南京江北地区菜地土壤重金属污染特征及评价

在南京市浦口和大厂的五大主要功能区（工业区、交通干线、居民区、蔬菜生产基地和风景区）分别布置采样点，共采集了75个菜地耕层土壤样品，以Cd、Cu、Pb和Zn等典型污染重金属元素的全量数据为基础，运用经典统计分析、综合污染指数和地统计分析相结合的方法对土壤重金属污染进行评价。结果表明，Cd、Cu和Zn分别超出其南京地区土壤背景值的5．42、1．84和1．14倍，Pb未超出。不同功能区菜地土壤的重金属全量水平存在明显差异，其中工业区菜地土壤的重金属污染较为严重。对于Cd和Cu，单因子污染指数大于1的样点数达100％，Zn为52％，Pb为2．67％。研究区内菜地土壤重金属的综合污染指数为4．12，属于中度污染。Cu的空间相关性很弱，Cd、Pb和Zn具有中等的空间结构性；四种重金属的空间相关尺度较为接近。Cd、Cu和Zn的单因子污染指数具有相似的空间分布，总体呈现出南高北低的带状递减趋势，且高峰值具有空间分布的趋同性，而Pb的单因子污染指数分布呈现西北和东南两端高，中间较低的趋势。综合污染指数的空间分布显示，研究区大部分菜地土壤处于中度重金属污染水平，钢铁生产厂周边的斑块状区域重金属污染更加严重。

Characteristics and Assessment of Heavy Metal Pollution in Vegetable Soils in Jiangbei Area of Nanjing City

Seventy five surface soil samples were collected from vegetable fields located in or nearby the 5 contrasting zones: industry, arterial highway, resident area, vegetable production base, and scenery site, across Pukou and Dachang districts of Nanjing City. We measured heavy metal (Cd, Cu, Pb and Zn) concentrations of the soils,based on which the heavy metal pollution of the vegetable land in the area was assessed by methods of normal statistical analysis,composite pollution index and geostatistical analysis. The results show that the concentrations of Cd, Cu and Zn were 5.42,1.84 and 1.14 times higher than the background values, respectively, but not for Pb. The concentrations of heavy metals were significantly different in relation to the functions of the zones. The metal concentrations of vegetable soils in the industrial zone were higher than those in non-industrial zones. All soil samples gave a single factor pollution index of over 1 value for Cd and Cu,52% for Zn and 2. 67% for Pb. The composite pollution index was 4. 12, which suggests a moderate pollution by heavy metals of vegetable farmlands in the area. Cu was weak in spatial correlation, Cd, Pb and Zn were moderate in spatial structure, and all the four metals were approximate in spatial correlation scale. Cd, Cu and Zn were similar to each other in the spatial distribution of single factor pollution index, with a trend of decreasing from the south to the north and spatial convergence to the peak value. However, the single factor pollution index of Pb re-presented a different spatial distribution that the index was high in the two ends of northwest and south-east of the area while low in the middle zone. The overall heavy metal pollution was moderate for most vegetable soils in the area, much severer near by a steel factory.