Effects of organic manure on Pb speciation in soil

Four types of commercial organic manures collected from Hainan Province were used in the incubation experiment of organic manure with lead contaminated soil in order to investigate the effects of commercial organic manures on lead (Pb) speciation in high and low concentration Pb contaminated soil. Results show that the major lead fractions in the original control soil were exchangeable fraction (33.43%) and residual fraction (30.03%). The exchangeable fraction of lead in high concentration Pb contaminated soils was significantly decreased with the increasing amount of algae organic manure (HK01) and sheep-manure (DF01), while the organic matter bound lead was increased from 9.56% to 22.05%. The main lead fractions in soils contaminated at 250 mg·kg-1 Pb were exchangeable fraction (36.21%), Fe-Mn oxides bound pool (27.03%) and carbonates bound pool (23.54%).With increased contents of BT06 and BT03, the exchangeable fraction of Pb in the contaminated soil was reduced, and reduced the lowest rate (27.8%) when treated with 10% BT06. Proportions of organic bound and residual lead increased and were the highest (13.66%, 13.35%, respectively) at 20%. Exchangeable and carbonate bound fractions of Pb treated by 20% BT03 were decreased by 11.75%, 11.89%, respectively while the ratio of Fe-Mn oxides bound lead did not change significantly (P<0.05). Lead forms in soil were mainly organic bound and residual fractions at average growth rates of 8.42%, 3.03%, respectively. Available Pb in soil transformed into stable phases. Therefore, organic fertilizer had a greater effect on the remediation of contaminated soil after a long period of aging.