| Lead-zinc ore has made significant contributions to China’s industrial growth as a valuable metal resource.The tailing slag from lead-zinc mining and smelting,on the other hand,is deposited at random.The heavy metals in tailing slag can damage the surrounding soil and enter crops through the plant roots,posing a health risk to humans.This study explored the pollution effects of tailing ponds on the surrounding environment by analyzing the soil-crop heavy metal content and soil heavy metal morphological characteristics around the tailing ponds,as well as analyzing the migration and transformation characteristics of an essential lead-zinc deposit output area-the Duyun Niujiaotang Pb-Zn tailings concentration area in the Qiannan region of Guizhou Province.The potential ecological risk index method,the ground accumulation index method,and the risk assessment code method were used to evaluate the risk from the total amount and morphology of the soil in its entirety,and the integrated quality index was used to evaluate the integrated quality of the soil-rice system and analyze the synergistic contamination risk of the soil-crop system.This paper elucidates the heavy metal pollution characteristics and environmental and ecological risks of the environment around the lead-zinc tailings concentration area,and provides data reference and theoretical support for future local soil heavy metal pollution remediation.The following findings were obtained after summarizing the entire paper:(1)The average concentration of soil heavy metals Zn,Pb,As,Cd,Ni and Cr in the study area exceeded the background values of soil in Guizhou Province,and the degree of contamination of rice soil in agricultural land was higher than that of vegetable land.The average concentration of Zn,Pb,As and Cd exceeded the screening values of soil heavy metal risks,and the areas with high concentration of heavy metals were all found near tailing ponds.Soil heavy metal morphology is dominated by residue state except for Cd in weak acid extracted state.The results of correlation and principal component analysis show that the first principal component of soil(Pb-As-Ni-Cr)is mainly influenced by soil-forming parent material.The second principal component(Zn-Cd)is mainly influenced by mining,smelting,transportation,and other mining influences.(2)The content of all 6 heavy metal elements in the soil around the tailings was negatively correlated with the distance from the tailings pond,with the greatest decrease in Zn and Pb.The concentration of heavy metals in agricultural land was significantly higher than that in forest land.Except for Ni and Cr,the concentration of the other 4 heavy metals exceeded the background value in Guizhou Province.The percentage of weak acid extraction state of Zn,Pb and Cd in agricultural land was higher than that in forest land,and these 3 heavy metals were more migratory and biologically effective in agricultural land.The crops in the study area were seriously contaminated with heavy metals,among which the average concentration of Zn,Pb,As,Cd,Ni and Cr in rice,leafy vegetables and non-leafy vegetables were significantly higher than the national standard limit values.The order of enrichment capacity of edible parts of crops for different heavy metals is: Cd > Pb > As > Zn > Cr > Ni.The order of enrichment capacity exhibited by the edible fraction of different crops was leafy rice> vegetables > non-leafy vegetables.Heavy metals Pb in crop and Zn in soil showed synergistic effects;heavy metals Zn,As and Cr in soil were significantly and positively correlated with as in crop,which would promote the uptake of As in crop;Cd in crop and Cd in soil had a highly significant positive correlation.The results of multiple linear regression were basically consistent with the correlation analysis.(3)The results of potential ecological risk evaluation showed that the single potential ecological risks of six heavy metals were ranked as follows: Cd > Pb > As > Zn > Ni > Cr.The combined potential ecological risk results show that the vast majority of sample sites are at very strong and extreme risk levels,and Cd is the cause of serious potential ecological risk.The results of the ground accumulation index evaluation method showed that the soils in the whole study area were significantly contaminated with Zn,Pb,As and Cd.The risk assessment code method resulted in the highest risk for the soil heavy metal Cd in the study area,and the RAC values for both Zn and Pb were at moderate risk levels,with Pb at a slightly higher risk level than Zn.The soil comprehensive quality impact index is much higher than the crop comprehensive impact index,indicating that the comprehensive quality impact index is mainly affected by the soil comprehensive quality impact index.In the soil crop system,the soil has been seriously polluted by heavy metals.The pollution degree of different kinds of crops is leafy vegetables > non leafy vegetables > rice.The iicq values in the study area are all greater than 5,and the high value areas appear around the tailings of Xinqiao,shuanglongquan and caiyuanhe,indicating that these tailings ponds cause extremely serious heavy metal pollution to the surrounding soil crop system.Although it is a low value area near the residential area,the iicq value is still greater than 5,which is a heavily polluted area. |
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