Identifying the Signature of the Natural Attenuation of MTBE in Groundwater using Molecular Methods and Bug Traps

Natural attenuation through intrinsic bioremediation is the risk-based management approach commonly used for gasoline (BTEX) contamination sites. This approach has not yet been utilized for the fuel oxygenate methyl tertiary-butyl ether (MTBE). MTBE is more resistant to biodegradation than BTEX. MTBE is more abundant than benzene in oxygenated gasoline, has a greater water solubility than BTEX, and sorbs weakly to soil. These properties complicate developing a risk based management option to be implemented as easily as for BTEX. The purpose of this project is to contribute to a growing database containing information on MTBE contaminated sites nationwide with a variety of environmental conditions. Characterizing a highly monitored MTBE biodegradation site will determine the possible microbial “signature” of the natural attenuation of MTBE. To correlate microbial community shifts with changes in MTBE product patterns, “Bug traps” consisting of Ambersorb® Bio-Sep® beads and regular Bio-Sep® beads were deployed into the polluted groundwater and into control wells at a highly monitored service station to concentrate the microorganisms for analysis. They were retrieved after 30 and 60 days of deployment. Phospholipid fatty acid and nucleic acid analysis (denaturing gradient electrophoresis (DGGE) and quantitative PCR) were used to analyze the microbial community in the groundwater. The samples from the plume showed a difference from the control samples. Gram-negative communities in the samples closest to the plume did not show a lack of limiting nutrients (i.e. carbon) as did other wells further from the plume and were in log growth phase. Also the Gram-negative community in the highest contaminated well showed the highest adaptation to the environmentally stressful conditions through decreased membrane permeability. The site showed microbial and geochemical evidence for methanogenesis, which may have been responsible for the observed degradation of MTBE and BTEX. Sulfate-reduction was also evident throughout the site and may also have been a responsible process for the observed biodegradation. Iron-reduction (Pelobacter, Geobacter) was only evident in wells within the plume and downgradient of the plume and may have played a role in degradation. In addition notable organisms that were identified in other studies of MTBE biodegradation included Methylosinus trichosporium OB3b, and environmental clones associated to the Flexibacter-Cytophaga-Bacteroides phylum associated with hydrocarbon intrinsic bioremediation. The results of this study provided evidence for anaerobic biodegradation of MTBE