黔西北地区土壤重金属地球化学背景及管理目标值
Geochemical background and management target values of heavy metals in soil in northwestern Guizhou Province
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摘要: 基于贵州省毕节地区;25万土地质量地球化学调查的1 308件深层土壤样品重金属含量数据,研究了土壤重金属含量分布及其地球化学背景特征,与全国土壤比较,黔西北土壤重金属地球化学背景值显著高于全国土壤元素背景值,但是,与我国西南地区土壤元素背景值接近。黔西北地区土壤重金属含量与地质背景关系密切,不同地质单元区土壤重金属含量存在显著差异,石炭系地层发育的土壤呈Pb、Zn地球化学高背景,二叠系中统风化形成的土壤呈Cd、Hg地球化学高背景,黔西北地区不仅存在土法炼锌造成的土壤重金属污染,土壤重金属地球化学高背景也是影响土壤重金属富集的重要因素。统计表明,黔西北地区二叠系中统风化土壤Cd管理目标值高于我国农用地土壤Cd风险管制值(2.0×10-6),认为在确定黔西北地区土壤重金属管理目标时,应充分考虑不同地质单元区土壤重金属地球化学背景值差异及其生态环境效应的影响。Abstract: Based on the heavy metal content data of 1 308 deep soil samples taken from the ;250 000 geochemical survey of land qualityin the Bijie area, Guizhou Province, the content distribution and geochemical background characteristics of heavy metals in soil in the area were studied. The geochemical background values of heavy metals in soil in northwestern Guizhou Provinceare significantly higher than those in soil nationwide but are close to those in soil in southwestern China. The heavy metal content in soil in northwestern Guizhou is closely related to the geological background and is significantly different between different geological units. The soil developing in Carboniferous strata has high geochemical background values of Pb and Zn, while the Middle Permian soil formed due to weathering hashigh geochemical background values of Cd and Hg. All these mean that besides heavy metal pollution in soil caused by zinc melting using indigenous methods,another important factor causing the heavy metal enrichment is the high geochemical background values of heavy metals in soil.The statistics show that the management target value of Cd in the Middle Permian weathered soil in northwestern Guizhou is higher than thecontrol value (2.0×10-6) of Cd stipulated in the Risk Management Standard for Agricultural Land for Soil Pollution in China. It is considered that the differences in geochemical background values of heavy metals in soil between different geological units and their impacts on the ecological environment should be fully considered when determining the management target values of heavy metals in soil in northwestern Guizhou Province.
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