Oxidation‐reduction chemistry of chromium: Relevance to the regulation and remediation of chromate‐contaminated soils

Developing health‐protective clean‐up standards and remediation strategies for chromium‐contaminated soils based on the hexavalent forms of this heavy metal is a complex and controversial issue, because certain forms of Cr(III) can oxidize to Cr(VI) and Cr(VI) can be reduced to Cr(III) under diverse soil conditions. The extent of oxidation of Cr(III) in soils amended with wastes is based on four interacting parameters: (1) solubility and form of Cr(III) related to oxidation (waste oxidation potential, or WOP), (2) reactive soil Mn(III,IV) (hydr)oxide levels (soil oxidation potential for Cr(III), or SOP), (3) soil potential for Cr(VI) reduction (soil reduction potential, or SRP), and (4) soil‐waste pH as a modifier of the first three parameters (pH modification value, or PMV). Each of these four parameters can be quantified with laboratory tests and ranked numerically; the sum of which is the Potential Chromium Oxidation Score (PCOS) for assessing the relative hazard of a waste‐soil combination. The PCOS v...