粘土矿物调控土壤中二噁英的生成与机制

Previous studies have documented the ubiquitous high levels of dioxins in natural clays. Their PCDD/F congener profiles are characterized by the predominance of octachlorodibenzodioxin (OCDD) and low levels of PCDFs. Such a unique PCDD/F congener profile does not match any known anthropogengic or natural dioxin sources, suggesting a novel dioxin origin. On the basis of these observations, a scenario is proposed that clay minerals may in situ catalyze dioxins synthesis using chlorinated pollutants as precursors. However, knowledge on the formation of dioxin via the reaction of chlorinated compounds with clay minerals is poorly understood. The primary objective of this study is to obtain a mechanistic understanding on the formation of dioxins from the oxidation of chlorophenols (CPs) by clay minerals. Specifically, we intend to select some ubiquitous CPs as the representative chlorinated compounds and natural clays, iron oxides and manganese oxides as the model clays. This project aims to i) understand the efficacy of dioxin synthesis from the oxidation of CPs by clays, ii) gain insight into the kinetics of dioxin congener formation, iii) evaluate the effects of coexisting organic matters (e.g., humic acid), co-solutes (e.g., Ca2+ and Mg2+) and pH on the reaction, iv) propose routes and mechanism to the formation of dioxin in clays through intermediates analysis and density functional theroy caluations, v) explore the relationship between the chemical structure of CPs (different chlorinated numbers and positions) and efficacy of dioxin formation. Results of this work will provide a better understanding on the dioxin origin in soils and clays.

研究表明天然粘土矿物含有不明来因的高浓度二噁英，其同系物以OCDD为主，PCDFs相对较少，这种与已知人为源和自然源显然不同的二噁英同系物分布特征表明其可能另有来源。那么，是不是粘土矿物利用氯代污染物原位合成了二噁英？为回答这个问题，本项目将系统地研究粘土矿物强化氯代酚类化合物氧化合成二噁英的过程与机制。实验拟选择环境中广泛存在的氯代酚类化合物为模型化合物，研究这些化合物在粘土矿物（包括天物粘土、含铁矿物和含锰矿物等）作用下氧化合成二噁英的能力与效率，分析生成的二噁英产物，建立二噁英生成动力学模型，考察环境因素如粘土矿物中共存有机质（如腐殖酸）、其他溶解质（如Ca2+、Mg2+等）和pH值等对二噁英生成的调控作用，结合量子化学理论计算，剖析反应机理，同时探讨氯代酚类化合物化学结构（氯原子取代位置和数目不同）对其氧化合成二噁英的影响。本研究成果将为土壤和粘土中二噁英的污染源解析提供新的参考。

粘土矿物含有不明来因的高浓度二噁英及其独特的同系物分布，表明粘土矿物中的二噁英可能另有来源。粘土矿物能否利用卤代污染物合成二噁英？为回答这个问题，项目以环境中广泛存在的卤代酚类化合物为模型化合物，以粘土矿物中的主要金属矿化物如α-FeOOH、α-Fe2O3和MnO2为代表矿物，系统研究了粘土矿物氧化氯代酚类化合物合成二噁英的反应，建立了二噁英生成的动力学模型，考察了一些环境因素对二噁英生成的调控作用，分析了反应生成的二噁英及中间产物，剖析了反应机理。总体而言，项目揭示了环境氧化作用下从苯酚逐步转化为卤代苯酚再到OH-PXDEs和 PXDDs/PXDFs的过程与机制。研究成果为环境中的二噁英及其类似物的自然源解析提供有价值的参考。项目共发表论文9篇，其中ES&T期刊论文2篇和Chemosphere期刊论文3篇；培养博士1名、硕士9名，其中1篇论文入选浙江工业大学优秀硕士学位论文；在国内外学术会议上做口头报告3次。研究成果获国内外同行正面评价，被SCI引用共30次，其中1篇ES&T论文入选ESI高被引论文扩展版（TOP 3%）。