Master of Science (MSc)
Faculty of Science
Dr. Jim McGeer
Principle Investigator and Supervisor
Chromite and rare earth element development was identified in the 2015 Canadian Federal budget as a significant opportunity, however, key data gaps exist regarding the environmental concerns related to these resource developments. Chromium is essential in the production of stainless steel, and no suitable substitute is known. Rare earth elements (REEs) are a series of metals that are composed of 15 lanthanides, as well as scandium and yttrium. Uses for REEs range from electronic devices (i.e. cell phones, computers, televisions) to magnets and controlling nuclear reactors. While commercial production of REEs signify a great economic opportunity for Canada, key data gaps regarding chemicals involved in processing REEs has been identified. The first objective of this study was to determine the acute toxicity of hexavalent chromium (Cr (VI)) to the invertebrate species Hyalella azteca and to identify the potential mitigating influences of cations and dissolved organic matter (DOM). The second objective was to evaluate the acute toxicity of flotation reagent AERO 6493, conduct toxicity identification/reduction studies, and test REE processing wastewater toxicity to H. azteca and Daphnia magna. Standard methods were followed for both 48 h (D. magna) and 96 h (H. azteca) acute toxicity tests, in media with pH 7.3 and water hardness of 120 mg CaCO3 /L (D. magna) and 60 mg CaCO3 /L (H. azteca) for both objectives. For objective 1, effect of altering water chemistry on Cr (VI) toxicity to H. azteca was tested with additions of Ca (0.5-3.5mM), Na (0.5-3 mM), Mg (0.13-0.64mM), as well as additions of natural sources of DOC (from Pickle Lake and Luther Marsh) at concentrations of 5 and 12 mg DOC/L. No protective effect was observed with additions of Na+, Pickle Lake and 2016 Luther Marsh DOC sources, but a significant protective effect was observed for 2015 Luther Marsh DOC, elevated Mg2+ and Ca2+ concentrations. For objective 2, LC50 was calculated based on survival/mortality for H. azteca (2.6 E-16 % dilution of parent AERO 6493 compound for fresh, 3.9 E-18 % for aged) and immobilization for D. magna (2.0E-5 %). Acute REE processing wastewater toxicity was also calculated for H. azteca (2.44%) and D. magna (23.35%). Studies conducted to determine acute toxicity of Cr (VI) to H. azteca not only lead to an improved understanding of site-specific Cr (VI) toxicity, but also may help to improve the water quality guidelines for protection of aquatic life. As for the toxicity of REE processing reagent AERO 6493, dilutions anticipating the worst possible scenario was tested to invertebrate species. Calculated LC50s and EC50s of parent AERO 6493 and wastewater will help develop a better understanding of toxicity of chemicals incorporated in REE processing, as well as potential suggestions for risk assessment and remediation steps.
Choi, So Yeon, "Potential impact of northern resource development on aquatic biota: toxicity of chromium and rare earth element processing reagent" (2019). Theses and Dissertations (Comprehensive). 2169.
Available for download on Thursday, May 28, 2020