No abstract

Results are reported from an ongoing passive air monitoring study for polycyclic aromatic compounds (PACs) in the Athabasca oil sands region in Alberta, Canada. Polyurethane foam (PUF) disk passive air samplers were deployed for consecutive 2-month periods from November 2010 to June 2012 at 17 sites. Samples were analyzed for polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs, dibenzothiophene and its alkylated derivatives (DBTs). Relative to parent PAHs, alkylated PAHs and DBTs are enriched in bitumen and therefore considered to be petrogenic markers. Concentrations in air were in the range 0.03-210 ng/m(3), 0.15-230 ng/m(3) and 0.01-61 ng/m(3) for ∑PAHs, ∑alkylated PAHs and ΣDBTs, respectively. An exponential decline of the PAC concentrations in air with distance from mining areas and related petrogenic sources was observed. The most significant exponential declines were for the alkylated PAHs and DBTs and attributed to their association with mining-related emissions and near-source deposition, due to their lower volatility and greater association with depositing particles. Seasonal trends in concentrations in air for PACs were not observed for any of the compound classes. However, a forest fire episode during April to July 2011 resulted in greatly elevated PAH levels at all passive sampling locations. Alkylated PAHs and DBTs were not elevated during the forest fire period, supporting their association with petrogenic sources. Based on the results of this study, an "Athabasca PAC profile" is proposed as a potential source marker for the oil sands region. The profile is characterized by ∑PAHs/∑Alkylated PAHs = ∼0.2 and ∑PAHs/∑DBTs = ∼5.

The chiral pesticide heptachlor can undergo photolysis to yield the racemic products heptachlor-exo-epoxide (HEPX) and photoheptachlor. Heptachlor is also metabolized to nonracemic HEPX in biological systems and soils. HEPX in ambient air samples from the southern United States and Lakes Ontario and Superior was nonracemic and enriched in the (+) enantiomer. Average enantiomer ratios (ER ) areas of (+)/(-) HEPX) in these locations ranged from 1.51 to 2.02, and were similar to ER values of HEPX reported for agricultural soils. Airborne heptachlor was racemic, with ERs of 0.98-1.02. These results suggest that the main source of HEPX in ambient air is not photolysis of heptachlor, but rather metabolism of heptachlor in soils followed by volatilization of HEPX. The study exemplifies the use of chiral analysis for investigating the environmental fate of pesticides.