Effects-Directed
Analysis of Dissolved Organic Compounds
in Oil Sands Process-Affected Water
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Abstract
Acute toxicity of oil sands process-affected
water (OSPW) is caused
by its complex mixture of bitumen-derived organics, but the specific
chemical classes that are most toxic have not been demonstrated. Here,
effects-directed analysis was used to determine the most acutely toxic
chemical classes in OSPW collected from the world’s first oil
sands end-pit lake. Three sequential rounds of fractionation, chemical
analysis (ultrahigh resolution mass spectrometry), and acute toxicity
testing (96 h fathead minnow embryo lethality and 15 min Microtox
bioassay) were conducted. Following primary fractionation, toxicity
was primarily attributable to the neutral extractable fraction (F1-NE),
containing 27% of original organics mass. In secondary fractionation,
F1-NE was subfractionated by alkaline water washing, and toxicity
was primarily isolated to the ionizable fraction (F2-NE2), containing
18.5% of the original organic mass. In the final round, chromatographic
subfractionation of F2-NE2 resulted in two toxic fractions, with the
most potent (F3-NE2a, 11% of original organic mass) containing predominantly
naphthenic acids (O<sub>2</sub><sup>–</sup>). The less-toxic
fraction (F3-NE2b, 8% of original organic mass) contained predominantly
nonacid species (O<sup>+</sup>, O<sub>2</sub><sup>+</sup>, SO<sup>+</sup>, NO<sup>+</sup>). Evidence supports naphthenic acids as among
the most acutely toxic chemical classes in OSPW, but nonacidic species
also contribute to acute toxicity of OSPW