渝西北土壤重金属分布特征及其风险评价

Distribution Characteristics and Risk Assessment of Soil Heavy Metals in Northwest Chongqing

为全面了解重庆西北地区(潼南区、铜梁区、合川区和大足区)土壤中重金属质量分数、分布特征及其生态风险,在该区共采集表层土壤样品6 792件,测定了As,Cd,Cr,Cu,Hg,Ni,Pb和Zn等8种重金属元素质量分数,并用土壤环境质量标准(GB15618-1995)和潜在生态风险指数对土壤重金属污染进行评价.结果表明:1)表层土壤Cd质量分数累积效应最大,是背景值的2.43倍,超标比例为18.67%,其余7种重金属元素质量分数平均值低于土壤环境质量一级标准值;2)空间分布特征表明,Zn,Cd,Pb,As,Ni,Cu和Cr 7种元素在研究区西部质量分数较高,Hg在东部质量分数较高,主要受地层控制和土地利用方式的影响;3)研究区重金属污染对该区构成的潜在生态危害由强至弱依次为:Cd,Hg,As,Pb,Cu,Ni,Cr,Zn,整体处于中等潜在生态风险等级,主要受Cd和Hg元素的影响,二者可能造成的生态危害应引起重视.

In order to have a detailed knowledge of the mass fraction,distribution and ecological risk of heavy metals in the soils of northwest Chongqing,6 792 soil samples were collected from Tongnan district,Tongliang district,Hechuan district and Dazu district of the municipality and analyzed for the mass fraction of As,Cd,Cr,Cu,Hg,Ni,Pb and Zn.Soil environmental quality standard（GB15618-1995）and potential ecological risk index were used to evaluate the degree of pollution by the heavy metals.The results indicated that Cd mass fraction in topsoil had the greatest accumulative effect,being as much as 2.43 times that of the background value and above GradeⅡ Criterion by 18.67%.However,the average contents of the other heavy metals were all below Grade I Criterion.Influenced by different strata and land utilization forms,the spatial distribution of these heavy metals were characterized by higher mass fraction of Zn,Cd,Pb,As,Ni,Cu and Cr in the western part of the study area and higher mass fraction of Hg in its eastern part.Comparatively speaking,the potential ecological risk of soil heavy metals in the study area was found to be in the middle level of potential ecological risk.It was characterized by the order of Cd〉Hg〉As〉Pb〉Cu〉Ni〉Cr〉Zn,with the predominant risk factors being Cd and Hg.The possible ecological hazards caused by Cd and Hg should be paid more attention to.