Canada has experienced a significant increase in the transport of diluted bitumen (dilbit), a predominant oil sands product that combines bitumen with diluents derived from oil-gas condensates and other proprietary compounds. The toxicity of dilbit to fish embryos, which are immobile and thus at a high risk of exposure to oil in the event of a spill, remains largely unknown for most species. This study assessed the toxicity of water accommodated fractions (WAF) and chemically enhanced water accommodated fractions (CEWAF) of two winter dilbit blends, Access Western Blend (AWB) and Cold Lake Blend (CLB), to fathead minnow (Pimephales promelas) embryos. The TPH-F EC50s for malformations were 834 and 1058 μg/L for AWB WAF and CEWAF, respectively, and 500 and 715 μg/L for CLB WAF and CEWAF, respectively. Levels of cyp1a mRNA increased up to 46- and 69-fold, respectively, reflecting increasing exposure to polycyclic aromatic compounds (PACs) in AWB and CLB. Similarly, levels of gst mRNA were elevated up to 3.8-fold and 2.7-fold with increasing total concentrations of PACs in AWB and CLB, respectively. However, there were no significant changes in mRNA levels of p53, sod, cat, and gsr. These results suggest that the expression of cyp1a and gst may serve as biomarkers for dilbit exposure in fathead minnow, furthering our understanding of dilbit-responsive indicators of toxicity in fish species native to North America. This study is important as it utilizes the same exposure methodology to examine the toxicity of two commonly used Canadian dilbits, facilitating comparison of dilbit toxicity.

加拿大的稀释沥青（dilbit）是一种主要的油砂产品，其结合了沥青和从油气凝析油和其他专有化合物中得到的稀释剂，其运输量显着增加。对于大多数物种而言，假阳具对鱼胚的毒性仍然不为人所知，鱼胚是不动的，因此在发生溢油事故时极有可能暴露于油中。这项研究评估了两种冬季Dilbit混合饲料（Access Western Blend（AWB）和Cold Lake Blend（CLB））的水份（WAF）和化学增强的水份（CEWAF）对黑头now鱼（Pimephales promelas）胚胎的毒性。对于AWB WAF和CEWAF，用于畸形的TPH-F EC50分别为834和1058μg/ L，对于CLB WAF和CEWAF，分别为500和715μg/ L。的水平cyp1a mRNA分别增加了46倍和69倍，反映出AWB和CLB中对多环芳族化合物（PACs）的暴露增加。同样，随着AWB和CLB中PAC总浓度的增加，gst mRNA的水平分别升高至3.8倍和2.7倍。但是，p53，sod，cat和gsr的mRNA水平没有明显变化。这些结果表明cyp1a和gst的表达可能作为fat鱼min鱼中dilbit暴露的生物标志物，进一步加深了我们对北美本地鱼类物种的dilbit反应性毒性指标的了解。这项研究很重要，因为它利用相同的暴露方法来检查两种常用的加拿大假牙的毒性，从而有助于比较假阳具的毒性。