三种土壤铅和镉的质量基准初步研究

DEVELOPMENT IN THE QUALITY CRITERIA OFLEAD AND CADMIUM FOR THREE TYPES OF SOIL

在制定地下水源保护区污染控制措施时，最常遇到的问题之一是缺少土壤包气带和含水层中化学物质的基准和标准。文中以铅、镉为例，结合北京、唐山地下水水源地实际情况，运用“平衡分配法”，根据土壤对铅和镉的吸附容量和分配系数研究包气带土壤中的铅和镉的质量基准。结果表明，土壤中铅和镉的质量基准与溶液ｐＨ值成对数线性关系，据此可计算不同ｐＨ条件下的土壤中重金属的质量基准。

t 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.