Laboratory microcosms containing subsamples of a complex environmental sediment were used to evaluate the addition of oxidized manganese as the primary electron acceptor in the presence of pentachlorophenol (PCP) as the primary electron donor. Manganese oxide (MnO2) particles were added to poisoned abiotic and non-poisoned biotic microcosms and incubated at 11°C in the presence of sediment samples that were shown capable of mineralizing PCP with indigenous microorganisms. Reduction in PCP concentration and production of reduced manganese was measured for both abiotic and biotic systems.

PCP was observed to be transformed most rapidly and to the greatest extent in non-poisoned microcosms. Rate and extent of PCP transformation were increased when MnO2 was added. Rate and extent of PCP transformation were least, but still significant, in abiotic (poisoned) microcosms when MnO2 was added. Reduction in PCP sediment concentration was consistently correlated with an increase in production of reduced manganese (Mn+2). The addition of MnO2 was therefore shown to cause a decrease in PCP concentration in a naturally occurring complex environmental sediment. Reduced iron was observed suggesting that both manganese and iron were used as primary electron acceptors. Moreover, higher concentrations of Mn+2 were found in solution than +2Fe. This may support thermodynamic evidence that manganese is preferentially used over iron in some redox reactions. Addition of synthetic MnO2 particles via a permeable reaction wall or direct slurry injection, may represent a potential treatment approach for the abiotic as well as biotic reduction of PCP in sediment and ground water environments.