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MTBE and TBA Degradation at the Vandenberg Air Force Base and Other Sites


A major emphasis of our lab is the study of methyl tertiary butyl ether (MTBE) biodegradation in groundwater. MTBE made up a substantial portion of reformulated gasoline and was originally added to decrease air emissions. Despite its contribution to improving air quality, MTBE became a ubiquitous groundwater contaminant in California and other states throughout the U.S. as well as in parts of Great Britain and Europe. Contamination stemmed from spills, drips and slow leaks usually from underground storage tanks at gas stations and pumping stations. MTBE is highly water soluble, has a low sorption partition coefficient, and usually degrades slowly in the field (especially under anaerobic conditions), making it a serious pollution threat to groundwater resources. Many microorganisms, both bacteria and fungi, can degrade MTBE (under both aerobic and, more slowly, anaerobic conditions), but research with pure cultures indicates that many known organisms are co-metabolizers, and/or require other growth substances, or only partially degrade MTBE, e.g. to tertiary butyl alcohol (TBA).

Jessica Hanson in our lab isolated a bacterial pure culture, dubbed Strain PM1, who can grow on MTBE as its sole carbon and energy source, converting MTBE into CO2 and new biomass, usually with no accumulation of TBA (Hansen et al. 1998). PM1 was isolated from a compost-filled biofilter treating off-gases from a POTW in Los Angeles that receives discharges from refineries (Eweis et al.). PM1 is an aerobic, flagellated, Gram negative rod, and its 16S rDNA sequence indicates it is a member of the family Comamonaceae and related to Rubrivivax and Leptothrix (the beta sub-group of the proteobacteria)

Our research on Strain PM1 has focused on understanding its physiological needs and characterization of its metabolic pathway. Research on the metabolic pathway has led to collaborations with Cindy Nakatsu at Purdue University and Mike Hyman at North Carolina State. In collaboration with Barbara Sherwood-Loller's group at U. of Toronto, we found isotopic fractionation of both C and H during MTBE biodegradation in both pure cultures of PM1 and Vandenberg microbial communities (Gray et al., 2002).


Our interest in remediation has led to a primary collaboration with Doug Mackay in the Dept of LAWR at UC Davis, as well as collaborations with researchers at the Air Force and Navy and engineers from several engineering/consulting firms. We started a major field trial of remediation of contaminated groundwater in late 1999 at Port Hueneme Naval Base. PM1 was injected into test plots along with oxygen and compared to plots receiving only oxygen. Both plots show substantial removal of MTBE initially suggesting that native organisms are as effective as PM1 at removing the chemical (also supported by results from lab microcosms) (Smith et al, in press).

At Vandenburg Air Force Base, in collaboration with Doug Mackay, we are studying the response of native microbial communities (which includes PM1! See below) to the addition of oxygen via diffusion across permeable membranes. This research is described in an Env. Sci. Technol. Paper (Wilson et al., 2002). As part of our NSF funded Microbial Observatory project, we have characterized microbial diversity along a contamination gradient at Vandenberg (Feris et al., 2004) and are investigating the response of microbial communities to a controlled ethanol and BTX release at the site.

We have collaborated in a bioaugmentation study with EPA Cincinnati where PM1 and oxygen was added to groundwater at an MTBE spill site in Ronan, Montana (Davis-Hoover et al). We were able to detect the presence of PM1 after surviving two Montana winters and MTBE removal was evident where PM1 was inoculated. We also are conducting a pilot scale study of MTBE bioremediation in LA with Tesoro and Haley and Aldrich.

Much of our research in the field focuses on the microbial underpinning of MTBE remediation, including biostimulation of native populations and bioaugmentation with PM1. Our biggest and unexpected discovery has been to find PM1-like (if not PM1 itself) organisms at many MTBE-contaminated sites in California (total of 7 so far) and at locations in Ohio and Maryland. This is unexpected because PM1 is a previously unidentified organism and not closely related to common groundwater organisms. This discovery was possible because we use very specific molecular tools for detecting PM1 DNA in the environment (16S rRNA with DGGE or real time quantitative PCR, also ITS fingerprinting). We have not found PM1 DNA at numerous other groundwater locations in Montana, Sheffield, GB and New Jersey, nor in soil samples from several locations in California. Using quantitative PCR, we can relate densities of PM1 to in situ manipulation of their environment (increasing MTBE concentration, turning oxygen on and off, adding other substrates). We are now trying to determine if PM1 presence is correlated with a potential to biodegrade MTBE if oxygen is provided.