太原市郊区农田土壤重金属的形态特征及其风险分析

Morphological Characteristics and Risk Analysis of Heavy Metals in Farmland Soil in the Suburb of Taiyuan

在太原市郊区采集农田表层(0~20 cm)土壤样品36个,测定土壤样品中的Cu,Pb,Zn和Cd的总含量,并进行主成分分析。采用改进BCR提取法分析土壤样品重金属的各形态组分,运用风险评价编码法(RAC)和次生相与原生相分布比值法(RSP)对重金属的生物有效性和环境风险进行评估。结果表明,土壤样品中重金属Cu,Pb,Zn和Cd的总含量分别为38.07,25.06,84.94和0.16 mg·kg-1,均高于山西省土壤背景值。主成分分析发现,第一主成分Pb,Zn和Cd含量变化受人为因素影响;第二主成分Cu含量变化受成土母质或成土过程的影响。Cu,Pb,Zn和Cd的形态分布表现为:残渣态>可氧化态>弱酸溶态>可还原态,各形态组分含量与总量均呈现极显著正相关关系。重金属生物有效性表现为Cd>Zn>Cu>Pb,有效态含量低于稳定态。风险评价编码法评估结果表明,太原市郊区农田土壤重金属Cd的环境风险程度为中度,Cu和Zn为低风险。通过次生相与原生相分布比值法评估,Cu,Pb,Zn和Cd的RSP值为0.08,0.19,0.13和0.62,表明土壤未受到Cu,Pb和Zn的污染,但存在一定的Cd污染。太原市郊区农田土壤的Cd污染风险较高,其他三种金属元素风险较低,应该对重金属的形态组分予以重视。

A total of 36 soil samples were collected from farmland surface(0-20 cm) in the suburb of Taiyuan to determine the contents of Cu, Pb, Zn and Cd and conduct principal component analysis. We have measured the various morphological components of heavy metal in soil samples by using the improved BCR extraction method, the bioavailability and environmental risk of heavy metals were evaluated by risk assessment coding(RAC) and secondary to primary phase distribution ratio(RSP). The results of the above analysis show that: the total contents of heavy metals Cu, Pb, Zn and Cd in soil samples were 38.07, 25.06, 84.94 and 0.16 mg kg-1, respectively, which proved to be higher than the soil background values in Shanxi Province. Furthermore, the principal component analysis also demonstrates that, the content of Pb, Zn and Cd in the first main component can be affected by human factors, and the change of the content of Cu in the second principal component was influenced by the parent material or the process of soil formation.The morphological distribution of Cu, Pb, Zn and Cd was ranked as: residue>oxidizable state >weak-acid soluble>reducible state, and there were significantly positively correlations between different morphological components and the total contents. In addition, the order of heavy metal bioavailability was Cd > Zn > Cu > Pb, and the concentrations of available heavy metals were much lower than stable heavy metals. Risk assessment code(RAC) showed that Cd was at moderate environmental risk level, and Cu and Zn were mostly slightly polluted in farmland soil in the suburb of Taiyuan. The ratio of secondary phase and primary phase(RSP) showed that the RSP values of Cu, Pb, Zn and Cd were 0.08, 0.19, 0.13 and 0.62, respectively, most of the soil samples were not polluted by Cu, Pb and Zn,as well as that of Cd pollution to some extents. Therefore, the environmental risk and pollution of Cd of farmland soil in the suburb of Taiyuan are at a high level, and enough attentions need to be paid on morphological components of heavy metals.