Ecological Risk Assessment And Source Identification Of Heavy Metals In Surface Sediments Of West Lake And Tiaoxi River

With the rapid development of urbanization and industrialization,a great quantity of heavy metals are discharged into the water environment.As the important containers of heavy metals,sediments are heavily polluted by heavy metals which will cause damages to ecological environment and human health if not controlled.In this study,the sediments of West Lake and Tiaoxi River were selected as the main research object,we analyzed the heavy metals(Mn,Cu,Pb,Zn,Cd,Cr,As,Co,and Ni)in the sediments on the spatial distribution,pollution characteristic,potential ecological risk based on total content and active component content and explored the differences of heavy metal pollution in West Lake and Tiaoxi River under different land use conditions.Based on the multivariate statistical methods(principal component analysis,clustering analysis,and correlation analysis)to analyze the sources of heavy metal pollution.Geo-accumulation index method and potential ecological risk assessment method are used for pollution evaluation of total amounts of heavy metals in sediments,and risk assessment code method are used to evaluate the risk of characteristics of occurrence speciations of heavy metals in sediments.The main results were given as follows:(1)The average concentrations of As,Cd,Co,Pb and Zn are higher than their corresponding background values in West Lake.The average concentrations of As,Cd,Co,Cu,Pb,Zn and Mn are higher than their corresponding background values in Tiaoxi River.In general,the content of heavy metals in the sediments of Tiaoxi River is higher than that of West Lake,espcial the concentration of As.Based on the results of multivariate statistical analyses,the reason for this phenomenon may be that there are agricultural and industrial areas in East Tiaoxi River Basin,in where As mainly originate from chemical fertilizer and arsenical pesticide,Cu,Zn,Cr,Ni,Mn,Co and Cd might originate from both natural sources and anthropogenic sources(e.g.agricultural and industrial waste water).However,the value of heavy metal Pb in West Lake sediments is higher than that in Tiaoxi River,the reason for this phenomenon may be that Pb mainly originates from the fuel consumption and exhaust emissions.West Lake is a urban lake,there are a large number of motor vehicles and diesel fuel ships,which will cause the Pb pollution.(2)A predominance proportion of Cd is presented as exchangeable fraction,which is sensitive to environmental and prone to migrate.Substantial amount of.Cu was observed as oxidizable fraction because organic particle and its superstratum have a strong affinity for copper ion so it is adsorbed by organic matter easily.A portion of Pb in reducible fraction may be due to the fact that they can be wrapped up by the associated iron manganese oxide.Substantial amount of Mn was observed as exchangeable fraction,reducible fraction and residual fraction.Mn changes rapidly in the migration,and will adapt to the environment gradually.Other heavy metals are dominated by residual fraction.(3)Based on the results of Igeo,PERI and RAC,West Lake posed a moderate ecological risk,Pb and Cd were identified as the major heavy metal pollutants in surface sediments of West Lake.Tiaoxi River posed a moderate ecological risk,As and Cd were identified as the major heavy metal pollutants in surface sediments of Tiaoxi River.Those areas presenting considerable and high ecological risks should be identified as priority regions for environmental monitoring and management.