- 270 views
- 274 downloads
Evaluating the Persistence of Dissolved Heteroatomic Organic Chemicals in Oil Sands Process-Affected Water by Non-Targeted Analysis
- Author / Creator
- Evelyn Kwabuaa Asiedu
Over 1 billion m3 of wastewater in tailings ponds currently awaits remediation as a result of the extraction of bitumen – the Canadian oil sands ore. Relative to the Athabasca River and regional tributaries, oil sands process-affected water (OSPW) has increased levels of salts, metals and a complex mixture of toxic organic chemicals including naphthenic acids (NAs). One current strategy for treating OSPW employs the use of end pit lakes (EPLs). In this method, OSPW will be placed on top of a layer of fluid fine tailings (FFT) for long term storage in evacuated mines, while the FFT dewaters, and the toxicity of the overlying cap water is reduced through natural or managed processes. However, one requirement for future approvals of EPLs is the effective removal of chemicals in OSPW which are known to be hard to degrade. Syncrude’s Base Mine Lake (BML) is the only existing oil sands EPL. Using BML OSPW, the persistence of thousands of dissolved organic species was monitored here, for the first time. The central null hypothesis was that all organics in OSPW have equal rates of biodegradation. The hypothesis was tested using three distinct strategies: a field study of OSPW of different ages, a laboratory study monitoring in situ biodegradation of BML OSPW dissolved organics, and the metabolism of toxic components in BML OSPW by subcellular fractions of model fish species.
The organic profile of BML was compared to field samples representing fresh and aged OSPW ( <1 year to 31 years). Principal components analyses distinguished OSPW of different ages based on relative contribution of chemical classes. Aged samples had the lowest concentrations of organics and larger proportions of oxidized heteroatomic chemicals. Overall, the most acutely toxic OSPW chemicals degraded in aged OSPW (i.e., O2- species), but the residual toxicity of aged OSPW may be explained by persistent degradation products, possibly due to photolysis and microbial degradation.
In situ microbial biotransformation of BML OSPW was monitored in laboratory microcosms containing BML OSPW alongside positive (containing commercial NAs) and negative (autoclaved, chemically treated) controls for 424 days. Samples were analyzed using high pressure liquid chromatography-Orbitrap mass spectrometry in negative ionization mode. After 272 days, the profile of organics in BML OSPW showed no difference compared with negative controls. Following a series of treatability experiments, nitrogen and phosphorus were added on day 389 to support microbial growth. By the end of the experiment (day 424), chemicals in the O2- class had decreased by 60% as did one other chemical class (O2S-). Changes were not observed in any other heteroatomic class.
Rainbow trout are native to the Athabasca Oil Sands region and thus will eventually be exposed to reclaimed OSPW. To study the ability for these fish to metabolize OSPW organics, in vitro biotransformation was monitored in sub-cellular fractions from rainbow trout liver homogenate. Phase I hydroxylation and phase II glucuronidation were assessed. Microsomes and S9 fractions each demonstrated trout have some capacity to metabolize dissolved toxic organics, but most dissolved organics were unchanged. All products generated in the assays were generated were only from phase I metabolism; no glucuronide products were observed.
This thesis investigated the biodegradability and degradation kinetics of the dissolved organics in OSPW. It is the first application of non-targeted analysis to compare OSPW of different ages. Here, I demonstrate that NAs can be slowly degraded over time and show that other heteroatomic classes are more persistent. The use of trout subcellular fractions has never before been applied to assess the biotransformation potential of trout. Biotransformation observed in microsomes suggests trout have some capacity to metabolize toxic components in OSPW and provide a starting point for the targeted analysis of metabolites in bile or urine. Collectively, these results suggest that NAs may be degraded in EPLs, and therefore remove the acute toxicity, but other dissolved organics may contribute to chronic toxicity.
- Graduation date
- Spring 2021
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.