| 其他摘要 | Soil is an important component of the natural environment. Soil organic matter (SOM), which may be subdivided into three components of humic acids (HAs), fulvic acids (FAs) and humin (HM), is an important component and functional unit of natural soil. The research on the soil organic matters has become a focus in the field of soil and environmental sciences. SOM is a major component for adsorbing organic pollutants in the soil and plays an important role in distribution and migration of pollutants in the natural environment. According to the different physicochemical characteristics of the ambient environment, sorption/desorption properties of SOM are different coordinately; sorption/desorption behaviors of SOM are also different during its different evolution stages. The principles underlie the environmental risk assessment of organic pollutants are on the basis of the isotherms of organic pollutants on the selected media, which were measured mainly in the artificial environments. However，the time scales of processes in the natural environment may be much longer than those of in the laboratory. Given enough time, either organic pollutants can penetrate deeply into the matrix of soil and enter into micropores or physicochemical properties of soil can be changed to cause irreversible sorption, even sequestration, of organic pollutants in soil. Therefore, remarkable errors are often found between the results of field observation and laboratory modeling of risk assessments. A concept of “aging effect” was proposed to interpret and to complement the errors. The “aging effect” is very important for accurately evaluating environmental risks and bioavailability of organic pollutants. The prior studies of “aging effect” mainly focused on the effects of long time scales to interactions of organic pollutants and soils in stable systems, hardly any attention was paid to the evolutions of the environment and the soil itself. This study advised that some naturally occurred processes to the soil are also the reasons of “aging effect”. Actually, in the natural environment, many surficial geochemical processes, such as, wetting and drying, freezing and melting, dissolving and precipitating, etc., are never stopped themselves on the soil to keep changing the properties and the structures of the soil during or after organic pollutants sorption. It is not difficult to tell that these surficial geochemical processes will change the sorption/desorption behaviors of the soil to cause the “aging effect”, and, in certain circumstance, the “aging effect” will be done in a short time. Unfortunately, the studies of the role of surficial geochemical processes in the “aging effect” are scarce. The goal of this study is to demonstrate that the surficial geochemical processes are important mechanisms of “aging effect” by simulating these processes in the laboratory. To achieve this goal, I selected two natural soils and their humin fractions as the experiment samples and two polycyclic aromatic hydrocarbons (PAHs), phenanthrene and pyrene, as the target chemicals, two common soil minerals, Fe(OH)3 and CaCO3, were chosen to “age” the samples by simulating their precipitating on the surface or soils and soil fractions. This study systematically studied the sorption/desorption behaviors of the chemicals on the treated and the untreated soil samples to reveal how the surficial geochemical processes affect the bioavailability of the chemicals. The major findings of this study are as following: 1. The sorption/desorption isotherms of phenanthrene and pyrene on the soils and soil humin fractions are well fit by the Freundlich Equation. All the sorption/desorption hysteresis indices (HI) are greater than zero, indicating that all sorbent samples are highly heterogeneous and show remarkable desorption hysteresis2. The soil humin fractions (HM) show much higher sorption capacity of organic chemicals than the soils do. In the case of phenanthrene，sorption coefficients Kf and n of HM component of yellow soil (HRT) are 9597.2 (ug?kg-1)/(ug?L-1 |
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