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

Abstract

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 εCl/εC 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.

Chlorine Isotope Effects from Isotope Ratio Mass Spectrometry Suggest Intramolecular C-Cl Bond Competition in Trichloroethene (TCE) Reductive Dehalogenation

“…Finally, the value of  13 C PCE / 37 Cl PCE = 3.8 ± 0.2 coincides with the range of 2.2 to 4.2 observed by Wigert et al [28] in an enrichment culture from a contaminated site (calculated from their value ε chlorine /ε carbon = 0.35 ± 0.11). The combined results give a first indication of the range of …”

“…Even though the recent introduction of chlorine isotope GC-IRMS-combined with routine carbon isotope GC-IRMS-has brought about first dual (carbon and chlorine) isotope effect investigations, these studies have, therefore, only targeted compound-average isotope effects of the reactant [27][28][29][30]. While they could delineate similarities and differences between experimental systems (different microorganisms, chemical reactants) [29] direct insight into underlying mechanisms remained elusive.…”

Identification of abiotic and biotic reductive dechlorination in a chlorinated ethene plume after thermal source remediation by means of isotopic and molecular biology tools

“…The range of laboratory determined dual C\ \Cl isotope slopes associated with various chlorinated ethene degradation processes has increased in recent years, thus enriching the database to which dual C\ \Cl isotope slopes measured in the field can be compared for process identification ( Fig. 1) (Abe et al, 2009;Audí-Miró et al, 2013;Kuder et al, 2013;Wiegert et al, 2013;Badin et al, 2014;Cretnik et al, 2014;Renpenning et al, 2014). Moreover, rapid advances in molecular biology open new possibilities for the characterization of microbial communities present in the subsurface and the assessment of their activity based on mRNA analysis.…”

Application of non-traditional stable isotopes in analytical ecogeochemistry assessed by MC ICP-MS - A critical review

“…Mass-dependent isotope fractionation was shown for cassiterite samples from Japan and China (revealing fractionation of 0.77 ‰ in 124 Sn/ 120 Sn) as well by Yamazaki et al [120].…”