Hydrogen Isotope Fractionation during the Biodegradation of 1,2-Dichloroethane: Potential for Pathway Identification Using a Multi-element (C, Cl, and H) Isotope Approach

Even though multi-element isotope fractionation patterns provide crucial information with which to identify contaminant degradation pathways in the field, those involving hydrogen are still lacking for many halogenated groundwater contaminants and degradation pathways. This study investigates for the first time hydrogen isotope fractionation during both aerobic and anaerobic biodegradation of 1,2-dichloroethane (1,2-DCA) using five microbial cultures. Transformation-associated isotope fractionation values (ebulkH) were −115 ± 18‰ (aerobic C–H bond oxidation), −34 ± 4‰ and −38 ± 4‰ (aerobic C–Cl bond cleavage via hydrolytic dehalogenation), and −57 ± 3‰ and −77 ± 9‰ (anaerobic C–Cl bond cleavage via reductive dihaloelimination). The dual-element C–H isotope approach (ΛC–H = Δδ2H/Δδ13C ≈ ebulkH/ebulkC, where Δδ2H and Δδ13C are changes in isotope ratios during degradation) resulted in clearly different ΛC–H values: 28 ± 4 (oxidation), 0.7 ± 0.1 and 0.9 ± 0.1 (hydrolytic dehalogenation), and 1.76 ± 0.05 and 3...