Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Dr. Jim McGeer

Advisor Role

Supervisor

Second Advisor

Dr. D. Scott Smith

Advisor Role

Co-Supervisor

Abstract

Rare earth elements (REEs) are increasingly being used in modern technologies and as such, there is an increasing concern for the potential environmental risk associated with anthropogenic contamination. In addition to there being very little data available for individual REEs, there is also a lack of knowledge concerning mixtures. The objective of my study was to investigate the chronic effects of lanthanum (La) and yttrium (Y) as well as the acute effects of neodymium (Nd), praseodymium (Pr) and Y as a single metal and as a mixture to Daphnia magna. Standard 21-d chronic tests and 48-h single metal acute tests following U.S. EPA and Environment and Climate Change Canada methods were conducted in an artificial soft water medium with a hardness of 50 mg CaCO3/L and a pH of 6.8 with no added bicarbonate at 21°C. Daphnia neonates (<24h old) were used with immobility (acute), growth and reproduction (chronic) as endpoints. Mixture exposures were designed using a toxic unit (TU) approach, based on converting the EC50 concentrations to toxic units and applying a matrix isobologram approach. The dissolved 48-h EC50 for Y was 0.699 mg/L (95% CI of 0.602-0.802 mg/L), for Pr it was 0.689 mg/L (95% CI of 0.530 - 0.916 mg/L), and for Nd it was 0.332 mg/L (95% CI of 0.265 - 0.408 mg/L). The total 21-d EC10 and EC20 values were 35.42 µg/L and 44.83 µg/L for La and 32.62 µg/L and 56.37 µg/L for Y. Chronic mixture tests used combinations of 0.2 (EC10) and 0.4 (EC20) TUs and acute tests used combinations of 0.2, 0.4, and 0.6 (EC30) TUs to observe whether the responses would follow an additive interaction. La and Y had similar toxicities at chronic levels and La-Y mixture tests elicited a less than additive interaction. Nd had a significantly higher toxicity than Pr or Y and the ternary mixture of Nd, Pr, and Y elicited additive and more than additive mixture interactions. This project contributes data towards the knowledge available on the toxicity of REEs individually and as a mixture in aquatic environments.

Convocation Year

2024

Convocation Season

Spring

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