内蒙古半干旱草原某铅锌矿区土壤性质及重金属污染生态风险评价

Soil properties and pollution assessment of heavy metals in a lead-zinc mining area of semiarid grassland in Inner Mongolia

半干旱草原地区是我国重要的生态脆弱区,频繁的矿业活动会对草原土壤造成一定程度的污染.本文以位于内蒙古半干旱草原的某铅锌多金属矿区土壤为研究对象,对其土壤性质和重金属含量及赋存形态进行了调查研究,并利用单因子指数法、潜在生态风险指数法和RAC风险评价法对土壤受污染程度进行了评价.结果显示,研究区土壤偏中碱性,矿物组成以石英、长石和粘土矿物为主.矿区土壤中Pb、Zn含量(分别为51.2 mg·kg^(-1)和226.4 mg·kg^(-1))远高于背景土壤,分别为内蒙古土壤几何均值的3.4和4.7倍;矿区土壤Cu含量和背景区土壤含量相当.元素赋存形态分析表明,Cu主要以残渣态和有机质结合态形式存在,Pb和Zn则以残渣态、铁锰氧化物结合态、有机质结合态为主,3种元素可交换态和碳酸盐结合态含量均较低.单因子指数法评价结果表明,矿区41%和35%土壤受到严重的Pb、Zn污染;潜在生态风险评价结果表明,矿区土壤重金属的综合潜在生态风险指数RI为29.40,属于轻微生态危害,Pb是综合潜在生态风险主要的贡献因子;RAC风险评价表明,矿区土壤中生态风险系数由大到小为Zn>Cu>Pb,Zn的生态风险相对较大.综合来看,Pb、Zn的污染控制是该矿区需要关注的重点.

Semi-arid grassland is an important ecologically fragile area in China. In this study,soil properties,content and speciation,and ecological risk assessment of heavy metals in a lead ／ ｜ zinc（ Pb-Zn） ploymetallic mining area of semiarid grassland in Inner Mongolia were investigated. Three methods（ single factor index evaluation, potential ecological risk assessment and RAC） were employed to evaluate the pollution level. The results showed that the p H of soil was neutral and alkaline. The soil was mainly composed of quartz, feldspar and clay minerals. Clay mineralsconcentration in background area was lower than that in the mining area. The average contents of Pb and Zn was 51.2 mg·kg^-1 and 226. 4 mg·kg^-1,which was 3.4 and 4.7 times the geometric mean value of the soil in Inner Mongolia. It indicated that the soil had been polluted by mining activities.According to the results of sequential extraction,the major fractions of copper（ Cu） were residual fraction and organic phase,while the major phases of Zn and Pb were residual fraction,organic phase and Fe-Mn oxide phase. Migration ability of Cu,Pb and Zn was weak in the mining areas. The single factor index evaluation showed that the percent of sites with soil contaminated by Pb and Zn was 41% and 35%,respectively. The potential ecological risk assessment stated that RI was 29.4,indicating a low ecological risk in this mining area. And the results of RAC concluded that the sequence of ecological risk of Zn is the highest,followed by Cu and Pb. Taken together,the pollution and ecological risk of Pb and Zn in this area should be a major concern.