Chlorine Isotope Fractionation during Reductive Dechlorination of Chlorinated Ethenes by Anaerobic Bacteria

Abstract

Chlorine isotope fractionation during reductive dechlorination of trichloroethene (TCE) and tetrachloroethene (PCE) to cis-1,2-dichloroethene (cDCE) by anaerobic bacteria was investigated. The changes in the 37Cl/35Cl ratio observed during the one-step reaction (TCE to cDCE) can be explained by the regioselective elimination of chlorine accompanied by the Rayleigh fractionation. The fractionation factors (alpha) of the TCE dechlorination by three kinds of anaerobic cultures were approximately 0.994-0.995 at 30 degrees C. The enrichment of 37Cl in the organic chlorine during the two-step reaction (PCE to cDCE) can be explained by the random elimination of one chlorine atom in the PCE molecule followed by the regioselective elimination of one chlorine atom in the TCE molecule. The fractionation factors for the first step of the PCE dechlorination with three kinds of anaerobic cultures were estimated to be 0.987-0.991 at 30 degrees C using a mathematical model. Isotope fractionation during the first step would be the primary factor for the chlorine isotope fractionation during the PCE dechorination to cDCE. The developed models can be utilized to evaluate the fractionation factors of regioselective and multistep reactions.

Microbial Isotopic Fractionation of Perchlorate Chlorine

“…Because of the low-level chloride contamination in the basal medium associated with the use of chloride salts in the trace metal and vitamin stock solutions, chloride data were not of sufficient quality to calculate an independent estimate of ␣. However, The extent of this fractionation is much greater than for chlorine isotopic fractionation (ϽϪ2.2 ‰) previously observed during microbial reductive dechlorination of TCE and tetrachlroethene (to cis-dichloroethene) (23). Interestingly, although previous studies (13) have demonstrated that microbial fractionation of some stable isotopes, such as sulfur, is a function of the rate of microbial reduction, the results presented here indicate that the microbial fractionation of chlorine by D. suillum was constant throughout growth and show no indication of any rate-dependent effects (Fig.…”

Stable Isotope Fractionation of Tetrachloroethene during Reductive Dechlorination by Sulfurospirillum multivorans and Desulfitobacterium sp. Strain PCE-S and Abiotic Reactions with Cyanocobalamin

“…Major carbon and significant chlorine isotope fractionation has been observed during dechlorination of PCE (28). The extent of the carbon isotope effect, which points to a primary kinetic isotope effect, suggests that the rate-limiting step in the dehalogenation reaction is probably controlled by cleavage of a bond.…”

“…Apparently, the protonation reaction of the substrate is to some extent only a reaction step which controls the overall kinetics of the reaction and may occur after the electron has been transferred and the chlorine cleaved (10). This reaction scheme would explain the carbon isotope and chlorine isotope fractionation typically associated with the dehalogenation of PCE and TCE and halogenated benzenes (4,28,34). In addition to the reaction mechanism, a number of other factors such as binding of the chlorinated substrate to the catalytic centre of the enzyme or passive or active transport of the substrate across the membrane may affect carbon isotope fractionation (29,32).…”

Applications of Stable Isotopes in Hydrocarbon Exploration and Environmental Forensics

“…d 37 Cl analysis has also been used in the investigation of reductive dechlorination of chlorinated ethylenes (Sturchio et al 1998;Heraty et al 1999;Numata et al 2002) and the anaerobic degradation of PCE and TCE by testing various bacteria (Numata et al 2002). Heraty et al (1999) reported smaller chlorine isotope effects for the aerobic degradation of DCM and TCE and noted the d…”