Research Brief 109Superfund Basic Research ProgramQuantifying Enhanced In Situ TCE BiodegradationRelease Date: 01/07/2004 Trichloroethene (TCE) is a colorless, volatile, nonflammable liquid that is soluble in water and organic solvents. TCE is used primarily as a metal degreaser but also in products such as dyes, printing ink, and paint. Because of widespread use and poor handling, storage and disposal practices, TCE has become one of the nation's most prevalent groundwater pollutants - TCE is present at one-third to one-half of all Superfund sites. The most common method for removing TCE from groundwater is to pump the water from the aquifer and treat it above ground, which is costly and time-consuming. Researchers from the Oregon Health & Science University's SBRP are working to develop and evaluate technologies for monitoring and enhancing in-situ TCE biodegradation in anaerobic groundwater. Anaerobic TCE degradation occurs by reductive dechlorination, a reaction in which hydrogen atoms sequentially replace chlorine substituents. In the commonly observed TCE transformation pathway, TCE is sequentially reduced to dichloroethene (DCE), vinyl chloride (VC), and ethene. In situ TCE transformation rates are needed to assess the potential for intrinsic bioremediation and to design and monitor engineered bioremediation projects. Because vinyl chloride is a potent human carcinogen, it is critical to determine both the rate and extent of dechlorination. Dr. Jennifer Field leads a team of scientists using several approaches to determine the rates of TCE biodegradation. Much of their work uses a fundamentally new field method developed by the investigators, "push-pull" field tests. Push-pull tests are conducted by injecting ("pushing") an aqueous test solution containing a nonsorbing, nonreactive tracer and one or more reactants into the saturated zone of an aquifer via a monitoring well. Samples of the test solution/groundwater mixture are then extracted ("pulled") from the same well over time and analyzed for tracer, reactant and product concentrations. The researchers have used push-pull tests to evaluate strategies for determining rates of TCE biodegradation. These include:
The researchers are currently applying these techniques to evaluate strategies to enhance rates of the reductive dechlorination of TCE. They are focused on selecting and optimizing electron donors for the purpose of enhancing the rates of anaerobic TCE degradation. The researchers conducted push-pull field tests in which fumarate was added to five wells exhibiting varying reductive chlorination rates. At each location, they observed increased in situ reductive dechlorination rates and increased number of transformation products. These findings indicate that fumarate amendment has the potential to stimulate reductive dechlorination, even in aquifers where no reductive dechlorination activity has been reported previously. By finding effective methods for increasing the rate and extent of TCE biotransformation, the amount and toxicity of this groundwater contaminant can be effectively reduced, ultimately reducing the potential for human exposures. The accurate measurement and prediction of in situ rates of transformation obtainable through the application of methods developed by this research are critical to the improvement of risk assessment capabilities, the development and validation of bioremediation strategies, and determination of the potential for bioremediation of TCE-contaminated sites. For More Information Contact: Jennifer A. FieldDepartment of Environmental and Molecular Toxicology 1007 Ag and Life Science Bldg Corvallis, OR 97331-3701 Tel: 541-737-2265 Email: To learn more about this research, please refer to the following sources:
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