In vitro bioassay monitoring to assess baseline conditions prior to potential discharge of treated oil sands process water in receiving aquatic environments

The Alberta oil sands is one of the largest oil reserves in the world. However, there are concerns regarding the potential environmental and human health impacts of the oil sands development. During oil sands mining, large volumes of oil sands process-affected water (OSPW) is produced, which can only be recycled and/or stored in tailings ponds as there currently are no guidelines regarding its treatment and release into the receiving environment. OSPW is a complex mixture consisting of bitumen, organic and inorganic compounds, and solid materials, which can cause acute and sub-chronic toxicity to a range of aquatic organisms including invertebrates and fish. Recently, there have been efforts in motion by the oil sands industry to treat and release OSPW into the Lower Athabasca River, which is being assessed by the Federal and Alberta governments. This study uses a battery of seven in vitro bioassay tests to perform a bioanalytical assessment of untreated OSPW, surface water samples from 15 sites along the Lower Athabasca River and the effluents from two regional municipal wastewater treatment plants (WWTPs). All samples were filtered and enriched using solid phase extraction and the reconstituted extracts were used for chemical (FTIR) and bioanalyses. The main objective of this research was to assess the current bioactivity of the Lower Athabasca River. The same battery of in vitro bioassays was used to investigate whether in vitro bioassays can differentiate untreated OSPW from other types of water samples (i.e., municipal effluents and surface waters) by determining the relevant toxicity pathways. Finally, the bioassay responses were compared to the ecological effects-based trigger (EBT) values appropriate for each assay. The tests covered five toxicity endpoints: cytotoxicity, estrogenicity, mutagenicity, oxidative stress response and xenobiotic metabolism. Untreated OSPW showed high responses to all bioassay tests employed where 5 out of 7 signals exceeded the published EBT values. This result indicated that in vitro bioassays can be applied in the oil sands industry, and that all endpoints targeted in this study are relevant to this industry with cytotoxicity, estrogenicity, mutagenicity, and binding to the PPARɣ as primary toxicity indicators and oxidative stress and the induction of the AhR as secondary indicators. Although the WWTPs were active in most bioassays, the potential toxicity risks associated with direct exposure to these effluents are likely reduced due to the mixing patterns of the river. The low bioactivity responses of samples from the Lower Athabasca River suggests that there are low toxicity risks with its current stressors, but there is the potential for increased toxicity risks due to the discharge of OSPW-related contaminants if treated OSPW is released into the river. Finally, this study demonstrates that there is a relationship between bioactivity of the river and its hydrologic conditions due to the higher responses observed in June during high-flow conditions than in August (low-flow). However, further investigation is needed to establish this relationship.

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