Respirable quartz dust exposure and airway obstruction: a systematic review and meta-analysis

A study of inflammatory biomarkers in crystalline silica exposed rock drillers

BACKGROUND

Crystalline silica (CS) exposure can cause serious lung disease in humans, but mechanisms of pulmonary toxicity have not been completely elucidated.

AIMS

To assess pro-inflammatory and anti-inflammatory biomarkers and biomarkers related to the development of chronic obstructive pulmonary disease and fibrosis in serum of rock drillers exposed to CS.

METHODS

Rock drillers (N = 123) exposed to CS and non-specified particulate matter (PM) were compared to 48 referents without current or past exposure to PM in a cross-sectional study.

RESULTS

The rock drillers had been exposed to CS for 10.7 years on average. Geometric mean (GM) current exposure was estimated to 36 µg/m3. Their GM concentration of matrix metalloproteinase 12 (MMP-12) was significantly higher (16 vs. 13 ng/L; p = 0.04), while interleukin (IL) 6 and IL-8 were significantly lower compared to the referents. Also pentraxin 3 was significantly lower (3558 vs. 4592 ng/L; p = 0.01) in the rock drillers. A dose-response relationship was observed between cumulative exposure to CS and MMP-12, the highest exposed subgroup having significantly higher MMP-12 concentrations than the referents.

CONCLUSION

Exposure to CS may increase circulating MMP-12 concentrations in a dose-response related fashion. The results may also suggest a down-regulation of pro-inflammatory pathways.

Cardiovascular toxic effects of nanoparticles and corresponding molecular mechanisms

Rapid advancements in nanotechnology have been integrated into various disciplines, leading to an increased prevalence of nanoparticle exposure. The widespread utilization of nanomaterials and heightened levels of particulate pollution have prompted government departments to intensify their focus on assessing the safety of nanoparticles (NPs). The cardiovascular system, crucial for maintaining human health, has emerged as vulnerable to damage from nanoparticle exposure. A mounting body of evidence indicates that interactions can occur when NPs come into contact with components of the cardiovascular system, contributing to adverse cardiovascular disease (CVD). However, the underlying molecular mechanisms driving these events remain elusive. This work provides a comprehensive review of recent advance on nanoparticle-induced adverse cardiovascular events and offers insight into the associated molecular mechanisms. Finally, the influencing factors of NPs-induced cardiovascular toxicity are discussed.

Application of artificial intelligence algorithms and low-cost sensors to estimate respirable dust in the workplace

The Internet of Things (IoT) and low-cost sensor technology have become common tools for environmental exposure monitoring; however, their application in measuring respirable dust (RD) in the workplace remains limited. This study aimed to develop a predictive model for RD using artificial intelligence (AI) algorithms and low-cost sensors and subsequently assess its validity using a standard sampling approach. Various low-cost sensors were combined into an RD sensor module and mounted on a portable aerosol monitor (GRIMM 11-D) for two weeks. AI algorithms were used to capture data per minute over 14 days to establish predictive RD models. The best-fitting model was validated using an aluminum cyclone equipped with an air pump and polytetrafluoroethylene filters to sample the 8-hour RD for 5 days at an aircraft manufacturing company. This module was continuously monitored for two weeks to evaluate its stability. The RD concentration measured by GRIMM 11-D in a general outdoor environment over two weeks was 28.1 ± 16.1 μg/m3 (range: 2.4-85.3 μg/m3). Among the various established models, random forest regression was observed to have the best prediction capacity (R2 = 0.97 and root mean square error = 2.82 μg/m3) in comparison to the other 19 methods. Field-based validation revealed that the predicted RD concentration (35.9 ± 4.1 μg/m3, range: 32.7-42.9 μg/m3) closely approximated the results obtained by the traditional method (38.1 ± 8.9 μg/m3, range: 28.1-52.5 μg/m3), and a strong positive Spearman correlation was observed between the two (rs = 0.70). The average bias was -2.2 μg/m3 and the precision was 5.8 μg/m3, resulting in an accuracy of 6.2 μg/m3 (94.2 %). Data completeness was 99.7 % during the continuous two-week monitoring period. The developed sensor module of RD exhibited excellent predictive performance and good data stability that can be applied to exposure assessments in occupational epidemiological studies.

Silica Exposure and Cardiovascular, Cerebrovascular, and Respiratory Morbidity in a Cohort of Male Swedish Iron Foundry Workers

OBJECTIVE

We present quantitative exposure-response data on silica exposure in male Swedish iron foundry workers for cardiovascular, cerebrovascular, and respiratory morbidity.

METHODS

This research is a cohort study of 2063 male Swedish iron foundry workers. From the Swedish National Patient Registers, data on morbidity incidence were retrieved. A historical measurement database of 1667 respirable silica exposure measurements from 10 Swedish iron foundries was used to calculate the cumulative exposure dose for each worker.

RESULTS

Increased morbidity risk for the whole group of foundry workers was determined for ischemic heart disease, cerebrovascular disease, chronic obstructive pulmonary disease (COPD), bronchitis, and pneumonia. In addition, an increased risk for COPD at cumulative silica exposures ranging from 0.11 to 0.84 mg/m 3 year is presented.

CONCLUSIONS

The study presents a significantly increased COPD risk at cumulative silica exposures below the Swedish occupational exposure limit.

Nine human epidemiological studies on synthetic amorphous silica and respiratory health

The respiratory health effects of Synthetic Amorphous Silica (SAS) have been studied in human epidemiological research. This article presents a historical overview and review of nine occupational worker studies that have been conducted so far on this topic. The combined study population of all of these studies included 1172 employees, and exposure concentrations ranged from < 1 mg/m3 to 100 mg/m3. In two studies with a total of 293 workers, the incidence of silicosis was investigated after long-term exposure to precipitated SAS, and no cases of silicosis were found (Plunkett and Dewitt, 1962; Volk, 1960). In another study, the spirometry results of 40 workers were normal (Vitums et al., 1977). In a study of 28 workers, 4 cases of silicosis were identified, but it is possible that contamination with cristobalite occurred and detailed information about the amorphous silica origin was not provided (Mohrmann and Kahn, 1985). Ferch et al. (1987) found that lung impairment was associated with confounding factors (smoking) but not with exposure to precipitated SAS in a study of 143 workers. Choudat et al. (1990) reported a reduction in forced expiratory flow in a group exposed to precipitated SAS compared to a control group. Still, they found no correlation between the extent of exposure and pulmonary function was found in a study of 131 workers. Wilson et al. (1979) also failed to show a significant association between the degree of exposure to precipitated SAS and annual changes in lung function in a study of 165 workers. In the most recent and most extensive study (Taeger et al., 2016; Yong et al., 2022) in Germany, involving 462 factory workers, no association between inhalable or respirable SAS dust exposure and respiratory health was reported. Based on the available data, there is no evidence-base to support a relationship between SAS and respiratory health in humans.

The impact of occupational exposure to crystalline silica dust on respiratory function (airway obstruction and FEF25-75) in the French general population

INTRODUCTION

Although several studies have studied the relationship between occupational exposure to crystalline silica dust and respiratory mortality, few have examined the relationship with impairments in respiratory function and the exposure threshold triggering spirometric monitoring in exposed workers. The objective of the present study was to evaluate the impact of exposure to crystalline silica dust on respiratory function.

METHODS

We included 1428 male participants (aged 40 to 65) recruited from the French general population, at random from electoral rolls, in the cross-sectional ELISABET study and for whom data on forced expiratory flow-volume curve indices z-scores (calculated using the Global Lung Function Initiative 2012 equations) and exposure (via a questionnaire) were available. A cumulative exposure index (CEI) for crystalline silica dust (CEI_silica, expressed in mg.m^-3.year) was calculated using the Matgéné occupational exposure matrix.

RESULTS

293 of the 1428 participants (20.52%) reported exposure to silica dust. We found that the adjusted z-scores for the forced expiratory volume in the first second/forced vital capacity (FEV₁/FVC) ratio decreased significantly as CEI_silica increased. After adjustment, the adjusted z-scores for FEV₁/FVC (β: -0.426 (95% confidence interval (CI): -0.792, -0.060) per 1 mg m^-3.year increment) and the mean forced expiratory flow between 25 and 75% of the forced vital capacity (FEF_25-75) (β: -0.552 (95% CI: -0.947, -0.157)) were significantly lower in the participants with CEI_silica ≥1 mg m^-3.year than in non-exposed participants. The likelihoods of having airway obstruction (odds ratio (OR): 3.056 (95% CI: 1.107, 7.626)) or having an impaired FEF_25-75 (OR: 4.305 (95% CI: 1.393, 11.79)) were also significantly higher in participants with CEI_silica ≥1 mg m^-3.year.

CONCLUSION

Our results emphasize the importance of spirometry-based monitoring in workers exposed to more than 1 mg m^-3.year of crystalline silica dust, in order to identify small airway obstruction or airway obstruction as early as possible.

Silica-associated lung disease in developing countries

PURPOSE OF REVIEW

There is a considerable burden of silica-associated lung diseases in the developing world. This review summarizes the epidemiology of these diseases, especially silicosis and silico-tuberculosis, mitigative efforts and treatment, especially in the context of developing countries.

RECENT FINDINGS

In 2017, the highest incidence of silicosis was in China, India and Brazil among the developing countries. The prevalence of silicosis amongst exposed workers may vary from 4 to 55%; there is a risk of underestimation because of the 'healthy worker effect'. The permissible exposure limit for respirable silica adopted by governments in developing countries remains higher than the proposed 0.025 mg/m3. Silica exposure in informal or unorganized industries is challenging, as it falls outside statutory controls. Recent efforts on regulation and compensation by various governments in developing countries are encouraging but need proper implementation on the ground. Biomarkers such as club cell protein 16 and imaging methods such as computed tomography may offer earlier and easier detection of silicosis. Advanced silicosis remains incurable; novel treatments such as antifibrotics agents may be potentially effective.

SUMMARY

Silica-associated lung diseases are prevalent in developing countries. Efforts directed at preventing or minimizing exposure to respirable crystalline silica are required for mitigation.

Ever and cumulative occupational exposure and lung function decline in longitudinal population-based studies: a systematic review and meta-analysis

OBJECTIVES

Adverse occupational exposures can accelerate age-related lung function decline. Some longitudinal population-based studies have investigated this association. This study aims to examine this association using findings reported by longitudinal population-based studies.

METHODS

Ovid Medline, PubMed, Embase, and Web of Science were searched using keywords and text words related to occupational exposures and lung function and 12 longitudinal population-based studies were identified using predefined inclusion criteria. The quality of the studies was assessed using the Newcastle-Ottawa Scale. Lung function decline was defined as annual loss of forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) or the ratio (FEV₁/FVC). Fixed and random-effects meta-analyses were conducted to calculate pooled estimates for ever and cumulative exposures. Heterogeneity was assessed using the I² test, and publication bias was evaluated using funnel plots.

RESULTS

Ever exposures to gases/fumes, vapours, gases, dusts, fumes (VGDF) and aromatic solvents were significantly associated with FEV₁ decline in meta-analyses. Cumulative exposures for these three occupational agents observed a similar trend of FEV₁ decline. Ever exposures to fungicides and cumulative exposures to biological dust, fungicides and insecticides were associated with FEV₁ decline in fixed-effect models only. No statistically significant association was observed between mineral dust, herbicides and metals and FEV₁ decline in meta-analyses.

CONCLUSION

Pooled estimates from the longitudinal population-based studies have provided evidence that occupational exposures are associated with FEV₁ decline. Specific exposure control and respiratory health surveillance are required to protect the lung health of the workers.

Pulmonary Toxicity of Silica Linked to Its Micro- or Nanometric Particle Size and Crystal Structure: A Review

Silicon dioxide (SiO2) is a mineral compound present in the Earth’s crust in two mineral forms: crystalline and amorphous. Based on epidemiological and/or biological evidence, the pulmonary effects of crystalline silica are considered well understood, with the development of silicosis, emphysema, chronic bronchitis, or chronic obstructive pulmonary disease. The structure and capacity to trigger oxidative stress are recognized as relevant determinants in crystalline silica’s toxicity. In contrast, natural amorphous silica was long considered nontoxic, and was often used as a negative control in experimental studies. However, as manufactured amorphous silica nanoparticles (or nanosilica or SiNP) are becoming widely used in industrial applications, these paradigms must now be reconsidered at the nanoscale (<100 nm). Indeed, recent experimental studies appear to point towards significant toxicity of manufactured amorphous silica nanoparticles similar to that of micrometric crystalline silica. In this article, we present an extensive review of the nontumoral pulmonary effects of silica based on in vitro and in vivo experimental studies. The findings of this review are presented both for micro- and nanoscale particles, but also based on the crystalline structure of the silica particles.

Respirable Dust and Silica: Respiratory Diseases Among Swedish Iron Foundry Workers

OBJECTIVE

The mortality and morbidity pattern for respiratory diseases was determined in a cohort of 1752 Swedish foundry workers, particularly for respirable silica dust exposure.

METHODS

The morbidity follow-up in the Swedish National Non-primary Outpatient Register covered 2001 to 2017 (NPR; specialist not in care patients), the mortality from the National Causes of Death Register covered 2001 to 2017. Cumulative exposures to silica and dust were determined.

RESULTS

The morbidity in COPD showed significantly increased risk for all exposure groups, as did silicosis in the high exposure group, these cases corresponded to silica exposure levels below 0.05 mg/m3. The mortality of all causes and respiratory diseases was significantly increased by cumulative silica exposure in the high exposure group.

CONCLUSIONS

Significantly increased morbidity for respiratory diseases and COPD was determined at silica exposure levels below the current Swedish OEL.

A study of pneumoproteins in crystalline silica exposed rock drillers

Objective: The objective was to assess serum concentrations of club cell protein 16 (CC-16) and the surfactant proteins A (SPs-A) and D (SP-D) in male rock drillers (N = 123) exposed to crystalline silica and in 48 occupationally non-exposed. Methods: The arithmetic mean (AM) duration of exposure was 10.7 years. The geometric mean (GM) crystalline silica exposure was 36 µg/m³ at the time of the study. The GM cumulative exposure was 239 µg/m³. Results: The concentrations of SP-D (GM 12.7 vs. 8.8 µg/L, p < 0.001) and SP-A (AM 1847 vs. 1378 ng/L, p = 0.051) were higher among rock drillers than among occupationally non-exposed. A positive significant association was observed between cumulative crystalline silica exposure and the SP-D concentrations (β = 0.07; p < 0.05). Rock drillers with small airway obstruction with maximal mid-expiratory flow % (MMEF%) <70% (N = 29) had higher SP-D concentrations than rock drillers with MMEF% ≥ 70% (N = 91) (GM 17.3 vs. 11.4 µg/L, p = 0.001). Rock drillers with MMEF% ≥70% (N = 91) had higher concentrations of SP-A (1957 vs. 1287 ng/L, p = 0.01) and SP-D (11.4 vs. 9.0 µg/L, p = 0.007) than non-exposed with MMEF% ≥70% (N = 39). Rock drillers with airway obstruction (FEV1/FVC < 0.70, N = 11) had significantly lower CC-16 concentrations than rock drillers with FEV1/FVC ≥0.70 (N = 109) after adjusting for relevant potential confounders (p = 0.02). Conclusion: The results indicate that pulmonary surfactant is a target for crystalline silica toxicity. The alterations appear to be driven by pulmonary alterations in the small airways and by exposure itself. Further studies on pneumoproteins and pulmonary function in other groups of workers exposed to crystalline silica are needed.

Airborne Occupational Exposures and Lung Function in the Lifelines Cohort Study

Rationale: The association between airborne occupational exposures and lung function level is inconsistent in the general population. Moreover, little is known about the association between occupational exposures and annual lung function decline.Objectives: We investigated the association between occupational exposures and lung function level and annual lung function decline in the population-based Lifelines cohort study.Methods: We included 55,631 adults with baseline spirometry and reliable job code-13,759 of these subjects were aged ≥30 years and underwent spirometry again after 4.5 years of follow-up. Occupational exposures in the current or last-held job at baseline were estimated with the ALOHA+ job-exposure matrix. Linear regression analyses adjusted for covariates were used to test the association between each occupational exposure-biological dust, mineral dust, gases and fumes, pesticides, solvents, and metals-and lung function level and annual lung function decline. Interactions were used to test effect modification by sex or smoking.Results: Exposures to biological dust, mineral dust, gases and fumes, insecticides, fungicides, and aromatic solvents were associated with a lower lung function level at baseline. The effects were larger in males and smokers compared with females and nonsmokers, respectively. However, no association between occupational exposures and the rate of annual lung function decline was found between baseline and follow-up.Conclusions: In this study, airborne occupational exposures are associated with lower lung function level but not with a faster lung function decline. These negative effects are more pronounced among males and smokers.

Smoking, occupational exposures, and idiopathic pulmonary fibrosis among Swedish construction workers

BACKGROUND

Cigarette smoking and occupational exposures each have been reported to increase the risk of idiopathic pulmonary fibrosis (IPF), a disease previously considered of unknown origin. We investigated the risk of IPF mortality associated with combined smoking and occupational exposures.

METHODS

A registry study of Swedish construction workers (N = 389,132), linked baseline smoking and occupational data with registry data on cause of death and hospital care diagnoses. Occupation was classified by the likelihood of exposure to vapors, gases, dusts, or fumes using a job-exposure matrix. Those likely exposed to asbestos or silica were excluded from the analysis. Age-adjusted relative risks [RRs] were calculated using Poisson regression. Follow-up observation began at age 40 and ended at age 89.

RESULTS

Heavy smokers at baseline who were exposed to inorganic dusts during their working life had an increased risk of IPF mortality (RR 1.70; 95% confidence interval [CI] 1.11-2.60), while there was no statistically increased risk in the other exposure groups. There were dose-response relationships between smoking at baseline and IPF mortality among both unexposed and dust exposed workers, with similar risk for dust exposed and unexposed, except among baseline heavy smokers, where workers exposed to inorganic dust manifested the highest risk (RR 4.22; 95% CI 2.69-6.60). Excluding workers with chronic obstructive pulmonary disease or emphysema did not affect the results substantively.

CONCLUSION

A clear dose-response relationship was seen between smoking at baseline and IPF, supporting a causal relationship. Occupational exposure to inorganic dusts, excluding silica and asbestos, was associated with increased risk of IPF in baseline heavy current smokers.

Rapid Induction of Pulmonary Inflammation, Autoimmune Gene Expression, and Ectopic Lymphoid Neogenesis Following Acute Silica Exposure in Lupus-Prone Mice

Occupational exposure to crystalline silica (cSiO2) is etiologically associated with systemic lupus erythematosus (lupus) and other autoimmune diseases. cSiO2's autoimmune effects in humans can be mimicked chronically in female lupus-prone NZBWF1 mice following repeated exposure to the particle. However, the immediate and short-term effects of cSiO2 in this widely used model of autoimmune disease are not well-understood. In the present study, we tested the hypothesis that a single acute cSiO2 dose triggers early presentation of cellular, histopathological, transcriptomic, and protein biomarkers of inflammation and autoimmunity in lupus-prone mice. Eight-week old female NZBWF1 mice were intranasally instilled once with 2.5 mg cSiO2 or saline vehicle and necropsied at 1, 7, 14, 21, and 28 d post-instillation (PI). Analyses of bronchoalveolar lavage fluid (BALF) and lung tissue revealed that by 7 d PI, acute cSiO2 exposure persistently provoked: (i) robust recruitment of macrophages, neutrophils, and lymphocytes into the alveoli, (ii) cell death as reflected by increased protein, double-stranded DNA, and lactate dehydrogenase activity, (iii) elevated secretion of the cytokines IL-1α, IL-1β, IL-18, TNF-α, IL-6, MCP-1, and B cell activation factor (BAFF), and (iv) upregulation of genes associated with chemokines, proinflammatory cytokines, lymphocyte activation, and type I interferon signaling. The appearance of these endpoints was subsequently followed by the emergence in the lung of organized CD3+ T cells (14 d PI) and CD45R+ B cells (21 d PI) that were indicative of ectopic lymphoid structure (ELS) development. Taken together, acute cSiO2 exposure triggered a rapid onset of autoimmune disease pathogenesis that was heralded in the lung by unresolved inflammation and cell death, proinflammatory cytokine production, chemokine-driven recruitment of leukocytes, an interferon response signature, B and T cell activation, and ELS neogenesis. This short-term murine model provides valuable new insight into potential early mechanisms of cSiO2-induced lupus flaring and, furthermore, offers a rapid venue for evaluating interventions against respirable particle-triggered inflammation and autoimmunity.

Estimation of an Exposure Threshold Value for Compensation of Silica-Induced COPD Based on Longitudinal Changes in Pulmonary Function

(1) Background: To estimate the cumulative exposure to respirable crystalline silica (RCS) that reduces lung function to an extent corresponding with airway obstruction equivalent to chronic obstructive pulmonary disease (COPD). (2) Methods: The study is based on a miners' cohort with longitudinal data on lung function and RCS exposure. Random-effects linear regression models, allowing for a possible threshold concerning the exposure concentration were used to analyze the impact of RCS on the ratio of forced expiratory volume in 1 s and forced vital capacity (FEV₁/FVC). The proposed threshold is the amount of RCS resulting in a decrease in FEV₁/FVC from the expected value to the lower limit of normal. (3) Results: The analysis shows that a threshold model fits the data significantly better than the usual linear model. The estimated threshold value for the exposure concentration is 0.089 mg/m³. Using this threshold, the estimate for the corresponding reference dose for RCS is 2.33 mg/m³·y. (4) Conclusions: The analysis confirmed that RCS has a negative impact on lung function. The effect is primarily due to exposure above a concentration threshold of 0.1 mg/m³. It is recommended that COPD should be compensated as an occupational disease if cumulative exposure was at least 2 mg/m³·y above this threshold.

Pulmonary function and high-resolution computed tomography in outdoor rock drillers exposed to crystalline silica

OBJECTIVES

Chronic obstructive pulmonary disease and silicosis are associated with exposure to crystalline silica. We determined the exposure to respirable crystalline silica and estimated exposure-response relationships between cumulative exposure and pulmonary function in outdoor rock drillers.

METHODS

136 rock drillers and 48 referents were recruited from three heavy construction companies. 98 air samples were collected by personal sampling for determination of respirable particulate matter and crystalline silica. Information about individual job tasks, type of drilling equipment and years of exposure in different job categories was obtained by interview. Cumulative exposure to crystalline silica was calculated for all workers. Pulmonary function was assessed by spirometry. A subgroup of 39 subjects with high cumulative exposure to crystalline silica underwent high-resolution computed tomography (HRCT).

RESULTS

Cumulative exposure (mean (min-max)) to crystalline silica was 0.69 mg٠years m^-3 (0.01-5.89) in the exposed group. Mean time of exposure among rock drillers was 10.7 years (1-42). Compared with referents, the rock drillers had a lower forced expiratory volume in one second/forced vital capacity ratio (79.4 vs 81.4, p<0.05) and maximal mid-expiratory flow% (85.6 vs 93.9, p<0.05). Further, by stratifying the exposed workers into three equally large groups, a dose-response relationship was demonstrated in the highest exposed group, also in never smokers, at a mean cumulative exposure of 21.7 years at 0.08 mg٠m^-3/years. Silicosis was not detected in HRCT, but other patterns of fibrosis and emphysema were seen.

CONCLUSIONS

Outdoor rock drillers exposed to crystalline silica had significantly lower pulmonary function than referents, and signs of airflow obstruction. Silicosis was not detected.

Influence of silica particles on mucociliary structure and MUC5B expression in airways of C57BL/6 mice

Purpose: Impaired mucociliary clearance is an initial characteristic of recurrent cough, respiratory infection and chronic respiratory diseases. It has been demonstrated that prolonged inhalation of respirable silica particles results in a variety of pulmonary diseases, but whether the mucociliary system is involved in this process is unclear. This study aims to evaluate the effects of silica particles on mucociliary structure and MUC5B production in respiratory tract.Materials and Methods: C57BL/6 mice were administered with 2.5 mg silica particles through a single intratracheal instillation. The changes of mucociliary structure and MUC5B expression in trachea was evaluated by HE and AB-PAS staining, transmission electron microscopy and immunohistochemistry on days 1, 7, 28 and 84 post-exposure.Results: The mucociliary structure of airway epithelium was obviously impaired by silica particles, showing disordered, shortened or partially lost cilia on the surface, increased mucus in mucous layer and submucosal glands from day 7 to day 84. A variety of ultrastructural abnormalities were discovered in silica-exposed airway cilia, including absence of central pair microtubules, disorganized microtubules and clusters of axoneme on day 1 and 7. The numbers of ciliary axonemes and basal bodies in ciliated epithelial cells were significantly decreased, whereas the proportion of abnormal axonemes was gradually increased with exposure to silica particles (P < 0.05). In addition, silica particles significantly decreased MUC5B expression on the surface of airway epithelium on day 28 and 84, but obviously increased its production in submucosal glands from day 1 to day 84 (P < 0.01).Conclusions: Silica particles could lead to ultrastructural defects in airway cilia, mucus hypersecretion and altered MUC5B expression in trachea, indicating that impaired mucociliary structure and altered MUC5B production might participate in the development of silica-related respiratory diseases.

Submersion in Industrial Powders That Lead to Tracheal Impaction and an Unusual Intubation

BACKGROUND

Silica, also known as quartz, is a naturally occurring compound that has many common uses, such as for glass, pottery, and concrete. Similarly, bentonite, another natural compound found in many clays, has been used for a variety of purposes from cat litter to bulk laxatives. Both are known for their fluid-absorptive properties. The long-term effects of exposure such as developing silica pneumoconiosis are well studied; acute inhalational injuries of similar substances are also documented.

CASE REPORT

We discuss the difficult airway case of a 32-year-old man who presented to the emergency department (ED) in cardiac arrest after he was buried in a mound of powdered silica and bentonite due to an industrial accident. The combination of the naturally fluid-absorptive properties of silica and bentonite, and the moist environment of the oropharynx, led to a unique circumstance. Most foreign bodies in the airway can be remedied, at least in part, by standard irrigation for decontamination. However, irrigation of dry bentonite and silica would produce a clay-like substance that could occlude the trachea, leading to an avoidably more difficult airway presentation. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: The difficulties experienced with his intubation can serve as a learning point to other providers who encounter a similar presentation. In the event that the inhaled substance is known to be fluid-absorptive, deviation from standard irrigation for decontamination may permit avoidance of a tracheal impaction, and facilitate establishment of a definitive airway. When there is suspicion for the potential of tracheal impaction, proceeding with bronchoscopy either in the ED or operating room as quickly as possible rather than continuing attempts at intubation may deliver the patient a definitive airway in a more timely fashion.

The Burden of Silicosis in Michigan: 1988-2016

RATIONALE

Exposure to respirable crystalline silica causes silicosis, a preventable, progressive occupational lung disease. A more rigorous occupational health standard for silica could help protect silica-exposed workers.

OBJECTIVES

To describe trends over 29 years of silicosis surveillance in Michigan.

METHODS

Michigan law requires the reporting of silicosis. We confirmed the diagnosis of silicosis in reported cases using medical questionnaires, review of medical records, and chest radiographs. The Michigan Occupational Safety and Health Administration (OSHA) conducted enforcement inspections at the workplaces of the silicosis cases, including air monitoring for silica and evaluation of workplace medical surveillance programs.

RESULTS

The Michigan surveillance program identified 1,048 silicosis cases from 1988 to 2016, which decreased from 620 during 1988-1997, to 292 during 1998-2007, to 136 during 2008-2016. The cumulative incidence rate of silicosis decreased from 3.7 to 1.4 to 0.7 cases per 100,000 men 40 years of age and older in Michigan over the same three periods. African Americans had a higher cumulative incidence rate of silicosis, with 6.0 cases per 100,000 African American men 40 years of age and older in Michigan compared with 1.2 cases per 100,000 white men 40 years of age and older in Michigan. The cases identified had severe disease; 59% had progressive massive fibrosis or category 2 or 3 small opacities per B-reading classification of the chest radiograph. Seventeen percent reported ever having active tuberculosis. On spirometry, 76% of ever smokers and 72% of never smokers demonstrated either a restrictive or an obstructive pattern. Most (65%) had not applied for workers' compensation benefits; the percentage who applied for benefits decreased from 42% to 28-16% over the three periods. Thirty-four of 55 (62%) workplace inspections found exposures above the new OSHA 50 μg/m3 respirable crystalline silica permissible exposure limit, and only 11% of inspected companies screened their workers for silicosis.

CONCLUSIONS

Adults with confirmed cases of silicosis have advanced disease and morbidity. Most are not using workers' compensation to pay for their care. The new OSHA silica standard, which lowers the permissible exposure limit for silica and requires medical monitoring to identify workers with silicosis, will help reduce the burden of silica exposure. It is critical for pulmonologists to be vigilant to recognize and manage this preventable occupational lung disease.

Association between Work and Chronic Obstructive Pulmonary Disease (COPD)

To support occupational physicians in their assessment and notification of occupational diseases, diagnostic registration guidelines are developed with information about associations between work-related risk factors and diseases. The objective of this review of systematic reviews is to examine whether work-related risk factors are associated with chronic pulmonary obstructive disease (COPD). We searched the electronic database of Medline for systematic reviews published between 1 January 2009 and 20 June 2017. Reviews were included when COPD was assessed by data on lung function and when work-related exposures to vapors, dusts, gases, or fumes (VDGF) were described. One author selected studies and extracted data; two authors assessed study quality using A MeaSurement Tool to Assess systematic Reviews (AMSTAR). In all eight systematic reviews included, various exposures to vapors, dusts, gases, and fumes (VGDF) at work are associated with COPD. Two-thirds of the included studies are cross-sectional and show a high heterogeneity in population, setting, and mostly self-reported-exposures. Two high-quality reviews (AMSTAR score ≥ 9) including meta-analyses show associations and excess risk of COPD for work-related general exposure to VDGF with a summary odds ratio of 1.4 (95% confidence interval (CI) 1.19⁻1.73) and to inorganic dust with a mean difference in predicted forced expiratory volume in one second (FEV₁) of -5.7% (95% CI: -8.62% to -2.71%). Exposure to VGDF at work is associated with a small but increased risk of COPD. More detailed workplace measurements of specific VGDF are warranted to gain an insight into dose⁻response relationships.

Current and new challenges in occupational lung diseases

Occupational lung diseases are an important public health issue and are avoidable through preventive interventions in the workplace. Up-to-date knowledge about changes in exposure to occupational hazards as a result of technological and industrial developments is essential to the design and implementation of efficient and effective workplace preventive measures. New occupational agents with unknown respiratory health effects are constantly introduced to the market and require periodic health surveillance among exposed workers to detect early signs of adverse respiratory effects. In addition, the ageing workforce, many of whom have pre-existing respiratory conditions, poses new challenges in terms of the diagnosis and management of occupational lung diseases. Primary preventive interventions aimed to reduce exposure levels in the workplace remain pivotal for elimination of the occupational lung disease burden. To achieve this goal there is still a clear need for setting standard occupational exposure limits based on transparent evidence-based methodology, in particular for carcinogens and sensitising agents that expose large working populations to risk. The present overview, focused on the occupational lung disease burden in Europe, proposes directions for all parties involved in the prevention of occupational lung disease, from researchers and occupational and respiratory health professionals to workers and employers.

Trends in exposure to respirable crystalline silica (1986-2014) in Australian mining

BACKGROUND

Respirable crystalline silica (RCS) has been associated with severe health risks. Exposures in Western Australia (WA) have been typically high in hard-rock mining and have reduced substantially since the mid-1900s. We described trends in RCS exposure in WA miners over the past 30 years.

METHODS

A total of 79 445 reported personal RCS exposure measurements, covering the years 1986-2014, were examined. Mixed-effects models were applied to estimate RCS exposure levels, including spline terms to estimate a time trend.

RESULTS

An overall downward trend of about -8% per year was observed for RCS exposures in WA mining. Highest RCS exposure levels were modeled for base metal mining and exploration settings. Drilling occupations were among the highest exposed jobs.

CONCLUSION

RCS exposure levels have fallen considerably in the last three decades. However, there are still mining occupations that may need further attention to avoid adverse health effects in these workers.

Indices of iron homeostasis correlate with airway obstruction in an NHANES III cohort

Cigarette smoking results in the accumulation of iron both systemically and locally, in the lung thereby causing imbalance in iron homeostasis. This disruption in iron homeostasis can be associated with oxidative stress and consequent tissue injury. Therefore, in this study, we tested the association between iron homeostasis and airway obstruction by examining a large cohort of smokers and non-smokers for relationships between 1) serum ferritin and iron concentrations and transferrin saturation and 2) forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), and their ratio (FEV₁/FVC). Data from the National Health and Examination Survey III were analyzed. The study population included persons aged 20 years and above with their following data recorded: race, gender, serum ferritin and iron concentrations, and transferrin saturation; the final sample number was 7,251. In the total population, Pearson correlation coefficients between 1) serum ferritin and iron concentrations and transferrin saturation and 2) FVC and FEV₁ were significantly positive; whereas those between 1) serum ferritin concentrations and transferrin saturation and 2) FEV₁/FVC were significantly negative. With separate analyses, serum ferritin concentrations demonstrated positive associations with FVC and FEV₁ but an inverse relationship with FEV₁/FVC in smokers and non-smokers. Serum ferritin levels increased with worsening airway obstruction among smokers, and its highest concentrations were found among those with the lowest values of FEV₁/FVC ratio (<60%). Comparable to cigarette smokers, serum ferritin concentrations among non-smokers were greatest in those with the lowest FEV₁/FVC ratio. Furthermore, elevated levels of serum iron and saturation of transferrin also corresponded with decreased FEV₁/FVC ratio among non-smokers. Thus, we conclude that indices of iron homeostasis are associated with airway obstruction in both smokers and non-smokers.

Lung function impact from working in the pre-revolution Libyan quarry industry

The purpose of this study was to determine the lung impact from working within the Libyan quarry industry, and if the length of work impacted the degree of degradation. Eighty three workers from eight silica quarries in the Nafusa Mountains of Libya opted to participate. These quarries were working the upper cretaceous geological structure. Eighty-five individuals who lived in Gharyan City with no affiliation to quarry operations participated as controls. Spirometry variables evaluated were Forced Vital Capacity (FVC), Forced Expiratory Volume at 1.0 second (FEV1), FVC/FEV1 and Peak Expiratory Flow (PEF). Control and exposed groups had no differences in terms of height, weight, or smoking status (p = 0.18, 0.20, 0.98, respectively). Prior to adjustment for other variables, FVC, FEV1, and PEF are all significantly lower in the exposed group (p = 0.003, 0.009, 0.03, respectively). After adjustment for age, height, weight, and smoking status, there remain significant differences between the control and exposed groups for FVC, FEV1, and PEF. This analysis demonstrated that exposure to quarry dust has a detrimental effect on lung function, and that pre-revolution Libyan quarry workers were being exposed. This study shows that any exposure is harmful, as the reduction in lung function was not significantly associated with years of exposure.