Heavy metal dynamics in the Athabasca River: Sediment concentrations prior to major Alberta oil sands development

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  • Exploitation of the bituminous sands may elevate heavy metal levels in the sediments of drainage systems of the AOSERP area via waterborne or airborne emissions. One hundred and six dredged sediments and twenty-four sediment cores were collected from the Athabasca River system from just above Fort McMurray to the confluence of Riviere des Rochers with the Slave River. A preliminary sample suite representing all of the drainage units and textural variations was selected for detailed analyses by several total and partial extraction techniques. The objective was to document the natural heavy metal geochemistry of the sediment and to assess cultural influences if any on concentrations. These preliminary analyses indicate that absolute concentrations are low when compared to data for polluted sediments or even for sediments from different natural geological terrains elsewhere. Concentration variations appear to be functions of natural sedimentological, mineralogical and geochemical controls. Highest heavy metal concentrations occurred in the finest grained sediments from Lake Athabasca. Vanadium, the heavy metal most commonly associated with the oil sands, appeared to be present in the drainage sediments in a stable organic compound, which was unextractable by hydrochloric acid, sodium hydroxide, or benzene/mcthanol. Its occurrence in the drainage sediment may be in the same general form as in the original bituminous oil sands. If so, it appears to be unaffected by chemical or bacterial degradation in the bottom sediment. Recommendations for further work, which will require additional funding, are in decreasing order of priority: x-ray diffraction of selected sediments; organic extraction and fractionation of selected sediments; analyses of selected sediment cores; determination of sedimentation rates for selected cores; completion of analyses of the dredged sample suite; analyses of lake sediments from lakes off the mainstream system; detailed grid sediment sampling immediately downstream from extraction plant effluents; collection of a suspended sediment sample suite; and analyses of oil slicks (air-water interface).

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