Geochemical Evaluation Of Soil Environment In High Metal Background Area Of Xuanwei City,Yunnan Province

In order to promote the ecological geochemical evolution of the land quality in high background areas,whilst help the poverty alleviation in Wumeng Mountainous Areas,the key cultivated areas in Xuanwei City,Yunnan Province were studied to 1)the vertical migration of eight heavy metal elements(such as As,Cd,Cr,Cu,Hg,Ni,Pb,Zn)in the profile to study the content characteristics and spatial distribution characteristics in surface soil and the enrichment regulations of heavy metal elements from the parent soil to the surface soil;2)classification of soil environmental quality in the study area;3)and the morphological analysis and bio-enrichment characteristics of supporting crop samples are superimposed,revealing the ecological risk of soil heavy metals in the geological high background area of carbonate rocks(limestone areas).In terms of element content,the average content of eight heavy metals such as As,Cd,and Cr is significantly higher than the national soil background value,and Cd,Cr,Cu,Hg,Ni,and Zn are higher than the background values in Yunnan Province.This proves that the study area is one of the high geological background areas of soil heavy metals in China.From the perspective of element spatial distribution,the spatial distribution of the eight heavy metals is greatly affected by the geological background.The distribution of Cd,Cr,Hg,and Ni content is affected by the distribution of limestone,while the highvalue areas of As and Pb are controlled by lithological distribution and human activities.Based on vertical distribution of elements,the distribution of Cd content in different vertical profiles is consistent,and it gradually enriches from deep to surface layers.Cu is less affected by the host rock,degenerating in different regions.The distribution of As,Hg,and Zn in different sections is similar which As,Hg,and Zn contents in different profiles from the parent rock to the weathered parent material layer and then to the symbiotic soil covering it appear to decrease first and then enrich,while the differences of Cr,Ni,and Pb in different sections are obvious.Heavy metals such as As,Cd,Cr,and Cu have been contaminated in the soils where the parent material of carbonate rocks(limestones)developed in Yunnan Province.The Igeo of Cd is the highest,indicating that Cd pollution is the most serious and As,Cr,Cu follow the by Cd.The results of geochemical evaluation of land quality showed that As,Cd,Cr,and Cu are significantly enriched in the soil in which the parent material of carbonate(limestone)develops in Yunnan Province.The proportions of As,Cd,Cr,and Cu exceeding the screening risk for agricultural land pollution were 26.14%,99.16%,32.04%,and 80.29%,respectively.It is shown that the elements with high background properties such as As,Cd,Cr,Cu,etc.in the study area are the most severely polluted elements in the study area.We should strengthen research on pollution risks in high geological background areas.In the bioavailability analysis,As mainly exists in the residue state,which indicates that it shows low biological activity,but Cd has high biological activity.The proportion of the active components of Cd is equivalent to that of non-geological high background areas,accounting for 40.07%,but its biological enrichment rate is low,and the crop exceeding standard is only 2.86%.This shows that there is no significant correlation between the excess of heavy metals in corn seeds and the total amount of Cd in the soil,and monitoring of Cd needs to be strengthened to prevent similar outbreaks of cadmium pollution in the Xiangjiang River basin.