Pollution Status And Risk Assessment Of Heavy Metals In Agricultural Soils Of Baiyun Strict In Guiyang

In this paper,in order to investigate the pollution level with heavy metals in agricultural soils in Baiyun district in Guiyang,100 surface soil samples were collected as research object.Using the HNO3-HClO4-HF digestion method and BCR sequential extraction to analysis the concentration and fraction distribution of heavy metals in soils,determination about bioaccessibility of heavy metals using SBET extraction.According to corresponding methods in《Analytical methods of Soil Agricultural Chemistry》to analysis the physical chemistry properties,such as pH,OM,total nitrogen,phosphorus and potassium.By correlation analysis,cluster analysis and principal component analysis method to analyze the distribution and source of heavy metals in soils;Nemero comprehensive index method,potential ecological index and pollution load index method were used to evaluate the pollution level and potential ecological risk of heavy metals;Results of fraction distribution and bioavailability of heavy metals to analysize the availability of soils;Using the selected physicochemical properties to establish multivariate regression prediction model to bioavailability of heavy metals;With the total amount and bioavailability of heavy metals as the reference,using USPEA(EPA)human health risk assessment model to estimate the health risk for human body;to apply the theoretical basis for the study on soil heavy metal pollution prevention and remediation,results show that:(1)the results showed that the heavy metal content determination of 8 kinds of elements in soils of the study area,except Cd,the other elements were higher than the control sample and soil background values of Guizhou province;Compared with the second national standards,Ni,Cu and Cd were exceeded it seriously,the excessive rates were 67.19%,62.5%,35.94%,respectively;followed by As and Cr.Correlation analysis results and principal component analysis showed that heavy metals in soils have 3 sources: the first source of elements by Cu,Zn,Ni and Cr,may be derived from traffic pollution and chemical fertilizer;second by Hg,As and Pb,maybe from the dust of local coal combustion and pesticide,third pollution source is Cd,Cd and other heavy metal elements were different,may be derived from the parent rocks and other natural factors.The results of cluster analysis showed that Hg,As and Cd were a class,Cu,Ni and Pb,and Zn and Cr were of a class.There is a slight difference between the results of the principal component analysis.The specific reasons for further research need to be further studied.(2)Three evaluation results showed that,Nemero comprehensive pollution index and pollution load index evaluation results aii show that the study area mainly polluted by Cu,Pb,Hg,As,and Cu,Pb,Hg and As were in mild to moderate pollution levels,need to pay great attention to the control the pollution source of the 4 kinds heavy metals;potential ecological risk assessment results showed that Hg and Cd are the main pollution factors of farmland soil.(3)Except oxidizable percentage of Hg is relatively high,the other elements were mainly in residual form,the activity form of Hg,Cd and Pb had a high proportion,can be absorbed by plants and can participate in the chain of matter the part of the cycle,so Hg,Cd and Pb have a higher damage.The lowest proportion of active form in soil is As,and less harmful.The results of RAC assessment result show that Cd is at the the middle degree level,and has a high risk,Zn and Hg follow them,are at a low risk level,Pb,the bioavailability of Cr,As and Ni is very low,have no risk.While Hg and Pb at low or no risk level,but because of its higher proportion of active state,when pH value,temperature,oxidation-reduction potential,organic matter content and types of the migration have changed,eventually transformed into acid extractable.As a result,Hg and Pb in soils may have some potential risks.(4)The biological availability of Cd in the soil is much larger than that other elements,to Cd,Zn,As,the selected physical-chemical properties have better prediction effect for biological availability.(5)With the total concentration and biological availability of heavy metals in soil as reference,to evaluate the potential health risk of heavy metal pollution on the human body;with total amount of heavy metal for reference,the potential non carcinogenic risk for adults and children can be ignored,but the potential carcinogenic risk can not be ignored for adults and children,especially As and Cr,with reference to the amount of biological,adult and childrens’ potential non carcinogenic risk and carcinogenic risk are within the acceptable range,can be ignored.