Abstract
Chlorofluorocarbons including 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) often occur in groundwater plumes comingled with chlorinated solvents such as trichloroethene (TCE). We show that CFC-113 inhibits reductive dechlorination by Dehalococcoides mccartyi (Dhc) in a concentration-dependent manner, causing cis-1,2-dichloroethene (cis-DCE) stalls. Following a 17-day exposure of Dhc-containing consortium SDC-9 to 76 μM CFC-113, cis-DCE dechlorination activity did not recover after CFC-113 removal. River sediment microcosms demonstrated that CFC-113 was subject to microbial degradation under anoxic conditions, and chlorotrifluoroethene (CTFE) was observed as a transformation product. No degradation of CFC-113 was observed in killed controls and in incubations with reactive minerals including mackinawite, green rust, magnetite, and manganese dioxide. In vitro experiments with reduced corrinoid (i.e., vitamin B12) mediated reductive dechlorination of CFC-113 to CTFE and trifluoroethene (TFE) followed by reductive defluorination of TFE to cis-1,2-difluoroethene (cis-DFE) as an end product. This biomimetic degradation of CFC-113 to cis-DFE was also demonstrated in vivo using the corrinoid-producing homoacetogen Sporomusa ovata, suggesting the cometabolic microbial reductive dechlorination and reductive defluorination of CFC-113 to cis-DFE is feasible under anoxic in situ conditions. The CFC-113 degradation intermediates CTFE, TFE, and cis-DFE did not inhibit TCE dechlorination by Dhc, indicating that the initial reductive transformation step can overcome cis-DCE stalls.
