Redox and reduction potentials as parameters to predict the degradation pathway of chlorinated benzenes in anaerobic environments

The anaerobic degradation pathway of hexachlorobenzene starts with a series of reductive dehalogeneration steps. In the present paper it was evaluated whether the dehalogenation pathway observed in microbial ecosystems could be predicted by the redox potential and/or the reduction potential (the latter determined in dimethylsulfoxide) of the various potential intermediates. It was found that these two parameters suggest different pathways. The redox potential correctly predicts the dominant pathway observed in microbial systems, while the reduction potential does not. The redox potential of the various redox couples showed no correlation with the kinetic constants for the various dechlorination steps as determined with a quantitative structure-activity relationship developed for the environmental reductive dehalogenation of chlorinated aromatic compounds, even though both approaches predicted the same pathway.