard ratio is the incidence of an event in an exposed group divided by its incidence in an unexposed group. Notably, there was significantly increased mortality from all causes, ischemic heart disease, and silicosis among workers exposed to respirable silica concentrations at or below 0.1 mg/m3, the workplace exposure limit for silica dust set by the US Occupational Safety and Health Administration. For example, the standardized mortality ratio (SMR) for silicosis among people exposed to low levels of silica dust was 11.01; an SMR is the ratio of observed deaths in a cohort to expected deaths calculated from recorded deaths in the general population. Finally, the researchers used their data to estimate that, in 2008, 4.2% of deaths among industrial workers in China (231,104 deaths) were attributable to silica dust exposure.What Do These Findings Mean?These findings indicate that long-term silica dust exposure is associated with substantially increased mortality among Chinese workers. They confirm that there is an exposure\u2013response relationship between silica dust exposure and a heightened risk of death from respiratory diseases and lung cancer. That is, the risk of death from these diseases increases as exposure to silica dust increases. In addition, they show a significant relationship between silica dust exposure and death from cardiovascular diseases. Importantly, these findings suggest that even levels of silica dust that are considered safe increase the risk of death. The accuracy of these findings may be affected by the accuracy of the silica dust exposure estimates and/or by confounding (other factors shared by the people exposed to silica such as diet may have affected their risk of death). Nevertheless, these findings highlight the need to tighten regulations on workplace dust control in China and elsewhere.Additional InformationPlease access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001206.2012711

An Ubuntu-based reflection on the public health impact of silica dust exposure in the South African mining industry

Issuing fitness certificates to South African mine workers with early and mild silicosis to continue risk work underground is a public health concern. This article draws on the view of solidarity to contend this practice. We employed a normative ethics approach and the concept of solidarity in African 'Ubuntu' philosophy to report and reflect on the public health implications of silica dust exposure among South African miners. We argued that since silicosis is irreversible, incurable, and could be progressive, leading to death, thus, issuing certificates of fitness to individuals who have early and mild silicosis, in many ways, is inappropriate and the practice ought to be rejected. We recommend more studies to reflect on the ethical management of silica dust exposure in the South African gold mining industry

Silicosis, Tuberculosis (tb) And Hiv/aids: The Triple Epidemic Among Gold Mineworkers In South Africa (literature Review And Policy Analysis)

The scourge of the triple epidemic of silicosis, tuberculosis (TB) and HIV/AIDS has plagued the South African gold mineworkers, with black mineworkers in particular, for over two decades now. Factors such as oscillating migration patterns, hazardous working conditions, and crowded living arrangements allow for the perfect conditions needed to sustain and amplify the epidemic within this population. The objective of this thesis is to provide a detailed review of the epidemiological literature regarding the different aspects of the silicosis, TB and HIV epidemic in South Africa, followed by an in-depth analysis of the current policy response, and its implications for directing the next phase of response to this epidemic. Review of the epidemiological literature provides strong and cogent evidence for the rapid and concomitant increase in the incidence and prevalence of silicosis and TB among gold mineworkers in South Africa over the last two decades, and shows that silica dust exposure is an independent risk factor for TB even among gold mineworkers without silicosis, thereby putting miners at increased risk of TB even after the exposure to silica dust has ceased. The policy analysis shows that there are serious gaps in research, policy and implementation regarding the approach and strategy to address the epidemic so far, especially with the steady decline in research expenditure on mining-related occupational health and safety research over the last few years. There has also been a wide-ranging failure to reduce silica dust exposure levels in gold mines, resulting in the failure to prevent new cases of silicosis among mineworkers

Association between Crystalline Silica Dust Exposure and Silicosis Development in Artificial Stone Workers

Occupational exposure to respirable crystalline silica (SiO2 ) is one of the most common and serious risks because of the health consequences for the workers involved. Silicosis is a progressive, irreversible, and incurable fibrotic lung disease caused by the inhalation of respirable crystalline silica dust. A cross-sectional epidemiological study was carried out to assess the occupational risk factors that may contribute to the onset of silicosis in workers carrying out work activities with the inhalation of silica compact dust. The study population consisted of 311 artificial stone workers from the province of Almeria (southeast of Spain). Among them, 64 were previously diagnosed with silicosis and the rest of the participants (n = 247 workers) were not diagnosed with such a disease. The workers showing a greater risk of developing silicosis were those who installed kitchen worktops at consumers’ homes, as they did not use face-masks or were not provided with personal protective equipment (PPE) by their business. The results of this study provide support for the evidence indicating that silicosis is a major emerging health concern for workers in the artificial stone sector. Exposure to crystalline silica dust thus can influence the development of silicosis in those cases where individual and collective protection measures are not used or adequately applied

Occupational exposure to crystalline silica and autoimmune disease.

Occupational exposure to silica dust has been examined as a possible risk factor with respect to several systemic autoimmune diseases, including scleroderma, rheumatoid arthritis, systemic lupus erythematosus, and some of the small vessel vasculitidies with renal involvement (e.g., Wegener granulomatosis). Crystalline silica, or quartz, is an abundant mineral found in sand, rock, and soil. High-level exposure to respirable silica dust can cause chronic inflammation and fibrosis in the lung and other organs. Studies of specific occupational groups with high-level silica exposure (e.g., miners) have shown increased rates of autoimmune diseases compared to the expected rates in the general population. However, some clinic- and population-based studies have not demonstrated an association between silica exposure and risk of autoimmune diseases. This lack of effect may be due to the limited statistical power of these studies to examine this association or because the lower- or moderate-level exposures that may be more common in the general population were not considered. Experimental studies demonstrate that silica can act as an adjuvant to nonspecifically enhance the immune response. This is one mechanism by which silica might be involved in the development of autoimmune diseases. Given that several different autoimmune diseases may be associated with silica dust exposure, silica dust may act to promote or accelerate disease development, requiring some other factor to break immune tolerance or initiate autoimmunity. The specific manifestation of this effect may depend on underlying differences in genetic susceptibility or other environmental exposures

Pulmonary function among stone quarry workers in India: The effect of duration of exposure, smoking status and job profile on pulmonary function tests

Introduction: Despite advances in technology, in India workers of stone processing industry continue to be at high risk for lung function deterioration. This study was designed to analyse the effect of duration of exposure, job profile and smoking on lung function of stone quarry workers from Jammu city, Jammu and Kashmir State, India. Methods: A cross-sectional study was carried out among 100 male stone crusher workers, selected through multi-stage random sampling technique. Effect of risk factors on the pulmonary function tests of the workers was analysed by ‘Students independent t-test’, one-way ANOVA and simple linear regression. The significance threshold was set up at P < 0.05. Results: We observed a significant reduction in lung function in subjects having duration of exposure above 10 years (Group III) with respect of stone crushers with duration of exposure up to 5 years (Group I) and 6 to 10 years of exposure (Group II). Lung function tests revealed a statistically significant (P < 0.05) reduction in lung function test parameters among manual workers compared to non-manual group of workers and among smokers compared to non-smokers. However, simple linear regression analysis revealed that only increase in duration of silica dust exposure was significantly associated with a reduction in pulmonary function tests, specifically in FVC (P = 0.019), FEV3 needs to be as subscript (P = 0.016), FEF25 (P = 0.016), FEF0.2-1.2 (P = 0.048), PEFR (P = 0.019) and MVV (P = 0.001) values. Conclusion: Duration of silica dust exposure is the most important determinant of pulmonary function deterioration. Therefore, limiting cumulative silica dust exposure can effectively reduce damage to airways in silica-exposed workers

Pilot Feasibility Stud

BackgroundThe use of formative research as a critical component of intervention planning is highly supported in the literature. However, studies that report such processes in practice are minimal. This paper reports on the formative data collection and analysis that informed the development of a multilevel intervention that utilizes mine assessment technology to bridge health communication between workers and management to reduce mine worker overexposure to respirable silica dust.MethodsFormative research to assess the feasibility and utility of this intervention design included stakeholder meetings and feedback, mine visits and observations, interviews with mine workers, and a focus group with mine management. Data collection took place at several US industrial mineral mine sites and a southeastern regional safety meeting. Interviews inquired about workers\ue2\u20ac\u2122 perceived susceptibility and severity to respirable silica exposure, barriers to preventing overexposure, behaviors that reduce exposure, and perceptions about respirable dust-monitoring technology. A focus group discussed mine stakeholders\ue2\u20ac\u2122 uses of various dust assessment technology.ResultsThe data was qualitatively analyzed and coded using a thematic and theoretical analysis. Researchers found recurring themes for both target audiences that informed the need and subsequent development of a mixed-method multilevel intervention to improve communication quantity and quality around dust-control practices.ConclusionsResults indicate that formative research is critical to: identify and develop an intervention that meets target audience needs; accurately represent the health problem; and develop positive relationships with research partners and stakeholders.CC999999/Intramural CDC HHS/United States2016-03-01T00:00:00Z26941960PMC477084