关键词: 地下水, 土壤质量基准, 铅, 镉

Abstract: At present, a major problem in site remediation is frequently the lack of appropriate standards for chemicals in soils. While there are a few standards of organic and inorganic materials for exposure routes in waste treatment such as direct ingestion of soil, no standards are applicable to prediction of groundwater contaminated by metals. In this research, the "Equilibrium Partitioning" method is applied to study the adsorption capacity of trace elements (lead and cadmium) to the unsaturated zone in Beijing and Tangshan City. The partition coefficients (K_d) for lead and cadmium are computed from the percentage of metal absorbed K_d=(fraction absorbed)/(1-fraction absorbed)×100, and the maximum levels of metals in soil, for which the equilibrium soluble metals do not exceed the drinking water standard, are calculated from K_d (C_s=K_d×C_w, C_s:the maximum concentration, C_w:drinking water standard). The conclusions are as follows:1. The percentage of lead or cadmium absorbed obviously depends on pH values. The curve, which is S-shaped, can be fitted with the following function:F(x)=a×e^bx/(1+a×e^bx);2. The shapes of the logarithmic maximum metal permissible values in soil depending on pH values are linear, and the maximum metal permissible values in soil at certain pH values can be calculated with the regression formulas;3. Different soils have different "maximum metal permissible values" (criteria), to which the soils' physical and chemical properties are decisive factors;4. Given the same conditions, lead has higher concentration without causing an exceedence of the drinking water standard than cadmium.

Key words: groundwater, soil quality criteria, lead, cadmium