Distribution Characteristics And Risk Assessment Of Heavy Metals In The Flooded Area Of Lean River

Under the effect of Seasonal hydrological conditions, in order to clarify the influencein spatial distribution characteristics and the influence degree of heavy metal pollution forthe rice planting area, where located near the downstream of the non-ferrous metalmining area. In this paper, we focused on the downstream of Lean river as the study area,where located near the Dexing copper mine. And29sampling points were arranged in theflood plains, farming area and background region of9typical villages. The total contentsand speciation of Cu、Zn、Pb、Cd、Cr and As were analyzed and tested in soil, and presentedtheir spatial distribution characteristics; Finally on this basis, the risks of heavy metalpollution in the study area were evaluated. The main contents, methods and conclusions inthis research are as follows:(1) The total contents and speciation of each element in soil were respectivelyextracted by the mixed acid digestion method and optimized BCR sequential extractionprocedure, and the final concentration in the samples were tested by ICP-MS7700. Resultsshowed that, The average values of the total contents of Cu、Zn、Pb、Cd、Cr and As are allgreater than the local background values, which indicated that the study area has beenpolluted by heavy metal seriously. For different types of regions, the highest total contentsof each heavy metal are appeared in the floodplains, followed by the farming area and thebackground region, and the total contents of heavy metals in background area are close tothe local background values, which indicated that this region has not affected by humanactivities; For the speciation of heavy metals, the residual fraction of each element are allshowing the lowest level, and there is not distinct regularity in other fraction, whichindicated that different soil sampling points have different physical and chemicalconditions.(2) Distribution characteristics of the total contents and speciation for each elementare determined by inverse distance weighted interpolation (IDW). The research showedthat the total contents of heavy metals are mainly distributed in the middle of the study areaand Mingkou village, and low levels distributed in both ends of the region. For typicalvillages, they are mainly distributed in the floodplains. For the speciation of each element,the distribution of heavy metals among different types of laws vary greatly, with a heavymetal of different forms of distribution is also different, The area of high values are notdistributed into pieces, but concentrated in the single typical villages.(3) The sources of heavy metal pollution in the study region was studied by themethods of factor analysis and cluster analysis, and the analysis results of the3kindsof methods are consistent. Conclusions are as follows,6kinds of heavy metals have4sources of emissions, Cu and As mainly come from the Dexing copper mine; Zn and Pbmay be derived from the emission source of lead-zinc mine in Yinshan Lead Zinc Mine represented; Cr may be derived from the associated minerals of Cr or the chemicalindustry、building materials industry and the pharmaceutical factory; and Cd may bederived from the associated minerals of Cd or the cement factory、chemical industry,et al.(4) Based on the results of the analysis of the total contents in soil sampling point, andused the Nemerow index method、potential ecological hazard index (Hakanson) andgeoaccumulation index (Igeo) to evaluate the risk of heavy metals in the soil of this area.Heavy metals pollution index for each speciation was calculated by the risk assessmentcode method (RCA). From the total contents of heavy metals, evaluation results of allmethods are consistent, which showed that all the6kinds of heavy metals are exist highrisk of contamination; And for their speciation, only Cr is in the state of low-risk, andothers are in the state of medium-risk. Judging from the regional location, The spatialdistribution of the polluted risk are high in the middle of the study area and low in the othersurrounding area. For typical villages, the floodplains are in the state of high-risk, followedby the farming area and the background regions are in the state of low-risk, the spatialdistribution of total contents and the polluted risk tend to consistent.