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.
Highlights
Chromium is a metallic element that exists primarily in the mineral chromite with is presents in soils, waters, rocks, fauna and gases
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 25oC in dark
The soil which shown the highest pH (Encín), presented the highest Cr+6 concentrations in the three fractions. This fact indicates that the reduction to Cr+3 process is lesser than in soils from Escorial and Talamanca, both with pH
Summary
Chromium is a metallic element that exists primarily in the mineral chromite with is presents in soils, waters, rocks, fauna and gases. It can exit in several chemical forms between 0 and 6, but Cr+3 and Cr+6 are the most stable forms. Cr+3 occurs as a cation which could be adsorbed to the negatively charged particles of soils, especially in the smallest fraction. It could precipitate as insoluble oxide and hydroxide compounds. The presence of each chemical form is mainly affected by pH and redox potential. In contrast under alkaline conditions (pH 7-10) the redox potential decreases rendering in Cr+6 stabilization
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