Methods Study Of Sources Identification Of Pb And Other Harmful Elementsin Topsoils Around Mineralizationarea In Chenzhou,Hunan Province

With the development of regional economy,the accumulation of Pb and other harmful elements which caused by anthropogenic activity has become increasingly serious,the enrichment of harmful elements in soil caused ecological events happened frequently,serious affected the safety of food production and clean of living environment,especially near the metal,phosphorus deposit et al harmful heavy metal-rich area and coal,smelting,steel mills and other heavy metal pollution enterprises,the soil pollution is unusually severe.In these areas,except some exogenous input caused by human activities,soil harmful elements also include the part of inheriting the parent rock or enrichment in pedogenesis.There is great difference in biological effect between different sources of harmful elements in soil,so,identify the sources of harmful elements in soil is meaningful for soil remediation and safe use of land resources.Now,genesis research of the source of harmful elements in soil has become a key point in environmental geochemical research.In this paper we identify the source of Pb and other harmful elements in soil profiles from Chenzhou,Hunan by using the methods of enrichment coefficient and morphological analysis The basic idea of enrichment coefficient method is looking for reference elements which geochemical properties are similar to harmful elements.Calculate the proportion between harmful elements and reference lelments,inversion the narure content of harmful elements using this proportion,then use the actual content of harmful elements in soil profile minus the harmful elements natural source content is the artificial source harmful element content.In this research,choosing some common reference elements to identify the source of harmful elements:Ti as reference of Pb,Se as reference of Hg,Ge as reference of Cd,Sb as reference of As.The advantage of enrichment coefficient method is that it can quantify different sources of harmful elements,while the limitation lies in the different areas and soil profiles develop from different soil parent material,the type of the reference elements also different,so as to an element being study,find a suitable reference elements will not be easy.Research shows that in the process of pedogenesis,with the increase of soil maturity,active elements gradually leached into water,the stability of elements residues in soil increase.So in the absence of human activities areas,different phase ratio of Cd,Hg,Pb,As in soil profiles show regular change,the closer to soil surface,the more residual state ratio,the less ion exchange state ratio,the stability of element increase.while in intense human activity impact areas,the state proportion of elements will change when artificial source elements insert into soil.Studies show that artificial source input Cd and Pb make ion exchange state proportion of Cd and Pb increase significantly,and the residual state shows a trend of decrease;Due to As is half metal element,it can not only form simply cation and anion,but also form complex compound with oxygen,sulfur,selenium,tellurium.Therefore,when artificial source elements input into soil,As5+ can form arsenic acid radical complex anion [As O4]3-,it can leached into surface water from soil with soil solution,and also form arsenoferrite Fe3(As O4)2·8H2O,ecornwallite Cu5(As O4)2(OH)4·H2O with e3+,Cu,Pb,Zn and other heavy metal.So in the areas of artificial source input As,Fe-Mn oxide state proportion As increase,proportion of water soluble+ion exchange state decrease,residues proportion change little.Hence,using the change trendence of soil element in different phase ratio in soil profiles can effectively recognize if there is artificial source harmful elements input into soil surface.Element state proportion in soil not only associate with different sources,but also associate with soil p H?TOC?texture and other physical and chemical properties and total content of elements and so on.For example,soil p H reduce can improve the active state proportion of Cd and Pb,soil organic matters content increase can improve the proportion of organic combination of weak state of Cd,Pb,Hg,As.As a result,using the method of state ratio of harmful element to identify the sources of elements must attach importance to the various factors which affect existing forms of elements.