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Open Access Thesis

Abstract

Though the use of pesticides has resulted in increased crop production and other benefits, concerns have been raised about potential adverse effects on the environment, especially the hydrologic system which supports aquatic life. To chemically analyze for all possible contaminants at all at-risk sites would not only be costly, but practically infeasible and would yield no information about biological effects. Therefore, a significant portion of the scientific community has turned their investigative focus to biomarkers as a measurement of sublethal contaminant exposure and effect. A biomarker that has been the recent focus of much research is the family of heat shock proteins (HSPs) because of their protective role in the cell against proteotoxic effects of contaminants and other stressors. To date, the heat shock response has been observed in a variety of aquatic species exposed to a multitude of xenobiotics, including heavy metals and organic compounds and pesticides. Therefore, the focus of this laboratory study was on the applicability of HSP70 as a biomarker of sublethal exposure to environmentally relevant concentrations of commonly used agricultural pesticides, using Chironomus tentans as a model. Three hypotheses were explored and tested. First was whether C. tentans would exhibit a heat shock response due to exposure to atrazine, metolachlor, glyphosate, chlorpyrifos, or terbufos at concentrations corresponding to aquatic life criteria, as well as an order of magnitude above and below the criteria. Second was whether there was any significant mortality in C. tentans exposed to these conditions. And lastly was whether any heat shock response induced would be correlated with increased mortality.

In this study, the mortalities were highly variable and did not always follow expectations with regard to increases in pesticide concentrations. The mean mortalities for larvae exposed to each of the different pesticide concentrations and controls were below 50%, except for the highest concentration of atrazine, which resulted in 57% mortality, allowing sublethal effects to be investigated. Though there appears to be a trend for increasing mortalities in the two highest concentrations of atrazine and chlorpyrifos, the only statistically significant mean mortality compared to the control resulted from the highest concentration of chlorpyrifos (0.4 mg/L), which caused a mean mortality of 49%. For the HSP70 analysis, each concentration of atrazine, chlorpyrifos, and terbufos resulted in elevated mean HSP70 band densities compared to their respective controls, but were all statistically insignificant. In addition, the HSP70 band densities corresponding to metolachlor and glyphosate exposures exhibited even less of a trend (in conjunction with a lack of trend for mortality) and were also statistically insignificant compared to their respective controls. Because there was no significant induction of HSP70, a correlation between HSP induction and mortality was unattainable. Therefore, the results of this study indicate that the acute water quality criteria for the pesticides investigated may indeed be protective for C. tentans under these conditions, but that due to high variability (biological or experimental), HSP70 may not a suitable biomarker for pesticide exposure in C. tentans.

Year of Submission

2002

Degree Name

Master of Science

Department

Department of Biology

First Advisor

Maureen E. Clayton

Second Advisor

Edward J. Brown

Third Advisor

Kavita R. Dhanwada

Comments

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Date Original

2002

Object Description

1 PDF file (73 leaves)

Language

en

File Format

application/pdf

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