Speciation Analysis And Risk Assessment Of Heavy Metals In Farmland Soils Of An Uranium Mining Area

In this paper,select the farmland soils and crops in an uranium mine of Le'an County as the research object,and investigate and determine the contents of heavy metals,using the modified BCR four-step sequential extraction method to study its chemical speciation of heavy metals in farmland soils and an invention patent of our research group that the micro titration method(Patent number:CN203616300U)for microtitering the contents of uranium in soils and crops.Use the mathematical statistics and analysis methods and an improved Nemero comprehensive Pollution Index,Geoaccumulation Index,the Potential Ecological Risk Index and other evaluation methods to analyse and evaluate on the status of heavy metal pollution in farmland soils;based on the food / agriculture industry standard limit in our country,analyse the exceed situation and enrichment characteristics of heavy metals in crops;study on the current status of heavy metal pollution in farmland soils of the study area,and exactly grasp its harzards,chemical speciation,bioavailability in order to assess the risk of regional ecological environment and human health.What's more important,provide the theoretical foundation for the subsequent development of the remediation in a uranium mine,and make sure the sustainable development of the local agriculture and the healthy life of residents,which has a certain important practical significance and application value.The main conclusions are as follows:(1)The average contents of Pb,Cd,Cr,Cu,U in farmland soils of the study area are179 mg/kg,10.78 mg/kg,120 mg/kg,163 mg/kg,18.25 mg/kg,respectively,which are6.88 times,111 times,1.97 times,7.21 times,6.54 times of the national soil background values.And 5 kinds of heavy metals are accumulated in different degrees,among which the accumulation of Cd is the most significant and the most serious.In general,the pollution levels of Pb,Cd,Cr,Cu in farmland soils are that Shannan mine <Water smelter < Mine tailings dam,and the pollution level of U is that Shannan mine < Mine tailings dam < Water smelter.(2)The correlation analysis,principal component analysis,and cluster analysis showthat the contents of Cd and U in farmland soils seriously exceed the standard,in addition,and U plays a decisive role in the sources of heavy metal pollution in farmland soils of the mine.Pb,Cr and Cu have similar sources of pollution and are greatly influenced by human activities.(3)The modified BCR four-step sequential extraction method shows that the chemical speciations of Pb,Cd,Cr,Cu and U in farmland soils of the study area are mainly in residual fraction,while the sum of the weak acid extractable state,the reducible state and the oxidizable state make up the content of bio-available state,which accounts for30%~40% of the total,and is far less than the residual content in farmland soils.(4)The results of pollution assessment show that the concentrations of Cd,Cu and U in farmland soils of the three sampling areas lead to from the intensity to the moderate pollution level,and Pb and Cr lead to the slight level.Furthermore,the study area is heavily polluted.(5)Generally speaking,the contents of Pb,Cd,Cr,Cu,U of collected crops in the study area exceed the standard limit,among which Pb is the most serious,and Cr is the second,and Cd,U,Cu are slightly exceeded.Most of the crops show high enrichment characteristics for U.