The Geochemical Characteristics Of Heavy Metal Elements In Surface Soil And Its Quality Evaluation In Typical Agricultural Region Of Deyang

Soil is not only the foundation of human survival,but also the important resource and basic elements to the development of social and economic.In recent years,because of rapid economic development and increasing population in our country,heavy metal pollution in soil should not be ignored.Heavy metal is closely related to human health,the heavy metal in soil absorbed by skin contact,inhalation,the food chain,and many kinds of ways to enter and accumulate in body,which will endanger human health.This paper which based on the geological survey projects “Cd source identification and risk assessment of heavy metal in topsoil of tyopical agricultural area,southwest region”(12120113002301)of China Geological Survey takes the typical agricultural region in Deyang as research object,has ascertained the distribution characteristics of p H,organic matter and heavy metal element content in soil.The results has been compared with report in 2003 to analyse the evolutionary quality and evaluate the soil environmental quality.The results of this study showed as follows:1?The study area soil p H is acidic and coefficient of heavy metal elements varied from big to small is: Cd>Hg>As>Zn>Pb>Ni>Cu>Cr.The bioconcentration factors of heavy metal elements in topsoil decreased as: Cd>Hg>Zn>Pb>Cu>Cr>Ni>As.Bioconcentration factors of Cd,Hg reached 4.21 and 3.80.The spatial distribution of As,Cr,Cu,Ni is similar,while Cd,Pb,Zn comes to the same.High value area of heavy metal elements content are mainly in Mianyuan town-Fuxin town,Lingjie town,Guanyu town-Shuangsheng town-Zhaojiao town,Yunxi town,Yuanshi town-Yinfeng town.2?Heavy metal elements content in Mianyuanhe River basin vertical profile is generally higher than the other two vertical profile,probably because of the influence of geological background.Due to the possibilities of phosphorus gypsum stacked in the upstream or other pollution sources.Heavy metal elements in Mianyuanhe River basin vertical profile downward migration distance is large,whose migration depth is more than 1 meter.Heavy metal elements in Mianyuanhe River-Shitingjiang River basin and Shitingjiang River basin vertical profile substantially show the surface enrichment regularity.Heavy metal elements basically stable at 35 cm or less from the surface,and significantly human impact is obvious.3?Compared with the spatial distribution of heavy metal elements in the surface soil in 2015 and 2003,it show that soil acidification is obvious.High content area of Cd,Zn,Hg,Pb,As,Cu,Ni increase,especially the Cd,while high content area of Cr reduces.Heavy metal elements content in study area is significantly higher compared with Cd and Pb in other areas,and pollution degree is relatively high.4?Combined with “Environmental quality standard for soils”(GB 15618-1995)to assess the surface soil environmental quality,the results show that Cd in the surface soil of the study area xceeded the most serious.There are 95.88% of the soil Cd exceeded;followed by 9.8% of Hg;As,Ni,Zn coms less and Cr,Cu,Pb dose not exceeded.Soil environmental quality in the study area overall shows a slight contamination and a small part of the moderate or severe pollution.The soil environment quality distribution basically matches with the distribution of Cd,which indicates that the soil environment quality most affected by Cd.The potential ecological risk assessment result shows that Cd has a high single potential ecological risk and the study area has a slight potential ecological risk level as a whole.Geo-accumulation index result shows that the overall pollution of Cd and Hg reach moderate level,and individual points contamination level reaches the extreme.