| 1. |
- Wiegert, Charline, 1980-, et al.
(författare)
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Carbon and Chlorine Isotope Fractionation During Microbial Degradation of Tetra- and Trichloroethene
- 2013
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:12, s. 6449-6456
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Tidskriftsartikel (refereegranskat)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., epsilon(C) and epsilon(Cl)) were determined for biodegradation of tetrachloroethene (PCE) and trichloroethene (TCE) using microbial enrichment cultures from a heavily CE-contaminated aquifer. The obtained values were epsilon(C) = -5.6 +/- 0.7 parts per thousand (95% CI) and epsilon(Cl) = -2.0 +/- 0.5 parts per thousand for PCE degradation and epsilon(C) = -8.8 +/- 0.2 parts per thousand and epsilon(Cl) = -3.5 +/- 0.5 parts per thousand for TCE degradation. Combining the values for both epsilon(C) and epsilon(Cl) yielded mechanism-diagnostic epsilon(Cl)/epsilon(C) ratios of 0.35 +/- 0.11 and 0.37 +/- 0.11 degradation of PCE and TCE, respectively. Application of the obtained epsilon(C) and epsilon(Cl) 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.
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| 2. |
- Wiegert, Charline, 1980-, et al.
(författare)
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Dual carbon chlorine stable isotope investigation of sources and fate of chlorinated ethenes in contaminated groundwater
- 2012
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 46:20, s. 10918-10925
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Tidskriftsartikel (refereegranskat)abstract
- Chlorinated ethenes (CEs) are ubiquitous groundwater contaminants, yet there remains a need for a method to efficiently monitor their in situ degradation. We report here the first field application of combined stable carbon and chlorine isotope analysis of tetrachloroethene (PCE) and trichloroethene (TCE) to investigate their biodegradation in a heavily contaminated aquifer. The two-dimensional Compound Specific Isotope Analysis (2D-CSIA) approach was facilitated by a recently developed gas chromatography-quadrupole mass spectrometry (GCqMS) method for delta Cl-37 determination. Both C and Cl isotopes showed evidence of ongoing PCE transformation. Applying published C isotope enrichment factors (epsilon(C)) enabled evaluation of the extent of in situ PCE degradation (11-78%). We interpreted C and Cl isotopes using a numerical reactive transport model along a 60-m flow path. It revealed that combined PCE and TCE mass load was dechlorinated by less than 10%, and that cis-dichloroethene was not further dechlorinated. Furthermore, the 2D-CSIA approach allowed estimation of Cl isotope enrichment factors epsilon(Cl) (-7.8 to -0.8 parts per thousand) and characteristic epsilon(Cl)/epsilon(C) values (0.42-1.12) for reductive PCE dechlorination at this field site. This investigation demonstrates the benefit of 2D-CSIA to assess in situ degradation of CEs and the applicability of Cl isotope fractionation to evaluate PCE and TCE dechlorination.
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