The Pollution Characteristics Of Heavy Metals In Soil Around The Coal-fired Power Plant In The Hill Area Of Zhejiang Province

The coal-fired power plant(CFPP)is one of the most impotant sources of the heavy metals.The emission of the heavy metal from the CFPP can enter the soil through dry and wet deposition and do a harm to the surrounding environment.Investigating the distribution characteristics of the heavy metal around the CFPP is very meaningful.In this study,top soil and profile soils nearby the coal-fired power plant(CFPP)in Zhejiang Province was selected as research object.31 sampling spots were selected using radial sampling method and 16 of them were selected to collect profile soils.79 soil samples were collected aggregately and the concentration of Hg,Pb,Cr and Cd in them were analyzed.Geostatistics and ArcGIS were used to study the spatial distribution characteristics of contents of heavy metals(Hg,Pb,Cr,Cd)and Correlation analysis was used to analysis their influence factors and pollution sources.Single factor pollution index and Nemero index were calculated in order to evaluate heavy metal pollution in the soils.Tiesser five-step continuous extraction method was used to analysis morphological distribution characteristics of Hg,Pb,Cr,Cd.On the basis of contents of different Heavy metal forms,the bio-availability of heavy metals around the CFPP was evaluated.The main conclusions are summarized as follows:(1)The concentration of Hg,Pb,Cr,Cd in topsoil around the CFPP were 0.009～0.946 mg/kg,41.896～92.503 mg/kg,9.246～87.595 mg/kg and 0.075～0.960 mg/kg.The concentrations of Hg and Pb in soil of the study areas were higher than those of Jinhua soils.The Single factor pollution index and Nemero index of the heavy metals indicated that soil around the CFPP was slightly polluted.According to the results of Geostatistics,Cr has a strong spatial autocorrelation,while Hg,Pb and Cd showed moderate spatial autocorrelation.According to Kriging analysis,the concentration levels of Hg,Pb,Cr and Cd were different with each other,suggesting that the four heavy metals might come from different sources and human activities.Hg may be greatly influenced by the CFPP,while Pb,Cr and Cd were less affected by the CFPP.(2)The concentration of Hg,Pb,Cr,Cd in profile soil(0-80 cm)around the CFPP were 0.014～0.34 mg/kg,17.637～75.934 mg/kg,8.643～35.544 mg/kg and 0.021～0.960 mg/kg.Hg,Pb and Cd showed more apparent surface enrichment phenomenon and the content decreased with the depth of soil layer,while the content of Cr in each layer is similar with each other.There was no significant correlation between the pH and the four kinds of heavy metals in the profile soil.Hg,Pb and Cd had significant positive correlation with soil organic matter(SOM)content,while there was no significant correlation between Cr content and organic matter content.(3)The distribution of the chemical fraction of Hg in the top soil around the CFPP is:residuals>organic-bounds>Fe-Mn oxides>carbonates>exchangeable.The concentration of MeHg in the profile soil was 0.01～0.96ng/g,and the mean value was 0.19ng/g.The methylation rate of mercury was 0.021%～2.273%,which was relatively low.The content of MeHg had significant positive correlation with total Hg and SOM,which indicated that the input of Hg and the increase of SOM might contribution to the increase the content of MeHg.The distribution of the chemical fraction of Pb was:residuals>Fe-Mn oxides>organic-bounds>carbonates>exchangeable.The distribution of the chemical fraction of Cr was:residuals>organic-bounds>Fe-Mn oxides>exchangeable>carbonates.The distribution of the chemical fraction of Cd was:exchangeable>carbonates>residuals>Fe-Mn oxides>organic-bounds.There was a significant positive correlation between the total amount of heavy metals and the various chemical fraction,but the pH and the SOM had a complicated correlation with each fraction,and the correlation was not significant.(4)The potential environmental risk of different heavy metals in the surrounding soil of the CFPP is different.Hg mainly existed as the form of residue in soil,and had less harmful to the environment.Pb and Cr were mainly existed as potential biological effective fraction and residual fraction,which indicated that Pb and Crmight be harmful to the environment.Partition coefficient of the bio-available Cd was more than 50%,and partition coefficient of residue state was only 21.69%,which indicated that Cd might have a significant potential hazard.