Natural and anthropogenic inputs of arsenic and selenium to the environment in the Athabasca Bituminous Sands Region

• Author / Creator

  Donner, Mark

• Industrial development of the Athabasca Bituminous Sands (ABS) in northern Alberta, Canada, has raised concerns that emissions of arsenic and selenium to the surrounding landscape and waterbodies have been increasing over time. To test this hypothesis, a comprehensive study of arsenic and selenium in a variety of environmental media from the ABS region was conducted. The foci included: i) bituminous ores and the distribution of arsenic and selenium between mineral and bitumen fractions ii) Sphagnum moss from ombrotrophic bogs to determine contemporary atmospheric deposition iii) age-dated (210Pb, 14C) peat cores to determine historical trends in arsenic and selenium deposition iv) chemical speciation in Athabasca River water and v) Trout-perch (Percopsis omiscomaycus) from the Athabasca River as a biological indictor of selenium inputs. Similar to other potentially toxic trace elements (Ag, Be, Bi, Cd, Pb, Sb, Tl), analyses of laboratory separated mineral and bitumen components of ABS revealed that As is contained predominantly in the mineral fraction of ABS ores. In contrast, selenium was found predominantly (ca. 80%) in the bitumen fraction. Therefore, due to the high degree of chemical stability of mineral material in ABS, selenium likely exhibits greater mobility than As during the bitumen upgrading process. To examine potential emissions to the aquatic environment, the concentration and chemical speciation of arsenic and selenium were determined along a ~125 km transect of the Athabasca River. Despite nearby bitumen mines and upgraders, as well as natural inputs of salts, humic material, naphthenic acids and suspended solids, dissolved (i.e., < 0.45 µm) concentrations of both elements (arsenic ~0.4 µg/L; selenium ~0.2 µg/L) remained remarkably consistent in time (2014, 2015) and space, with no increasing trend in concentrations observed upstream to downstream of industry. The chemical speciation of both elements also remained consistent upstream to downstream, with As(V) and Se(VI) being the predominant forms determined in surface water. The average concentration of selenium in Trout-Perch muscle (2.2 ± 0.4 mg/kg; n=34) was below U.S. EPA guideline values and concentrations were not significantly different (p >0.05) between upstream and midstream or downstream reaches. The average concentration of selenium in Sphagnum moss collected from peat bogs around the ABS region (57.5 ± 13.1 µg/kg; n = 75) was similar to concentrations in moss collected from other parts of Alberta. Moss from the east and west coasts of Canada were found to contain much greater concentrations (~ 3x) of selenium than moss collected from the ABS region due to natural inputs from the marine biosphere. An age-dated peat core from an ombrotrophic (rain-fed) bog near open-pit mines and upgraders did not reveal an increasing trend in selenium deposition over time. Arsenic concentrations in the same peat core demonstrated an increase with time; however, the apparent increase was attributed to greater mineral dust deposition, which has been increasing in the region due to industrial activities. A peat core collected from the Utikuma Region Study Area (UTK), a remote reference site approximately 250 km upwind from the ABS region, revealed a 2700-year record of atmospheric arsenic and selenium deposition. Accumulation rates of arsenic and selenium in UTK demonstrated a considerable increase beginning in the early 20th century, peaking in ~1970, before going into a steady decline. The timing of these increases implicates coal combustion and base metal smelting and refining, combined with long-range atmospheric transport, as predominant sources of both elements to the bog and provides important perspective on the limited nature of atmospheric arsenic and selenium deposition in the ABS region. Viewed together, these findings suggest that inputs of arsenic and selenium to the environment in northern Alberta due to bitumen mining and upgrading are difficult to distinguish from natural inputs.

• Subjects / Keywords

  • Arsenic
  • Selenium
  • Oil sands

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-g6x7-cf97

• License

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