南昌市不同功能区绿化带土壤重金属污染特征及生态风险评价

Pollution Characteristics of Heavy Metals in Green Belt Soil of Different Functional Areas in Nanchang and the Ecological Risk Assessment

城市绿化带土壤是城市生态系统的重要组成部分,对污染物的吸纳、环境的净化起重要作用,更是市民接触重金属的主要风险源。深入分析城市重金属污染的空间分布特征、污染来源及其生态风险,对于改善城市土壤环境质量和人居环境有重要作用。以南昌市居民区、科教区、商业区、工业区、城市公园和郊区这6个功能区的绿化带土壤为研究对象,共采集了231个样品。分析不同功能区绿化带土壤重金属含量,采用单因子污染指数和内梅罗综合污染指数评价重金属污染的程度,采用Hakanson潜在生态风险指数法评价土壤重金属的潜在生态风险。结果表明,Cu、Zn、Pb、Cd这4种重金属元素平均值均未超过《国家土壤环境质量标准》(GB15618—1995)中的二级标准,但4种元素的平均值分别是江西省土壤背景值的2.58、2.57、2.08、1.13倍。以江西省土壤背景值作为评价标准,单因子污染指数大小为Zn>Cd>Pb>Cu,除城郊的各项单因子指数较小外,其他各功能区的单因子指数基本大于1;工业区、商业区和城市公园的综合污染指数在2-3之间,属于中污染。南昌市绿化带土壤重金属中Cu、Zn、Pb这3种重金属的生态风险指数均值分别为6.61、2.191、9.49,Zn、Cu全部处于低生态风险水平;少量地区Pb处于中等生态风险水平;Cd的潜在生态危害指数为60.88,有29.87%处于低生态风险程度,39.39%处于中等生态风险水平,30.30%处于较重生态风险水平,0.43%处于重生态风险水平。由生态危险指数RI可知,工业区、商业区和城市公园属于中等生态危害,居民区、科教区和郊区则是轻度生态危害。以《国家土壤环境质量标准》(GB15618—1995)中的二级标准作为评价标准,仅0.43%的样点处于严重生态风险水平,但仍有22.08%的样点重金属综合污染指数达到重度污染水平。

The green belt soil in city,which plays an important role on the pollutants absorption and environment purification,is a significant component of urban ecosystem,and the main risk sources of heavy metals for citizens.Depth analysis of the spatial distribution characteristics,pollution sources and ecological risks of heavy metals pollution in city soil plays an essential part in improving the quality of city soil and human settlements.In this paper,the green belt soil of the residential area,culture and education area,commercial areas,industrial area,city park and suburb in six different functional area of Nanchang City were taken as research subjects,with 231 soil samples being gathered.The concentrations of soil heavy metals were measured and their pollution levels were evaluated by single factor pollution index(Pi)and Nemerow comprehensive pollution index(PN).The ecological risks of soil heavy metals were discussed in light of Hakanson potential ecological risk index(r Ei and RI).The results showed that the average values of all heavy metals were below the National Standard,but they were 2.58,2.57,2.08 and 1.13 times compared to the background values of Jiangxi province.The single factor pollution index was in the following order:Zn>Cd>Pb>Cu,the single factor pollution index of other function areas were basically greater than 1,except for suburb.Nemerow comprehensive pollution index indicated that heavy metals had the moderate pollution in industrial area,commercial area and city park PN of those were 2?3.The single ecological risk index of Cu,Zn and Pb in the greenbelt soils of Nanchang city were 6.61,2.191 and 9.49,respectively.The comprehensive ecological risk index of Zn and Cu were all at slight ecological risk level;Pb was at moderate ecological risk level in a small number of areas;the ecological risk index of Cd was 60.88,29.87%at low ecological risk level,39.39%at medium ecological risk level and 30.30%at high ecological risk level,only 0.43%of soil samples reached strong ecological risk levels.According to RI,industrial area,commercial area and city park belonged to moderate ecological risk levels,and culture and education area,residential area and suburb belonged to slight ecological risk levels.Compared with the secondary standard of Environmental Quality Standard(GB15618—1995)for soils,only 0.43%of the samples were at the level of serious ecological risk,but 22.08%PN of soil samples reveals high risk of heavy metals pollution.