| Abstract
| - Equilibrium headspace analysis of toluene for δ2H isotopiccomposition by continuous flow compound specificisotope mass spectrometry was determined to have anaccuracy and reproducibility of ±5‰. Using this analyticalapproach, the hydrogen isotope fractionation producedby anaerobic biodegradation of toluene was evaluated inlaboratory experiments using a mixed methanogenicconsortium. A large, reproducible 2H-enrichment in theresidual toluene of greater than 60‰ was observed at greaterthan 95% degradation, reflecting the preferential biodegradation of molecules containing the light (1H) isotope. Recentstudies evaluating the magnitude of carbon isotopefractionation produced during biodegradation of aromatichydrocarbons have documented heavy isotope (13C)enrichment in the residual contaminant approximately anorder of magnitude smaller than those reported here for 2H.The very large isotopic enrichment in 2H suggests thatunder anaerobic conditions compound specific hydrogenisotope analysis may provide a more reliable means ofvalidating intrinsic bioremediation of aromatic hydrocarbonsthan stable carbon isotope analysis. Combined applicationof stable carbon and hydrogen isotope analysis in ananaerobic groundwater has the potential to provide twoimportant diagnostic tools. Relatively insensitive tobiodegradation by mixed consortia, stable carbon isotopevalues may provide information about different sourcesof contaminant, while hydrogen isotope values provide anassessment of the degree of attenuation due to biodegradation.
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