Study of Cr⁺⁶ behavior in three agricultural soils

Department of Agroenvironmental Research, IMIDRA, 28800, Alcalá de Henares, Spain

^a ana.elena.pradas@madrid.org
^b carmen.lobo@madrid.org
^c araceli.perez@madrid.org

Abstract

Chromium is a heavy metal widely used in industry. Its two most stable oxidation states are Cr⁺³ and Cr⁺⁶. Cr⁺³ is less soluble and remains adsorbed or precipitated in soils, meanwhile Cr⁺⁶ is soluble and also a high toxic specie for living organisms. In natural environments, Cr⁺³ is the most common specie, but industrial sources of Cr(VI) could cause environmental problems in soils, especially in agricultural systems. To some extent Cr⁺⁶ could be reduced to Cr⁺³ by the action of low pH and organic matter. In order to evaluate the influence of soil characteristics on bioavalability and stability of Cr⁺⁶, three different agricultural soils from Madrid region (Spain) were spiked with K₂O₂O₇ to reach a Cr+6 concentration of 250 mg·L⁻¹ and incubated at 25°C in dark. After 14, 28 and 42 days of incubation, Cr⁺³ was measured in the following fractions: 1) water soluble fraction, 2) exchangeable fraction and 3) total in soil. Most of Cr⁺³ remaining in soil was found in the water soluble or exchangeable fraction, especially in the batch of basic soil. Results from this study confirm the environmental hazard caused by chromium spills in soils as it is available to plants and could be leachated to the ground water for long time.