Mn oxides have the potential to affect the speciation, mobility, and ultimate fate of both metal contaminants and trace metal nutrients in environmental systems.  The surfaces of Mn-oxide phases can adsorb a wide variety of metal cations and/or catalyze oxidation/reduction reactions, thus affecting metal transport and bioavailability.  We present results from metal (Zn, Cu, As) uptake experiments performed on synthetic mineral phases (e.g., Bixbyite, Mn₂O₃), Mn-colloids (δ-MnO2), and biogenic Mn-oxides produced by the sheathed Leptothrix discophora SP-6 bacteria.  Batch experiments were conducted over a range of sorbate:sorbent ratios and pH.  The results are discussed within the context of surface complexation modeling, and complemented by redox state and binding coordination data obtained by X-ray Absorption Spectrocopy (XAS).  .