Measurement of polynuclear aromatic hydrocarbons (PAHs) in epiphytic lichens for receptor modeling in the Athabasca Oil Sands Region (AOSR)

Abstract

The use of measurements of polycyclic aromatic hydrocarbons (PAHs) in lichens was evaluated in a pilot study as a tool for receptor modeling of air pollution from mining and oil extraction activities in the Athabasca Oil Sands Region (AOSR). Lichen samples (Hypogymnia physodes) were collected at 20 locations within 150 km of the mining and oil extraction center located near Fort McKay. Samples were cleaned, homogenized using a cryogenic impactor, and extracted with cyclohexane. Extracts were cleaned up using Florisil solid-phase extraction and analyzed by gas chromatography with mass selective detection (GC/MS). Total PAHs (20 compounds) ranged from 52 to 350 μg/kg, comparable to values reported from other studies of PAHs in lichens. Analysis of air samples collected using polyurethane foam or dichotomous air sampler filters showed that PAHs were dominated by naphthalene and 3-ring congeners, whereas lichen samples from comparable locations yielded significant contributions from 4-, 5-, and 6-ring PAHs. The concentration of total PAHs in lichen samples and the relative contribution of higher ring number PAHs both decreased with increasing distance from the mining and oil extraction centers, consistent with less efficient vapor-phase transport of the less-volatile higher ring number PAHs. PAH congener profiles for samples varied depending on distance from the mines. Principal components analysis incorporating analytical data from a variety of matrices indicated multiple factors contribute to PAH content in a given sample. Measurements of metals in the 20 lichen samples showed significant correlations (r2 > 0.8, p < 0.05) between crustal element levels and total PAHs. Taken together, the results suggest that PAH concentrations and profiles in lichens depend on influences from multiple sources and transport mechanisms. A more fully validated approach is needed to develop an understanding of sampling and analytical variability and bias, and a review of recent research in this area indicates that this is a significant gap in many lichen-PAH biomonitoring studies.