Surface properties of silica in mixed dust.
Wallace-WE; Keane-MJ; Harrison-JC; Stephens-JW; Brower-PS; Grayson-RL; Attfield-MD
Silica and silica-induced lung diseases. Castranova V, Vallyathan V, Wallace WE, eds. Boca Raton, FL: CRC Press, 1995 Dec; :107-117
Attempts to distinguish the contribution of quartz to the pathogenic potential of mixed-composition work place dusts are not without ambiguity. While exposure to pure respirable quartz is known to induce pulmonary fibrosis, epidemiological studies of workers exposed to mixed dusts have not always shown a clear role for quartz in disease induction. This anomaly has been extensively detailed in British and European epidemiological studies of coal workers' pneumoconiosis (CWP) and progressive massive fibrosis (PMF). Those studies generally have shown a correlation of disease prevalence with cumulative exposure to total respirable dust and coal rank, but not with the explicit quartz component of the cumulative dust exposure. A general hypothesis to explain the seeming failure of quartz, a strongly pathogenic agent for fibrosis, to contribute to CWP or PMF, especially when the other components of the dust are not so strong in isolation, is that the mass percent silica component of a dust, as conventionally measured, is not necessarily a measure of biologically available of toxic silica surface. Several methods are being used to characterize the degree of availability or purity of the surface of silica particles in mixed-composition dusts. We review here a fraction of the literature of studies of silica exposure and CWP, and of experimental silicosis in lab animals exposed to mixed-composition dusts. One method used to detect surface "occlusion," or sub-micrometer coating, of aluminosilicate clay on respirable-sized silica particle is outlined. Application of the method to a set of Pennsylvania coal mine dusts is reviewed, demonstrating the occurrence of such clay occlusion of silica particles and showing that the fraction of such silica particles can significantly vary between exposure situations.
Silica-dusts; Quartz-dust; Exposure-assessment; Dust-particles; Dust-exposure; Airborne-particles; Airborne-dusts; Particulate-dust; Pulmonary-system-disorders; Respiratory-system-disorders; Respiratory-irritants; Lung-disease; Lung-irritants; Fibrosis; Fibrous-dusts; Surfactants; Coal-mining; Coal-dust; Mining-industry; Silicosis; Silicon-compounds; Silicates
Castranova-V; Vallyathan-V; Wallace-WE
Silica and silica-induced lung diseases