Geochemical background and management target values of heavy metals in soil in northwestern Guizhou Province

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.