SURFACE-REACTIONS OF CHROMIUM IN SOILS AND WATERS

Chromium is a redox active metal that persists as either Cr(III) or Cr (VI) in the environment. These two oxidation states have opposing toxi cities and mobilities: Cr(III) is rather benign and immobile in soils while Cr(VI) is toxic and readily transported. Reactions influencing C r chemistry in soils and waters must be known in order to predict and understand the fate of this potentially hazardous element. Reactions a t the solid-water interface have important consequences on the bioavai lability (sorption reactions) and hazard (redox reactions) of Cr. Acco rdingly, this paper describes surface reactions that influence Cr chem istry in soils. Specifically, retention reactions of Cr(III) and Cr(VI ) are described, e.g., adsorption of Cr(III) and Cr(VI) reduction by F e(II). The influences of organic chelates on these reactions are also detailed. Direct evidence on the specific reactions of Cr at the solid -water interface are provided; techniques used in this paper to detail the reactions of Cr include X-ray absorption fine structure spectrosc opy, scanning probing microscopies, and high-resolution transmission e lectron microscopy.