| Abstract
| - Carbon and hydrogen isotopic fractionation duringaerobic biodegradation of MTBE by a bacterial pureculture (PM1) and a mixed consortia from Vandenberg AirForce Base (VAFB) were studied in order to assess therelative merits of stable carbon versus hydrogen isotopicanalysis as an indicator of biodegradation. Carbon isotopicenrichment in residual MTBE of up to 8.1‰ was observedat 99.7% biodegradation. Carbon fractionation wasreproducible in the PM1 and VAFB experiments, yieldingsimilar enrichment factors (ε) of −2.0‰ ± 0.1‰ to −2.4‰± 0.3‰ for replicates in the PM1 experiment and −1.5‰± 0.1‰ to −1.8‰ ± 0.1‰ for replicates in the VAFBexperiment. Hydrogen isotopic fractionation was highlyreproducible for the PM1 pure cultures, with ε values of−33‰ ± 5‰ to −37‰ ± 4‰ for replicate samples. In theVAFB microcosms, there was considerably more variabilityin ε values, with values of −29‰ ± 4‰ and −66‰ ±3‰ measured for duplicate sample bottles. Despite thisvariability, hydrogen isotopic fractionation always resultedin 2H enrichment of the residual MTBE of >80‰ at 90%biodegradation. The reproducible carbon fractionationsuggests that compound-specific carbon isotope analysismay be used to estimate the extent of biodegradationat contaminated sites. Conversely, the large hydrogenisotopic fractionation documented during biodegradationof MTBE suggests that compound-specific hydrogen isotopeanalysis offers the most conclusive means of identifying in-situ biodegradation at contaminated sites.
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