Distribution Characteristics And Ecological Risk Assessment Of Heavy Metals In Overlying Water And Surface Sediments In The Representative Lakes And Rivers In Zhenjiang City,China

Heavy metals,such as lead（Pb）,chromium（Cr）,cadmium（Cd）,zinc（Zn）,and copper（Cu）,have become one of the most serious pollutants in freshwater ecosystems due to their environmental persistence,toxic effects,and the ability of bioaccumulation in organisms and biomagnification in food webs.In recent decades,heavy metals quantity dramatically increased owing to rapidly urbanization,industrialization and agricultural developments,population exploitation and its consequently activities.Therefore,investigated the distribution characteristics of heavy metals and assessed its ecological risks would play crucial roles in the controlled heavy metals pollution in aquatic environment management.In the current study,seasonal and spatial distribution patterns of heavy metals,including lead（Pb）,chromium（Cr）,cadmium（Cd）,zinc（Zn）,and copper（Cu）,in the overlying water samples and surface sediment from the representative lake and rivers in Zhenjiang,China,were investigated and analyzed from 21 selected sampling sites,in winter and summer seasons,respectively.The single-factor（P_i）,Nemerow pollution indices（P_z）,the contamination factor（CF）,geo-accumulation index(I_geo)and potential ecological risk（E_rⁱ）were jointly used to assess the contamination,pollution degree and their ecological risk posed to freshwater ecosystem by the aforementioned elements.Multivariate analysis techniques,including Pearson’s correlation and Principal component analysis,were also used to identify potential sources of five metals in this research area.Study results showed that:（1）Study results of distribution characteristics and ecological risk assessment of heavy metals in overlying water showed that:1)the average Cd,Cr,Cu,Pb and Zn concentrations were 0.50,2.25,3.33,1.30 and 21.92μg/L in the winter samples and0.40,1.91,2.72,1.23 and 30.76μg/L in the summer samples,respectively.The concentrations of these elements were within the concentration ranges of published data on rivers or lakes in China;2)ANOVA revealed obvious spatial,not seasonal,variations in the overlying water in this research area,except for Cd and Zn;3)The single-factor and Nemerow pollution index values were below 0.7 in all sites in the winter and summer samples,indicating that the water body had not been affected by Cd,Cr,Cu,Pb and Zn yet;the water quality was relatively good and free from the influence of these pollutants;4)The correlations results indicated that the possible source of Cd,Cr,Cu and Pb was geochemical role,whereas complex original sources caused by human activities may have affected Zn concentrations for the overlying water in this research region.（2）Study results of distribution characteristics and ecological risk assessment of heavy metals in surface sediment showed that:1)the concentrations values ranged0.84-3.10 mg/kg and 0.43-3.31 mg/kg for Cd,24.85-117.3 mg/kg and 28.64-128.07mg/kg for Cu,60.86-128.85 mg/kg and 34.38-95.29 mg/kg for Cr,11.77-54.72 mg/kg and 12.28-52.13 mg/kg for Pb,29.64-218.30 mg/kg and 61.62-1310.78 mg/kg for Zn,and their mean concentrations decreased in the order of Cr?Zn?Cu?Pb?C in winter and Zn?Cu?Cr?Pb?Cd in summer,respectively;2)The CF and Igeo indicated a varying degree of heavy metals contamination in the surface sediment,especially for Cd,followed by Cr/Cu elements,indicated contamination caused by Cd was much severe as compared with the other heavy metals both in winter and summer sediments.3)Cd posted the moderate,considerable and very high ecological risks in different sites,while other elements（Cu,Cr,Pb and Zn）presented a low degree of ecological risk for each site.Furthermore,the contributions of each element to RI were:Cd?Pb?Cu?Cr?Zn in winter sediment,while Cd?Cu?Pb?Cr?Zn in summer sediment,indicated that Cd posed the main ecological risk on the research area.4)Multivariate statistical analyses results indicated Cu,Pb and Zn had similar geochemical characteristics,therefore,Pb,Cu and Zn probably originated from the same sources,while,Cd and Cr might come from different mixed sources derived from natural sources or human activities.