Characterization of Surface Properties Affecting the Activity of the 'Free Silica' Fraction of Respirable Dusts

摘要

A two-part study was conducted to investigate the surface properties of the quartz (14808607) or 'free silica' fraction of respirable mine dusts. The degree of surface contamination of respirable quartz particles was studied using scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDX) to distinguish alumino/silicate and magnesium silicate surface occlusions from the silicate particles. By varying the electron beam accelerating voltage, the depth of penetration could be reduced, so that the surface layer could be distinguished from the substrate material. Experiments were conducted on the relationship of measured SEM-EDX signal coming from the substrate to coating thickness and electron beam accelerating voltage. In the second part, modifications were made of respirable quartz particle cytotoxicity by surface treatment. As measured by erythrocyte hemolysis and pulmonary macrophage release of lactate dehydrogenase in-vitro, respirable quartz cytotoxicity was neutralized by boiling in water in glass test tubes for 10 to 40 minutes. The membranolytic potential was reduced to near zero by boiling up to 10 milligrams of quartz per milliliter of water. Replacing the medium with fresh water midway through the boiling resulted in full detoxification. Preboiling the medium with silica reduced the effect. Detoxification persisted after mild drying at 110 C for 8 hours and persisted after 3 days of resuspension in water at room temperature.