北京市凉凤灌区土壤重金属的积累及其变化趋势

Accumulation and temporal variation of heavy metals in the soils from the Liangfeng Irrigated Area, Beijing City

其含量的几何平均值(0.147mg·kg-1)为北京市土壤Hg背景值(0.0576mg·kg-1)的2.5倍.除Cd、Ni外,其它5种重金属都存在不同程度的积累现象(超过基线值),Hg的超标率(超过基线值)高达34.5%;Pb、Cu次之,超标率分别为8.86%、8.33%;Zn、Cr、As污染相对较轻一些,超标率为2.41%、1.20%、1.19%;没有发现Cd、Ni污染问题.与20世纪70年代中期的调查结果比较发现,经过近30年后,该地区的土壤Hg、Pb、Cu、As含量分别增加了11.4%、40%、26%、9.0%.结果表明,污水灌溉是导致土壤重金属积累的重要原因之一,Hg、Pb是该灌区土壤中需要优先控制的重金属.

To identify the pollution risks associated with wastewater irrigation, 84 samples of surface soils （0-20cm） were collected from the Liangfeng Irrigated Area in Beijing. The results indicated that the concentrations of Hg, Pb, Cu, Cr, As, and Zn were significantly higher than background levels. Mercury had the highest levels of accumulation with a geometric mean （0.147mg·kg^-1） of 1.6 times higher than its background concentration （0.05767mg·kg^-1）. Meanwhile, levels of Cd and Ni were not significantly different from the respective background concentration. Moreover, 34.5% of soil samples had higher concentrations of Hg （ compared to the baseline）, while 8.86% and 8.33% of the samples had higher concentrations than baseline of Pb and Cu, respectively. Only 2.41%, 1.20%, and 1.19% of the soil samples had greater concentrations than baseline of Zn, Cr, and As, respectively. No obvious accumulations of Cd or Ni in the irrigated soils were observed in the studied area. Compared with the results investigated in the 1970s, the concentrations of Hg, Pb, Cu, and As increased 11.36%, 40%, 26%, and 9.0%, respectively. Based on the distance of the sampling sites from the Liangshui river, three transects were divided to distinguish the relation between the concentrations of heavy metals and different transects. It was found that the concentrations of heavy metals in these soil samples, especially Hg, Pb, Cu, and As, declined with the increase of distance from the Liangshui River. It can be concluded that wastewater irrigation is an important factor of the obvious accumulation of heavy metals in the irrigated soils, especially Hg, Pb, and Cu. Consequently, Hg and Pb, which are the priority pollutants, should be frequently monitored and closely regulated in the wastewater-irrigated soils in Beijing City.