Distinct Dual C–Cl Isotope Fractionation Patterns during Anaerobic Biodegradation of 1,2-Dichloroethane: Potential To Characterize Microbial Degradation in the Field

Abstract

This study investigates, for the first time, dual C-Cl isotope fractionation during anaerobic biodegradation of 1,2-dichloroethane (1,2-DCA) via dihaloelimination by Dehalococcoides and Dehalogenimonas-containing enrichment cultures. Isotopic fractionation of 1,2-DCA (ε and ε) for Dehalococcoides (-33.0 ± 0.4‰ and -5.1 ± 0.1‰) and Dehalogenimonas-containing microcosms (-23 ± 2‰ and -12.0 ± 0.8‰) resulted in distinctly different dual element C-Cl isotope correlations (Λ = ΔδC/ΔδCl ≈ ε/ε), 6.8 ± 0.2 and 1.89 ± 0.02, respectively. Determined isotope effects and detected products suggest that the difference on the obtained Λ values for biodihaloelimination could be associated with a different mode of concerted bond cleavage rather than two different reaction pathways (i.e., stepwise vs concerted). Λ values of 1,2-DCA were, for the first time, determined in two field sites under reducing conditions (2.1 ± 0.1 and 2.2 ± 2.9). They were similar to the one obtained for the Dehalogenimonas-containing microcosms (1.89 ± 0.02) and very different from those reported for aerobic degradation pathways in a previous laboratory study (7.6 ± 0.1 and 0.78 ± 0.03). Thus, this study illustrates the potential of a dual isotope analysis to differentiate between aerobic and anaerobic biodegradation pathways of 1,2-DCA in the field and suggests that this approach might also be used to characterize dihaloelimination of 1,2-DCA by different bacteria, which needs to be confirmed in future studies.

Triple-element compound-specific stable isotope analysis of 1,2-dichloroethane for characterization of the underlying dehalogenation reaction in two Dehalococcoides mccartyi strains

“…(ε Cl bulk = -3.8 ± 0.2 ‰) (Palau et al, 2014). A recent study (Palau et al, 2017) with a Dehalococcoidescontaining enrichment culture showed a high similarity in chlorine isotope fractionation (ε Cl bulk = -5.1 ± 0.1 ‰) to the values observed in this study for pure cultures, but contrasted with anaerobic dihaloelimination by a Dehalogenimonas-containing enrichment culture,…”

“…Different studies have targeted aerobic degradation of 1,2-DCA using carbon and chlorine isotope fractionation to investigate the predominant reaction mechanism (Table 1) (Janssen, 1985, van den Wijngaard et al, 1992, Klečka et al, 1998, Hage & Hartmans, 1999, Hunkeler & Aravena, 2000, Hirschorn et al, 2004, Palau et al, 2014, Palau et al, 2017. While carbon isotope fractionation analysis is well established for decades, only recently developed methods enable chlorine and hydrogen analysis (Shouakar-Stash et al, 2005, Nijenhuis et al, 2016.…”

“…While carbon isotope fractionation analysis is well established for decades, only recently developed methods enable chlorine and hydrogen analysis (Shouakar-Stash et al, 2005, Nijenhuis et al, 2016. A recent study of Palau et al (2017) presented two-element analysis for anaerobic dehalogenation of 1,2-DCA and highlighted differences in isotope effects between Dehalococcoides-and Dehalogenimonas-containing enrichment cultures. In comparison, thus far solely a single-element study has targeted reductive 1,2-DCA dehalogenation by Dehalococcoides spp.…”

Use of dual element isotope analysis and microcosm studies to determine the origin and potential anaerobic biodegradation of dichloromethane in two multi-contaminated aquifers

“…The reason is that contaminant concentration changes at the field are also related to processes other than its transformation (such as sorption and hydrodynamic dispersion), preventing accurate calculation of ε values. Thus, Λ values determined from laboratory studied reactions can be compared with those obtained from groundwater samples to investigate degradation processes at the field scale (Badin et al, 2014;Hermon et al, 2018;Hunkeler et al, 2009;Palau et al, 2017;Rodríguez-Fernández et al, 2018b).…”

Optimization of compound‐specific chlorine stable isotope analysis of chloroform using the Taguchi design of experiments

“…Hunkeler et al 9 and Breider et al 18 demonstrated the separation of natural from anthropogenic origins of chloroform using carbon (C)‐CSIA and chlorine (Cl)‐CSIA, respectively. Dual isotope data of C‐ and Cl‐CSIA reported by Palau et al 19 have shown a typical fractionation pattern for 1,2‐dichloroethane (1,2‐DCA) during reductive biodegradation in the field to distinguish aerobic from anaerobic conditions, and the same technique was used for pathway identification, 20 confirming CSIA as a powerful tool in environmental forensics.…”