Isotopic and Geochemical Analysis of Microbial Processes in Uncontaminated and Contaminated Ground Water and Sediment: Innovative Application of Radiocarbon

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Aelion, MarjorieStone, PeterMCB-9975223AbstractQuantifying biodegradation of chlorinated hydrocarbons (CHCs) in the subsurface is problematic because of the recalcitrant nature of the compounds and the complexity of the degradation processes. The overall objective of this innovative field study is to investigate in situ microbial mineralization of CHCs and naturally-occurring organic carbon in the subsurface using radiocarbon (14C), and carbon and hydrogen stable isotopes (13C and deuterium (2H)) of carbon dioxide (CO2) and methane (CH4). This research will quantify, compare and evaluate tetrachloroethylene (PCE) and trichloroethylene (TCE) biodegradation in the vadose zone and groundwater from a contaminated field site and uncontaminated adjacent area, under varying redox conditions. PCE, TCE, concentrations of their metabolites, and geochemical parameters will be measured using standard techniques (gas chromatography, spectrophotometry). In addition, sediment vadose zone CO2 and CH4, and groundwater dissolved inorganic carbon and CH4 will be collected and purified cryogenically for 14C and 13C analysis by accelerator mass spectrometry (AMS) and mass spectrometry (MS). Combining isotopic monitoring of 14C, 13C and 2H of CO2 and CH4 with limited contaminant monitoring can better differentiate between biochemical processes occurring in uncontaminated and contaminted groundwater. This technique distinguishes between CO2 and CH4 produced from natural substrate biodegradation versus CHC biodegradation, and can be used under varying and low contaminant and CO2 and CH4 concentrations. Although the use of radiocarbon in environmental biodegradation studies is relatively new, it is used commonly in geological and archeological dating. Currently, indirect evidence and measurements of microbial degradation are used to estimate the contribution of naturally-occurring bacteria to contaminant removal. Radiocarbon measurements will be used in conjunction with stable carbon measurement and metabolite monitoring to improve the detection of microbial degradation of organic pollutants in groundwater. Although this research will examine microbial degradation of chlorinated solvents used in dry cleaning and industrial applications, this technique should apply to any petroleum-derived contaminant such as polycyclic aromatic hydrocarbons (PAHs), diesel and jet fuel, heating oil and trinitrotoluene (TNT), because 14C is depleted in these compounds. The proposed research will expand the use radiocarbon as an environmental tracer and lay the groundwork for the application of this technique to other biochemical contaminant studies.This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry solicitation NSF 99-9 and is being funded jointly by the Divisions of BIO and EAR.