Lowering reporting limit values for respirable crystalline silica analysis by X-ray diffraction in preparation of the 0.025 mg/m3 occupational exposure limit.

Internationally, respirable crystalline silica (RCS) occupational exposure limits (OELs) are being reassessed and, in some jurisdictions, lowered, putting pressure on the capabilities of the analytical techniques used to achieve robust analyses and reliable detection limits. In preparation of a lower OEL, options for lowering the limit of detection (LoD) for RCS analysis have been assessed. Using a Direct-on-Filter X-Ray Diffraction (XRD) analysis under reduced scan speeds in combination with low-noise RCS sampling filters, an LoD of 0.25 µg/filter and a limit of quantification (LoQ) of 0.82 µg/filter can be achieved. Both limits would translate in an LoD of 0.24 µg/m3 and LoQ of 0.78 µg/m3 when sampling respirable dust for 8 h at 2.2 L/min, providing a technical solution to monitor exposures at the proposed OEL of 0.025 mg/m3 (25 µg /m3) and below, with general sampling conditions as typically applied in Australia. This is the first report showing that the OEL of 0.025 mg/m3 (25 µg /m3) is measurable by one of the standardized, direct-on-filter XRD methods.

Respirable dust and crystalline silica exposure among rice mill workers of northeast India.

Crystalline silica is a Group I lung carcinogen primarily known as a causative agent for silicosis. A study was performed to quantify respirable dust, and respirable crystalline silica (RCS) in the rice mills of northeast India. Seventy-two respirable dust samples were collected from the worker's breathing zone from four rice mills at three locations: feeding, sieving, and polishing sections for two paddy varieties: Ranjit and Sali. The National Institute of Occupational Safety and Health (NIOSH), method #7602, was used to determine RCS. The results show that geometric mean TWA dust and RCS emissions in the rice mills varied from 3.97 to 455.00 mg/m3 and 0.02 to 5.38 mg/m3, respectively. RCS exposures were higher during milling of the Sali variety paddy (GM: 0.76 mg/m3) than the Ranjit variety paddy (GM: 0.25 mg/m3). Respirable dust and RCS emissions were considerably higher in the feeding and sieving sections than in the polishing section. Respirable dust and RCS exposure varied significantly (p < 0.001) with paddy variety. Respirable dust and RCS were highly correlated for different rice mills; however, the proportion of RCS in the dust was higher in the Sali variety paddy than in the Ranjit variety paddy. RCS exposure to the workers at the feeding and sieving sections was observed to be higher than the occupational exposure limits (OELs) published by Safe Work Australia, American Conference of Governmental Industrial Hygienists (ACGIH), National Institute for Occupational Safety and Health (NIOSH), Health and Safety Executive (HSE), and Factories Amendment Act, 1987, Government of India.

Evaluation of PVC and PTFE filters for direct-on-filter crystalline silica quantification by FTIR.

Direct-on-Filter (DoF) analysis of respirable crystalline silica (RCS) by Fourier Transform Infrared (FTIR) spectroscopy is a useful tool for assessing exposure risks. With the RCS exposure limits becoming lower, it is important to characterize and reduce measurement uncertainties. This study systematically evaluated two filter types (i.e., polyvinyl chloride [PVC] and polytetrafluoroethylene [PTFE]) for RCS measurements by DoF FTIR spectroscopy, including the filter-to-filter and day-to-day variability of blank filter FTIR reference spectra, particle deposition patterns, filtration efficiencies, and pressure drops. For PVC filters sampled at a flow rate of 2.5 L/min for 8 h, the RCS limit of detection (LOD) was 7.4 µg/m3 when a designated laboratory reference filter was used to correct the absorption by the filter media. When the spectrum of the pre-sample filter (blank filter before dust sampling) was used for correction, the LOD could be up to 5.9 µg/m3. The PVC absorption increased linearly with reference filter mass, providing a means to correct the absorption differences between the pre-sample and reference filters. For PTFE, the LODs were 12 and 1.2 µg/m3 when a designated laboratory blank or the pre-sample filter spectrum was used for blank correction, respectively, indicating that using the pre-sample blank spectrum will reduce RCS quantification uncertainty. Both filter types exhibited a consistent radially symmetric deposition pattern when particles were collected using 3-piece cassettes, indicating that RCS can be quantified from a single measurement at the filter center. The most penetrating aerodynamic diameters were around 0.1 µm with filtration efficiencies ≥ 98.8% across the measured particle size range with low-pressure drops (0.2-0.3 kPa) at a flow rate of 2.5 L/min. This study concludes that either the PVC or the PTFE filters are suitable for RCS analysis by DoF FTIR, but proper methods are needed to account for the variability of blank absorption among different filters.

Measuring Respirable Crystalline Silica (Quartz) from Powdery Materials through Sedimentation and X-ray Diffractometry.

When possible, choosing materials with a low quartz content is the most effective and cost-efficient way to prevent the respirable quartz exposure of workers and other end users of powdery products. Therefore, methods are needed to analyze low amounts of quartz from powdery products, such as sand, gravel, plaster, cement, and concrete. To this end, we present a method to analyze respirable dust and quartz from powdered materials, such as construction products. The method includes separation of the respirable dust fraction by liquid sedimentation, followed by gravimetric analysis and determination of the crystalline silica content by X-ray diffractometry. While also aiding in the development of less harmful products, analysis of the quartz concentration of powdery products is statutory in Eu countries, excluding natural products not chemically modified. According to EU Regulation No. 1272/2008, products must be classified if they contain harmful substances in concentrations above 0.1 wt.%, and clauses pertaining to cancerous properties and harmfulness to lungs should be included. Also, mineral producers in the EU recommend that products containing respirable quartz should be labelled based on their quartz concentration, provided the concentration exceeds 1 wt.%. The present method meets these needs. The analysis can be performed in parallel from 50 to 1000 mg (dry weight) of powdery materials. The quantitative limit of determination was 10 µg per sample, corresponding to 0.01 wt.%, and the linear range 0.02-10 wt.% (10-5000 µg quartz per sample, Pearson correlation coefficient 0.99). The accuracy of the method was 82% and the repeatability 11%.

Respirable Silica Dust Exposure of Migrant Workers Informing Regulatory Intervention in Engineered Stone Fabrication.

Background: Silicosis among workers who fabricate engineered stone products in micro or small-sized enterprises (MSEs) was reported from several countries. Workplace exposure data of these workers at high risk of exposure to respirable crystalline silica (RCS) dust are limited. Methods: We surveyed workers performing cutting, shaping and polishing tasks at 6 engineered stone fabricating MSEs in Sydney, Australia prior to regulatory intervention. Personal exposure to airborne RCS dust in 34 workers was measured, work practices were observed using a checklist and worker demography recorded. Results: Personal respirable dust measurements showed exposures above the Australian workplace exposure standard (WES) of 0.1 mg/m3 TWA-8 hours for RCS in 85% of workers who performed dry tasks and amongst 71% using water-fed tools. Dust exposure controls were inadequate with ineffective ventilation and inappropriate respiratory protection. All 34 workers sampled were identified as overseas-born migrants, mostly from three linguistic groups. Conclusions: Workplace exposure data from this survey showed that workers in engineered stone fabricating MSEs were exposed to RCS dust levels which may be associated with a high risk of developing silicosis. The survey findings were useful to inform a comprehensive regulatory intervention program involving diverse hazard communication tools and enforcing improved exposure controls. We conclude that modest occupational hygiene surveys in MSEs, with attention to workers' demographic factors can influence the effectiveness of intervention programs. Occupational health practitioners should address these potential determinants of hazardous exposures in their workplace surveys to prevent illness such as silicosis in vulnerable workers.

Personal respirable dust and respirable crystalline silica exposure in two shafts and a concentrator of a Zambian copper mine.

OBJECTIVES: Since the 1920s, Zambia's mining sector has experienced growth, which has increased the number of mine workers employed in the industry. Consequently, the potential for occupational exposure and prevalence of occupational diseases have also increased. Unfortunately, Zambia does not currently have legislative guidelines for workplace air monitoring and compliance. This study's objectives were to evaluate copper miners' personal exposure to respirable dust and respirable crystalline silica (RCS) and to assess workplace compliance using the European Standard for workplace air monitoring and measurement (EN689:2018). METHODS: This cross-sectional study collected 100 personal respirable dust exposure samples at a Zambian copper mine in 2023. These samples were weighed using NIOSH method 0600 and analyzed for crystalline silica using Fourier transform infrared spectroscopy (KBr pellet) (NIOSH method 7602). Additionally, 253 respirable dust exposure measurements collected at the mine between 2017 and 2022 were included for comparison. RESULTS: The median respirable dust exposure for the 2023 exposure measurements was 0.200 mg/m3 (95th percentile 2.871 mg/m3) compared to 0.400 mg/m3 (95th percentile 3.050 mg/m3) for the historic data. The median RCS exposure was 0.012 mg/m3 (95th percentile 0.163 mg/m3). Using EN689:2018, it was found that from 15 work areas, only six work areas complied with the standard for respirable dust exposure and only seven work areas complied with the standard for RCS exposure. CONCLUSIONS: At the mining site, several work areas had substantial exposure to respirable dust and RCS. Therefore, management needs to prioritize these areas when implementing control measures to reduce dust exposure. For the Zambia mining industry to manage exposure to respirable dust and RCS, it is necessary to implement standardized monitoring strategies. This study has demonstrated that EN689:2018 can be used successfully to determine compliance among Zambian mining work areas.

Concentrations of respirable crystalline silica and radon among tanzanite mining communities in Mererani, Tanzania.

BACKGROUND: Globally, the number of small-scale miners (SSM) is estimated to be more than 25 million, but it supports the livelihoods of around 100 million individuals. In Tanzania, the number of SSM has increased from an estimated 150,000 in 1987 to ~1.5 million in 2017. The miners are at a high risk of occupational-related health challenges. The study aimed to assess the concentrations of respirable crystalline silica (RCS) and radon among the tanzanite mining communities in Simanjiro District, Tanzania. METHODS: We carried out a cross-sectional study involving the Mererani mines in Tanzania. These are underground mines comprised of informally employed miners, i.e. SSM. Concentrations of RCS and radon gas were measured in 44 study units, i.e. 22 mining pits and within 22 houses in the general community, e.g. shops in the peri-mining community. A total of 132 respirable personal dust exposure samples (PDS), 3 from each of the study units were taken, but only 66 PDS from the mining pits were analysed, as this was the main interest of this study. Radon concentration was measured by continuous monitoring throughout the working shift (and overnight for residences) using AlphaGuard monitor. The medians and comparison to the reference values, OSHA USA PEL and WHO/IARC references, were done for RCS and radon, respectively, using SPSS Ver. 27.0.0). RESULTS: The median time-weighted average (TWA) concentration of the RCS in the mining pits was 1.23 mg/m3. Of all 66 personal dust samples from the mining pits, 65 (98.5%) had concentrations of RCS above the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 0.05 mg/m3. Mining pits had a median radon concentration of 169.50 bq/m3, which is above the World Health Organization (WHO)/International Commission on Radiation Protection (ICRP) recommended reference of 100.00 bq/m3 but not above the upper reference of 300.00 bq/m3, while the community buildings had a median radon concentration of 88.00 bq/m3. Overall, 9 (20.5%) and 17 (38.6%) radon measurements were above 300.00 bq/m3 and between 100.00 and 300.00 bq/m3 references, respectively. Specifically, in the mining pits, 9 (40.9%) test results were above 300.00 bq/m3, while none of the test results in the community was above 300.00 bq/m3. CONCLUSION: The tanzanite SSM in Mererani we highly exposed to RCS, which increases the risk of pulmonary diseases, including silicosis, tuberculosis, and pulmonary malignancies. Immediate action by OSHA Tanzania should be enforcement of wearing respirators by all miners throughout the working hours. Health education programmes to the SSM must be strengthened and OSHA Tanzania should adopt the 0.05 mg/m3 PEL, and enforce other occupational health and safety measures, including regular use of dust suppression mechanisms (water spray and wet drilling) and monitoring of RCS exposures among SSM. Monitoring of radon exposure both in the mining pits and community buildings should be conducted, and mitigation measures should be implemented in areas that exceed the reference level of 100.00 bq/m3.

An assessment of worker exposure to respirable dust and crystalline silica in workshops fabricating engineered stone.

There is a significant silicosis risk for workers fabricating engineered stone (ES) products containing crystalline silica. The aims of this study by SafeWork NSW were to: (i) assess current worker exposure to respirable dust (RD) and respirable crystalline silica (RCS) following a 5-y awareness and compliance program of inspections in ES workshops and (ii) to identify improvements in work practices from the available evidence base to further reduce exposures. One hundred and twenty-three personal full shift samples taken on as many workers and 34 static samples across 27 workshops fabricating ES were included in the final assessment. The exposure assessment was conducted using Casella Higgins-Dewell cyclones (Casella TSI) placed in the breathing zone of workers attached to SKC Air Check XR 5000 or SKC Chek TOUCH sampling pumps. Sample filters were sent to an ISO (2017) 17025:2017 accredited laboratory for gravimetric analysis for RD and X-Ray Diffraction (XRD) analysis to determine the amount of deposited RCS i.e. alpha-quartz and cristobalite. All workshops used wet methods of fabrication. The geometric mean (GM) of the pooled result for respirable dust (RD) was 0.09 mg/m3 TWA-8 h and 0.034 mg/m3 TWA-8 h for RCS. The highest exposed workers with a GM RCS of 0.062 mg/m3 TWA-8 h were those using pneumatic hand tools for cutting or grinding combined with polishing tasks. Workers operating semiautomated routers and edge polishers had the lowest GM RCS exposures of 0.022 mg/m3 TWA-8 h and 0.018 mg/m3 TWA-8 h respectively. Although ES workers remain exposed to RCS above the workplace exposure limit (WEL) of 0.05 mg/m 3 TWA-8 h, these results point to a very substantial reduction in exposures compared to poorly controlled dry methods of fabrication. Therefore, the wearing of respiratory protection by workers remains necessary until further control measures are more widely adopted across the entire industry e.g. reduction in the crystalline silica content of ES.

[Analysis of Hospital Care Registers due to Silicosis in Spain, 1997-2020]. / Análisis de los procesos asistenciales hospitalarios por silicosis en España, 1997-2020.

OBJECTIVE: The re-emergence of silicosis in Spain since 2007 has been identified by the increase in the number of occupational disease reports. The aim of our study was to analyse the silicosis care processes attended by the National Health System between 1997 and 2020 to better understand the epidemiological dimension of the problem. METHODS: Processes were obtained from the Registro de Actividad Sanitaria Especializada (RAE-CMBD), with ICD-9-CM codes 500 and 502 (1997-2016) and ICD-10-CM J60, J62.0 and J62.8 (2017-2020). Descriptive statistical methods and modelling by logistic regression and Joinpoint regression methodology were applied. RESULTS: A total of 111,325 records were obtained (ages twenty-one hundred years), 4.3% for silicosis as the main diagnosis (PD) and 95.7% as a secondary diagnosis (SD). Men accounted for 98% and women for 2%. The mean age for SD processes was 75.1, and 68.7 for PD processes. The median age increased by eight years for SD and decreased by three years for PD. Although the overall burden of care decreased, under-fifty PD procedures between 2006 and 2009 showed an upward trend (APC=27.01%). SD processes showed a non-significant upward trend (APC=1.92%) between 2005 and 2020. CONCLUSIONS: The upward trend in silicosis care processes in people under fifty years of age since 2005 confirms the healthcare impact of the re-emergence of silicosis in Spain. The associated burden of care constitutes a present and future public health problem given the decreasing age of those affected.

OBJECTIVE: La remergencia de la silicosis en España desde 2007 ha sido objetivada por el incremento de partes de enfermedad profesional. El objetivo de nuestro estudio fue analizar los procesos asistenciales por silicosis atendidos por el Sistema Nacional de Salud entre 1997 y 2020 para una mejor comprensión de la dimensión epidemiológica del problema. METHODS: Se empleó el RAE-CMBD, aplicando los códigos CIE-9-CM 500 y 502 (1997-2016) y CIE-10-CM J60, J62.0 y J62.8 (2017-2020). Se aplicaron métodos de estadística descriptiva y modelización por regresiones logísticas y metodología de regresión Joinpoint. RESULTS: Se obtuvieron 111.325 registros (veinte-cien años), el 4,3% por silicosis como diagnóstico principal (DP) y el 95,7% como diagnóstico secundario (DS). El 98% eran hombres y el 2% mujeres. La edad media de los procesos por DS fue de 75,1, y de 68,7 para los procesos por DP. La mediana de edad aumentó ocho años para los DS y disminuyó tres para los DP. Aunque la carga asistencial global disminuyó, los procesos en menores de cincuenta años por DP entre 2006 y 2009 registraron una tendencia ascendente (APC=27,01%). Los procesos por DS mostraron una tendencia ascendente no significativa (APC=1,92%) entre 2005 y 2020. CONCLUSIONS: La tendencia al crecimiento de los procesos asistenciales por silicosis en menores de cincuenta años desde 2005 confirma el impacto asistencial de la remergencia de la silicosis en España. La carga asistencial asociada constituye un problema de Salud Pública presente y futuro dada la reducción de edad de los afectados.

Occupational exposure to respirable crystalline silica and lung cancer: a systematic review of cut-off points.

BACKGROUND: Respirable crystalline silica (RCS) is associated with the development of lung cancer. However, there is uncertainty around the exposure threshold at which exposure to RCS may pose a clear risk for the development of lung cancer. The objective of this study was to review the cut-off points at which the risk of mortality or incidence of lung cancer due to occupational exposure to RCS becomes evident through a systematic review. METHODS: We conducted a search in PubMed, including cohort and case-control studies which assessed various categories of RCS exposure. A search was also conducted on the webpages of institutional organizations. A qualitative data synthesis was performed. RESULTS: Twenty studies were included. Studies that assessed lung cancer mortality and incidence displayed wide variability both in RCS exposure categories and related risks. Although most studies found no significant association for RCS exposure categories, it appears to be a low risk of lung cancer for mean concentrations of less than 0.07mg/m3. Regulatory agencies set annual RCS exposure limits ranging from 0.025mg/m3 through 0.1mg/m3. CONCLUSIONS: There is a wide degree of heterogeneity in RCS exposure categories, with most studies observing no significant risk of lung cancer for the lowest exposure categories. Cut-off points differ between agencies but are nonetheless very similar and do not exceed 0.1mg/m3.

Respirable silica particles in coal mine dust: An image library dataset collected using scanning electron microscopy with energy dispersive X-ray spectroscopy.

This dataset comprises an image library of 282 respirable silica particles. The particles were identified in samples of respirable coal mine dust (RCMD) collected in numerous US underground mines, and samples of lab-generated respirable dust that were created using the primary dust source materials (e.g., raw coal and rock) obtained from those mines. (A limited number of particles were also identified in samples generated from silica-containing reference materials.) Silica particle identification was done by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and then each particle was imaged and analyzed at both low (5 kV) and high (20 kV) accelerating voltage. SEM micrographs were captured at high magnification (i.e., 5000-20,000 ×) and overlaid with elemental maps to visually indicate relative Si and Al content; spectra were also collected to determine Si and Al % in each particle. This dataset can inform the understanding of real respirable silica particles in coal mine environments, which may differ from idealized (i.e., pure, independent) silica particles. The dataset therefore provides valuable context for the design and interpretation of research related to: respirable silica exposure studies, sample analysis and monitoring techniques, or dust control.

Determinants of respirable crystalline silica exposure in construction in western Canada.

Task-based respirable crystalline silica (RCS) exposure monitoring data was collected from construction work sites across 3 Canadian provinces: Alberta, British Columbia (BC), and Manitoba. In total 373 RCS samples were obtained from 70 worksites across 44 companies. Sampling was conducted between May 2015 and August 2020. The overall geometric mean (GM) RCS exposure was 0.045 mg/m3 (geometric standard deviation, GSD = 6.8). Alberta had the highest average exposure and the highest variability with GM of 0.060 mg/m3 (GSD = 9.3), the GM in BC was 0.044 (GSD = 4.3), and in Manitoba the GM was 0.033 (GSD = 7.0). A multivariable model was built using forward stepwise linear regression modeling. Province, task type, work environment (indoor vs. outdoor), construction material, sampling duration, and engineering control use were all statistically significant predictors of exposure level in partial F-tests (P < 0.05). Overall, the model explained 42% of the RCS concentration variability. Task type contributed most to the model's explanatory power. The task type with highest average exposure levels was demolition (GM 0.30 mg/m3, GSD 0.49). Breaking (GM 0.16 mg/m3, GSD 8.4) and grinding (GM 0.081 m/m3, GSD 7.4) also had high-exposure levels. Working outdoors was associated with exposure levels 39% lower than indoors. Exposure control measures such as local exhaust ventilation and wetting were also associated with lower exposure levels. Among construction materials, Cement, sand, and stone were associated with higher RCS exposure levels relative to the reference material, concrete. The results of this study indicate that workers in western Canada remain exposed to RCS at levels that exceed the health-based American Congress for Governmental Industrial Hygienists Threshold Limit Value of 0.025 mg/m3. Although there were some differences in exposure levels between the provinces, the determinants of exposure were similar in all 3. The overall GM RCS exposure was 0.045 mg/m3 (geometric standard deviation, GSD = 6.8). Alberta had the highest average exposure and the highest variability with GM of 0.060 mg/m3 (GSD = 9.3), the GM in BC was 0.044 (GSD = 4.3), and in Manitoba the GM was 0.033 (GSD = 7.0).

Silicosis, asbestosis, and pulmonary fibrosis in Ontario, Canada from 1996 to 2019.

BACKGROUND: Silicosis is a fibrotic lung disease caused by exposure to respirable crystalline silica. Historically, silicosis was common among miners and other professions in the 20th century, and in recent decades has re-emerged in coal mining and appeared in new workplaces, including the manufacture of distressed jeans and artificial stone countertops. METHODS: Physician billing data for the province of Ontario between 1992 and 2019 were analyzed across six time-periods (1993-1995, 1996-2000, 2001-2005, 2006-2010, 2011-2015, and 2016-2019). The case definition was two or more billing records within 24 months with a silicosis diagnosis code (ICD-9 502, ICD-10 J62). Cases from 1993 to 1995 were excluded as prevalent cases. Crude incidence rates per 100,000 persons were calculated by time-period, age, sex, and region. Analyses were repeated in parallel for pulmonary fibrosis (PF) (ICD-9 515, ICD-10 J84) and asbestosis (ICD-9 501; ICD-10 J61). RESULTS: From 1996 to 2019, 444 cases of silicosis, 2719 cases of asbestosis and 59,228 cases of PF were identified. Silicosis rates decreased from 0.42 cases per 100,000 in 1996-2000 to 0.06 per 100,000 people in 2016-2019. A similar trend was observed for asbestosis (1.66 to 0.51 per 100,000 persons) but the incidence rate of PF increased from 11.6 to 33.9 per 100,000 persons. Incidence rates for all outcomes were higher among men and older adults. CONCLUSIONS: A decreasing incidence of silicosis was observed in this analysis. However, the incidence of PF increased, consistent with findings from other jurisdictions. While cases of silicosis have been recorded among artificial stone workers in Ontario these cases do not seem to have impacted the population rates thus far. Ongoing, periodic surveillance of occupational diseases is helpful for tracking population-level trends over time.

Managing Quartz Exposure in Apartment Building and Infrastructure Construction Work Tasks.

The present report describes exposure to respirable silica and dust in the construction industry, as well as means to manage them. The average exposure in studied work tasks (n = 148) amounted to 64% of the Finnish OEL value of 0.05 mg/m3. While 10% of exposure estimates exceeded the OEL, the 60% percentile was well below 10% of the OEL, as was the median exposure. In other words, exposure was low in more than half of the tasks. Work tasks where exposure was low included construction cleaning, work management, installation of concrete elements, rebar laying, driving work machines equipped with cabin air intake filtration, and landscaping, in addition to some road construction tasks. Excessive exposure (>OEL) was related to not using respiratory protection at all or not using it for long enough after the dusty activity ceased. Excessive exposures were found in sandblasting, dismantling facade elements, diamond drilling, drilling hollow-core slabs, drilling with a drilling rig, priming of explosives, tiling, use of cabinless earthmoving machines, and jackhammering, regardless of whether the hammering took place in an underpressurized compartment or not. Even in these tasks, it was possible to perform the work safely, following good dust prevention measures and, when necessary, using respiratory protection suitable for the job. Furthermore, in all tasks with generally low exposure, one could be significantly exposed through the general air or by making poor choices in terms of dust control.

Hazardous dusts from the fabrication of countertop: a review.

Artificial countertop materials, including solid surface composites (SSC) and engineered stone (ES) may pose significant pulmonary health risks for workers who manipulate them. These materials have rapidly become popular in the multibillion-dollar countertop industry, rivaling that of natural materials such as granite and marble due to their variety of desirable esthetic qualities and reduced costs. Both SSC and ES consist of a mineral substrate bound together in a polymer matrix. For SSC the mineral is about 70% aluminum trihydrate (ATH) while ES contains up to 95% crystalline silica by weight. Both materials emit airborne dusts when being manipulated with power tools during the fabrication process. Several deaths and dozens of cases of silicosis have been identified worldwide in workers who fabricate ES, while a single case of fatal pulmonary fibrosis has been associated with SCC dust exposure. This review examines the current state of knowledge for both SSC and ES regarding the composition, particle emission characteristics, workplace exposure data, particle constituent toxicity, and possible methods for reducing worker exposure.

Role of metabolic reprogramming in pro-inflammatory cytokine secretion from LPS or silica-activated macrophages.

In the lungs, macrophages constitute the first line of defense against pathogens and foreign bodies and play a fundamental role in maintaining tissue homeostasis. Activated macrophages show altered immunometabolism and metabolic changes governing immune effector mechanisms, such as cytokine secretion characterizing their classic (M1) or alternative (M2) activation. Lipopolysaccharide (LPS)-stimulated macrophages demonstrate enhanced glycolysis, blocked succinate dehydrogenase (SDH), and increased secretion of interleukin-1 beta (IL-1ß) and tumor necrosis factor-alpha (TNF-α). Glycolysis suppression using 2 deoxyglucose in LPS-stimulated macrophages inhibits IL-1ß secretion, but not TNF-α, indicating metabolic pathway specificity that determines cytokine production. In contrast to LPS, the nature of the immunometabolic responses induced by non-organic particles, such as silica, in macrophages, its contribution to cytokine specification, and disease pathogenesis are not well understood. Silica-stimulated macrophages activate pattern recognition receptors (PRRs) and NLRP3 inflammasome and release IL-1ß, TNF-α, and interferons, which are the key mediators of silicosis pathogenesis. In contrast to bacteria, silica particles cannot be degraded, and the persistent macrophage activation results in an increased NADPH oxidase (Phox) activation and mitochondrial reactive oxygen species (ROS) production, ultimately leading to macrophage death and release of silica particles that perpetuate inflammation. In this manuscript, we reviewed the effects of silica on macrophage mitochondrial respiration and central carbon metabolism determining cytokine specification responsible for the sustained inflammatory responses in the lungs.

Gaseous Air Pollutants and Respirable Crystalline Silica Inside and Outside Homes at Brick Kilns in Bhaktapur, Kathmandu Valley, Nepal.

Household and ambient air pollution remain public health problems in much of the world. Brick kiln employees in Nepal may be particularly at risk of high air pollution exposures and resulting health effects due to high levels of outdoor air pollution, substandard housing, and indoor biomass cooking. We conducted a cross-sectional study of indoor and outdoor air pollution concentrations at workers' homes at four fixed chimney Bull's trench brick kilns in Bhaktapur, Kathmandu Valley, Nepal. We measured air concentrations of carbon monoxide (CO), carbon dioxide (CO2), nitrogen dioxide (NO2), sulfur dioxide (SO2), and respirable crystalline silica (SiO2; cristobalite, quartz, tridymite) using established methods and conducted a survey about characteristics of homes or samples that may be associated with air pollution concentrations. Geometric mean concentrations of CO, CO2, and SiO2 (quartz) were 0.84 ppm, 1447.34 ppm, and 6.22 µg/m3, respectively, whereas concentrations of all other air pollutants measured below lower detection limits. Most characteristics of homes or samples were not associated with air pollution concentrations. We found a positive association between the variable how long lived in house and SiO2 (quartz) concentrations, which may reflect sustained take-home exposure to SiO2 (quartz) over time. Interventions should focus on administrative controls to reduce take-home exposure to SiO2 (quartz) in this population.

End-of-Shift Monitoring of Respirable Crystalline Silica: A Critical Review of Measurement Techniques and Factors Influencing Accurate Measurements.

This article presents the findings of a systematic literature review focusing on the impact of interferences in host materials on Respirable Crystalline Silica (RCS) measurement, and the development of a validated method of calibration for RCS instrumentation for in-field use. The impact of interferences in host materials on RCS measurement has been shown to be critical information required for in-field use of portable RCS devices. Portable RCS instruments such as FTIR and XRD have been established to have good sensitivity for measurement but relatively low specificity due to interference in host materials. It has been shown that correction factors are needed to be applied to account for known interferences, especially when calibrating portable RCS instrumentation in-field. The potential to obtain reliable and repeatable results from RCS analysis instrumentation has also been demonstrated. There was significant evidence that interference materials could be present in host materials, and they influence RCS measurement. There is the potential and possibility of using portable RCS instrument for in-field measurement however the challenge is the calibration of such instrumentation in the field to account for changing host materials and thus potential interferences.

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.

Rapid Assessment of Oxidative Damage Potential: A Comparative Study of Engineered Stone Dusts Using a Deoxyguanosine Assay.

The popularity of engineered stone (ES) has been associated with a global increase in occupational lung disease in workers exposed to respirable dust during the fabrication of benchtops and other ES products. In this study, the reactivity and subsequent oxidative reduction potential of freshly generated ES dusts were evaluated by (i) comparing different engineered and natural stones, (ii) comparing settled and respirable stone dust fractions and (iii) assessing the effect of ageing on the reactivity of freshly generated stone dust. An established cell-free deoxyguanosine hydroxylation assay was used to assess the potential for oxidative DNA damage. ES dust exhibited a higher relative reactivity than two of the three natural stones tested. Respirable dust fractions were found to be significantly more reactive than their corresponding settled fraction (ANOVA, p < 0.05) across all stone types and samples. However, settled dust still displayed high relative reactivity. The lower reactivity of the settled dust was not due to decay in reactivity of the respirable dust when it settled but rather a result of the admixture of larger nonrespirable particles. No significant change in respirable dust reactivity was observed for three ES samples over a 21-day time period, whereas a significant decrease in reactivity was observed in the natural stone studied. This study has practical implications for dust control and housekeeping in industry, risk assessment and hazard management.