The Anoxic Chemical Transformation of Organic Pollutants in Freshwater Wetland SedimentsEPA Grant Number: FP916354
Title: The Anoxic Chemical Transformation of Organic Pollutants in Freshwater Wetland Sediments
Investigators: Hakala, J. Alexandra
Institution: The Ohio State University
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2004 through December 31, 2007
Project Amount: $110,072
RFA: STAR Graduate Fellowships (2004) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Geology , Ecological Indicators/Assessment/Restoration
The objective of this study is to examine the abiotic, anoxic degradation of organic pollutants in freshwater wetland sediments and porewaters. The reaction kinetics and extent of degradation will depend upon the structure of the organic pollutants and the reactive properties of Fe(II) and natural organic matter (NOM) in the sediments.
Sediment cores will be collected from freshwater wetlands at Old Woman Creek National Estuarine Research Reserve, located in Huron, OH, and Bishop Creek, a U.S. Department of Agriculture site in Watkinsville, GA. Porewaters will be extracted from the sediments using a Jahnke-type core squeezer in a nitrogen atmosphere (Jahnke, 1988). In the first stage of this project, the propensity for porewater constituents to react with various nitroaromatic herbicides will be investigated. Reactions conducted anoxically will be quenched at various stages and analyzed via HPLC to monitor parent compound degradation and the generation of derivatives. In the second stage of this project, the behavior of Fe(II) in sediments will be examined in both clean systems and natural samples. Fe(II) sorption to Fe-(hydr)oxides as a function of pH will be studied in clean systems. Changes in mineral-sorbed Fe(II) oxidation state after reactions with various probe compounds will be analyzed by X-ray photoemission spectroscopy. Fe(II) interaction with isolated NOM from porewaters will be studied by adding known concentrations of Fe(II) to an isolated NOM solution, and free versus complexed Fe(II) will be determined using voltammetric methods. The coordination environment of Fe(II)-NOM complexes in solution will be studied with X-ray absorption near-edge spectroscopy in which spectra from natural porewater samples will be compared with spectra from known Fe(II)-organic compound complexes. In the third stage of this project, identification of porewater versus sediment-surface mediated processes will be assessed in situ using the 4-cyano-4-aminoazobenene (CAAB) probe compound bound to Sepharose beads and suspended in dialysis bags in the sediments (Weber, 1995). Reaction of these beads will delineate the relative importance of porewater-driven, as opposed to sediment-driven, reaction pathways.
This research will contribute vital knowledge towards understanding the abiotic reduction of nitroaromatics by NOM and Fe(II) in wetland sediments. These results may be used to assess the biogeochemical cycling of organic contaminants in freshwater wetlands and may alter how we model the fate of these substances in complex aquatic systems.