Tetrachloroethene anaerobic dechlorination

Three anaerobic dechlorinating consortia were used to examine fractionation during dechlorination of tetrachloroethene and TCE to cii-dichloroethene (Numata et al. 2002). Fractionation factors (a) for the first reaction ranged from 0.987 to 0.991 for the three consortia, and for the second reaction were 0.9944 for all consortia. Some important limitations were pointed out (a) the chlorinated ethenes were not separated so that the isotopic... 

Henriksen et al. 1991). A comparable phenomenon is the enhanced dechlorination of tetrachloroethene in anaerobic microcosms by the addition of carboxylic acids including lactate, propionate, butyrate, and crotonate (Gibson and Sewell 1992). 

Gibson SA, GW Sewell (1992) Stimulation of reductive dechlorination of tetrachloroethene in anaerobic aquifer microcosms by addition of short-chain organic acids or alcohols. Appl Environ Microbiol 58 1392-1393. 

Considerable effort has been devoted to the anaerobic transformation of polychlorinated Cj alkanes and C2 alkenes in view of their extensive use as industrial solvents and their identification as widely distributed groundwater contaminants. Early experiments, which showed that tetrachloroethene was transformed into chloroethene (Vogel and McCarty 1985) (Figure 7.67), aroused concern though it has now been shown that complete dechlorination can be accomplished by some organisms. 

Griffin BM, JM Tiedje, FE Loftier (2004) Anaerobic microbial reductive dechlorination of tetrachloroethene to predominantly fra 5-l,2-dichloroethene. Environ Sci Technol 38 4300-4303. 

Smatlak, C. R., J. M. Gossett, and S. H. Zinder, Comparative kinetics of hydrogen utilization for reductive dechlorination of tetrachloroethene and methanogenesis in an anaerobic enrichment culture , Environ. Sci. Technol., 30, 2850-2858... 

The foregoing reactions involve reductive dechlorination or elimination, but nucleophilic displacement of chloride may also be important in some circumstances. This has been examined with dihalomethanes using FIS at concentrations that might be encountered in environments where active anaerobic sulfate reduction is taking place. The rates of reaction with FIS exceeded those for hydrolysis, and at pFI values above 7 in systems in equilibrium with elementary sulfur, the rates with polysulfide exceeded those with FIS. The principal product from dihalomethanes is the polythiomethylene FIS-(CFI2.S)nFI (Roberts et al. 1992). Two examples of the potential role of FIS" in formally reductive dechlorination are provided by (1) the formation of tet-rachloroethene from hexachloroethane in the presence of 5-hydroxy-naph-tho-l,4-quinone (Perlinger et al. 1996) and (2) the reduction of hexachloroethane by both FIS" and polysulfides (S42 ) to tetrachloroethene and pentachloroethane (Miller et al. 1998). 

DiStefano, T.D., J.M. Gossett, and S.H. Zinder. 1991. Reductive dechlorination of High concentrations of tetrachloroethene to ethene by an anaerobic enrichment culture in the absence of methanogenesis. Appl. Environ. Microbiol. 57 2287-2292. Dodson, K.S. and G.F. White. 1983. Some microbial enzymes involved in the biodegradation of sulfated surfactants pp. 90-155. In Topics in Enzyme and Fermentation Technology, Vol. 7 (Ed. A. Wiseman). Ellis-Horwood, Chichester. 

DiStefano TD, Gossett JM, Zinder SH. (1992). Hydrogen as an electron donor for dechlorination of tetrachloroethene by an anaerobic mixed culture. Applied Environmental... 

At anaerobic sites, the solvents tetrachloroethene (PCE) and trichloroethene (TCE) can undergo reductive dechlorination to less-chlorinated ethenes, a process identified as halorespiration (Holliger and Schumacher, 1994). In this process H2 is transferred to the reactant which leads to loss of one chloride ion ... 

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