Quantifying Reactive Trivalent Manganese in Mycogenic Oxides.

Manganese (Mn) oxides are ubiquitous in natural soil and water systems, where they may largely control contaminant dynamics. These Mn(IV) oxides are mostly considered the product of microbially catalyzed Mn(II) oxidation. Although studies suggest that fungi play an equal or greater role in Mn(II) oxidation than bacteria in certain environments, properties of fungal Mn oxides are less understood, motivating their further characterization. In particular, structural Mn(III) may play crucial roles in the redox reactions of Mn oxides. Therefore, understanding valence properties of Mn oxides is crucial to predicting chemical processes at the soil-water interface. Traditional methods to determine valence properties of Mn oxides are tedious, and subject to numerous interferences. Here, we calculated average manganese oxidation number and valence composition for three synthetic Mn oxides and six Mn oxides produced by fungi isolated in a severely contaminated environment by using X-ray absorption spectroscopy, a potentiometric titration method, and a Mn(III) extraction using pyrophosphate. Determination of the valence properties of several fungal Mn oxides may provide insights into the potential reactivity of these minerals produced by Mn(II) fungi inhabiting a severely contaminated environment. This information helps to elucidate the potential impacts of fungal Mn oxides on the chemical processes of contaminated soil and water systems.