岩溶区土壤中重金属的富集机制及环境影响:以黔中平坝剖面为例

Enrichment Mechanism and Environmental Impact of Heavy Metals in Soil of Karst Area:A Case Study on Pingba Profile in Central Guizhou

选择黔中地区一条白云岩发育的土壤剖面(平坝剖面),通过对基岩酸不溶物提取,并结合重金属在剖面中的分布特征和质量平衡计算,初步讨论了土壤中重金属的富集机制及其环境影响。1)碳酸盐岩风化过程中,无论重金属是否强烈亏损,在其发育的土壤剖面中均明显富集,这种现象主要源于基岩中碳酸盐充分溶解导致酸不溶残余物体积的巨大缩小变化,进而使赋存期间的重金属显著残余富集;2)由基岩酸不溶物累积发育而成的土壤剖面中,重金属的进一步带入/带出引起质量比上的增加/减少,具有一般土壤剖面的演化特征;3)贫重金属碳酸盐岩发育的土壤中,大多数重金属质量比大于农用地土壤污染风险筛选值,存在潜在的环境风险,应引起重视。

A soil profile developed on dolomite rock in central Guizhou,China(i.e.,Pingba profile)was taken as a case study.Based on the extraction of acid-insoluble phases from the bedrock,combined with the distribution characteristics and the mass balance calculation of heavy metals such as U,Th,Cr,Ni,Cu,Zn,Cd and Pb in the profile,the enrichment mechanism of heavy metals in soil and their environmental impact were preliminarily discussed.(1)During weathering of carbonate rock,heavy metals are obviously enriched in soil,no matter whether they are strongly depleted or not.This phenomenon is mainly due to the fact that volume of acid-insoluble residues is greatly reduced along with the full dissolution of carbonate components in the bedrock,and then heavy metals are significantly enriched in the residues.(2)In the soil formed by the accumulation and development of acid-insoluble phases in the bedrock,the further loss/gain of heavy metals causes their content depletion/increase,which shows the developed characteristics of general soil profiles.(3)In soil derived from carbonate rock poor in heavy metals,the contents of the most of heavy metals are higher than the risk screening values for soil contamination of agricultural land,which has potential environmental risk and should be paid attention to.