Respirable mineral dust toxicity across mining locations: A comparative study of field samples in an underground mine

Modern high-efficiency rock cutting machinery in coal mines produces fine particles, raising health concerns. This study investigated whether particle size affects toxicity in underground mine dust and identified contributing factors using a human cell model. Dust samples were collected from multiple locations in a U.S. underground coal mine. Particle size and morphology were analyzed using dynamic light scattering (DLS), transmission, and scanning electron microscopy (T/SEM). Elemental composition was assessed via scanning TEM with energy-dispersive X-ray (STEM-EDX). Human THP-1 cell toxicity was evaluated through cell viability, mitochondrial stress, and inflammation, with TEM imaging of cell structure. Cellular uptake of particles was quantified using inductively coupled plasma mass spectrometry (ICP-MS). Fine particles were detected in all samples, with raw rock particles as small as 520 nm and field dust down to 530 nm. Dust from the "Sunset" location, which transports coal from the longwall mining site to the surface, ranged from 530 to 3345 nm. Dust from the "Longwall" location, where coal production occurs, contained larger particles (801-4609 nm). TEM images revealed altered cell morphology after dust exposure, and ICP-MS confirmed particle uptake varied with size and composition. Coal dust disrupted cellular metabolism and caused dose-dependent decreases in viability and increases in inflammatory markers. In conclusion, modern mining generates respirable particles (∼500 nm) whose toxicity depends on size and elemental composition. Particle characteristics and metal content drive cellular uptake, metabolic disruption, and inflammation, emphasizing the importance of assessing health risks, particularly in high-exposure areas like conveyor belts for coal transport.