The Endocrine Disrupting and Embryotoxic Effects of Untreated and Ozone-treated Oil Sands Process-Affected Water
Due to a policy of no release, oil sands process-affected water (OSPW) produced by the surface-mining oil sands industry in North Eastern Alberta, Canada, is stored on-site in tailings ponds. There is concern regarding the toxic effects of OSPW on aquatic organisms. Knowledge of the chemical composition and toxicity of OSPW is limited. Research is necessary for potential remediation and release of OSPW back into the environment. Due to the large volume and persistency of OSPW, active efforts are necessary for the remediation of OSPW before release and habitat reclamation. Currently, ozonation is considered one possible method for remediation of OSPW by reducing the concentrations of dissolved organic compounds, including naphthenic acids (NAs), which are considered among the primary toxic constituents. However, further work is needed to evaluate the effectiveness of ozonation in reducing the toxicity of OSPW and to ensure that ozonation does not increase the toxicity of OSPW. The overall objective of this work was to determine the toxic effects of OSPW on endocrine disruption and embryo development, using both in vitro and in vivo models, and the effectiveness of ozone treatment for reducing the toxicity of OSPW. In the first study, untreated and ozone-treated OSPW were examined for effects on sex steroid production using the H295R cell line steroidogenesis Assay. The results indicate that exposure to untreated OSPW can significantly decrease synthesis of testosterone (T) and increase synthesis of 17β-estradiol (E2) by 0.55±0.06 and 2.0±0.13-fold, respectively, compared to that of control groups (ρ < 0.05). These effects were due to increased aromatase enzyme activity and decreased E2 metabolism. The results also suggest that ozonation is an effective treatment to reduce concentrations of NAs in OSPW without altering steroidogenesis. In the second study, the T47D-kbluc (estrogen responsive) and MDA-kb2 (androgen responsive) cell assays were used to determine whether OSPW might act as either agonists or antagonists of the estrogen receptor (ER) or androgen receptor (AR), respectively. The estrogenic responses to untreated OSPW were significantly greater by 2.6±0.22-fold compared to control group (ρ < 0.05). Exposure to untreated OSPW produced significant antiandrogenic response in the presence of 0.01, 0.05 and 0.1 nM T by 16±6.5%, 47±7.6% and 75±9.7%, respectively, of that of the corresponding concentrations of T alone (ρ < 0.05). The results suggest that compounds in the dissolved organic fraction of OSPW have estrogenic and anti-androgenic properties, acting as ER agonists and/or AR antagonists. Ozonation of the OSPW partially mitigated the antiandrogenicity but had no effect on the estrogenicity of OSPW. In the third study, the endocrine-disrupting effects of OSPW and ozone-treated OSPW were determined by quantifying relative changes in the abundances of transcripts of genes along the brain-gonad-liver (BGL) axis in male and female fathead minnows (Pimephales promelas). The results indicate that OSPW has endocrine-disrupting effects at all levels of BGL axis and these effects of impaired expression of genes along the BGL axis are sex specific. For example, exposure to OSPW resulted in significantly greater abundances of transcripts of vtg (Vitellogenin), chg-l (Choriogenin L) and chg-h (Choriogenin H minor) by 4.9±1.2, 5.4±1.5 and 3.4±0.78-fold, respectively, compared to those of control groups (ρ < 0.05) in livers from male fathead minnow. However, in livers from female fathead minnows, exposure to OSPW resulted in significantly lesser abundances of transcripts of vtg, chg-l and chg-h by 0.002±0.0011, 0.022±0.007 and 0.036±0.024-fold, respectively, compared to those of control fish (ρ < 0.05). Ozonation of OSPW attenuated the effects on abundances of transcripts of some genes, and the attenuation was more prominent in males than in females. However, impact of ozonation on endocrine-disrupting effects of OSPW was less evident than in the in vitro studies described in Chapter 2 and 3. The results also provide a mechanistic basis for the endocrine-disrupting effects of OSPW from other studies, including impaired reproduction of fathead minnows exposed to OSPW. In the final study the effects of untreated, ozone-treated, and activated charcoal-treated OSPW (OSPW, O3-OSPW, and AC-OSPW) on the survival, growth, and development of embryos of fathead minnows were determined. Compared to the control group, which had an embryo survival rate of 98±2.1%, survival was significantly less when exposed to OSPW (44±7.1%; ρ < 0.05). Eggs exposed to untreated OSPW exhibited a significantly greater rate of premature hatching, and embryos exhibited more frequent spontaneous movements. Incidences of hemorrhage (50±3.4%), pericardial edema (56±7.1%), and malformation of the spine (38±5.4%) were significantly greater in embryos exposed to OSPW compared to control group (ρ < 0.05). Significantly greater concentrations of ROS (1.7±0.11-fold), and greater abundances of transcripts cyp3a, gst, sod, casp9, and apopen (2.4±0.34, 2.2±0.26, 3.1±0.74, 3.3±0.57 and 2.4±0.25-fold, respectively) compared to control groups (ρ < 0.05), indicated that exposure to OSPW caused oxidative stress, which can result in damage to mitochondria and promote activation of caspase enzymes and apoptotic cell death. Removal of dissolved organic constituents in OSPW by ozone treatment, or by activated charcoal, significantly attenuated all of the adverse effects associated with untreated OSPW. The results suggest that the organic fraction of OSPW can negatively impact the development of fathead minnow embryos through oxidative stress and apoptosis, and that ozonation attenuates this developmental toxicity. Overall, the findings from the research described in this thesis provide novel and important insights into the toxicity and mechanisms of the toxicity of OSPW with respect to endocrine disruption and development of embryos of fish. In addition, the research provides compelling evidence that ozonation might be an effective method for accelerating the remediation of OSPW. The results of the research might help regulators develop effective strategies for reclamation, remediation and potential release of OSPW back to the environment.
Oil Sands Process-Affected Water, Endocrine disruption, Embryo toxicity, Ozonation, Fathead minnow
Doctor of Philosophy (Ph.D.)
Veterinary Biomedical Sciences