Pathology and mineralogy demonstrate respirable crystalline silica is a major cause of severe pneumoconiosis in US coal miners

Rationale: The reasons for resurgent coal workers’ pneumoconiosis and its most severe forms, rapidly progressive pneumoconiosis and progressive massive fibrosis (PMF), in the United States (US) are not yet fully understood. Objective: To compare the pathologic and mineralogic features of contemporary coal miners suffering severe pneumoconiosis to their historical counterparts. Methods: Lung pathology specimens from 85 coal miners with PMF were included for evaluation and analysis. We compared the proportion of cases with pathologic and mineralogic findings in miners born between 1910 and 1930 (historical) to those born in or after 1930 (contemporary). Results: We found a significantly higher proportion of silica-type PMF (57% vs. 18%, p<0.001) among contemporary miners compared to their historical counterparts. Mineral dust alveolar proteinosis (MDAP) was also more common in contemporary miners compared to their historical counterparts (70% vs. 37%, p<0.01). In situ mineralogic analysis showed the percentage (26.1% vs. 17.8%, p<0.01) and concentration (47.3 x 108 vs. 25.8 X 108 particles/cm3, p=0.036) of silica particles was significantly greater in specimens from contemporary miners compared to their historical counterparts. The concentration of silica particles was significantly greater when silica-type PMF, MDAP, silicotic nodules, or immature silicotic nodules were present (p<0.05). Conclusions: Exposure to respirable crystalline silica appears causal in the unexpected surge in severe disease in contemporary miners. Our findings underscore the importance of controlling workplace silica exposure in order to prevent the disabling and untreatable adverse health effects afflicting US coal miners. Primary Source of Funding: Alpha Foundation for the Improvement of Mine Safety and Health, Inc.