The comparative toxicity of two Canadian diluted bitumens to developing yellow perch (Perca flavescens)

Abstract

Increasing demand for diluted bitumen (dilbit) has led to the development of the Alberta oil sands industry and the expansion of current and future transcontinental pipelines. However, the growth of oil transportation has led to public concern about the effects of potential dilbit spills to aquatic ecosystems. Because dilbit is an unresolved complex mixture (UCM) with variable diluent and bitumen composition, its toxic effects are little known. Thus, it is important to understand the effects of the two most transported dilbits in Canada, Access Western Blend (AWB) and Cold Lake Blend (CLB). We compared the toxicity of AWB and CLB to yellow perch (Perca flavescens), a species present throughout North America. Embryos were exposed to dilbit for 16 days, from <24 hours post-fertilization until hatch. The treatment regime was a static daily renewal of water accommodated fractions (WAF) and chemically-enhanced water accommodated fractions (CEWAF) at concentration ranges of 0.02 to 11 μg/L and 0.21 to 20 μg/L total polycyclic aromatic hydrocarbons (TPAH), respectively. Hatched embryos were assessed for malformations and preserved at -80 °C for analysis of gene expression associated with phase I and II detoxification, cellular stress, and xenobiotic metabolism. Results show that with increased TPAH concentration, the frequency of hatched embryos with developmental malformations increased proportionally. The highest concentration of AWB WAF caused a high rate of mortality. As well, WAF treatments caused a higher prevalence of malformations than CEWAF. These preliminary results were unexpected because previous studies demonstrated a greater toxicity of CEWAF. Relative mRNA of cyp1a showed induction up to 18-fold in WAF and 50-fold in CEWAF treatments, and AWB had lower EC50s than CLB. This is the first study assessing the toxicity of both AWB and CLB dilbits on wild-sourced fish. With recent approvals of pipelines in North America, these biomarkers will assist risk assessments and monitoring of Canadian ecosystems should a pipeline spill occur.