The Use of Stable Isotopes (¹³C/¹²C and ¹⁵N/¹⁴N) to Trace Exposure to Oil Sands Processed Material in the Alberta Oil Sands Region

Abstract

Various oil sands reclamation strategies incorporate oil sands processed material (OSPM) such as mature fine tailings (MFT), engineered tailings (consolidated tailings, CT), and tailings pond water (TPW) into reclamation components that need to develop into viable aquatic ecosystems. The OSPM will contain elevated salinity and organics such as naphthenic acids (NA) and polycyclic aromatic compounds (PAC) that can be chronically toxic to aquatic organisms depending upon levels and age. Due to the complexity of the chemical mixtures, analysis of these compounds in exposed organisms can be challenging. In this study, the stable carbon and nitrogen isotope signatures of selected invertebrates from various types of oil sands reclamation sites were analyzed to determine whether stable isotopes can be used to trace the exposure of aquatic organisms to organic constituents of OSPM. In a series of experimental reclamation ponds of similar age and size, there were trends of ¹³C depletion and ¹⁵N enrichment for benthic invertebrates along a gradient of increased levels of MFT and/or TPW. A survey of 16 sites revealed high δ¹⁵N values for invertebrates in aquatic systems containing MFT and CT (gypsum-treated mixes of MFT and tailings sand), which was attributed to the presence of NH₄ ⁺, a process by-product in OSPM. Findings of this study indicate a potential for the use of stable nitrogen isotopes to define exposure of biota to OSPM during environmental effects monitoring programs both in surface waters and in cases where groundwater seepage containing oil sands processed water enters surface receiving environments in the region.

This project was funded by Syncrude Canada Ltd. (grant E3166), Toxic Substances Research Initiative (TSRI), Canadian Water Network (CWN), and by an NSERC Discovery grant to D. G. Dixon. Suncor Energy, Inc., provided site logistical support and access to its sites and background information. Special thanks to Terry Van Meer, Neil Rutley, Melanie Ezekiel, Joanne Hogg, and others for their support while at Syncrude Canada Ltd. (Alberta). We greatly appreciate the efforts of Gina Hoar, Jason Vervoort, and Bill Mark (University of Waterloo).