ABSTRACT
Chromium is a heavy metal that is essential for human health in its trivalent form [Cr(III)], but may cause cancer if inhaled in the hexavalent state [Cr(VI)]. Trivalent Cr is only sparingly-soluble in neutral to alkaline natural waters, but it can be oxidized to Cr(VI) by manganese (III,IV) (hydr)oxides, hydrogen peroxide, ozone, chlorine gas, hypochlorite, and other electron acceptors. Hexavalent Cr can be reduced to Cr(III) by elemental iron and iron(II), sulfides, easily-oxidized organic compounds, and other electron donors. Both oxidation and reduction reactions of chromium are governed by redox potential (Eh) and acidity of natural waters (pH).
