Black-pigmented Particles in Airway Macrophages in Sputum: A Novel Biomarker in Coal Miners

Abstract Rationale: Coal workers’ pneumoconiosis (black lung disease) is caused by chronic exposure to coal mine dust. From the mid-1970s to the late 1990s, progressive pulmonary diseases declined. However, since 2000, black lung disease has resurged in coal miners, particularly from small Appalachian mines, likely due to larger, electric or diesel-powered mining equipment generating smaller, more toxic and inhalable particles. While the size distribution of coal mine dust has been studied, its deposition in coal miners’ lungs remains unclear. Methods: Cytology slides from spontaneously expectorated sputum from 10 current surface coal miners from New Mexico were analyzed to assess the size distribution of black-pigmented material in airway macrophages and were compared with non-miners from New Mexico. An artificial intelligence algorithm, based on Detectron2, the most advanced object detection and segmentation, was developed for counting black carbon in macrophages. Results: Among 319 macrophages, 506 black-pigmented particles were identified by the artificial intelligence algorithm. The algorithm showed excellent performance in recognizing macrophages (R² = 1) and black-pigmented particles (R² = 0.77) compared to manual counting. The size distribution in coal miners differed from non-miners, with particles peaking at 500-700 nm in miners, compared to 200-400 nm in non-miners. Additionally, 8% of black-pigmented particles in miners were 1-2 µm, compared to 2% in non-miners. Conclusions: Black-pigmented particles in airway macrophages of spontaneously expectorated sputum of coal miners are larger than those in non-miners suggesting distinct mechanisms of particle generation—likely mechanical processes in mining versus combustion in other environments. Using artificial intelligence for counting, this technique may allow for a novel exposure biomarker for coal miners. Our next step is to increase the sample size and examine whether job titles with higher mine dust exposure are associated with higher black-pigmented particle counts in airway macrophages