Use of Chiral Tracers to Determine Cycling of POPs in Stream Ecosystems

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CBET- 0828699Lee, Cindy M.Clemson UniversityUse of Chiral Tracers to Determine Cycling of POPs in Stream EcosystemsAlthough the manufacture and use of many persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) have been banned for decades, many US aquatic systems have fish advisories due to continuing body burdens considered dangerous to human health. Environmental scientists and engineers have proposed and investigated various hypotheses such as continuing inputs or ineffective remediation methods, yet there is still an inadequate understanding of the cycling of POPs in ecosystems, especially the role of biota. Using POPs that are chiral offers an innovative technique for the studying food webs. There are 19 chiral PCBs congeners due to restricted rotation around the biphenyl bond that makes them asymmetric. The resulting atropisomers or enantiomers have the same chemical and physical properties such as solubility and volatility but can have different reaction rates in asymmetric environments. Therefore, biotransformation can result in one enantiomer enriched over the other. The enrichment can be measured as the enantiomeric fraction (EF) by chromatography due to recent developments in technology. We propose to exploit chiral analysis of PCBs to improve understanding of their movement through food webs in a stream ecosystem. The combination of chiral, congener specific and stable isotope analyses will elucidate important questions such as the transfer from contaminated sediment to basal resources such as periphyton (biofilm) and decaying leaves, which serve as food sources for invertebrates, which in turn are prey for fish. We present preliminary data that shows the utility of chiral analysis. To test the working hypothesis that chiral analysis provides significant insight we will conduct field work in a river contaminated with polychlorinated biphenyls (PCBs) and a laboratory study over a three year period. The field study (initiated in Year 1) consists of achiral and chiral analysis of extracts from samples collected over two years (2003-2004) and the targeted collection of a comprehensive set of sediment samples. The laboratory study (initiated in Year 2) will be a controlled feeding study based on the field results.The results can be applied to other POPS which are chiral (eg. DDT, chlordane, toxaphene) as well as many pesticides and pharmaceuticals that are of emerging concern. Our understanding is largely incomplete of the various pathways for POPs as they move from contaminated sediment to fish, which are a major pathway for human exposure to POPs. Risk reduction strategies would benefit from the fundamental knowledge gained from this work. The knowledge will also advance fundamental concepts in ecology through improved understanding of complex food webs. Two graduate students will be supported by the project. They will benefit from the collaboration between Clemson University and the EPA that will expand their perspective of research opportunities. Clemson has a reputation for recruiting and retaining students from under-represented groups. Outreach will include presentations to citizen groups involved in the Superfund and NRDA processes for the study site. A middle school teacher will participate in the research through a supplement.