Electrochemical methods for the dechlorination and detection of chilorinated ethenes

Abstract

Chlorinated ethenes in the environment are dechlorinated by accepting electrons from electron donors found in nature. Such reductive dechlorination forms the basis of this research into remediation and detection of these compounds in the environment. The reducing abilities of one of the strongest electron donors known, tetraki s(dimethylamino)ethylene (TDAE), were used to abiotically simulate reductive dechlorination. TDAE was found to form an electron donor-acceptor complex with tetrachloroethene, and to very rapidly reduce trichloroethene and cis-dichloroethene via removal of the most positive chlorine. Microbiological studies of bacteria utilising chlorinated ethenes in their metabolic systems established that Vitamin B,2 (cyanocobalamm) is of great importance to the dechlorination process, acting as a cofactor for the organism's dehalogenase enzyme. The dechlorination mechanism involves cobalt (I) as the active transition metal in extremely reducing conditions. A series of analytical experiments were undertaken to establish the reductive capability of cobalt (I), both in a simple cobalt salt and in vitamin 812, under reducing conditions. Molasses was used as a hydrogen source and an electron donor in simulation of the biotic process. Results indicate that Vitamin B12 is more successful at dechlorination than simple cobalt salts, but neither system presents an ideal method for commercial dechlorination based on current experimental process. Remediation of environmental tetra- and trichloroethene contamination would be improved by the development of on-line sensors. Glutathione, an intracellular sulfhydryl tripeptide comprising glutamyl, cysteinyl, and glycinyl, bonds with alkyl halides via the thiol group in its cysteine moeity, and displays characteristic redox behaviour, presenting an ideal prospective system for development of a relevant biosensor. Potentiometric and amperometric studies have been carried out to determine the efficacy of the proposed system; results indicate that response to and selectivity for alkyl halides at environmental concentrations can be achieved.