The Alberta oil sands eroded bitumen/sediment transitional journey: Influence on sediment transport dynamics, PAH signatures and toxicological effect.

This paper investigated the sediment/contaminant continuum of bitumen containing sediment, from eroded exposed natural bitumen outcrops to river depositional zone, in order to improve our understanding of the transitional sediment, chemistry and toxicological influence on aquatic health. To achieve this aim, we linked a rainfall simulator with an annular flume to allow for connectivity between terrestrial erosion to stream flow. Bulk sediments were collected from the minable McMurray Formation (MF) on the Ells (EL) and Steepbank (STB) Rivers and from the Clearwater Formation (CF) on the STB. All plots generated similar washoff rates (~25 L hr-1) and fine eroded sediment (d50 = 5 µm) regardless of strata. The CF generated the highest total eroded sediment (TES) followed by EL-MF and STB-MF. The STB-MF generated up to three orders of magnitude lower TES than the STB-CF. The EL generated the highest PAH concentrations, however, when normalizing by TES mass delivered to the flume, STB-MF PAH was one to two orders of magnitude higher per unit mass than EL-MF. The TES concentrations were inversely proportional to the degree of bitumen within the sediment (STB-MF > EL-MF > STB-CF). Once the TES was suspended in the flume, there was a change in the dominant PAH for most classes [e.g., Dibenzothiophenes C4 (parent material) to a C3 (TES)]. Further, no flocculation and the buoyant properties of the TES suggested that the sediment and associated PAHs may travel long distances. The EL-MF proved to be the most toxic to fathead minnow embryo survival due principally to the high PAH concentrations and sediment loads. The CF exhibited no toxicological effect. This work has shown the importance of assessing sediment/contaminant characteristics over the continuum (terrestrial erosion/washoff to river deposition) in order to support basin wide management strategies for the protection of aquatic health.

Temporal and spatial trends in riverine suspended sediment and associated polycyclic aromatic compounds (PAC) within the Athabasca oil sands region.

Bitumen-bearing suspended sediment (SS) eroded from the McMurray Formation (MF) are fine grained (silts and clays) and coated with natural hydrophobic oils. This results in poor settling and long range transport of associated contaminants. There was a longitudinal increase in polycyclic aromatic compound (PAC) concentrations for rivers that erode the MF from upstream to downstream regardless of time-of-year, while loads were substantially increased during high flow periods when the erosive forces are the greatest and the overland flow contribution is high. Within the MF, variation in PAC contributions is seen by the Ells River having higher loads than the Steepbank River. Using the Ells and Steepbank as examples, double plot PACs ratios suggest that the PAC concentrations and signatures vary spatially within the MF but that the weathering processes may be the same. Plots of the various homologs of PACs generally illustrated a normal distribution which suggests petrogenic origins. However, several PAC ratios suggested that both the parent material and the SS are pyrogenic in nature. While it is likely that some level of atmospheric deposition (anthropogenic or from forest fire) is incorporated into the SS of the rivers, it is likely to be limited relative to the proportion of naturally eroded MF sediments. Additional analysis will be needed to distinguish the relative risk of both anthropogenic (e.g., industrial operations) and natural sources (bitumen deposits, forest fire) of PACs to the SS and to long-range depositional environments, as they may have potential aquatic ecological effects.