西溪湿地土壤重金属分布特征及其生态风险评价

Distribution and Ecological Risk Assessment of Heavy Metal Elements in Soils of Xixi Wetland

测试和研究了杭州西溪湿地土壤中铜(Cu)、锌(Zn)、铅(Pb)、镉(Cd)、汞(Hg)、砷(As)和铬(Cr)的含量与分布特征,采用内梅罗综合污染指数和Hakanson潜在生态危害指数法对湿地土壤重金属污染环境质量和潜在生态风险进行了评价。结果表明,西溪湿地土壤表层7种重金属平均含量的质量比分别为36.8 mg/kg(Cu)、91.5 mg/kg(Zn)、39.2 mg/kg(Pb)、0.23 mg/kg(Cd)、0.19 mg/kg(Hg)、6.3 mg/kg(As)和64.9 mg/kg(Cr)。由于受各种人为作用的影响,与浙江省土壤背景值相比,Cu、Pb、Cd和Zn在湿地土壤中的积累较大,有3个采样点[菜地、芦苇(Phram ites austrlis)滩地和靠马路的居民区]土壤中的Cd含量超过《土壤环境质量标准》(GB15618-1995)标准值的二级标准(pH<6.5)。湿地土壤重金属污染环境质量和生态风险评价结果显示,内梅罗综合污染指数平均值为1.73,多种重金属潜在生态风险指数平均值为114.6,说明总体上西溪湿地土壤重金属污染及其潜在生态风险为轻微级。最后,讨论了西溪湿地公园土壤重金属的可能来源,对比了重金属污染评价中不同评价标准和评价方法的差异性。

In order to know clearly soil environment status, the accumulation and distributions of heavy metal el- ements, copper, zinc, lead, cadmium, mercury, arsenic and chromium, in soils of Xixi Wetland, a National Wetland Park were researched. Methods suggested by Nemerow and Hakanson were applied to assess the inte- grated pollution and potentially ecological risk in this area. The results indicated that, the mean contents of Cu, Zn, Pb, Cd, Hg, As and Cr in soils （ depth of 0 - 20 cm） were 36.8 mg/kg, 91.5 mg/kg, 39.2 mg/kg, 0.23 mg/kg, 0.19 mg/kg, 6.3 mg/kg and 64.9 mg/kg, respectively. Because of the influences from human activi- ties, Cu, Pb, Cd and Zn had high accumulation in soils by comparison to the background concentrations of soil elements in Zhejiang province. And Cd content in 3 sampling sites had exceeded the second grade standard values of Chinese environmental quality standards for soils （GB 15618 -1995 ）. The pollution degree of heavy metals in Xixi Wetland was light with a mean Nemerow index of 1.73. The potentially ecological risk was also light as the mean integrated index was low （114.59）. The possible sources of heavy metal elements in soils of Xixi Wetland were identified, and the similarities and differences of different standards and methods in pollution assessment were compared. Pb and Zn accumulation in soils might be caused by the exhaust fume and tires of automobiles running on the road nearby. Cu accumulation in soils had relation to the use of feed additive. Cd and Hg accumulation in soils might be caused by polluted water flowing into wetland. By using of 2 evaluation standards, the related management department could get more decision - making information to take effective methods for controlling or remedying soils with different pollution levels. The Nemerrow integrated pollution index and multi -heavy metal elements potential ecological risk index had a similar assessment result.