Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Shawn P. McElmurry

Abstract

Anthropogenic activities negatively impact fresh water ecosystems through toxic contaminants that are released into the environment. Copper (Cu) is a water contaminant that is fundamentally persistent once introduced into the environment that has the potential for bioaccumulation. Although Cu toxicity has been studied for decades, there is still a continuing problem with new sources and pathways. New approaches are needed to understand distribution and transport of Cu and its potential for complex biological impacts beyond the simple assessment of lethality. Several novel approaches were used in this research project to advance our understanding of Cu toxicity, including fast scan cyclic voltammetry (FSCV) and two optical bioassays. Fast scan cyclic voltammetry (FSCV) is a powerful new method for measuring electroactive species with high sensitivity and sub-second temporal resolution. The ability to mitigate Cu as an environmental pollutant is largely determined by understanding the movement and complexation of Cu ions in the aqueous state with dissolved organic matter (DOM) and other competing ions. The FSCV analytical technique was used to demonstrate that the type of DOM present influences the Cu binding capacity. In addition, the ability of another metal, aluminum (Al), to cause the release of DOM bound Cu was examined. This series of experiments addressed factors that can influence the distribution of Cu in the aquatic environment and its bioavailability using a method (FSCV) with very high temporal resolution. Daphnia magna, a microcrustacean is a model freshwater species for commonly used in ecotoxicological studies. Novel optical bioassays were used to investigate both the behavioral and physiological changes resulting from exposure to Cu or Cu-DOM complexes. The behavioral bioassay examined swimming behavior by tracking two parameters: (1) maximum accumulated distance that Daphnia travel and (2) changes in mean angle that occur over time. The physiological bioassay investigated changes to Daphnid heart rate (HR) and appendage beat rate (ABR) after Cu exposure. These optical bioassays demonstrated that the type and amount of available DOM significantly affected the toxic effects of Cu in both the behavioral and physiological assays. Cu was also shown to significantly affect negative-phototactic behavior of D. magna. FSCV was used to measure the release of neurotransmitters from Daphnia in response to light stimulation. A carbon fiber microelectrode was placed in the brain of the D. magna and neurotransmitter release was measured using two different waveforms, one for histamine (histamine-like neurotransmitters) that was less selective, and one waveform that was more selective for serotonin. Light-sensitive neurotransmitter release was detected using both waveforms. When animals were exposed to 0.1 µM Cu there was a significant reduction in the light-coupled release of serotonin observed when using the serotonin waveform. This suggests that the serotonin may be involved in the effects of Cu on negative phototactic behavior. The use of FSCV and these optical assays are capable of advancing our knowledge of Cu distribution in the environment, its bioavailability and potential for sublethal toxicity.

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