Relationship between cumulative silica exposure and silicosis: a systematic review and dose-response meta-analysis.

BACKGROUND: Silicosis, a chronic respiratory disease caused by crystalline silica exposure, is a persistent global lung health issue. No systematic review of the relationship between cumulative respirable crystalline silica (RCS) exposure and silicosis exists. UK exposure limits are currently under review. We therefore performed a systematic review and dose-response meta-analysis of this relationship. METHODS: Web of Science, Medline and Embase were searched on 24 February 2023. Studies of radiographic, autopsy or death certificate silicosis, with an estimated average follow-up of over 20 years since first employment, were included. Cumulative silicosis risk methods were compared. The relative risks (RR) of silicosis at increasing cumulative exposures were calculated and used to estimate the absolute risk reduction (ARR). RESULTS: Eight eligible studies, including 10 cohorts, contributed 8792 cases of silicosis among 65 977 participants. Substantial differences in cumulative risk estimates between methodologies exist. Using the same method, we observed higher cumulative silicosis risks among mining compared with non-mining cohorts. A reduction from 4 to 2 mg/m³-years in cumulative RCS exposure corresponded to substantial risk reductions among miners (RR 0.23 (95% CI 0.18 to 0.29, I2=92.9%) with an ARR of 323 (95% CI 298 to 344) per 1000) and non-miners (RR 0.55 (95% CI 0.36 to 0.83, I2=77.0%) with an ARR of 23 (95% CI 9 to 33) per 1000). CONCLUSION: Despite significant heterogeneity, our findings support a reduction in permissible exposure limits from 0.1 mg/m3 to 0.05 mg/m³, particularly among mining populations. Further research is needed among non-miners as only two studies were eligible.

Feasibility of respirable crystalline silica exposure reduction in small-scale tanzanite mining in Tanzania.

INTRODUCTION: Respirable crystalline silica (RCS) exposures in tanzanite gem mining have been linked to tuberculosis and silicosis among miners. We conducted a plot study to assess RCS exposures and to introduce safer mining practices in one small-scale underground tanzanite mine. MATERIALS AND METHODS: Personal and area air samples for RCS were collected during tanzanite mining operations before and after improved work practices employed to reduce exposures and analyzed using X-ray diffraction. Area samples were collected at the rest area, located approximately 300 m underground and 100 m from other work activities. Improved practices included the use of wet drilling methods and drilling with new bits. RESULTS: A total of 33 personal and 4 area air samples were collected. Pre-intervention, mean exposures for all operations, drilling operations, non-drilling activities, and area samples were 122 mg/m3, 247 mg/m3, 34.3 mg/m3, and 1.95 mg/m3, respectively which exceeded the U.S. OSHA Permissible Exposure Limit (PEL) by 2,440 times for all operations, by 4,946 times for drilling operations, by 686 times for non-drilling activities and 39 times for area samples collected at an underground rest area. The post-intervention results showed a 99% reduction of RCS exposures for wet drilling operations, 98.5% reduction for non-drilling activities, and 36% reduction for area samples. Despite improvements, post-intervention RCS exposures during drilling had a mean of 2.08 mg/m3 or more than 41 times the OSHA PEL. CONCLUSIONS: We successfully piloted a program to work with small-scale tanzanite miners to reduce RCS exposures and raise awareness about the occupational health risks of RCS, though additional measures are recommended to further reduce RCS exposures. Similar programs should be taken to scale throughout underground mining sites in Tanzania and other countries.

Knowledge, attitudes and practices regarding respirable silica exposure and personal protective equipment use among brick kiln workers in Nepal.

OBJECTIVES: Brick kiln workers in Nepal are a neglected population who are exposed to high respirable silica concentrations, and few use interventions to reduce exposure. We aimed to characterise the prevalence of respiratory personal protective equipment (PPE) use, understand knowledge and attitudes towards kiln dust and respiratory PPE and identify factors associated with respiratory PPE use. METHODS: We conducted a cross-sectional study in Bhaktapur, Nepal. We used simple random selection to identify 10 out of 64 total kilns and stratified random sampling of 30 households to enrol workers aged ≥14 years within selected kilns. Field workers surveyed participants using structured questionnaires. Our primary outcome was to characterise the prevalence of current respiratory PPE use and secondary outcomes were summaries of knowledge, attitudes and practice of PPE use. RESULTS: We surveyed 83 workers (mean age 30.8 years, 77.1% male). Of these, 28.9% reported current respiratory PPE use at work, 3.6% heard of silicosis prior to the survey and 24.1% correctly identified the best respiratory PPE (N95, compared with surgical masks and barrier face coverings) for reducing dust exposure. Respiratory PPE users had higher income (mean monthly household income US$206 vs US$145; p=0.04) and education levels (25% vs 5.1% completed more than primary school; p=0.02) compared with non-users. CONCLUSIONS: Respiratory PPE use was low. Workers had poor knowledge of kiln dust health effects and proper respiratory PPE. We highlight important barriers to PPE use, particularly knowledge gaps, which can guide future investigations to reduce the silicosis burden among brick kiln workers.

[Australia's engineered stone ban. A sound decision]. / La prohibición de los aglomerados de cuarzo en Australia, una decisión modélica.

Australia se convirtió en diciembre de 2023 en el primer país en prohibir el uso de los aglomerados de cuarzo. El consumo de estos materiales sintéticos, que contienen más del 80% de sílice cristalina y que desde los años 90 se han empleado para la fabricación de encimeras de cocina y baños, ha contribuido al resurgimiento en numerosos países de formas aceleradas de silicosis y a una notable incidencia de enfermedades sistémicas. El objeto de este trabajo es analizar los fundamentos que sustentan la decisión australiana. Dichos fundamentos están principalmente recogidos en el informe elaborado en 2023 por la agencia gubernamental Safe Work Australia (SWA), que recomendó la prohibición del producto. SWA llevó a cabo una consulta pública entre todos los actores sociales y científicos interesados en el problema. El informe de SWA señaló la ausencia de evidencia científica sobre un umbral de sílice toxicológicamente seguro cuestionando la estrategia de los fabricantes del material de presentar como productos seguros a los aglomerados con menos del 40% de contenido de sílice. La recomendación de SWA tomó en consideración la evaluación del nivel de cumplimiento de las estrictas medidas de prevención implementadas entre 2019 y 2023, constatando que el incumplimiento siguió siendo generalizado en el sector. Además se realizó un análisis coste-beneficio para valorar el número de casos de silicosis que sería necesario evitar para "compensar" los costes económicos asociados a cada opción de prohibición. Para ello empleó el Valor Estadístico de la Vida (VEV) actualizado en 2023 en Australia y estimó en 4,9 millones de dólares australianos cada vida salvada y silicosis evitada. En nuestra opinión, la prohibición australiana es modélica por la forma en que se ha gestado la decisión, por su sólida fundamentación científica y socio-laboral, y por la aplicación del principio de precaución.

Evaluating silicosis risk: Assessing dust constitution and influence of water as a primary prevention measure in cutting and polishing of silica agglomerates, granite and marble.

An increasing number of silicosis cases have been reported related to the use of silica agglomerates. Many studies agree on the severity of this disease, which often presents with severe clinical forms in young workers and after a short latency period. Are there differences in the composition of dust generated by cutting and polishing with silica agglomerates versus granite and marble? Does the use of water injection reduce the risk associated with the use of these materials? We carried out a comparative observational-analytical study, measuring the concentration of dust generated during different machining operations on three different materials: granite, marble, and silica agglomerates. The effect of water injection on dust generation was evaluated. Personal sampling pumps were used, connected to a cyclone with polyvinyl chloride filters. The flow rate of the pumps was adjusted using a piston flowmeter. Measurements with a cascade impactor were made to assess the size distribution of respirable crystalline silica particles within the respirable fraction. In addition, environmental measurements with a spectrometer were made. 10 tests were carried out on granite and silica agglomerates for each procedure. In the case of marble, with very low silica content, only 2 tests of each type were carried out. Duration of each measurement was between 6 and 25 min. Cleaning times were set for each of the operations. The amount of dust collected in the respirable fraction was 70.85, 32.50 and 35.78 mg/m3 for dry cutting; 6.50, 3.75 and 3.95 mg/m3 for wet cutting; and 21.35, 13.68 and 17.50 mg/m3 for dry polishing, for granite, marble, and silica agglomerates respectively. Dry procedures in marble, silica agglomerates and granite showed higher dust concentration of particles smaller than 0.5 µm. Silica agglomerates showed higher concentrations of respirable crystalline silica particles than granite and marble, mainly with dry procedures. The greater production of small particles in dry and wet procedures with silica agglomerates shows that water injection is an insufficient preventive measure.

Celastrol Pyrazine Derivative Alleviates Silicosis Progression via Inducing ROS-Mediated Apoptosis in Activated Fibroblasts.

Silicosis is a complex occupational disease without recognized effective treatment. Celastrol, a natural product, has shown antioxidant, anti-inflammatory, and anti-fibrotic activities, but the narrow therapeutic window and high toxicity severely limit its clinical application. Through structural optimization, we have identified a highly efficient and low-toxicity celastrol derivative, CEL-07. In this study, we systematically investigated the therapeutic potential and underlying mechanisms of CEL-07 in silicosis fibrosis. By constructing a silicosis mouse model and analyzing with HE, Masson, Sirius Red, and immunohistochemical staining, CEL-07 significantly prevented the progress of inflammation and fibrosis, and it effectively improved the lung respiratory function of silicosis mice. Additionally, CEL-07 markedly suppressed the expression of inflammatory factors (IL-6, IL-1α, TNF-α, and TNF-ß) and fibrotic factors (α-SMA, collagen I, and collagen III), and promoted apoptosis of fibroblasts by increasing ROS accumulation. Moreover, bioinformatics analysis combined with experimental validation revealed that CEL-07 inhibited the pathways associated with inflammation (PI3K-AKT and JAK2-STAT3) and the expression of apoptosis-related proteins. Overall, these results suggest that CEL-07 may serve as a potential candidate for the treatment of silicosis.

Analyzing the incidence of silicosis across various industries in Taiwan: a study of occupational disease surveillance by linking national-based workers' and medicoadministrative databases.

OBJECTIVES: This study aimed to establish an occupational disease surveillance system by identifying high-risk industries for silicosis in Taiwan using a national database linkage approach. METHODS: The study was based on a comprehensive analysis of benefit claims from the National Labor Insurance Research Database and medical records from the National Health Insurance Research Database between 2004 and 2020, providing coverage for more than 88.5% of the workforce and 99.9% of citizens. Silicosis was defined as having received compensation for labor insurance benefits or having received a diagnosis of silicosis (International Classification of Diseases, 10th Revision: J62 or International Classification of Diseases, Ninth Revision: 502). The study used the International Standard Industrial Classification of All Economic Activities for industry-specific classification. Cox proportional hazard models were used to compare the silicosis incidence and risk among each industry and identify high-risk industries for silicosis. RESULTS: This study analyzed 1466 cases of silicosis between 2004 and 2020 and found that 28 industries had incidence rates of over 40 cases per 100,000 workers, indicating more than double the risk of developing silicosis. Of these industries, 14 were considered high risk (relative risk of over four times). Among these, this study identified industries rarely mentioned in the past, such as wholesale of brick, sand, cement, and products, artistic creation, landscape construction, and materials recovery. Stratification by years of work experience reveals those industries such as quarrying of stone, sand, clay, and other mining, construction of buildings, landscape construction, site preparation, foundation and structure construction, building completion and finishing, manufacture of ships, boats, and floating structures, and plumbing, heat, and air conditioning installation display higher hazard ratios for individuals with <10 years of work experience. CONCLUSIONS: The current surveillance system has identified certain industries that are at a higher risk of developing silicosis, which could be used for future occupational epidemiological surveys and targeted preventive measures in these sectors.

Concept of health surveillance programme for workers exposed to respirable crystalline silica at present and in the past.

In the paper authors present general assumptions of health surveillance programme concept for workers employed in respirable crystalline silica (RCS) exposure at present and in the past. There is no effective treatment for silicosis thus disease prevention is of paramount significance. For decades efforts of World Health Organization (WHO) and International Work Organization (ILO) have been focused on eliminating silicosis globally. Unfortunately silicosis is still one of the most lethal occupational diseases and the preventative programmes have not yet been successful. The authors identify main steps to complete an overview of RCS exposure and suggest lines of actions to be taken before launching the health surveillance programme. Introduction of the health surveillance programme would increase awareness of harmful health effects of the RCS exposure, emphasize the significance of preventive medical check-ups and early diagnostics of occupational diseases as well as the importance of using appropriate protective equipment. The programme development on a national level might be carried out with the cooperation of multiple backgrounds and institutions. This would allow for detailed planning, implementation, monitoring and effective evaluation of its results. Having a better and updated knowledge of silicosis epidemiology, early diagnostics, the possible sources of RCS occupational exposure and evaluation of undertaken preventive actions are crucial factors in disease prevention. The programme introduction would be of educational significance for all the stakeholders and the groups engaged in the project implementation, which would contribute to high effectiveness of the preventive activities and their improvement in the future. Med Pr Work Health Saf. 2023;74(4):341-6.

Silicosis: Emerging Trends and How to Screen for Early Detection.

BACKGROUND: National investigations are finding silicosis in young workers. We developed a silicosis case-finding process and conducted follow-up interviews to identify emerging exposure sources. METHODS: Probable cases were identified through Wisconsin hospital discharge and emergency department data and Wisconsin lung transplant programs. Interviews were attempted with case-patients under age 60. RESULTS: We identified 68 probable silicosis cases and interviewed 4 case-patients. Occupational exposures for cases under age 60 included sandblasting, quarry work, foundry work, coal mining, and stone fabrication. Two stone fabrication workers were diagnosed before age 40. DISCUSSION: Prevention is critically important to eliminate occupational silicosis. Clinicians should obtain the occupational and exposure history to identify cases of occupational lung disease and notify public health to identify and prevent workplace exposures.

Prevention of the Occupational Silicosis Epidemic in Australia: What Do Those Who Assess Workplace Health Risk Think Should Be Done Now?

An Australian National Dust Disease Taskforce was established to address the re-emergence of occupational lung disease, in particular silicosis. Exposure to respirable crystalline silica (RCS) occurs in various industries in Australia. We asked occupational hygienists about their practical experiences and perspectives on RCS exposure and regulatory action. A total of 105 members of the Australian Institute of Occupational Hygienists completed an anonymous questionnaire, which addressed individual characteristics, experience, perceived level of employer awareness, effectiveness of current regulation, and recommendations for improvement, across three main industrial sectors. Based on professional experience, 71% were concerned about the potential for RCS over-exposure. Barriers to adequate exposure control included lack of management commitment and financial resources. The employment of specialist occupational hygiene inspectors was considered to be the most effective regulatory strategy. Given the large number of exposed workers in the construction industry, with only a moderate awareness, there is the potential for significant cost shifting of the burden of occupational lung disease from employers on to individuals and the public health system. A nationally consistent approach to RCS exposure control across all industrial sectors is now recommended, with an increased focus on measuring and controlling exposure.

Inhibition of Galectin-3 attenuates silica particles-induced silicosis via regulating the GSK-3ß/ß-catenin signal pathway-mediated epithelial-mesenchymal transition.

Silica is a very common and important chemical raw material with a wide range of uses. Long-term inhalation of silica particles could cause lung toxicity, of which the most important representative is silicosis. Silicosis is a serious and fatal occupational pulmonary disease, characterized by persistent pulmonary inflammation and fibrosis. Despite intensive research, the toxic mechanism of silicosis caused by silica particles is not completely clear, which deserves further research and exploration. Many studies have indicated that the epithelial cells partially participate in the formation, accumulation, and activation of fibroblasts through epithelial-mesenchymal transition (EMT), which is conducive to the occurrence of fibrosis. Galectin-3 (Gal-3), widely expressed in epithelial cells, was observed to induce EMT in fibrotic diseases and tumors by regulating the GSK-3ß and ß-catenin. Previous studies have demonstrated that silica particles is indeed involved in the silicosis process by inducing EMT. However, it remains to be further studied whether there is a certain relationship between silica particles and Gal-3 expression, and whether Gal-3 also mediates the development of the silica particles-induced silicosis by regulating GSK-3ß/ß-catenin signal pathway-mediated EMT. Our research results showed that silica particles could significantly induce Gal-3 expression to promote the development of EMT through activating the GSK-3ß/ß-catenin signal pathway in mice and in A549 cells, which then significantly exacerbated the pulmonary fibrosis caused by silica particles. And the inhibition of Gal-3 could effectively inhibit the occurrence of EMT, and then effectively alleviate silicosis caused by silica particles. These findings would help us to further clarify the toxicological mechanisms of silicosis caused by silica particles and provide a novel target for prevention and intervention of silicosis.

Elevated exposures to respirable crystalline silica among engineered stone fabrication workers in California, January 2019-February 2020.

BACKGROUND: Workers fabricating engineered stone face high risk for exposure to respirable crystalline silica (RCS) and subsequent development of silicosis. In response, the California Division of Occupational Safety and Health (Cal/OSHA) performed targeted enforcement inspections at engineered stone fabrication worksites. We investigated RCS exposures and employer adherence to Cal/OSHA's RCS and respiratory protection standards from these inspections to assess ongoing risk to stone fabrication workers. METHODS: We extracted employee personal air sampling results from Cal/OSHA inspection files and calculated RCS exposures. Standards require that employers continue monitoring employee RCS exposures and perform medical surveillance when exposures are at or above the action level (AL; 25 µg/m3 ); exposures above the permissible exposure limit (PEL; 50 µg/m3 ) are prohibited. We obtained RCS and respiratory protection standard violation citations from a federal database. RESULTS: We analyzed RCS exposures for 152 employees at 47 workplaces. Thirty-eight (25%) employees had exposures above the PEL (median = 89.7 µg/m3 ; range = 50.7-670.7 µg/m3 ); 17 (11%) had exposures between the AL and PEL. Twenty-four (51%) workplaces had ≥1 exposure above the PEL; 7 (15%) had ≥1 exposure between the AL and PEL. Thirty-four (72%) workplaces were cited for ≥1 RCS standard violation. Twenty-seven (57%) workplaces were cited for ≥1 respiratory protection standard violation. CONCLUSIONS: Our investigation demonstrates widespread RCS overexposure among workers and numerous employer Cal/OSHA standard violation citations. More enforcement and educational efforts could improve employer compliance with Cal/OSHA standards and inform employers and employees of the risks for RCS exposure and strategies for reducing exposure.

Protective effects of intranasal curcumin on silica-induced lung damage.

OBJECTIVE: Being anti-inflammatory and an antioxidant in nature, curcumin has been studied for its anti-asthmatic effects, but its impact on silicosis has not been investigated before. It is a form of occupational lung illness caused by inhaling crystalline silica. It is particularly common among those who work in construction-related sectors. Therefore, present study has been undertaken to investigate impact of intranasal curcumin on silica induced lung damage in mice model of silicosis. MATERIALS AND METHODS: Mice model of silicosis was developed by intranasal silica instillation (2.5 mg/mice) for different durations mainly 7, 14 and 21 days, where the longest duration of silica exposure (21 days) mimics chronic occupational exposure of silica dust leading to silicosis. Curcumin (5 mg/kg,i.n) and /or dexamethasone, a known corticosteroid (10 mg/kg,i.p) was administered an hour prior to silica administration. RESULTS: Present study revealed silica induced lung damage in the mice model of silicosis characterized by airway inflammation, collagen deposition and enhanced expression of fibrosis markers (MMP-9, α-SMA, Hydroxyproline), which were significantly reduced in curcumin treatment groups. Inhibitory effects of curcumin were compared with standard drug, dexamethasone, a corticosteroid and was found better in protecting structural alterations in the lung. Damaged and abnormal mitochondria (enlarged and irregular shapes) were observed in silicosis group which were reduced in curcumin and dexamethasone treatment groups as revealed in transmission electron microscopic studies. CONCLUSIONS: Present study shows protective effects of intranasal curcumin on silica-induced airway inflammation and structural changes thereby lung damage. Hence, it can be considered as an alternative and complementary medication for silicosis.

Trading One Risk for Another: Consequences of the Unauthenticated Treatment and Prevention of Silicosis in Ontario Miners in the McIntyre Powder Aluminum Inhalation Program.

From 1943 to 1979, miners and factory workers in more than two hundred work sites globally were subjected to mandatory medical treatments by their employers as an unproven, and ultimately ineffective, treatment to prevent the lung disease silicosis. The treatments involved inhaling finely ground aluminum dust known as McIntyre Powder, blown into miners' change rooms each shift using compressed air systems. Tens of thousands of industrial laborers were exposed to McIntyre Powder, yet their story is scarcely known, and the possible health impacts of their aluminum treatments were rarely studied. This paper integrates the history of the aluminum prophylaxis program and its control by the northern Ontario mining industry with the lived experience of one of the affected miners, whose daughter created a voluntary registry which documents health issues in exposed miners, and stimulated research that found a link to her father's Parkinson disease.

3-methyadenine inhibits lipopolysaccharides-induced pulmonary inflammation at the early stage of silicosis via blocking NF-κB signaling pathway.

Occupational exposure to silica dust is related to pulmonary inflammation and silicosis. Lipopolysaccharides (LPSs) could aggravate apoptosis in alveolar macrophages (AMs) of human silicosis through autophagy, yet how the reduction of autophagy attenuated LPS-induced lung injury and the related mechanisms need to be investigated. In the study, we aim to understand the role of 3-methyladenine (3-MA), an inhibitor of autophagy, in LPS-mediated inflammatory responses and fibrosis. We collected AMs from observers/silicosis patients. The results showed that LPS induced NF-κB-related pulmonary inflammation in observers and silicosis patients, as confirmed by an increase in the expression of IL-1ß, IL-6, TNF-α, and p65, which could be inhibited by 3-MA treatment. In mice models, at the early stage (7d) of silicosis, but not the late (28d) stage, blocking autophagy reversed the increased levels of IL-1ß, IL-6, TNF-α, and p65 caused by LPS. Mechanism study revealed that LPS triggered the expression of LC3 II, p62, and cleaved caspase-3 at the early stage exposed to silica, which could be restored by 3-MA, while there was no difference in the expression of LAMP1 either at the early or late stage of silicosis in different groups. Similarly, 3-MA treatment did not prevent fibrosis characterized by destroyed alveoli, collagen deposition, and increased expression of α-SMA and Col-1 induced by LPS at the late stage of silicosis. The results suggested that 3-MA has a role in the protection of lung injury at the early stage of silicosis and provided an experimental basis for preventive strategies of pulmonary inflammation and silicosis.