北京城区土壤中Hg、Pb、Cd、Cu及Zn化学形态及环境效应

为弄清北京城区土壤中Hg、Pb、Cd、Cu及Zn五种重金属元素的化学形态分布特征,系统采集了126件城区表层土壤样品,采用连续提取法对重金属元素各化学形态含量进行了测定。结果表明:土壤中土壤中Hg、Pb、Cd、Cu、Zn含量差异显著。Hg元素以残渣态和强有机结合态为主,Cd元素离子交换态、碳酸盐结合态、残渣态、铁锰氧化物结合态含量较高,Pb、Cu、Zn元素以残渣态、铁锰氧化物结合态为主。Hg元素的有效态含量最低(不足1%),现情况下不会对环境造成污染;Cd元素的有效态含量最高(40%),生物有效性和潜在生态危害性较大,运用植物修复技术对其治理为经济有效的方法;Pb、Cu、Zn有效态含量较低(约10%),生物有效性和潜在生态危害性均有限。各元素形态与全量之间相关程度虽有差别,但基本呈正相关关系。

Chemical Forms of Hg,Pb, Cd,Cu and Zn in Beijing Urban Soil and Its Environmental Effects

The urban soil samples in Beijing city were studied for the chemical forms of Hg, Pb, Cd, Cu and Zn by a sequential extraction procedure. A total of 126 soil samples were collected and analyzed. The results show that the contents of Hg, Pb, Cd, Cu and Zn are more than their background values of Beijing plain respectively. The chemical form of Hg is mainly in residual and strong organic state; Cd is greatly associated with the ion-exchangeable state, carbonate state, Fe-Mn oxide state and residual state; and Pb, Cu and Zn are mainly in the residual and Fe-Mn oxide state. The percentage contents of Hg and Cd associated with effective states are the lowest and the highest respectively. Therefore, their biological effectiveness and potential ecological hazards are different. Hg can not cause bioavailability and potential ecological hazards. Cd has much heavier bioavailability and potential ecological hazards, whereas Pb, Cu and Zn have limited bioavailability and potential ecological hazards. Due to Cd’ s potential impact on environment, so more attention should be paid and phytoremediation should be adopted to remedy Cd contaminated soil. The results of correlation coefficient analysis show that the concentration of the total metals bound to chemical forms has commonly positively correlation with total concentration.