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Project ID: 2003KY17B

Title: Biochemical and hormonal effects of incomplete site remediation: evaluating resident fish species

Project Type: Research

Focus Categories: Toxic Substances, Water Quality, Ecology

Keywords: polychlorinated biphenyls, endocrine disruptors, bioindicators

Start Date: 03/01/2003

End Date: 02/28/2004

Federal Funds: $6200.00

Matching Funds: $12436.00

Congressional District: Kentucky 6th


Abstract: It has become increasingly clear that many of the pollutants present in our waterbodies today exert sublethal effects with far-reaching impacts on future generations. Polychlorinated biphenyls (PCBs) are ubiquitous aquatic pollutants with significant sublethal effects in both humans and fish, including altered reproduction, hormone disruption, immunosuppression and carcinogenesis. Significant levels of environmental PCBs in Kentucky have led to the posting of fish advisories in several Kentucky waterways (Kentucky Division of Water). The focus of the present study is the Town Branch-Mud River (TB/MR) system in Southwestern Kentucky, a PCB-contaminated area currently undergoing remediation. This proposal addresses several needs identified by the Water Science and Technology Board 4, including the need to understand the impact of contaminants on higher organisms, to monitor the time course of recovery following contamination, and to evaluate the effectiveness of management efforts to improve water quality. The problem: Results of our current USGS research project (O1HQGR0133) demonstrate that remediation of the PCB-contaminated TB/MR system has not been wholly successful. We found elevated levels of the biomarker enzyme, CYP1A, in both gill and liver of trout caged in remediated sections of the TB/MR waterway. Induction of CYP1A1 occurs only in response to exposure to xenobiotic organic pollutants, such as PCBs, making it likely that biologically significant levels of these compounds are still present and bioavailable in this system, due to either incomplete remediation or new inputs. Chronic exposure to PCBs can lead to the development of PCB-resistance in vertebrates, including fish, an effect associated with suppressed CYP1A expression. Exposure to PCBs can also disrupt endocrine systems in fish, including altering levels of thyroid hormone, a hormone involved in fish growth, reproduction, and the ability to cope with environmental stress. Both chemical resistance and endocrine disruption have population-level effects. UDP-GT, a key enzyme in TH metabolism and one that is altered by PCBs, and CYP1A are both regulated through the aryl hydrocarbon receptor, suggesting there may be a common link between PCB effects on CYP1A and TH. We propose to examine whether resident fish in the TB/MR have developed resistance to PCBs and whether this resistance confers additional resistance to the hormone disrupting effects of these compounds. We hypothesize that TB/MR resident fish have developed resistance to PCBs due to chronic environmental exposure and that this resistance confers additional resistance to the hormone disrupting actions of these compounds. Our objectives are to determine 1) if resident species in the TB/MR system with unexpectedly low CYP1A levels have developed resistance to PCBs, and 2) if resistant resident species also demonstrate resistance to disruption of thyroid hormone by PCBs. Approach: We will collect resident fish from the remediated, unremediated and reference sites in the TB/MR system used in our caging studies. Initial collections at those sites indicate the presence of species known to develop resistance and those known to remain responsive when chronically exposed to PCBs 7, 57, 58. Based on their relative CYP1A levels, resident populations will be tentatively characterized as resistant or responsive and PCB challenge experiments conducted to confirm these designations. Those populations that fail to respond to PCBs as measured by CYP1A induction will be characterized as resistant. Laboratory PCB dose-response experiments will be conducted on confirmed resistant and responsive resident populations and hepatic CYP1A, UDPGT and plasma TH levels measured to evaluate possible correlations among these parameters. Significance: The current clean-up efforts in the TB/MR system provide an unparalleled opportunity to evaluate the effects of chronic chemical exposure and site remediation on local populations. The results of these studies will provide insight into the response of resident fish to present conditions in the TB/MR, specifically whether resident species have acquired chemical resistance and/or show signs of hormone disruption. Chemical resistance in fish is a recently recognized phenomenon and almost nothing is known regarding the consequences in affected populations. Because resistance has 'costs', tolerant populations may demonstrate heightened susceptibility to further stressors (e.g. site remediation), resulting in unexpected population crashes during cleanup efforts. The results of the proposed study will enable managers to make more informed decisions as to the severity and extent of pollution problems and -facilitate predictions as to the effects of acquired chemical resistance on potential population responses to remediation.

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