Spatial Distribution Characteristics And Risk Assessment Of Heavy Metals In Soils Of Typical Industrial Regions(Handan And The Pearl River Delta)

Traditional industrial production has become an important sourceof soil heavy metalpollution in China,Understanding the spatial distribution characteristics of heavy metals in the soils in typical industrial areas,and assessing the contribution of industrial operations to the accumulation of heavy metalsin soils and the impact on soil environmental quality is of great significance.Concentrations of soil heavy metals,their spatial distribution characteristics and potential ecological risk in industrial regions,including Handan of Heibei Province and the Pearl River Deltaof Guangdong Province were investigated.In this study,264 surface and 260 deep soil samples from Handan,50 surface soil samples from Qingyuan city and Guiyu town,and 20 surface soil samples from Dongguan,Zhuhai,and Zhongshan cities were analyzed.The total concentrations and chemical fraction of heavy metals in these soil samples were analyzed to evaluate their spatial distribution characteristics in these areas.In addition,correlation analysis and principal component analysis were used to analyze the possible sources of heavy metals in the soils.Finally,the pollution levels and potential ecological risk of soil heavy metals in these areas were assessed based single factor evaluation and potential ecological risk assessment.The major findings of this study are:(1)The distribution of heavy metal in the soils of Handan was uneven,the mean concentrations of Cr,Ni,Cu,Zn,As,Cd and Pb in the surface soil were 50.80,30.81,26.00,87.21,13.77,0.26 and 24.26 mg/kg respectively,while the average concentrations of these metals in deep soil were 51.15,31.64,23.40,67.10,12.72,0.17 and 26.08 mg/kg.Concentrations of Cu,Zn and Cd in the surface soils of Handan were higher than those in the deep soils,indicating exogenousinputs of Cu,Zn and Cd.The chemical fractionation of Cr,Ni,Cu,Zn,As,Cd and Pb in the surface soil was similar to that in the deep soils,34.66% and 29.26% of Cd in the surface and deep soils was presented in acid soluble fraction with strong migration and biological availability,while the reducible fraction of Pb was over 30%,suggesting Pb has potential ecological risk.(2)Cr,Ni and Asin the surface soils of Handan were mainly derived from natural sources.In contrast,Cu in the surface soils was mainly contributed by agriculturalinput while Cd and Pb in the soils originated mostly from the industrial operations.Heavy metals in the deep soils of Handan city were mainly contributed by natural sources.(3)The single factor pollution indices show that Ni,Cu,Zn,As,Cd and Pb had accumulated in the surface soils of Handan to a certain degree,and 78.03% of the surface soil samples were slightly contaminated by Cd.Potential ecological risk index of heavy metals in the surface soils decreased in the order of Cd(84.59)> As(10.59)> Cu(5.96)> Pb(5.75)> Ni(5.10)> Cr(1.49)> Zn(1.41),with Cd posing considerable potential ecological risk.Moreover,the potential ecological risk indices of Cr,Ni,Cu,Zn,As,Cd and Pb in the deep soils were 1.50,5.24,5.37,1.08,9.78,55.06 and 6.18,indicating Cd posed moderate potential ecological risk.Overall,the comprehensive ecological risk indices of the heavy metals in the surface and deep soils were 114.90 and 84.22,respectively,which were both dominated by Cd.(4)Cu,Zn and As accumulated to a certain degree in the surface soils of e-waste recycling areas in the Pearl River Delta.Concentrations of Cu,Zn and As were 33.77,141.42,20.55 mg/kg in the surface soils of Qingyuan city,and the concentration of these metals in the surface soils of Guiyu town were 17.34,127.94,6.65 mg/kg,respectively.The concentrations of Cu,Zn,Cd and Pb were 31.7,19.66,0.14,38.90 mg/kg in the surface soils of Dongguan,and 14.12,203.81,0.37,83.62 mg/kg in the surface soils of Zhuhai,and 18.78,157.28,0.23,25.44 mg/kg in Zhongshan,respectively.Cr、Ni and Zn were mainly distributed in the residual fraction,which posed almost no risk to the environment,while 63.55%,60.10%,66.50%,61.70% and 53.63% of Cd was present in the acid soluble fraction in the surface soils of Qingyuan,Guiyu,Dongguan,Zhuhai and Zhongshan,respectively.Cu and Pb were maily distributed in the non-residual fractions,indicating their ecological risk can not be ignored.(5)Statistical analysis results showed that Cu,Cd,Pb and Zn were mainly derived from human activities while As,Cr and Ni originated primarily from natural sources in the surface soils of the Pearl River Delta.No apparent spatial clustering of the sampling sites was observed,suggesting that the occurrence patterns of heavy metals in the e-waste recycling areas were similar to those in the traditional regions in the Pearl River Delta.(6)The potential ecological risk index of Cd in the surface soils of the Pearl River Delta was in the ranged of 70.53~269.91,indicating it posed low to moderate risk.The comprehensive ecological risk index of soil heavy metals in the Pearl River Delta decreased in the order of:Qingyuan(316.34)> Zhuhai(227.58)> Zhongshan(159.31)> Dongguan(123.43)> Guiyu(94.31).Overall,these results suggest that heavy metals in the surface soils posed considerable risk in Qingyuan,moderate risk in Zhuhai and Zhongshan,but low risk in Dongguan and Guiyu.