| Soil is one of the most important natural resources on which human beings rely for existing, and sustainable use of soil resources is the guarantee and prerequisite of sustainable development of social economy. But with the advancement of industrialization and traditional developing mode of agriculture, more and more kinds and amounts of poisonous and deleterious matters lead to soils were contaminated by means of pesticide use, sewage irrigation, solid landfill leakage, etc. And this situation of soil pollution has already gotten worse and worse, even tended to endanger all over the world. Compared with heavy metals, the harm of organic pollutants is much more serious. Many of them may have carcinogenic, tumorigenic and mutagenic properties, moreover, their accumulation, transfer and transformation in soil-water environment could destroy the safety of agricultural products, ecosystem and human beings'health. Therefore, preventing and curing the soil pollution and protecting soil safety in order to make sustainable use of soil resources come true that has become a hot-studying issue now. Whereas the adsorption behavior could control and effect transfer and transformation of organic pollutants in soil-water system, so researches on the adsorption processes, principles of organic pollutants and the relationship between each composition and organic compounds that would help solve a series of remediation to organic compounds.The pentachlorophenol(PCP)was once applied widely in the world as herbicide, antiseptic and pesticide. It is considered as the main persistent organic pollutants(POPs)in environment because of its broad-spectrum toxicity and mutation for organisms. PCP is also a kind of ionizable hydrophobic organic contaminants(HIOCs), and the physicochemistry properties of itself cause great harm to soil-water and ecosystem environment. Studying on its adsorption behavior can further understand the rules of migration and transformation for organic pollutants in soil-water environment and the final end-result and biological and ecology effect in the environment. As to this problem about PCP contamination, many researchers all commit themselves to pursue good scientific methods and measures to eliminate organic contamination and recover the natural function of soil. Nowadays, with the development of phytoremediation, there are new approaches applied in the management to organic contamination. Especially, a combined and integrated method of chemistry and biology is the best and most potential one for remedying organic pollution in soil. Compared with the traditional physical and chemical method, phytoremediation has a lot of advantages, such as low cost, abroad practicality, easy popularization and so on. Thus in this paper, a series of adsorption experiments including PCP, sunflower root exudates, and lucerne root exudates adsorbed respectively and PCP with root exudates from different sources adsorbed together in soil samples(original soil, soil removed organic matter, soil removed Mn oxides, soil removed Fe-Mn oxides and soil removed dissolved organic matter). The aim of these studies is to explore the adsorption behavior and rules of PCP, sunflower root exudates and lucerne root exudates and to elucidate the effect of these root exudates on PCP in the soil samples, and the differences between the two kinds of root exudates.The obtained results are shown as follows:(1) Take use of the ultraviolet spectrophotometric method of determining pentachlorophenol in soil suspension. PCP was measured in soil suspension at the wavelength of 255.6nm and under alkaline condition. These experimental datas showed that this method was fast, convenient and repeatable; this method would be suitable for measuring the content of pentachlorophenol in soil and also helpful to study its environmental behaviors.(2) Adsorption isotherms of PCP in original soil, soil removed Mn oxides, soil removed Fe-Mn oxides and soil removed dissolved organic matter samples were fitted with the Langmuir and Freundlich equation. The correlation was good and it achieved a significant level. The thermodynamics adsorption experiments of PCP in original soil and its another four important compositions showed that PCP had huge differences in different soil samples. The order of the adsorption capacities of PCP is: soil removed Mn oxides>soil removed Fe-Mn oxides>soil removed dissolved organic matter>original soil>soil removed organic matter.(3) The sunflower root exudates have more high-weight-molecular and hydrophobic fractions than lucerne root exudates do, in contrast, lucerne root exudates have more low-weigh-molecular and hydrophilic fractions.(4) Adsorption isotherms of the sunflower root exudates in five soil samples were fitted with the Langmuir and Freundlich equation, and the experimental results showed that the order of the adsorption capacities of sunflower root exudates is: soil removed organic matter>soil removed DOM>original soil>soil removed Mn oxides>soil removed Fe-Mn oxides; however, the quantity of lucerne root exudates adsorbed in different soil samples were subtractive, and decreased with the concentration of root exudates gradually. Through fitting the experimental datas with the Linear equation, it's known that the order of the absolute value of subtractive adsorption is: original soil>soil removed DOM>soil removed Mn oxides>soil removed Fe-Mn oxides>soil removed organic matter at the same original concentration.(5) The different sorts of root exudates had great differences in original soil and its another four important compositions due to the various physicochemistries between them, especially the content of high/low-weight-molecular and hydrophobic/hydrophilic fractions; the root exudates containing more high-weight-molecular and hydrophobic fractions were usually adsorbed easily in soils; vice versa.(6) Compared with PCP adsorbed respectively in different soils, the content of PCP adsorption increased with the concentration of sunflower root exudates, but decreased with the concentration of lucerne root exudates. It elucidated that sunflower root exudates could promote PCP adsorption, but lucerne root exudates could restrain PCP adsorption.(7) Provide phytoremediation to the organic pollutants with basic theories through researching the root exudates. |
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