Centre Eau Terre Environnment, Institut national de la recherche scientifique (INRS), Quebec City, QC, Canada.
Department of Biology, Queen's University, Kingston, ON, Canada.
Environ Pollut. 2019 Mar;246:501-508. doi: 10.1016/j.envpol.2018.12.039. Epub 2018 Dec 15.
In order for Alberta's thick bitumen to be transported through pipelines, condensates are added creating a diluted bitumen (dilbit) mixture. Recent pipeline expansion projects have generated concern about potential dilbit spills on aquatic wildlife health. Studies have suggested that polycyclic aromatic compounds (PACs) are toxic to aquatic vertebrates and could potentially also interfere with their endocrine system. The research objectives of this study were to investigate the toxicity of dilbit to developing frog embryos and to identify the molecular mechanisms of action involved. Fertilized embryos of Western clawed frog (Silurana tropicalis) were exposed for 72 h to water accommodated fractions (WAF; 0.7-8.9 μg/L TPACs) and chemically-enhanced WAFs (CEWAF; 0.09-56.7 μg/L TPACs) of Access Western Blend (AWB) and Cold Lake Blend (CLB) dilbits. Both dilbit's CEWAFs significantly increased embryonic mortality and malformation incidence in the highest treatments tested, while WAF treatments led to no visible toxic effects. Increases of the cytochrome P450 1A (cyp1a) mRNA levels were observed for all WAF and CEWAF dilbit treatments suggesting that phase I detoxification is activated in the dilbit-exposed larvae. When exposed to PAC concentrations ranging from 0.09 to 8.9 μg/L, the frogs displayed no observable malformations, but expressed significant increases of cyp1a mRNA levels (2- to 25-fold; indicating a suitable biomarker of exposure); however, when concentrations were of 46.6 μg/L or higher, both malformed frog phenotype and induction of cyp1a mRNA level (>250-fold) were measured (indicating a suitable biomarker of response). The expression of several genes related to cellular detoxification and endocrine disruption were also measured, but were not significantly altered by the treatments. In sum, cyp1a mRNA level is a highly sensitive endpoint to measure subtle molecular changes induced by PAC exposure in the frog embryos and larvae, and data suggest that PAC concentration higher than 46 μg/L would be toxic to the developing S. tropicalis.
为了使艾伯塔省的稠油能够通过管道运输，需要添加凝析油来制成稀释沥青（dilbit）混合物。最近的管道扩建项目引起了人们对潜在稀释沥青溢油对水生野生动物健康的担忧。研究表明，多环芳烃（PACs）对水生脊椎动物有毒，并且可能还会干扰其内分泌系统。本研究的目的是研究稀释沥青对发育中的青蛙胚胎的毒性，并确定涉及的作用机制。西爪蟾（Silurana tropicalis）受精卵在 72 小时内暴露于水可容纳分数（WAF；0.7-8.9μg/L 总多环芳烃）和化学增强 WAF（CEWAF；0.09-56.7μg/L 总多环芳烃）的艾伯塔 Access Western Blend（AWB）和冷湖 Blend（CLB）稀释沥青中。两种稀释沥青的 CEWAF 在最高浓度处理下显著增加了胚胎死亡率和畸形发生率，而 WAF 处理则没有导致可见的毒性作用。所有 WAF 和 CEWAF 稀释沥青处理均观察到细胞色素 P450 1A（cyp1a）mRNA 水平升高，表明相 I 解毒在暴露于稀释沥青的幼虫中被激活。当暴露于浓度范围为 0.09 至 8.9μg/L 的 PAC 时，青蛙没有表现出可观察到的畸形，但 cyp1a mRNA 水平显著升高（2-25 倍；表明是暴露的合适生物标志物）；然而，当浓度达到 46.6μg/L 或更高时，都测量到畸形青蛙表型和 cyp1a mRNA 水平的诱导（表明是反应的合适生物标志物）。还测量了与细胞解毒和内分泌干扰相关的几个基因的表达，但处理并未显著改变这些基因的表达。总之，cyp1a mRNA 水平是一个高度敏感的终点，可用于测量 PAC 暴露在青蛙胚胎和幼虫中引起的细微分子变化，并且数据表明，PAC 浓度高于 46μg/L 对发育中的 S. tropicalis 有毒。
