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Carbon and Chlorine Isotope Fractionation During Microbial Degradation of Tetra- and Trichloroethene

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journal contribution
posted on 19.02.2016, 05:52 by Charline Wiegert, Manolis Mandalakis, Tim Knowles, Paraskevi N. Polymenakou, Christoph Aeppli, Jiřina Macháčková, Henry Holmstrand, Richard P. Evershed, Richard D. Pancost, Örjan Gustafsson
Two-dimensional compound-specific isotope analysis (2D-CSIA), combining stable carbon and chlorine isotopes, holds potential for monitoring of natural attenuation of chlorinated ethenes (CEs) in contaminated soil and groundwater. However, interpretation of 2D-CSIA data sets is challenged by a shortage of experimental Cl isotope enrichment factors. Here, isotope enrichments factors for C and Cl (i.e., εC and εCl) were determined for biodegradation of tetrachloroethene (PCE) and trichloroethene (TCE) using microbial enrichment cultures from a heavily CE-contaminated aquifer. The obtained values were εC = −5.6 ± 0.7‰ (95% CI) and εCl = −2.0 ± 0.5‰ for PCE degradation and εC = −8.8 ± 0.2‰ and εCl = −3.5 ± 0.5‰ for TCE degradation. Combining the values for both εC and εCl yielded mechanism-diagnostic εClC ratios of 0.35 ± 0.11 and 0.37 ± 0.11 for the degradation of PCE and TCE, respectively. Application of the obtained εC and εCl values to a previously investigated field site gave similar estimates for the fraction of degraded contaminant as in the previous study, but with a reduced uncertainty in assessment of the natural attenuation. Furthermore, 16S rRNA gene clone library analyses were performed on three samples from the PCE degradation experiments. A species closely related to Desulfitobacterium aromaticivorans UKTL dominated the reductive dechlorination process. This study contributes to the development of 2D-CSIA as a tool for evaluating remediation strategies of CEs at contaminated sites.