Characterization of silica content in gold mine dust with respect to particle size

Globally, silicosis is responsible for thousands of deaths each year and is a major public health concern in industries like mining. Silicosis is caused by exposure to respirable crystalline silica, and while incidence of silicosis has declined in recent decades, its continued occurrence in young workers indicates that high crystalline silica exposures in the contemporary workforce persist despite monitoring efforts and regulatory enforcement. Crystalline silica exposure is monitored in the mining industry via collection of respirable dust samples, from which both dust and crystalline silica concentrations are determined. Accurate quantification of crystalline silica is vital to assessing workers’ exposure, and to limiting exposure through selection of appropriate engineering controls and personal protective equipment. To quantify crystalline silica in a sample, one of two analytic methods is used: X-ray diffraction and infrared spectroscopy. Previously, confounding effects of mineral composition and size distribution of dust were assumed to have only minor impact on the accuracy of both methods; however, as mining technologies evolve, so do the characteristics of the dust generated in mines, and such effects may no longer be negligible. Evaluating the characteristics of mine dust with respect to particle size and crystalline silica content is imperative to understanding how crystalline silica analysis may be affected by these characteristics. To date, few studies have investigated particle size-related crystalline silica content in occupational dusts, and while some efforts have been made to characterize coal mine dusts, there has been no such effort to characterize metal/non-metal mine dusts. This study undertakes detailed characterization of dusts from three gold mine operations, via analysis of size distribution using particle sizers and a cascade impactor; crystalline silica content by infrared and X-ray diffraction methods; and single-particle composition via scanning electron microscopy. Results indicate that the size distribution of crystalline silica within a particular dust is not equivalent to the dust’s size distribution; the abundance of crystalline silica in a dust varies with particle size; the two methods of quantifying crystalline silica yield variable results depending on particle size; and, like crystalline silica, particle types of different elemental composition vary in abundance with respect to particle size