The fuel oxygenate methyl tert-butyl ether (MTBE) has been frequently detected in groundwater and surface water. Since contaminated sites are often subsurface, anaerobic degradation of MTBE will likely be significant for remediation. As traditional approaches to evaluate biodegradation generally involve laboratory microcosm studies which require time and resources, innovative approaches are needed to demonstrate active in situ biodegradation of MTBE. This study was conducted to gather information at the laboratory level to evaluate the potential of applying carbon isotope fractionation as an indicator for in situ biodegradation of the fuel oxygenates MTBE and tert-amyl methyl ether (TAME). In this study, MTBE utilization was observed in a methanogenic sediment microcosm after a lengthy lag period of about 400 days. MTBE utilization was sustained upon refeeding and subculturing. tert-Butyl alcohol (TBA) was found to accumulate after propagation of cultures. The MTBE-grown cultures also utilized TAME and produced tert-amyl alcohol (TAA). The detection of TBA and TAA indicated that ether bond cleavage was the initial step in degradation for both compounds. Carbon isotope fractionation during anaerobic MTBE and TAME degradation was studied, and isotopic enrichment factors (epsilon) with 95% confidence intervals of -15.6 +/-4.1% and -13.7+/-4.5% were estimated for anaerobic MTBE and TAME degradation, respectively. Addition of 2-bromoethanesulfonic acid, an inhibitor of methanogenesis, substantially prolonged the lag period before transformation, but did not influence carbon isotope fractionation. Our experiment provided strong evidence of significant carbon isotope fractionation during anaerobic MTBE and TAME degradation, demonstrating that this technique can be used as an indicator for in situ MTBE and TAME degradation.

Methyl tert-butyl ether (MTBE), an octane enhancer and a fuel oxygenate in reformulated gasoline, has received increasing public attention after it was detected as a major contaminant of water resources. Although several techniques have been developed to remediate MTBE-contaminated sites, the fate of MTBE is mainly dependent upon natural degradation processes. Compound-specific stable isotope analysis has been proposed as a tool to distinguish the loss of MTBE due to biodegradation from other physical processes. Although MTBE is highly recalcitrant, anaerobic degradation has been demonstrated under different anoxic conditions and may be an important process. To accurately assess in situ MTBE degradation through carbon isotope analysis, carbon isotope fractionation during MTBE degradation by different cultures under different electron-accepting conditions needs to be investigated. In this study, carbon isotope fractionation during MTBE degradation under sulfate-reducing and methanogenic conditions was studied in anaerobic cultures enriched from two different sediments. Significant enrichment of 13 C in residual MTBE during anaerobic biotransformation was observed under both sulfate-reducing and methanogenic conditions. The isotopic enrichment factors () estimated for each enrichment were almost identical (؊13.4‰ to ؊14.6‰; r 2 ‫؍‬ 0.89 to 0.99). A value of ؊14.4‰ ؎ 0.7‰ was obtained from regression analysis (r 2 ‫؍‬ 0.97, n ‫؍‬ 55, 95% confidence interval), when all data from our MTBE-transforming anaerobic cultures were combined. The similar magnitude of carbon isotope fractionation in all enrichments regardless of culture or electron-accepting condition suggests that the terminal electron-accepting process may not significantly affect carbon isotope fractionation during anaerobic MTBE degradation.Methyl tert-butyl ether (MTBE) has been used extensively as an octane enhancer and later as a fuel oxygenate in reformulated gasoline, as required by the Clean Air Act Amendments of 1990. The widespread use of MTBE to reduce air pollution has, however, resulted in major contamination of water resources (3,11,22,(28)(29)(30). There has been increasing interest in the development of effective technologies to remediate MTBE-contaminated sites, for instance, pump-and-treat techniques, biostimulation, and bioaugmentation (7,9,15,31,33). The full-scale implementation of these techniques is considerably costly and is currently economically applicable for only a few sites with highly sensitive receptors. Therefore, the fate of MTBE in the environment is mainly dependent upon natural remediation processes.Monitored natural attenuation is being increasingly implemented for a number of environmental pollutants. Natural processes, including dispersion, sorption, dilution, volatilization, and biodegradation, control plume migration and reduce MTBE concentration. Among these processes, biodegradation is the most effective in reducing the mass of contaminant in the environment in a sustainable way. One challenge, however, is to accur...

Methyl tert-butyl ether (MTBE) contamination is widespread in aquifers near urban areas around the world. Since this synthetic fuel oxygenate is resistant to most physical methods of treating fuel-contaminated water, biodegradation may be a useful means of remediation. Currently, information on anaerobic MTBE degradation is scarce. Depletion has been observed in soil and sediment microcosms from a variety of locations and under several redox conditions, but the responsible organisms are unknown. We are studying anaerobic consortia, enriched from contaminated sediments for MTBE-utilizing microorganisms for over a decade. MTBE degradation occurred in the presence of other fuel components and was not affected by toluene, benzene, ethanol, methanol, or gasoline. Many aryl O-methyl ethers, such as syringic acid, that are O-demethylated by acetogenic bacteria, were also O-demethylated by the MTBE-utilizing enrichment cultures. The addition of these compounds as co-substrates increased the rate of MTBE degradation, offering a potentially useful method of stimulating the MTBE degradation rate in situ. Propyl iodide caused light-reversible inhibition of MTBE degradation, suggesting that the MTBE degradation process is corrinoid dependent. The anaerobic MTBE degradation process was not directly coupled to methanogenesis or sulfidogenesis and was inhibited by the bactericidal antibiotic, rifampicin. These results suggest that MTBE degradation is mediated by acetogenic bacteria.

The anaerobic biotransformation of methyl tert‐butyl ether (MTBE), ethyl tert‐butyl ether (ETBE), and methyl tert‐amyl ether (TAME) was evaluated under different anoxic electron‐accepting conditions. Enrichments were established with a polluted estuarine sediment inoculum under conditions promoting denitrification, sulfate reduction, Fe(III) reduction, or methanogenesis. Complete loss of MTBE and TAME was observed under sulfate‐reducing conditions, concomitant with the reduction of sulfate. A stoichiometric amount of tert‐butyl alcohol and tert‐amyl alcohol accumulated indicating that O‐demethylation was the initial step in MTBE and TAME biodegradation under sulfate‐reducing conditions. No transformation of MTBE or TAME was observed under the other electron‐accepting conditions over 3 years. Under all conditions tested, there was no biotic loss of ETBE observed. MTBE and TAME were depleted upon refeeding the sulfate‐reducing cultures. This study definitely demonstrates the anaerobic biodegradability of MTBE and TAME under sulfate‐reducing conditions.