Stable Isotope Probing with 13C-MTBE- and 13C-TBA-Amended Bio-Sep® Beads in Sulfate-Reducing Microcosms

Jennifer Busch-Harris and Kerry Sublette (University of Tulsa), John T. Wilson and Cherri Adair (U.S. EPA), Xiaomin Yang (BP Corporation North America), Tomasz Kuder and Paul Philip (University of Oklahoma), Greg Davis and Deborah McElroy (Microbial Insights), William E. Holmes and David Harris (University of California-Davis).

Microcosm studies have been conducted using several different anaerobic sediments from MTBE-impacted aquifers. All microcosms were amended with sulfate and Bio-Sep® beads containing one of four 13C-labeled substrates: 13C5-MTBE, 13C1-MTBE (methyoxy carbon labeled), 13C-MTBE (t-butyl group labeled) or 13C4-TBA. Pore water was sampled at 0, 2, and 4 months. After 4 months beads and sediment were harvested and analyzed for phospholipid fatty acids (PLFA) and 13C-labeling of derived fatty acid methyl esters (FAMEs) by GC-IRMS. Five out of seven sediments showed sulfate depletion and MTBE degradation with TBA accumulation. 13C labeling of PLFA was observed in 13C5-MTBE and 13C1-MTBE amended microcosms (with substantial labeling of a biomarker for sulfate reducing bacteria (SRB)) but no labeling of PLFA was observed in the 13C3-MTBE amended microcosms. 13C labeling of CH4 and CO2 was also observed in those microcosms which showed 13C labeling of PLFA. In the 13C4-TBA amended microcosms containing these same sediments, sulfate depletion was observed by a reduction in the TBA concentration. 13C labeling of PLFA and CO2 were detected. Interestingly, the SRB biomarker was not strongly labeled in the 13C4-TBA amended microcosms. Microcosms containing the remaining two sediments exhibited somewhat different behavior.  Most notably with one of these two sediments MTBE biodegradation with sulfate depletion was observed without TBA accumulation. Patterns of 13C labeling of PLFA were similar to those described above with the exception of a lack of significant labeling of the SRB biomarker. In the 13C4-TBA amended microcosms with this same sediment TBA degradation was accompanied by sulfate depletion and strong labeling of PLFA (except for the SRB biomarker) and CH4. At least two mechanisms for MTBE and TBA biodegradation under sulfate reducing conditions are indicated by this microcosm study.  Future work includes isolation of the TBA degrader(s) and isolation and analysis of 13CDNA from similar microcosms.  This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.

Abstract K-036, in: Bruce M. Sass (Conference Chair), Remediation of Chlorinated and Recalcitrant Compounds—2008.

Proceedings of the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey,CA; May 2008). ISBN 1-57477-163-9, published by Battelle, Columbus, OH, www.battelle.org/chlorcon.