Exemplary compositions, methods, and systems are disclosed that can be useful for reducing a concentration of a contaminant associated with a medium, which can be any substance or material, such as soil, water, air, and/or fluid. In one exemplary method, the medium is treated with Fe-MDGA and an oxidizing agent in amounts effective to oxidize at least a portion of the contaminant. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. This abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).