【作者】 何艳；

【导师】 徐建明；

【作者基本信息】 浙江大学 ， 土壤学， 2006， 博士

【摘要】 防治和修复土壤有机污染、保护土壤环境安全、以实现土壤资源的可持续利用是当前全球关注的一个焦点。研究有机污染物在土壤中的环境行为及作用原理,搞清土壤组分与有机污染物的相互作用关系,解决有机污染土壤根际修复中一些重要的根本性的基础科学问题及关键技术问题,将为针对性地拟订经济高效的土壤有机污染防治和修复的实用技术提供基础依据。 论文在评述有机污染物的土壤吸附行为研究现状、阐述有机污染土壤根际修复的影响因素、修复过程中的响应根际效应及根际修复机理的基础上,以氯酚类（CPs）有机污染物五氯酚（PCP）为代表性的可离解疏水性有机化合物（HIOCs）,围绕其在土壤矿物/腐殖质-水界面的非线性吸附特征、控制条件下的消减动态、以及毫米级根际中的微空间消减规律等内容,开展了相关PCP的土水界面行为及其在根际微域中的消减作用的细致研究,获得如下主要成果: （1） 以纯矿物及腐殖质为材料,开展了PCP在不同土壤有机、无机组分上吸附特征的对比试验,并结合去除有机质前后土壤中PCP吸附行为的差异研究,探讨了PCP吸附与矿物性质及腐殖质等的关系。发现PCP与各吸附剂的亲和力大小依次为:高岭石<针铁矿<Ca-蒙脱石<<K-蒙脱石<<HAs₁<HAs₂;经H₂O₂氧化处理后,土壤总有机碳水平显著降低,pH趋于一致,各土壤对PCP的吸附能力极大降低,其吸附不可逆行为也随各土壤中矿物组成的差异发生不同变化。由此证实了PCP在土壤矿物/腐殖质-水间的界面行为主要受到SOM和矿物组成的影响。这种机制中,SOM占支配地位,单离子饱和的膨胀型矿物存在一定作用;环境pH由于可改变吸附相的表面特性和PCP的存在形态也起一定的间接作用。基于不同单离子饱和的蒙脱石中PCP的吸附行为差异甚大的现象,推荐提出了利用矿物晶层间的离子交换作用修复污染土壤的技术措施。 （2） 从揭示PCP在土壤中吸附行为的角度出发,深入探讨了土壤性质对PCP的土壤-水界面行为的影响,验证了PCP在土壤中吸附不可逆的行为特性。发现PCP在10种土壤上的吸附表现为非线性,这种非线性吸附行为及其过程中存在的孔隙填充（表面吸附）和固相溶解（分配吸附）两种作用可用双模式模型（DMM）进行较好拟合。但这种非线性吸附特征与非极性疏水性有机化合物（HOCs）明显不同,表现出HIOCs在非线性吸附中的特异性;同时发现PCP在土壤中存在不可逆吸附行为,涉及的主要原因包括特定吸附位点的不可逆结合、慢解吸、吸附剂分子捕获及高平衡浓度条件下孔隙变形等机制。这种不可逆吸附现象,对污染土壤的生态修复意义重大,既是一种自净作用,又存在潜在危害,在评价PCP的环境风险时应综合考虑这两种相反的影响效应;在土壤性质对PCP的土壤-水界面行为的影响方面,研究揭示出pH、有机质及更多还原

【Abstract】 Pentachlorophenol （TCP, C₆Cl₅OH） is an ionizable hydrophobic organic contaminant （HIOC）. As a pesticide, herbicide, and antiseptic, it was once used worldwide, and has been designated as a priority pollutant and a probable human carcinogen. In the 1970s PCP was popularly used in China in fighting against snail fever and as a herbicide. Due to slow biodegradation, PCP may present a toxicity risk in contaminated soils for prolonged periods of time. Hence it is not surprising that it still causes environmental problems at many locations. The highest concentrations of PCP are usually found in soil and aquatic sediments. Understanding the behavior of PCP and its environmental risk requires an assessment of the processes influencing its fate, transport, bioactivity and persistence in soils. Investigation of the environmental behavior of PCP in soil (e.g. sorption/desorption, residue and dissipation, and the controlling key factors involved are thus necessary and effective.This dissertation, which is, in part, supported by the National Nature Science Foundation for Distinguished Young Scholars of China （No. 40425007） and the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of China, aimed to understand the interface behavior of PCP in the soil-water system, determining the potential contributions of soil physicochemical properties and its organic/inorganic components to PCP retention, evaluating the dissipation of PCP in the rhizosphere and the corresponding microbiological and biochemical responses, and developing alternative rhizo-remediation techniques to decrease PCP contamination. The information derived from this work will contribute to a better understanding of the soil-plant-microbe interactions and their impacts on the environmental behavior of organic contaminants in the soil-water system. The main experiments and conclusions are as follows:（1） Sorption of PCP by pure minerals and humic acids were measured to obtain additional perspective on the potential contributions of both clay minerals and soil organic matter （SOM） to contaminant retention in soils. Four types of common soil minerals and two kinds of humic acids （HAs） were tested. The sorption affinity for PCP was in the order: HAs >> K-montmorillonite>>Ca-montmorillonite > goethite > kaolinite. Such differences in sorption capacity were attributed to the crucial control of HAs. Clay minerals also had a contribution, especially K-montmorillonite, which played an important, if not dominant, role in the controlling process of PCP sorption. Modulating the cation type and composition onclay mineral surfaces through cation exchange processes provides an environmentaly-safe protocol to manipulate the mobility and availability of organic contaminants, which could have applications in environmental remediation. By removing 80 % （on average） of the organic carbon from the soils with H2O2, the sorption decreased by an average of 50 %. The sorption reversibility was also greatly increased. Considering the uncharged mineral fractions in soil before and after HzQrtreated, the main variation in sorption behavior of the soil might thus be related to the removed organic carbon and the reduced pH. This strongly indicated the interactions between SOM and clay minerals on PCP sorption as a function of pH.（2） Information about the sorption mechanism of PCP was gained by constructing highly detailed isotherms over the widest possible concentration range. Using the dual-mode model （DMM）, sorption isotherms of PCP were accurately predicted, the sorption capacities were determined, and the mechanisms of adsorption （hole-filling） and partitioning were elucidated. Sorption-desorption hysteresis in the present study was strongly indicated in ten soils with different properties. Such hysteresis might result from the pore deformation and entrapment of PCP molecules within organic matter. Total nitrogen in soils also has its contribution in these processes. Correlations obtained from stepwise regression analyses confirmed that pH, soil organic carbon and organic carbon fractions, as well as particle size distribution are the main factors responsible for the sorption and desorption hysteresis processes. These factors interacted to influence the fate of PCP sorption-desorption in soil. The empirical models developed in this study accurately predict PCP sorption and desorption hysteresis phenomena in the soils that were investigated.（3 ） Dissipation of PCP in soil was investigated and the chemical relationships with soil properties were studied. The results indicate that the dissipation of extractable PCP residues can be described using first-order kinetics equations, with a half-life （T1/2） ranging from 6.5 to 173.3 d. The sharply different patterns of PCP dissipation in different soils were closely related to soil properties. Correlations obtained from stepwise regression equations were significant （PO.01） between soil parameters and extractable PCP residues （R2=0.974**） as well as T1/2 values （R2= 0.882**）. The dissipation dynamics of PCP in soil was most accurately predicted by using pH together with organic carbon content （OC） and soil particle size distribution.（4） A glasshouse experiment was conducted using a specially designed rhizobox where ryegrass seedlings were grown for 53 days in a soil spiked with PCP at concentrations of 8.7 ±0.5 and 18+0.5 mg kg"1 soil to investigate rhizosphere effects on the dissipation of PCP. The soil in the rhizobox was divided into six separate compartments at various distances fromthe root surface. Changes in PCP concentrations with increasing distance from the root compartment of the rhizobox were then assessed. The largest and most rapid loss of PCP in planted soil was at 3 mm from the root zone where total PCP decreased to 0.20 and 0.65 mg kg"1 respectively with the two PCP treatments. The dissipation gradient followed the order: near-rhizosphere > root compartment > far-rhizosphere soil zones for both PCP concentrations where ryegrass was grown. In contrast, there was no difference in PCP concentration with distance in the unplanted soil. The increases in both soil microbial biomass carbon and the activities of soil urease and phosphatase were related to the enhanced dissipation of PCP, which was higher in the near-rhizosphere than far-rhizosphere soil. The results suggest that the effect of root proximity is important in the dissipation of xenobiotics such as PCP in soil.（5） Further investigations were conducted using phospholipid fatty acids （PLFAs） profiles to follow the millimeter spatial response of the soil microbial community with the purpose to illustrate the mechanism of dissipation gradients of PCP in the rhizosphere of ryegrass （Lolium perenne L）. The response of PLFAs profiles was related to the gradient influence of root exudates and PCP dissipation, showing a clear shift from hydroxyl to saturated taxa, then to fungi, then to gram-negative bacteria and gram-positive bacteria, then to actinomycetes, and then to arbuscular mycorrhizal fungi. This kind of development in microbial community finally resulted in the accumulation of arbuscular mycorrhizal fungi, actinomycetes and bacteria in the 3 mm rhizosphere layer, where the spiked PCP also exhibited both the highest dissipation rate and lowest residue concentration. Based on the stepwise regression analysis, the five fatty acids of 16:lto5,16:0, il7:0, al7:0 and 10Mel8:0 were confirmed to be the most important microbial factors controlling the rhizosphere specificity of PCP dissipation, strongly indicating the microbial synergistic controlling mechanisms of bacteria, arbuscular mycorrhiza and actinomycete that are involved in the accelerated process of PCP dissipation in the rhizosphere.（6） The remediation effect and mechanisms of root exudates on rhizo-remediation in PCP polluted soil were studied in a simulated rhizo environment. The residual dissipation of PCP in soil differed with addition of different rates of root exudates. There were significant correlations between the dissipation of PCP and the soil biochemical indices of microbial biomass carbon （0?）, nitrogen （Nmic）, carbon nitrogen ratio （Cmic/Nmic）, microbial quotient and enzyme activities in soil. At the lowest rate （13.38 TOC mg kg"1）, the PCP residual was smallest and remediation was most effective;at this time, the soil microbial biomass carbon, nitrogen, microbial quotient, dehydrogenase activities showed the largest responses. Themicrobial biomass nitrogen, microbial quotient and dehydrogenase activities appear to be sensitive biological indices indicating good soil environmental quality in rhizo-remediated soil, previously polluted with PCP.更多还原