有机组分土-水分配系数的确定(英文)

有机组分的土水分配系数(Kd)是描述有机组分在地下系统中吸附特征的重要参数。同时,它也是物质运移模拟和环境评价中的主要参数之一。影响Kd的因素可概括为三个方面:土壤性质、有机组分本身特征及水相的物理化学性质。一般而言,对于非极性和弱极性有机组分,土壤中的有机质含量(foc )是影响Kd的最主要因素。但是,对于极性有机组分(POCs), 特别是在土壤有机质含量较低的情况下,土壤中矿物的种类和含量、水化学组分特征(pH、离子力等)经常在吸附过程中起重要作用。实验室内测定Kd的方法包括批实验和柱实验方法。批实验法适用于研究Kd较高情况下的吸附。在Kd较低的情况下,如低有机质土壤对极性有机污染物的吸附,土柱色谱法(SCC)是更适宜的选择。另外,可用土柱色谱法快速了解各种因素对吸附过程的影响,并获取详细的吸附和解吸信息。应用土柱色谱法时应当注意非平衡吸附和可能的柱堵塞问题。很多文献中提到结合柱实验和已有的吸附数据来预测土壤有机碳标准化的分配系数Koc(=Kd/foc)。但是,如果没有考虑吸附中特定的作用过程(如矿物吸附),对极性有机组分Koc的预测将会产生很大的误差。在环境评价中,将从一种土壤测定的Koc 应用到不同性质的土壤中,可能会导致错误的认识。在进行室内实验时,应把标准土(如Eurosoi

BI Erping,SCHMIDT T.Determination of soil-water distribution coefficients of organic compounds

The soil-water distribution coefficient (K_(d)) of an organic compound is an important parameter to understand its transport in the subsurface, as well as a primary parameter in mass transport modeling and environmental assessments. The factors affecting K_(d) include properties of organic compounds, soils, and water. Generally, for apolar and weakly polar organic compounds, the organic matter content is considered the most significant factor influencing K_(d). However, with regard to polar organic compounds (POCs), soil minerals and the composition of the aqueous phase (pH, ionic strength etc.) often play important roles, in particular, when soil organic matter content (f_(oc)) is relatively low. Batch experiments are preferable for compounds with high K_(d) values, but might be inappropriate to determine the less strongly sorbing compounds (e.g., polar compounds). Therefore, soil column chromatography (SCC) has been suggested as an alternative to determine K_(d) values for POCs. In addition, SCC can be used to screen the sorption behaviour of compounds and the parameters affecting sorption in a relatively short time, and provide detailed information on the sorption and desorption processes. However, the problems of non-equilibrium sorption (sorption kinetics) and clogging of columns should be taken into account. Soil column experiments have been applied to predict partition coefficient K_(oc)(=K_(d)/f_(oc)). If the specific interactions (e.g., sorption to minerals) in sorption are not considered, K_(oc) prediction for POCs might result in large errors. In the environmental assessment, it might be misleading if K_(oc) of POCs obtained from one soil is applied to other soils of different composition. It is suggested that reference soils should be included in the batch and column experimental studies for setting up a standard database.