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COMPOUND-SPECIFIC STABLE ISOTOPE ANALYSIS TO DEMONSTRATE IN-SITU MTBE BIOTRANSFORMATION
Citation:
Kuder, T., P. Philip, J. Allen, R. Kolhatkar, J T. Wilson*, AND J. Landmeyer. COMPOUND-SPECIFIC STABLE ISOTOPE ANALYSIS TO DEMONSTRATE IN-SITU MTBE BIOTRANSFORMATION. 7th Symposium on In-Situ and On-Site Bioremediation, Orlando, FL, 06/2-5/2003.
Description:
Changes in the stable isotopic composition of organic contaminants (isotopic fractionation) are a useful indicator of biotransformation, and have been reported in literature for several volatile organic compounds. The technique offers an interesting alternative to time-consuming microcosm experiments as a third line of evidence to demonstrate natural biodegradation at a given site. The data on MTBE presented here along with published results confirm fractionation during biodegradation of MTBE, which can be measured relatively easily in ground water samples by purge and trap-gas chromatography isotope ratio mass spectrometry (PT-GCIRMS). The sensitivities are fully satisfactory for environmental purposes (lower ppb to sub-ppb levels). The focus of this presentation is to show different pathways of isotopic fractionation at different sites. Currently, the data suggest that the extent of C and H fractionation is strikingly different among MTBE plumes (and microcosm studies). They may be broadly divided into: 1) cases where major effects are observed for both C and H (shifts of tens of per mil of d13C and dD); and 2) cases where carbon fractionation is small (not exceeding few per mil d13C), but the hydrogen effect is an order or two of magnitude more intense than carbon effect (up to over a hundred per mil of dD). The former was verified by microcosm study of anaerobic cultures collected from one field site (carbon isotopes only). The latter case is consistent with aerobic microcosm studies published by other groups. Data sets representing both situations are shown and discussed as examples for field data evaluation.