SURFACE-COMPOSITION OF RESPIRABLE SILICA PARTICLES IN A SET OF US ANTHRACITE AND BITUMINOUS COAL-MINE DUSTS

Respirable particles of high-percentage silica content from anthracite and bituminous coal mine dust samples were analyzed for aluminosilica te clay surface coating, by measuring silicon and aluminum X-ray spect ra using scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDS). Silicon and aluminum elemental ratios were determined with incident electron energies of 20 and 5 keV to reveal whether surface occlusion was present. Some 20 respirable-sized, non-agglomerated part icles with silicon fraction of signal of 75% or more (for elements abo ve sodium) were analyzed for each of 12 coal mine dust samples. Mine d ust samples were from U.S. anthracite and bituminous coal mining regio ns involved in epidemiological studies of the U.S. National Study of C oal Workers' Pneumoconiosis. Some particles of high-percentage silica content exhibited a decrease in the ratio of silicon-to-aluminum K-alp ha line intensities with decreasing electron beam accelerating voltage , consistent with aluminosilicate clay surface contamination or occlus ion of a silica particle. Significantly lower frequencies of particles manifesting occluded behavior were found for anthracite dusts versus all bituminous dusts. It is suggested that such occlusion alters the b iological availability of the surface of those particles. This may be a factor in the results of attempts to correlate disease prevalence wi th conventionally measured dust composition, as in the classical failu re of coal workers' pneumoconiosis disease prevalence to correlate wit h silica exposure while being correlated with cumulative total respira ble dust exposure and with coal rank. Published by Elsevier Science Lt d.