Characteristics Of Soil Phosphorus And Its Effect On Lead Immobilization

Lead (Pb) is one of the most common polluting heavy metals in soil; the immobilizationof Pb with phosphate can substantially reduce the availability and mobility of Pb in soil. Theimmobilization of lead with phosphate may be affected by the speciation and availability ofphosphorus in soil. However, information about phosphorus in soils with different fertilitiesand its effect on the immobilization of Pb with phosphorus is scarce. The properties ofphosphorus in sterile and fertile soils, the immobilization of Pb in soils with differentfertilities with phosphorus and the relation between the availability of heavy metals andphosphorus in soils with different land uses were investigated in this work. The resultsindicated that,i) The average concentration of available phosphorus in uncultivated land and farmingland soils in Zhengzhou were3.54and10.0mg.kg-1, respectively, the average pH values were8.25and8.07, respectively. The Ca-P accounted to67.0%and69.1%of the total inorganicphosphorus in these two kinds of soils. The average Ca10-P concentrations of farming landsoils were slightly lower than the uncultivated land soils, while all other forms of inorganicphosphorus were higher than those of the latter, the difference between Ca2-P and that ofCa8-P were significant (p<0.05).ii) The average Olsen-P concentrations of soils of Zhengzhou City were30.2and21.8mg.kg-1in0-10and10-20cm layers, respectively. Accumulation of available phosphorus inthe topsoil in all land uses was observed. The average concentrations of Olsen-P in differentland uses ranked bus station> commercial center>community> street>park>industrial area.Positive correlations existed between Olsen-P concentrations and DTPA-Cu and–Ni (p<0.01),while those between Olsen-P and DTPA-Pb and–Zn were not significant (p>0.05).iii) Lead (0and500mg.kg-1) was applied in a sterile (S) and a fertile (F) soil andincubated for30days, then phosphate (0and1829mg.kg-1) was added and cultivated foranother105days. The results indicated that, Olsen-P concentrations of S and F soils amendedwith both Pb and phosphorus dropped5.65%and10.3%, respectively, compared with soilsonly amended with phosphorus, the DTPA-Pb concentrations dropped25.9%and42.8%,compared with soils amended only with Pb.iv) A sterile (S) and a fertile (F) soil were spiked with Pb at0and1000mg.kg-1, afterincubation, phosphate was added at0and1220mg.kg-1and incubated. The results indicated that, for the soils amended with both Pb and phosphorus, the DTPA-Pb concentrations of Ssoil was significantly higher than that of F soil (p<0.05), while for soils only amended with Pb,the DTPA-Pb concentrations of F soil was significantly higher than that of the S soil (p<0.05).For the control, soil amended only with Pb and those amended with both phosphorus and Pb,the difference of Ca2-P concentration between S and F soils was not significant (p>0.05). Forsoils amended only with phosphorus, the Ca2-P concentration of F soil was significantlyhigher than S soil (p<0.05). The Ca8-P concentrations of all the treatments and the controlwere significantly higher than those of the S soil (p<0.05).The results suggest that, the phosphorus availability and Ca8-P concentrations of fertilesoils are higher than those of sterile soils, the availability of Cu, Ni and phosphorus in urbansoils are affected by similar factors. The availability of phosphate decreases more readily insterile soils than in fertile soils, while the immobilization of phosphate of Pb in fertile soils ismore pronounced than in sterile soils.