Study On The Effects And The Mechanism Of Lime And Peat On The Availability Of Cadmium, Lead, Zinc And Copper In A Polluted Soil

The effects and the mechanism of the addition of lime, peat, lime+peat on the availability of cadmium, lead, zinc and copper in soil under both moist and water-logged conditions were studied by soil culture. The main results were as follows:1. The availability of Cd, Pb, Zn and Cu were decreased with the prolonging of submergence because of the increase of the carbonate and specific adsorbed Cd, Fe-Mn oxide-bound Cd and organic-bound Cd, Fe-Mn oxide-bound Pb, organic-bound Pb, Fe-Mn oxide-bound Zn, organic-bound Zn and residual Zn, carbonate and specific adsorbed Cu, organic-bound Cu and residual Cu, respectively.2. The addition of high amount of lime inhibited the availability of Cd, Pb, Zn and Cu under both moist and water-logged conditions. However, there were no apparent inhibitory effects on the availability of the metals when middle or low amounts of lime (<0.75g.kg-1) were added. The availability of Cd was decreased by the increase in Fe-Mn oxide-bound Cd while the availability of Pb was reduce by the increase in carbonate and specific adsorbed Pb under moist condition. Under water-logged condition, the availability of Cd was decreased mainly by the increase of Fe-Mn oxide-bound Cd.3. The availability of Cd, Pb, Zn and Cu was not apparently influenced by peat under moist condition while it was decreased under water-logged condition.4. The combined application of lime with peat further reduced the exchangeable Cd, Pb, Zn and Cu as compared with the separately application of peat. The combined application of lime with peat further decreased the exchangeable Cd, Pb, Zn and Cu during the early stage of the culture whereas further increased the exchangeable Cd, Pb, Zn and Cu during the late stage of the culture as compared with the separately application of lime. Under water-logged condition, the combined application of lime with peat generally showed better inhibitory effects on the availability of Cd, Pb, Zn and Cu than separately application of lime and peat. However, the better effects attenuated with the submergence.5. The exchangeable Cd, Pb and Zn of the moist soils were decreased with the increase in soil pH while the exchangeable Zn and Cu were reduced with the decrease in soil Eh. The increase in soil pH and the decrease in soil Eh and CEC all resulted in the decrease in the exchangeable Cd, Pd, Zn and Cu under water-logged conditions.6. Stepwise regression analysis showed that pH was the main reason for the change of the availability of Cd, Pb and Zn under moist condition .Under water-logged condition, the change of exchangeable Cd and Pb was mainly induced by the change in pH, CEC and Eh with Eh being the most important factor, the variation of exchangeable Zn was largely caused by Eh and pH while that of exchangeable Cu was mainly resulted from Eh and CEC.