The available forms and bioavailability of heavy metals in soil amended with sewage sludge

Abstract

This study, taking the soil amended with sewage sludge taken from the Northern Wastewater Treatment Plant (Shenyang, China) as research object, investigated the dose鄄response effects of sewage sludge on chemical form distribution of Cd, Pb, Cu and Zn in soil. Moreover, the bioavailability of different forms of heavy metals in soil amended with sewage sludge was studied by means of Perennial Ryegrass pot experiment. The soil samples amended with sewage sludge with a sludge dosage rate of 0、9. 1% 、16. 7% 、28. 6% 、37. 5% 、44. 4% and 50% (dry weight basis) were designated as CK、S 1 、S 2 、S 3 、S 4 、S 5 、S 6 , respectively. The chelated form, acid鄄soluble form, exchangeable form and bound form in neutral condition, alkali鄄soluble form and protein鄄binding form of heavy metals in soil amended with sewage sludge were extracted with 0. 05 mol / L EDTA, 0. 1 mol / L CH 3 COOH, 0. 01 mol / L CaC1 2 , 1 mol / L CH 3 COONH 4 , 0. 05 mol / L NaHCO 3 and 0. 05 mol / L Tris鄄HCl, respectively. Results showed that the relative content of the chelated form of heavy metals in soil amended with sewage was the highest, accounting for 20. 3%-40. 0% , followed by alkali鄄soluble form and bound form in neutral of heavy metals. The contents of the exchangeable form in neutral, alkali鄄soluble form and protein鄄 binding form of heavy metals were relatively low. The accumulation of Cd, Cu and Zn in ryegrass was found to increase with