Date of Award

12-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Toxicology

Advisor

Klaine, Stephen J

Committee Member

Baldwin , William S

Committee Member

Lee , Cindy M

Committee Member

Schoenfuss , Heiko L

Committee Member

Schwedler , Thomas E

Abstract

Advances in Analytical Chemistry have led to the detection of low concentrations of pharmaceuticals and personal care products (PPCPs) in wastewater treatment plant effluents as well as their receiving waters. Antidepressants are routinely found among these contaminants, but have been shown to be relatively non-toxic at environmentally measured concentrations using traditional toxicity testing techniques. The neurochemical mode of action of antidepressants warrants investigation of the effects these chemicals may have on fish behavior due to the highly conserved nature of neurotransmitter transporter targets. Using a predator prey bioassay designed in our laboratory, previous studies has shown that the antidepressant fluoxetine (Prozac®) causes significant effects on hybrid striped bass ability to capture prey. Increased time to capture prey was also correlated with decreasing brain serotonin concentrations. The goal of my dissertation was to expand our knowledge on the effects of antidepressant contaminants on the predation behavior and brain chemistry of hybrid striped bass (bass). Bass were exposed to the antidepressant fluoxetine for 27 days to determine if exposure duration has an effect on the behavioral toxicity of this chemical. We found that fluoxetine was only toxic at the same threshold found in our previous six day exposure studies and that longer term exposures did not decrease effective concentrations. Bass were exposed to the antidepressant venlafaxine (Effexor®) for six days followed by a six day recovery period at concentrations of 50, 250, and 500 µg/L. Concentrations of 250 and 500 µg/L had a significant effect on the time to capture prey 1-3 by day six while the 50 µg/L treatment only had a significant effect on bass ability to capture prey 3. Bass were able to recover their ability to capture prey 1 and 2 but time to capture prey 3 remained elevated for all treatments after six days of depuration. Venlafaxine had a significant effect on brain serotonin concentrations, which decreased in a dose dependent manner on day three and reached a basal level for all treatments on day six. Results indicated that venlafaxine may affect appetite at low concentrations and locomotor activity at high concentrations. Using the concentrations that caused a 15% decrease in brain serotonin concentrations from our previous studies with individual exposures to fluoxetine and venlafaxine, a simple mixture exposure was performed with 1 toxic unit representing 15 µg/L of fluoxetine and 25 µg/L of venlafaxine. Concentrations of 1, 2, and 4 toxic units caused a significant increase in the time to capture prey 2 and 3 by day six. Brain serotonin concentrations reached a basal level for all mixture treatments by day three and remained decreased through day six. There was a strong exponential correlation between brain serotonin concentrations and time to capture prey 1 and 2 on day six. When comparing mixture results to the results of individual antidepressant exposures, the data indicated low concentration mixtures may act in an additive manner causing increased time to capture prey and decreased brain serotonin concentrations at half the respective concentrations of each of the individual compounds. But this effect did not increase for the higher mixture exposure concentrations. Overall, the results of my dissertation indicate that antidepressants, even when present in low concentration mixtures, may present a significant risk aquatic organism behavior. Because effects on behavior can impact the fitness of an organism both directly and indirectly, it has implications for the population level. Though behavior is not typically used as an endpoint for risk assessment of aquatic contaminants, the behavioral mode of action of antidepressants and results of this study may warrant their inclusion.

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