A Weight of evidence Approach to Assess The Cycling Oil Sands Relevant Metals

Shell Albian Sands conducted a multi-year, multidisciplinary investigation (2011–2013) to assess the fate and effects of oil sands-relevant metals in the lower Athabasca River and associated tailings ponds. Using a weight of evidence approach, the study integrated abiotic and biotic data to validate and refine previous research. Its key objectives were to identify common metals in tailings ponds and the river, examine how physical and biological factors influence their movement and transformation across environmental media such as water, sediment, and suspended solids, and evaluate their ecological impacts through multi-trophic toxicity testing.

The study found that most metals in tailings pond water were below environmental guideline levels, except for aluminum. Metal concentrations varied between newer and older deposits, and microbial analysis showed depth-related shifts, with iron-reducing bacteria more common in upper layers and sulfate-reducing bacteria in sediments. Toxicity tests indicated that metals alone did not explain observed aquatic lethality, suggesting other contaminants were involved. Reduced toxicity at deeper levels, along with changes in microbial communities and mineral composition, pointed to upper fluid layers as the likely source of metal entry.