Variation in toxicity and ecological risks associated with some oil sands groundwaters Bruce Kilgour a, ⁎, Ashley Mahaffey b , Christine Brown c , Sarah Hughes d,e,f , Charles Hatry a , Liza Hamilton a a Kilgour & Associates Ltd, 16-2285C St. Laurent Boulevard, Ottawa, Ontario K1G 4Z6, Canada b Coral Waters Consulting, Shell Technology Centre Calgary, 3655 36 St NW, Calgary, AB T2L 1Y8, Canada c Shell Canada Ltd, Shell Technology Centre Calgary, 3655 36 St NW, Calgary, AB T2L 1Y8, Canada d Shell Health – Americas, 150 North Dairy Ashford Road, Houston, TX 77079, United States e Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 1H9, Canada f Department of Forestry and Environmental Conservation, Clemson University, Clemson, SC 29634, USA HIGHLIGHTS • Oil sands groundwaters were collected from nine wells at between 45 and 119 m depth. • Groundwaters were generally non- acutely toxic. • Sublethal responses best explained by conventional substances (chlorides). • Groundwaters pose modest risk of local eutrophication to surface waters. GRAPHICAL ABSTRACT abstract article info Article history: Received 4 September 2018 Received in revised form 18 December 2018 Accepted 18 December 2018 Available online 20 December 2018 Editor: Damia Barcelo The surface mining of oil sands deposits requires the removal of groundwater to stabilize the deposit (depressur- ization) and make it safe for mining. The chemistry and toxicity of deep groundwaters (from 45 to 144 m below an active mining operation) were characterized to determine if the release of groundwaters would pose a risk to a receiving aquatic environment. Concentrations of conventional chemicals such as nutrients and metals were gen- erally below CCME chronic guidelines. Concentrations of oil sands naphthenic acids (NAs) varied depending on the method of measurement and were routinely N1 mg L -1 . Groundwaters rarely caused lethality to fish and in- vertebrates in standard acute and chronic toxicity tests. Algal cell production was negatively correlated with chlo- rides and potentially negatively with NAs. Other chronic toxicity variations were less obviously correlated with measured chemistry. The groundwaters had moderately-high oxygen demand (2 to 33 mg L -1 ), likely associated with nutrients and organic substances, and thus have the potential to enrich receiving surface water environ- ments if left untreated and depending on the receiving environment. This paper presents for the first time a com- prehensive (3 year) pairing of water chemistry and toxicity data on groundwaters collected from aquifer depressurization wells below an active oil sands operation. These data will contribute to a better understanding of the environmental risk these waters potentially pose, and ultimately, to the improvement of water manage- ment strategies and the reduction of the overall surface mining footprint of oil sands operations. © 2018 Elsevier B.V. All rights reserved. Keywords: Oil sands Water quality Sublethal Groundwater Science of the Total Environment 659 (2019) 1224–1233 ⁎ Corresponding author. E-mail address: bkilgour@kilgourassociates.com (B. Kilgour). https://doi.org/10.1016/j.scitotenv.2018.12.287 0048-9697/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv