Abstract: A method of forming reactive oxygen species by solubilizing a metal ion from a metal oxy(hydr)oxide compound with an iron oxy(hydr)oxide solubilizing chelator to yield a first soluble metal ion chelate complex. The metal ion is transferred from the chelate complex to a free redox cycling chelator to form a second metal ion chelate complex which reduces the metal ion to a reduced metal species. The reduced metal species is reacted with an oxygen containing oxidant to yield a free redox cycling chelator and a reactive oxygen species. The reactive oxygen species may be used to oxidize a target substrate. The preferred metal ion is a cationic transition metal, such as iron or manganese. A preferred iron oxy(hydr)oxide solubilizing chelator is oxalic acid. The method is generally performed at acidic pH.