The term in situ treatment implies that the treatment process occurs primarily in place without removing large volumes of contaminated materials. In situ chemical treatment uses chemical processes such as chemical oxidation or reduction to break down the organic contaminants into non-hazardous compounds such as carbon dioxide and water, or to change the oxidation-reduction state of metals into a benign state, such as from hexavalent chromium to trivalent chromium. In situ chemical oxidation is the process by which an oxidant is injected into the subsurface and reacts with the contaminants, producing innocuous substances such as carbon dioxide and water. Permanganate has also been traditionally used as an oxidant in wastewater treatment. Its application as an in situ chemical oxidant for environmental remediation started in the 1990s. Persulfate is a strong oxidizing agent that is capable of breaking down many common contaminants. Hydrogen peroxide is commonly associated with Fenton's reagent, which is a mixture of hydrogen peroxide and ferrous iron.