多溴联苯醚及其羟基衍生物降解形成溴代二噁英的机理研究

Polybrominated diphenyl ethers (PBDEs) and its derivatives hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are ubiquitous in the natural environment. In addition to debrominate products, polybrominated dibenzo-p-dioxins (PBDDs) and polybromined dibenzofurans (PBDFs) will be generated from the process of degradation, migration and transformation of PBDEs and OH-PBDEs via the ring closure reaction of PBDEs or OH-PBDEs. PBDD/Fs have a higher toxicity than their parents. Currently, however, little research has been reported on the formation mechanism of PBDD/Fs from the degradation of OH-PBDEs or lower brominated diphenyl ethers. In order to reveal the formation law of PBDD/Fs and the influencing factors on the formation of PBDD/Fs, 17 kinds of PBDEs and OH-PBDEs will be selected as subjects, such as the main components of commercial pentabromodiphenyl ethers and typical OH-PBDEs, associated with the selected PBDEs as well. Their behavior of photolysis and thermolysis will be studied under UV light and heating in this project respectively. Via controlling the degradation conditions, the effect factors of the environment and the molecular structure (the positions of bromine and hydroxyl, the number of bromine substituted etc.) on the formation of PBDD/Fs will be studied, the pathway and mechanism of formation PBDD/Fs will be revealed. The purpose of this work is to understand the degradating conditions of OH-PBDEs and PBDEs, and to minimize the amount of PBDD/Fs generated from OH-PBDEs and from the products containing PBDEs during manufacture, using and disposal processing. In addition, the theoretical basis will be provided for assessing the environmental risks of OH-PBDEs and PBDEs.

多溴联苯醚及其衍生物羟基溴代联苯醚已无处不在，它们在降解、迁移和转化的过程中，除了脱溴外，还会闭环生成毒性效应更强的溴代二苯并-对-二噁英/呋喃（PBDD/Fs），增加了降解转化的毒性效应。目前，羟基多溴联苯醚和低溴代联苯醚的降解形成PBDD/Fs的机理鲜有研究。为了揭示它们转化为PBDD/Fs的规律和影响因素，本项目拟选用包括商用五溴联苯醚中的主要组分及与其相关的典型羟基多溴联苯醚共17种做研究对象，分别进行光化学降解和热降解研究，通过控制降解条件，探讨影响形成PBDD/Fs的环境因素和分子结构的（溴取代位置和数目、羟基的位置等）内在因素，揭示其形成途径和机理。通过本研究可以掌握羟基多溴联苯醚和多溴联苯醚的降解条件，尽量减少环境中的羟基多溴联苯醚和含有多溴联苯醚的产品在加工、使用、废弃后处理过程中产生PBDD/Fs；为评估羟基多溴联苯醚和多溴联苯醚的环境风险提供理论依据。

项目背景及意义：.多溴联苯醚（polybrominated diphenyl ethers, PBDEs）是一种添加型溴代阻燃剂，因其良好的阻燃性能和低廉的成本，曾被大量的生产和使用，在生产和使用中，PBDEs容易流入环境引起污染。因PBDEs具有生物毒性、生物蓄积性和持久性等特性，尤其是低溴代联苯醚毒性更强些，因此，五溴和八溴代联苯醚已被列入《斯德哥尔摩公约》，成为新型持久性有机污染物，研究此类污染物的降解、迁移转化、归趋可为环境中此类污染物消除提供理论支持和技术参考，因此，对其降解的研究具有重要的理论和实际意义。.研究内容及结果：.该项目主要对几种代表性的PBDEs进行了光降解、热降解和微波降解研究。研究中考察了不同性质的溶剂、不同的添加物以及不同外部环境对降解的影响；揭示了降解规律和降解机理；探讨了降解过程中形成溴代二噁英的影响因素；建立了相关的分析检测方法。研究结果如下：.高溴代联苯醚在降解过程有三种途径：一种是直接脱溴变成低溴代联苯醚；另一种是醚键断裂生成溴苯；还有一种闭环形成溴代二噁英。PBDEs的降解一般均符合一级动力学规律，以自由基猝灭剂实验证实PBDEs在含水溶剂中的降解是通过羟基自由基完成的；丙酮和腐殖酸明显抑制PBDEs的光降解，铜、铁和铵等离子具有双重作用；400℃左右热降解最容易形成溴代二噁英，碱性和某些含硫物质可抑制溴代二噁英的形成。硝酸铜、三氯化铁、氯化铝对BDE-209的热解起促进作用，促进程度的顺序为：硝酸铜>三氯化铁>氯化铝；氯化锌对BDE-209的热解起抑制作用。