Metal availability in contaminated soils: I. Effects of floodingand organic matter on changes in Eh, pH and solubility of Cd, Ni andZn

Soil pH and Eh play an important role in reducing heavy metal solubility in paddy soils. To assess the effects of flooding and organic matter application on changes in Eh, pH and solubility of Cd, Ni and Zn in contaminated soils, a growth chamber experiment with rice plants(Oryza sativa L.) was conducted. Eh values decreased with flooding time in all three soils. The changes of Eh values were more negative in the tannery and alum shale contaminated soils and stabilized after 30 days of submergence. The Eh changes were not so large in the city sewage contaminated soil as in the other two soils. Soil pH increased with flooding time. During the 65 days of submergence, pH increase was about 2, 1 and 0.6units in the tannery, city sewage and alum shale soils, respectively. In all three soils, organic matter treated soil showed lower Eh and higher pH values compared to untreated soil. Concentration of Cd, Ni and Zn in soil solution decreased with flooding time. The solution concentration of Cd and Zn in the city sewage soil and of Ni in the tannery soil was higher than in the alum shale soil. The soluble metal concentration in all three soils was lower inorganic matter treated soils. Reduced solubility of metals in the organic matter treated soils was related to larger changes of Eh and pH values in these soils. Correlation coefficient calculations also showed that metal solubility decreased with decreased Eh and increased pH in the soil solution. This revised version was published online in August 2006 with corrections to the Cover Date.