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Oil Sands Process-Affected Water Toxicity Attribution and Evaluating Ageing as a Remediation Strategy
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- Author / Creator
- Gault, Ian GM
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Oil sands process-affected water (OSPW) is a byproduct of bitumen extraction in the surface-mining oil sands industry of Northern Alberta. OSPW contains a complex and environmentally persistent dissolved organic mixture that can be toxic to aquatic organisms. One long-term remediation strategy involves ageing of OSPW in end-pit lakes such that in situ natural processes will eventually allow detoxification and safe environmental re-integration of this water. Over 30 end-pit lakes are planned, but only one has been established so far, Base Mine Lake (BML), which was commissioned in 2012 at Syncrude Canada Ltd. Predicting the effectiveness of this strategy relies on an understanding of what chemicals cause toxicity in fresh OSPW, and how the chemical mixture might change over time. This investigation used chemical fractionation and ultrahigh resolution mass spectrometry combined with cytotoxicity and endocrine disruption assays to further study the toxicity of candidate chemical classes in fresh and aged OSPW samples. Real-time cell analysis with human liver carcinoma cells (HepG2) was used with OSPW samples for the first time, while the yeast estrogenic/androgenic screens were used as a standardized and comparable assay to previous studies. A chemical fraction isolated from BML 2015 containing naphthenic acids (NAs) was largely responsible for the cytotoxicity observed towards HepG2 cells, with a point of departure (IC10) at 17 mg/L, similar to the estimated field concentration of NAs in BML 2015 (12.9 mg/L). A corresponding non-acid fraction, speculated to contain steroid-like chemicals, was not cytotoxic up to 12.5× above field concentrations in BML 2015. The total organic extract of BML 2017 was cytotoxic to HepG2 cells, generating an IC50 of 8× above field concentrations, with the point of departure marginally above 1×. Based on a series of BML water samples collected over a 4-year span, the cytotoxicity of BML extracts (i.e. toxicity per volume) decreased with ageing, while the toxic potency of the extracts (toxicity per mass of extract) was not significantly different between years. This toxicological result was supported by mass spectral evidence whereby total m/z intensity of BML organics decreased in samples over time, but the relative proportion of chemical classes remained unchanged. Older OSPW aged 23 years in an experimental pond had a unique biphasic toxicity profile (time-dependent), with a toxic potency greater than BML at 24 h post exposure, but not at 60 h. This sample also had a unique distribution of chemical classes compared to BML. Estrogen and androgen receptor antagonists, but not agonists, were identified in all BML 2015 fractions. Notably, the NA and non-acidic fractions showed endocrine activity below environmentally relevant concentrations and were more potent (toxicity per mass of extract) than positive control antagonistic hormones. Overall, with BML and experimental pond samples ranging up to 23 years of ageing in the field, there was little difference in the potency of estrogen and androgen receptor antagonism between the organic extracts, and always with EC50’s below environmental concentrations and similar to positive control antagonistic hormones. While organic acids, including naphthenic acids, decreased to a large extent in the aged samples, chemical classes detected in positive mode (i.e. polar organics) were less depleted and became relatively enriched in the total organic extract, suggesting that non-acid polar organics contribute to environmentally persistent estrogen and androgen receptor antagonism. Overall, decreases in cytotoxicity in BML over time, although promising for the end-pit lake strategy, are likely only due to a dilution effect. Also, this is the first report of an older experimental pond sample having a biphasic cytotoxicity profile, which, along with its chemical profile, remains to be understood. This highlights the importance of chemical composition, not only concentration, in determining risk, and warrants further research into chemical-specific regulatory limits needed to ensure environmental protection.
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- Graduation date
- Spring 2019
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.