Using Compound Specific Isotope Analysis to decipher the 1,2,3-trichloropropane-to-Allyl chloride transformation by groundwater microbial communities.

1,2,3-trichloropropane (TCP), a refractory contaminant, can be reductive dehalogenated to allyl chloride (AC) by microorganisms, which has been shown a potential in situ bioremediation (ISB) strategy for TCP remediation in groundwater. In practice, however, it is hard to monitor the bioreduction extent because the TCP concentrations may also be decreased by non-biodegradation processes. Compound specific isotope analysis (CSIA) can be promising in determining the extent of degradation by quantifying the isotope enrichment factors (ε) of relevant degradation mechanisms. To date, no CSIA study has been reported on TCP degradation. In this study, a novel TCP-to-AC transformation enrichment culture (dominated by Azotobacter, Parabacteroides, Fusibacter, Hydrogenophaga, Trichococcus Desulfovibrio, etc) in the absence of the already identified TCP anaerobic reductive dechlorinating microorganisms (e.g., Dehalogenimonas) was derived from a chlorinated hydrocarbon-contaminated aquifer. A TCP degradation experiment was carried out by adding yeast extract to produce hydrogen as an electron donor. The TCP-to-AC transformation was found to conform to zero-order conversion kinetics with the rate constant 11 ± 0.34 μmol L-1 d-1 during the main biodegradation stage. The bulk carbon isotope enrichment factor (εbulk ) of the TCP-to-AC transformation was firstly evaluated as -5.2 ± 0.1‰. This study for the first time characterized the carbon isotope fractionations during TCP biodegradation using a novel enrichment culture, which would provide a promising tool for the incorporation of ISB for TCP removal in the future.