اثرات باقيمانده و تجمعي لجن فاضلاب بر حركت كاديم ، روي، سرب و مس در خاك

Effect of Sewage Sludge on Accumulation and Transport of Cd, Zn, Cu and Pb

Sewage sludge is widely used as a fertilizer and soil conditioner on agricultural lands. However because of high concentration of heavy metals in sewage sludge, it increases soil heavy metals concentration. The objective of this study was to evaluate the residual and cumulative effect of sludge application on heavy metals availability. This study was conducted in Lavark experimental site with four rates (0, 25, 50 and 100 ton/ha) of sewage sludge. The plots received one, two, three or four years of sludge applications. Corn (Zea mays) and wheat (Triticum sativum) were planted in the first and second half of each year, respectively. Soil samples were collected at the end of wheat growing season at 20 cm increments to 100 cm depth from each plot. Soil samples were analyzed for pH and electrical conductivity (EC) using a saturated paste, organic carbon ,calcium carbonate and exchange capacity (CEC), extractable Cd, Pb, Cu, and Zn, and soil particle-size distribution, Chloride and bicarbonate concentrations were measured. Sewage sludge application result in heavy metals leaching^and movement down ward in the soil profile. There was a high correlation between the Cd and Zn availability and amount of organic carbon and CIʹ concentration and also between the Pb and Cu availability and amount of organic carbon in soil. It seems that the formation of Cd and Zn complexes with CI" and O.M and the formation of organic complex with Pb and Cu is the most important factors to increase the solubility and movement of these metals.