Chemical and biological assays have been carried out on the "pore water" that results from the settling of the tailings that accompany bitumen recovery from the Athabasca oil sands. Examination of the nonacidic extracts of pore water by gas chromatography-mass spectroscopy allowed the identification of numerous two- to three-ring polycyclic aromatic compounds (PACs), to a total concentration of 2.6 micrograms/L of pore water. The PACs were biodegraded by microflora naturally present in the pore water. Acute toxicity was associated principally with the acidic fraction (naphthenic acids) of pore water extracts according to the Microtox assay; other work has shown that acute toxicity dissipates fairly rapidly. Both individual PACs and concentrated pore water extracts showed minimal levels of binding to the rat Ah receptor and induced minimal ethoxyresorufin-O-deethylase activity in primary rat hepatocytes, showing an insignificant risk of inducing monooxygenase activity. Taken together with previous work showing negligible mutagenic activity of these extracts, we conclude that it should be possible to develop tailing slurries into biologically productive artificial lakes.

The oil sands in the Athabasca region of northeastern Alberta, Canada, represent a significant hydrocarbon resource that is currently exploited by mining, followed by separation of bitumen from sand using hot water flotation. This process generates large quantities of bitumen-contaminated tailings. Current research involves an assessment of whether the tailings ponds can ultimately be converted to biologically productive lakes, with one unresolved issue being the toxicity of the polycyclic aromatic compounds (PACs) that might be released from the tailings. In this paper, we have identified several polycyclic aromatic hydrocarbons in the porewater from oil sands mature fine tailings and have compared the responses of 17 PACs in the Ames and Mutatox genotoxicity assays. The Mutatox assay was unsuitable as a surrogate for the Ames test in this application; poor (50%) concordance between the two assays occurred because the mechanism of light emission in the Mutatox assay is uncertain, leading to positive responses that could not be unambiguously associated with genotoxicity. Benzo[a]pyrene equivalency factors (BEFs) in the Ames assay were determined for a large number of PACs, from this work and from literature data, to express the genotoxic potencies of environmental mixtures in terms of benzo[a]pyrene equivalent concentrations (BEQs). In the case of porewater samples obtained from the mature fine tailings, even extracts concentrated 10,000-fold were below the detection limit of 1 μg/L BEQ, consistent with the value of 0.14 μg/L calculated using BEFs of PACs identified in the porewater.