Concentration and character of PAHs and other hydrocarbons in coals of varying rank – Implications for environmental studies of soils and sediments containing particulate coal

Abstract

Particulate coal can occur in soils and sediments from both natural and anthropogenic sources. Its presence can influence the concentrations of regulated and more bioavailable pollutants through its geosorbent qualities and its own contribution of total extractable hydrocarbons (TEH), including polycyclic aromatic hydrocarbons (PAHs) and biomarkers. Extractable PAHs in coal also can potentially affect PAH-based “source” and “maturity” ratios of soil or sediment extracts, which can be used to assess the source(s) of PAHs. This study reports on the absolute concentrations of TEH, the 16 Priority Pollutant PAHs, 27 alkylated PAHs and sulfur containing aromatics, and selected biomarkers in 15 coals ranging in rank from lignite to anthracite. Unlike most previous studies in the fuel science or geochemical literature the coals herein were extracted using dichloromethane at room temperature, an EPA Method 3500 type method common in environmental laboratories, thereby allowing comparison of these results to environmental studies. The concentrations of TEH ranged from 8.2 to 2500 μg/g coal (dry wt) with a maximum yield among high volatile bituminous coals. The TEH “fingerprints” were variable and some of these resembled those of other forms of contamination. The concentrations of Priority Pollutant PAHs ranged from 35 to 11,000 ng/g coal (dry wt) or 38 to 12,000 ng/g carbon and varied with coal rank, reaching a maximum within the high volatile bituminous rank. The distributions of extractable PAHs and numerous PAH ratios conventionally used as “source” and/or “maturity” parameters also varied with coal rank emphasizing that particulate coal in soils and sediments cannot be universally represented by a single set of diagnostic parameters. Hopanoid and sterane biomarker yields also varied with rank, reaching a maximum in high volatile bituminous coals, and were low relative to PAHs. Because particulate coal often co-occurs with other sources of hydrocarbons in soils and sediments, the data presented herein may prove useful in allocating coal versus non-coal sources on a mass balance basis.