Year of Publication: 2011
One of the main issues associated with bitumen extraction in the Alberta oil sands is the production of oil sands process-affected water (OSPW). The OSPW is saline, alkaline, and containing high concentrations of inorganic and organic constituents, such as naphthenic acids (NAs). In accordance with environmental legislation, OSPW must be retained in on-site settling basins as the water has demonstrated toxicity towards a number of different aquatic and terrestrial organisms. Due to the large volumes of OSPW currently in containment, treatment methods are required to eliminate the toxicity and prepare the water for release in future reclamation scenarios. Benthic invertebrates, such as chironomids, represent an important component of aquatic food webs and ecosystems in the oil sands region, but the toxicity of OSPW towards these organisms had not been fully characterized. Additionally, the effects on toxicity of treating OSPW by aging or ozonation were unknown and needed to be assessed in preparation for a potential future release scenario. To assess the toxicity of untreated, aged, and ozonated OSPW, 10-day and chronic exposures of Chironomus dilutus to OSPW were conducted; endpoints of interest included survival, growth, development, and behavior. For the studies described in this thesis, relatively fresh OSPW was sampled in two batches (designated ‘WIP-OSPW-A’ and ‘WIP-OSPW-B’) from the Syncrude Canada Ltd. West In-Pit (WIP) settling pond and from three experimental reclamation ponds – Big Pit, FE5, and TPW. Larvae were exposed to each of the treatment waters for both a 10-d and a chronic (until adult emergence) exposure period. Real-time PCR was used to assess gene expression of hemoglobins, endocrine-related receptors, and ribosomal protein following 1-, 4-, or 7- d exposure to fresh or aged OSPW (WIP-OSPW or FE5) in order to investigate the underlying mechanisms of toxicity. The greatest concentrations of NAs were measured in the fresh WIP-OSPW (between 70 and 72 mg/L) and the total concentrations of NAs in the aged waters were between 13 and 35 mg/L.
Exposure to untreated OSPW resulted in both acute and chronic toxicity to C. dilutus larvae. Masses of larvae that were exposed to WIP-OSPW were 64% to 79% less than that of the respective control larvae (p<0.001). Cases built by larvae exposed to both fresh and aged OSPW were smaller and more fragile than those built by larvae exposed to freshwater. In terms of gene expression, the abundance profiles of transcripts of hemoglobin genes were significantly different in FE5-exposed larvae relative to the freshwater control. Exposure to both WIP-OSPW and FE5 resulted in differential expression of estrogen-related receptor, ultraspiracle protein, and ribosomal protein L15 in C. dilutus compared to the control. Similarly, chronic exposure to untreated OSPW resulted in significantly less pupation than in the controls, with 31% and 71% less pupation of larvae exposed to WIP-OSPW-A or WIP-OSPW-B, respectively (p<0.05). Rates of emergence were also significantly less for larvae exposed to WIP-OSPW, with only 13% and 8% of larvae emerging as adults when exposed to WIP-OSPW-A or WIP- OSPW-B, respectively, compared to 81% in the control (p<0.0001). However, larvae exposed to water from Big Pit, FE5 and TPW did not have significantly lesser masses than the controls (p>0.05). Aging of OSPW in reclamation ponds did not attenuate all chronic toxicity since exposure to TPW resulted in significantly less emergence and delayed emergence relative to the control. The OSPW aged in reclamation ponds retained toxicity and, therefore, more aggressive, targeted treatment, such as ozonation, of OSPW is required.
To evaluate the effectiveness of ozonation in eliminating toxicity of OSPW, WIP- OSPW-A and WIP-OSPW-B were treated with 30 and 80 mg/L of ozone (O3), respectively. There were no differences in survival of larvae exposed to ozonated-OSPW relative to the freshwater control (p>0.05). Ozonation also attenuated adverse effects on growth, pupation, and emergence seen in both batches of untreated OSPW, suggesting that ozonation may be an effective treatment for targeting the organic fraction of OSPW and reducing or possibly eliminating toxicity of OSPW to C. dilutus.