Exposure to respirable crystalline silica tied to ‘unexpected surge’ in black lung disease

Higher levels of crystalline silica were found in the lung tissue of contemporary coal miners in the U.S. compared with the lung tissue of previous generations of coal miners, researchers reported in Annals of the American Thoracic Society.

The results may help explain the recent increase in severe pneumoconiosis, often referred to as black lung disease, in coal miners in West Virginia, Virginia and Kentucky, according to an ATS press release.

“Based on integrated pathologic and mineralogic findings in lung tissues from two well-defined coal miner case series with progressive massive fibrosis, our study demonstrates that exposure to crystalline silica appears causal in the unexpected surge in severe disease in contemporary miners,” Robert A. Cohen, MD, director of the Mining Education and Research Center and clinical professor in the department of environmental and occupational health sciences at the University of Illinois School of Public Health and also with the division of respiratory health at the National Institute for Occupational Safety and Health in Morgantown, West Virginia, and colleagues wrote.

The rate of cases of black lung among U.S. coal miners declined from 1970 to 2005, largely due to improved occupational health practices required by federal regulations. But since 2005, black lung cases have increased threefold in general and increased 10-fold among long-term coal miners, according to the ATS.

Researchers evaluated lung pathology specimens from 85 coal miners with progressive massive fibrosis and compared the proportion of cases with pathologic and mineralogic findings in miners born 1910 to 1930 as the historical cohort (n = 62) and those born in or after 1930 as the contemporary cohort (n = 23).

“Historical miners worked mainly with conventional mining technology that relied on drilling and blasting, whereas contemporary miners spent at least a substantial portion of their mining tenure working with mechanized equipment [that] employ high-powered cutting heads to shear the coal from the mine face,” Cohen and colleagues wrote. “To date, no study has compared the pathologic and mineralogic features of contemporary miners suffering from this resurgent form of pneumoconiosis to historical counterparts to determine if silica is indeed an important culprit.”

More than 90% of rocks contain silica. Breathing in silica dust is highly toxic and prolonged exposure can lead to severe lung disease, according to the release.

Contemporary miners were younger (mean age, 61 vs. 65 years; P = .03) and had fewer years of underground mining (mean duration, 30 vs. 35 years; P = .03). The researchers also reported a trend toward fewer total mining years (31 vs. 36 years; P= .14) at the time of lung tissue collection.

The researchers reported a higher proportion of silica-type progressive massive fibrosis among contemporary miners compared with historical miners (57% vs. 18%; P < .001). In contemporary coal miners, mineral dust alveolar proteinosis was more common compared with historical miners (70% vs. 37%; P < .01).

In addition, there was a greater percentage (26.1% vs. 17.8%; P < .01) and concentration (47.3 x 10⁸ vs. 25.8 x 10⁸ particles/cm³; P = .036) of silica particles among specimens from contemporary miners compared with historical miners. The researchers also reported a greater concentration of silica particles when silica-type progressive massive fibrosis, mineral dust alveolar proteinosis, silicotic nodules or immature silicotic nodules were present (P < .05).

“Our findings underscore the importance of controlling workplace silica exposure in order to prevent the disabling and untreatable adverse health effects afflicting U.S. coal miners,” the researchers wrote.

Reference:

• New study shows increase in black lung disease in coal miners. Published April 14, 2022. Accessed April 14, 2022.