Dual Carbon–Chlorine Stable Isotope Investigation of Sources and Fate of Chlorinated Ethenes in Contaminated Groundwater

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 δ(37)Cl determination. Both C and Cl isotopes showed evidence of ongoing PCE transformation. Applying published C isotope enrichment factors (ε(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 ε(Cl) (-7.8 to -0.8‰) and characteristic ε(Cl)/ε(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.

Pesticide fate on catchment scale: conceptual modelling of stream CSIA data

“…CSIA has been previously applied to study in situ degradation of organic groundwater contaminants (Blum et al, 2009;Elsner et al, 2012;Hunkeler et al, 2005;Schmidt and Jochmann, 2012;Wiegert et al, 2012;Zwank et al, 2005). In the context of diffuse agricultural pollution, CSIA has mainly been used to distinguish natural from anthropogenic nitrate sources and discern denitrification (Divers et al, 2014;Johannsen et al, 2008;Kellman and HillaireMarcel, 2003;Voss et al, 2006;Wexler et al, 2014).…”

Unravelling long-term source removal effects and chlorinated methanes natural attenuation processes by C and Cl stable isotopic patterns at a complex field site

“…Monitored Natural Attenuation (MNA) is an alternative cost-effective treatment, although it requires appropriate quantification and evaluation over time (Wiegert et al, 2012). There are only few MNA case studies of CT and CF in polluted sites, mainly based on the detection and quantification of by-products (Devlin and Muller, 1999;Davis et al, 2003;Puigserver et al, 2013).…”

“…To overcome these limitations, compound specific isotope analysis (CSIA) is increasingly used for source apportionment and in situ assessment of chlorinated ethenes and ethanes MNA (Wiegert et al, 2012(Wiegert et al, , 2013Kuder et al, 2013;Badin et al, 2014Badin et al, , 2016Kaown et al, 2014;Palau et al, 2014Palau et al, , 2016Audí-Miró et al, 2015). Moreover, dual isotopic studies (2D-CSIA) with carbon and chlorine isotope analyses have allowed more precise identification of pollutants' origin and fate as dual isotope slopes (Λ) reflect ongoing degradation mechanisms and can be compared with characteristic slopes from laboratory studied reactions (Hunkeler et al, 2009).…”

“…However, an aged source of contamination would have undergone fractionation processes in the unsaturated zone distinctly or not to those occurred in the saturated zone Hunkeler, 2012, 2013) and, thus, it would hamper reliable degradation processes discrimination. Therefore, if the original pure phase is not available, the study and comparison of isotope values from wells respect to the ones located in source areas (Wiegert et al, 2012) or to the known range of commercial solvents values (Holt et al, 1997;Jendrzejewski et al, 2001;Shouakar-Stash et al, 2003) is strongly advisable (Imfeld et al, 2008;Palau et al, 2014). To our knowledge, there are only few field CSIA studies dedicated to CMs.…”

Ecophysiology and environmental distribution of organohalide-respiring bacteria

“…growth substrates, transport across membranes, binding to the enzyme) that may control the stable isotope fractionation of different organohalides during OHR [31], iv) and explore the central metabolism [36], such as study the Wood-Ljungdahl pathway in Dehalococcoides mccartyi [37]. Stable isotopic analysis, and in particular the high resolution dual carbon-chlorine isotopic analysis, has been applied as a useful complementary tool to evaluate (bio)remediation of organohalide pollutants [33,34,38]. In our study, carbon isotopic signatures of cis-dichloroethene (DCE) and vinyl chloride are investigated during biostimulation of a cis-DCE-contaminated aquifer and applied as an informative line of evidence to build up a conceptual model of metabolic interactions within microbial communities.…”