| Tungsten resources are one of the leading industries in the economic development of Ganzhou City,which is well known in the world for its reputation as the "World Tungsten Capital".As a large number of mineral resources,extensive mining mode,to promote economic development,but also bring some environmental pollution problems,especially heavy metal pollution in soil is most prominent,which has seriously damaged the ecological balance into the soil of heavy metals,not only damage the soil structure,function,also affect the growth of vegetables,and ultimately endanger the human health through the food chain.This paper,taking farmland soil?including paddy soil,vegetable soil?and vegetables in a tungsten mining area of Gannan as the research object,analyze and evaluate the pollution situation of heavy metals in soil and vegetables,and the degree of ecological risk in soil and the degree of human health risk in vegetables,for the subsequent soil heavy metal control and repair provide a theoretical basis.The main conclusions were as follows.?1?The pH value of farmland soils were in the range of 4.5-6.5,which were in accordance with the weak acidity of red-yellow soil in southern Jiangxi.More than half of the soil organic matter?SOM?was in the range of 10-20 g·kg-1,the cation exchange capacity?CEC?was less than 20 cmol·kg-1,and the total nitrogen content was about 1 g·kg-1,which could meet the growing demand.?2?The pollution of heavy metals in farmland soil were mainly Cd and Hg,among them,Cd,Hg were 4.68 mg·kg-1,1.16 mg·kg-1 and 4.65 mg·kg-1,1.95 mg·kg-1 in paddy soils and vegetable soils,respectively,the order of heavy metal contamination were: Cd > Hg > As > Cu > Cr > Pb > Zn;the distributions of heavy metals were almost the same,except Hg,As,the distribution characteristics of each layer were: upper layer > middle layer > lower layer,which indicated that the accumulation of heavy metals in the surface layer was affected by mining in farmland.?3?The results showed that there was a significant positive correlation between Cd,Cr and Pb;Cu,Zn and As in farmland soils,and there was a similar pollution source among farmland soils,mainly by mining,Hg had other pollution source,such as Hg associated with a higher background value in rock soil.The sources of Cd and Cr;Cu and Pb,as in vegetables were similar.The accumulation of heavy metals in vegetables were inhibited by Hg in vegetables soils,while the enrichment of heavy metals in vegetables were promoted by Pb.Except CEC,there is little correlation between the physical and chemical properties of farmland soils-heavy metals,suggesting that heavy metals in farmland soils may be affected by multiple factors,weakening the impact of single physical and chemical properties on heavy metal distribution.?4?Based on the speciation analysis of heavy metals,the contents of Cd,Cr,Pb,Cu and Zn were the lowest in the acid soluble form,with the average content of about 10% and the residual state about 50%.The sum of the reducible and oxidizable states was about 40%,all the sampling points were mainly residue;The five characteristics of heavy metal elements are low-medium risk level,showing heavy metal acid soluble state has a certain environmental risk.?5?The single pollution index?SPI?showed that the pollution degree of heavy metals in farmland soil was: Cd > Hg > As > Cu > Cr > Zn > Pb,which pollution in the upper layer is remarkable,SPI of Cd,Hg were: 57.61,22.90 and 60.56,16.76 in payyd soils and vegetable soils,respectively.The results of the ground accumulation index?Igeo?and nemerow comprehensive pollution index?NCPI?were consistent with the results of single pollution index,which C-6 pollution was most serious,NCPI was 44.22>>3,Igeo were 5.26?5.34 of Cd in payyd soils and vegetable soils surface.The contribution rate of vegetables to Cr pollution was the highest,NCPI were 30.93,48.42 in leafy and rhizomes vegetables,respectivliy,and the latter had a greater risk of consumption.?6?Analysis of soil-vegetable risk characteristics in farmland,the potential ecological risk showed that the risk of Cd and Hg was the most important,the degree of risk was: Cd > Hg > As > Cu > Cr > Pb > Zn,RI values of up to 4878,6281.48 for paddy soil and vegetable soil,s howing a strong ecological risk.The health risk of edible part of vegetables showed that the THQ value of As had the greatest contribution to TTHQ,about 73.56%,72.25% of the THQ values were accounted for TTHQ of the two types of vegetables,showing a strong health risk and the risk of adult consumption was less than that of children.In a word,the soil physical and chemical properties of farmland basically meet the growing demand of crops;farmland soil heavy metal pollution was dominated by Cd and Hg;the evaluation results showed that the soil pollution was great serious in the mining area,and the potential ecological risk was very strong;the heavy metal content of vegetable was the most serious,the health risk indicated that the THQ of As contributes more than 70% to TTHQ,and children were at greater risk of eating vegetables than adults. |
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