北京市五环内绿地土壤4种重金属的形态特征及其生物有效性

目的]了解北京市五环内绿地表层(0—20cm)土壤重金属(Cu,Cd,Pb和Zn)的形态特征及其生物有效性,为北京市绿地土壤重金属污染防治提供比较可靠的参考依据。方法]在建成时间为2~400a的绿化区内共采集表层土壤样品151个,运用改进BCR提取法分析样品中重金属的赋存形态,而后通过风险评价编码法(RAC)和次生相与原生相分布比值法(RSP)对重金属生物有效性进行评估。结果]样品中重金属Cu,Cd,Pb和Zn的含量分别为31.42,0.29,29.89,76.78 mg/kg,Cu,Zn在中部和东北部含量较高,Pb在中部地区含量较高,Cd在西北部、东北部和南部存在少量高值区。Cu,Cd,Pb和Zn形态分布的总体规律均为:残渣态可氧化态弱酸溶态可还原态,稳定态含量均远高于有效态,有效态含量比例表明重金属生物有效性大小顺序为:CdZnCuPb风险评价编码法(RAC)表明,Cd和Zn环境风险程度为低风险,Cu和Pb无环境风险。次生相与原生相分布比值法(RSP)显示,Cu,Cd,Pb和Zn元素RSP值分别为0.06,0.49,0.18,0.13,土壤整体上未受到重金属污染,但是有少部分地区存在被污染现象。结论]北京市五环内绿地土壤总体上不存在重金属Cu,Cd,Pb和Zn污染,环境风险较低,但应对重金属赋存形态保持关注。

Speciation and Bioavailability of Four Heavy Metals in Greenbelt Soil Within 5th Ring Road of Beijing City

Objective] To understand the characteristics of speciation and bioavailability of heavy metals (Cu, Cd, Pb, and Zn)in greenbelt surface (0-20 cm) soil within the 5th ring road of Beijing City in order to provide reliable information for soil heavy metal pollution control in Beijing City.Methods] A total of 151 surface soil samples were collected from greenbelt land built 2~400 years ago. A modified BCR extraction technique was used to analyze the chemical forms of heavy metals from the collected samples. Risk assessment code (RAC) and the ratio of secondary phase and primary phase (RSP) were used to evaluate the bioavailability of the heavy metals.Results] The average content of total Cu, Cd, Pb, and Zn in soil samples were 31.42, 0.29, 29.89 and 76.78 mg/kg, respectively. The content of total Cu and Zn were higher in the northeast and central region, Pb was higher in central region, and there were a few high-Cd areas existed in the northwest, northeast, and south region. The speciation distribution of Cu, Cd, Pb, and Zn were ranked as:residual > oxidizable > weak acid soluble > reducible, and the concentrations of stable heavy metals were much higher than available heavy metals. The bioavailability was ranked as:Cd > Zn > Cu > Pb. Risk assessment code (RAC) showed that Cd and Zn was at low environmental risk level, and Cu and Pb was no environmental risk. The ratio of secondary phase and primary phase (RSP) showed that the RSP values of Cu, Cd, Pb, and Zn was 0.06, 0.49, 0.18 and 0.13, respectively, most of the soil samples were not polluted by heavy metals.Conclusion] The environmental risk and pollution of heavy metals (Cu, Cd, Pb, and Zn) of greenbelt soil within the 5th ring road of Beijing City are at a low level, but enough attentions need to be paid on heavy mental occurrence form.