Gibbs free energy of formation of halogenated aromatic compounds and their potential role as electron acceptors in anaerobic environments

The Gibbs free energies of formation of various classes of halogenated aromatic compounds were estimated with Benson's method. The data were used to evaluate the potential of these compounds to serve as electron acceptors in anaerobic environments. The results indicate that for (chloro) benzenes, benzoates, and phenols, the redox potentials of the couples Ar-X/Ar-H are in the range of 266-478 mV. This implies that microorganisms can potentially conserve energy for growth by routing electrons in the form of H2 from anaerobic environments to halogenated aromatic compounds as electron acceptors. This theoretical prediction has been corroborated for 3-chlorobenzoate. The existence of enrichment cultures, obtained from anaerobic sediments and sewage sludges, that dechlorinate other halogenated aromatic compounds suggests the existence of more microorganisms that can benefit from the use of halogenated aromatic compounds as electron acceptors.