The kinetics of reduction and oxidation of soluble chromium in various soils (peat, clay, sand, and luvi-chromic cambisols) were studied at constant soil moisture and constant temperature. A total of 1500 g of each soil was incubated with different concentrations of aqueous solutions of K 2 Cr 2 O 7 or CrCl 3 [1-1000 µg (g of dry soil) -1 ]. The total exchangeable chromium and Cr(VI) were analyzed in soil extracts over a period of up to 10 days. The parameters influencing the reduction and oxidation of soluble chromium were studied. Reduction of soluble chromium was observed in all the soils examined. It depends mostly on the content of organic matter, on the concentration of the added chromium, and on the pH of the soil. Up to 3 days of the experiment, the reaction was found to be firstorder with respect to Cr(VI). Oxidation of soluble chromium was observed especially in soils high in manganese(IV) oxides and low in organic matter. The oxidation of added soluble chromium did not occur in peat soil. The results indicate that the oxidation and reduction of soluble chromium added to soils depends on the soil structure and on the reduction/oxidation conditions in the particular soil.

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