STP971: A Toxicity Assessment of Tar Sands Tailings

    Yong, RN
    Director and research associate, Geotechnical Research Centre, Environmental Geotechnology Division, McGill University, Montreal, Quebec

    Ludwig, RD
    Director and research associate, Geotechnical Research Centre, Environmental Geotechnology Division, McGill University, Montreal, Quebec

    Pages: 11    Published: Jan 1988


    Abstract

    Toxicity assessment was conducted on the liquid fractions of waste tailings generated from the hot water extraction process employed in recovering oil from the Athabasca tar sands. Indices of toxicity employed included a mixed culture of microorganisms indigenous to a major river flowing in the vicinity of containment ponds used to store the waste tailings. Toxicity assessment employing the mixed culture of microorganisms was conducted by monitoring the growth of microbial suspensions through turbidity measurements. Other indices of toxicity employed were the freshwater green alga Selenastrum capricornutum and the bacterium resembling Photobacterium phosphoreum. The liquid fractions considered for toxicity assessment included those of both fresh tailings and aged tailings. In addition, toxicity assessment was conducted on the fluid emanating from accumulated sludge in the containment ponds.

    Fresh tailings were observed to be highly toxic to all indices of toxicity employed. At a concentration of 40% by volume, fresh tailings were observed to support on average less than 38% of the growth observed in controls for the mixed culture of river microorganisms, while at a concentration of 25% by volume the fresh tailings brought about an average light emission reduction of greater than 65% in the bacterium resembling Photobacterium phosphoreum. Toxicity assessment with Selenastrum capricornutum gave an interpolated EC50 value of 24% by volume.

    Aged tailings were observed to exhibit only slight toxicity to Selenastrum capricornutum and the bacterium resembling Photobacterium phosphoreum and no toxicity to the mixed culture of river microorganisms. In fact, aged tailings at a concentration of 40% by volume appeared to stimulate growth in the mixed culture of river microorganisms over that observed in the controls. At 100% concentration by volume, an average light emission reduction of 16% was observed for the bacterium resembling Photobacterium phosphoreum, and an average 33% inhibition of growth relative to controls was observed for Selenastrum capricornutum.

    Emanated sludge fluid was observed to be highly toxic only to the alga Selenastrum capricornutum with an interpolated EC50 value of 29% by volume. At a concentration of 40% by volume, the emanated sludge fluid was observed to apparently stimulate growth in the mixed culture of river microorganisms over that observed in the controls. At a concentration of 100% by volume, an average light emission reduction of only 13% was observed for the bacterium resembling Photobacterium phosphoreum.

    The results suggest that, although initially very toxic, the waste tailings undergo a self-detoxification process with time. This may have important implications with regard to measures which might be implemented in the containment and treatment of the tailings.

    Keywords:

    oil, oil sands, wastes, tailings, toxicology, assessments, plankton, microorganisms, algae, bacteria, Selenastrum capricornutum, Photobacterium phosphoreum


    Paper ID: STP34057S

    Committee/Subcommittee: E47.01

    DOI: 10.1520/STP34057S


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