Beyond conventional metrics: Comprehensive characterization of respirable coal mine dust

Conventional practice in monitoring and control of respirable coal mine dust has focused on the total mass concentration and the crystalline silica mass fraction of personal exposures. For decades under this approach, as dust exposures in US mines declined, so did the incidence of occupational lung diseases. In the late 1990s, however, disease rates began to rise significantly with little or no apparent increase in the conventional dust metrics. Based on the geographic clustering of disease reports in parts of central Appalachia, several contributing factors have been suggested, including possible changes in dust characteristics as thin-seam mining has become increasingly common. However, data on anything beyond conventional dust metrics is almost non-existent. The current study represents an ongoing effort by the authors to comprehensively characterize respirable coal mine dust. Here, samples from eight mines in central and northern Appalachia were analyzed to determine: particle size and mineralogy distributions across a wide size range (~100–10,000 nm); potentially bioaccessible and total acid-soluble mass concentrations of metals and trace elements; and mass concentrations of polyaromatic hydrocarbons including 1-nitropyrene, which may be indicators of diesel exhaust. Results showed that dust characteristics can vary widely between and within mines. But several general observations were noted, such as a predominance of sub-micron particles, including those associated with both diesel exhaust and dust generated from cutting geologic strata in the mine or application of rock dusting products. Additionally, there appeared to be an inordinate amount of dust generated from cutting rock strata, as compared to coal strata. A correlation analysis was also conducted on a total of 40 dust characteristic variables, which may provide further insights to the source(s) of some constituents.