Carbon and chlorine isotope fractionation during Fenton-like degradation of trichloroethene

Dual isotope approach has been proposed as a viable tool for characterizing and assessing in situ contaminant transformation, however, little data is currently available on its applicability to chlorinated ethenes. This study determined carbon and chlorine isotope fractionation during Fenton-like degradation of trichloroethene (TCE). Carbon and chlorine isotope enrichment factors were εC = −2.9 ± 0.3‰ and εCl = −0.9 ± 0.1‰, respectively. An observed small secondary chlorine isotope effect (AKIECl = 1.001) was consistent with an initial transformation by adding hydroxyl radicals (OH) to CC bonds without cleavage of CCl bonds. The relative change in carbon and chlorine isotope ratios (Δ = Δδ13C/Δδ37Cl) was calculated to be 3.1 ± 0.2, approximately equal to the ratio of chlorine and carbon isotope enrichment factors (εC/εCl = 3.2). The similarity of the Δ (or εC/εCl) values between Fenton-like degradation and microbial reductive dechlorination of TCE was observed, indicating that application of solely dual isotope approach may be limited in distinguishing the two transformation pathways.