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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. Although the toxic effects of crude oils through exposure to polycyclic aromatic hydrocarbons (PAH) are well characterized, little is known about the toxic effects of dilbit because of the variable proportions of diluent added to bitumen. Here we assessed the toxicity of the two most transported dilbits in Canada, Access Western Blend (AWB) and Cold Lake Blend (CLB) to developing yellow perch (Perca flavescens), a species distributed throughout North America. Embryos were exposed to dilbit until hatch, or up to 16 days, using a static daily renewal treatment regime of water accommodated fractions (WAF) and chemically-enhanced water accommodated fractions (CEWAF) of dilbit at total PAH (TPAH) concentration ranges of 0.02 to 10.7 μg/L and 0.21 to 20.4 μg/L TPAH, respectively. Results show that with increased TPAH concentration, the frequency of hatched embryos with developmental malformations increased proportionally. Expression of genes associated with phase I and II detoxification, cellular stress, and xenobiotic metabolism were altered in higher TPAH concentrations. 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.

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