The use of mature fine tailings (MFT) at oil sand reclamation sites leaves benthic invertebrates exposed to elevated levels of polycyclic aromatic compounds (PACs). In this laboratory study, stable isotope analyses were used as a tool to trace oil sand carbon (C) and nitrogen (N) sources in microbes and primary consumers. The objective was to better understand the importance of PAC derived carbon as an energy source in oil sands aquatic reclamation. Blackworms (Lumbriculus variegates) were raised for 6 weeks on either whole sediment from different oil sands reclamation wetlands containing elevated levels of PACs, or on microbes cultured on oil sands derived PAC extracts. Within 4 weeks of exposure, the nitrogen isotope signatures of L. variegates were found to be similar to that of the sediment, while the carbon isotope signatures of L. variegates were approximately 2 per cent 13C enriched relative to the sediment. It was suggested that tracing stable nitrogen isotopes may be a useful tool for determining exposure of aquatic organisms to oil sands processed-material through channels such as groundwater pollution