Potential influences of pH and organic matter on the occurrence forms of chromium in chromium-contaminated soils

Key words: 
• chromium-contaminated soil /
• chromium fractionations /
• pH value /
• organic matter

Abstract: Variations in concentrations of different occurrence forms of chromium were evaluated in three chromium-contaminated soils with different properties, and the pH and organic matter content were tested to explore their potential influence on the different valence states and different fractionations of chromium in soils using acid digestion, alkaline digestioncoprecipitation, and modified BCR. The main findings were as follows. As the pH decreased and the organic matter content increased, the concentration of hexavalent chromium decreased in general, and trivalent chromium inversely increased. However, there were significant differences among all the treatments of soil 1, while the differences among some treatments of soil 2 and soil 3 were not significant. Simultaneously, the concentration of exchangeable and acidsoluble fractionation declined opposite to oxidizable fractionation and reducible fractionation with the drop of pH and the rise of organic matter content. The findings indicated that the lower pH, especially under acidic condition, and the higher organic carbon might enhance the deoxidization process of hexavalent chromium into trivalent chromium and the transformation process of exchangeable and acidsoluble fractionation chromium into oxidizable and reducible fractionations chromium.