The increasing extraction of bitumen from the oil sands region in Canada is creating a need for transport. Spills from current and projected pipelines represent a significant environmental risk, especially for freshwater ecosystems. The toxicity of diluted bitumen (dilbit) on freshwater fish is largely unknown. This study assessed the toxicity of two dilbits (Clearwater McMurray and Bluesky) and compared their toxicity to a conventional oil (Lloydminster Heavy) on fathead minnow (Pimephales promelas) larvae. Larvae were exposed to various concentrations of the water-accommodated fraction (WAF) of the oils during 7 days from hatching. In the WAF treatments, the concentrations of volatile organic compounds (VOCs), including benzene, toluene, ethylbenzene, xylene (BTEX), hydrocarbons containing 6 to 10 carbon atoms (C_6–10), and polycyclic aromatic hydrocarbons (PAHs) and their alkylated forms were measured. Both dilbits contained higher concentrations of light components, while the conventional oil contained the highest concentrations of PAHs and alkylated PAHs. The Clearwater McMurray dilbit induced a higher mortality, with a maximum of 65.3%, while the other oils induced a similar mortality up to 16.5% and 18.6% for Lloydminster and for Bluesky, respectively. All three oils induced an increase in gene expression of the phase I detoxification enzyme (cyp1a) with increasing total hydrocarbon concentrations. All three exposures induced a similar increase in glutathione S-transferase (GST) activity, but no change in gst gene expression. For the Bluesky and Lloydminster exposures, an increase in malondialdehyde concentration was also observed, suggesting a rate limiting capacity of GST and phase II enzymes to perform the biotransformation of the PAH metabolites. Overall, this study brings new insights on the toxicity of dilbits in comparison to conventional oils on early life stages of North American freshwater fish and demonstrated that dilbits can be more toxic than conventional oils, depending on their composition and diluent proportions.

从加拿大油砂地区越来越多地提取沥青正在产生运输需求。当前和预计管道的泄漏代表了重大的环境风险，尤其是对淡水生态系统而言。稀释的沥青（dilbit）对淡水鱼的毒性在很大程度上是未知的。本研究评估了两种 dilbits（Clearwater McMurray 和 Bluesky）的毒性，并将它们与传统油（Lloydminster Heavy）对黑头鲦鱼（Pimephales promelas）幼虫的毒性进行了比较。在孵化后的 7 天内，幼虫暴露于不同浓度的油中水溶部分 (WAF)。在 WAF 处理中，挥发性有机化合物 (VOC) 的浓度，包括苯、甲苯、乙苯、二甲苯 (BTEX)、含 6 至 10 个碳原子的碳氢化合物 (C _6-10)，并测量了多环芳烃 (PAH) 及其烷基化形式。两种dilbits 都含有较高浓度的轻组分，而传统油中含有最高浓度的PAHs 和烷基化PAHs。Clearwater McMurray dilbit 导致更高的死亡率，最高为 65.3%，而其他油类导致类似的死亡率分别为 Lloydminster 和 Bluesky 的 16.5% 和 18.6%。随着总烃浓度的增加，所有三种油都诱导了 I 相解毒酶 (cyp1a) 的基因表达增加。所有三种暴露都诱导了谷胱甘肽 S-转移酶 (GST) 活性的类似增加，但 gst 基因表达没有变化。对于 Bluesky 和 ​​Lloydminster 暴露，还观察到丙二醛浓度增加，表明 GST 和 II 相酶对 PAH 代谢物进行生物转化的限速能力。总体而言，这项研究为北美淡水鱼早期生命阶段的双尾鱼与常规油相比的毒性提供了新的见解，并证明了双尾鱼的毒性可能比常规油更大，这取决于它们的成分和稀释剂比例。