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

Abstract

Industrially important metals, such as Cu and Ni, sometimes are present at elevated concentrations in lakes, including those in the Sudbury, ON region. Although they are essential metals, their divalent-cation state (Cu2+ and Ni2+) can be toxic at high concentrations in the water. The free-ion toxicity of each of these metals has been studied in isolation, but rarely as a mixture. The economic importance of Cu2+ and Ni2+ makes them essential to study in the context of mixture toxicity. The objectives were to: (1) determine Cu and Ni mixture toxicity to Daphnia through acute LC50 tests; (2) determine the appropriate model (concentration addition, independent action, or toxic units) to analyze mixture effects; (3) determine how the toxicity modifying factor, dissolved organic carbon (DOC), influences toxic responses. These metals are transported across the membrane through different mechanisms, therefore mixture effects were hypothesized to be additive and follow an independent action (IA) model. Results indicate that Ni-Cu mixtures can be additive, synergistic or antagonistic depending on the concentration of metals. Most combinations tested produced a less-than-additive effect according to the IA model. This finding was also supported by the toxic unit approach. Single-metal acute tests revealed that the 48h LC50 for Cu was 2.43 µg/L (95% CI 2.15-2.82 µg/L) while Ni LC50 was 995 µg/L (877- 1125 µg/L). DOC was protective against Cu only and Cu+Ni mixture exposures but not Ni alone. DOC protection for mixtures varied by source composition. Clearwater Lake DOC was the most protective, Daisy Lake was intermediate, and Luther Marsh was least protective against Ni-Cu mixtures.

Convocation Year

2016

Convocation Season

Spring

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