Effects of Organic Matter Accumulation and Acidification on Release Potential of Heavy Metals from Polluted Soils

Afforestation of degraded soils could cause soil acidification and accumulation of organic matter, which increases the risk of heavy metal leaching. In this study, the chemical forms and release potential of heavy metals in a heavy metals-contaminated soil were investigated in the laboratory following the simulated acidification and organic matter accumulation of the soil. The release potential of the metals in the soil increased with decreasing pH. The effect of pH on metal release from soil varied with types of heavy metals. The releases of Zn and Cd were very sensitive to pH, and the release increased significantly when pH decreased to 6.0. The release of Pb, Cu and Cr from the soil increased significantly when pH decreased to 5.0. The effect of organic matter accumulation on release of the metals was related to soil pH and degree of organic matter accumulation. When soil pH was over 6, low and middle accumulation of organic matter could active heavy metals in the soils, and increase release potential of the metals from the soil. When pH was below 5 or the accumulation of organic matter reached high level, the accumulation of organic matter could decrease release of the metals from the soil.