Comparison of the Ames Salmonella assay and Mutatox genotoxicity assay forassessing the mutagenicity of polycyclic aromatic compounds in porewater from Athabasca oil sands mature fine tailings

The oil sands in the Athabasca region of northeastern Alberta, Canada, repr esent a significant hydrocarbon resource that is currently exploited by min ing, 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 u ltimately be converted to biologically productive lakes, with one unresolve d issue being the toxicity of the polycyclic aromatic compounds (PACs) that might be released from the tailings. In this paper, we have identified sev eral polycyclic aromatic hydrocarbons in the porewater from oil sands matur e fine tailings and have compared the responses of 17 PACs in the Ames and Mutatox genotoxicity assays. The Mutatox assay was unsuitable as a surrogat e for the Ames test in this application; poor(50%) concordance between the hive assays occurred because the mechanism of light emission in the Mutatox assay is un certain, leading to positive responses that could not be unamb iguously associated with genotoxicity. Benzo[a]pyrene equivalency factors ( BEFs) in the Ames assay were determined for a large number of PACs, from th is work and from literature data, to express the genotoxic potencies of env ironmental mixtures in terms of benzo[a]pyrene equivalent concentrations (B EQs). In the case of porewater samples obtained from the mature fine tailin gs, even extracts concentrated 10,000-fold we re below the detection limit of 1 mu g/L BEQ, consistent with the value of 0.14 mu g/L calculated using BEFs of PACs identified in the porewater.