Study on kinetics and mechanism of typical PPCPs chlorination process

药物及个人护理品（PPCPs）近年来得到越来越多的关注。PPCPs类微污染物在水环境中的浓度普遍较低，但是其对环境具有潜在的危害，并且可能对人类的身体健康造成威胁。由于传统的水处理工艺，如混凝，沉淀，过滤等对PPCPs的去除效率很低，所以PPCPs存在于各种水体环境中，包括在地下水和饮用水中也有检出。氯消毒是最常用的一种消毒方式，考虑到PPCPs潜在的危害性，研究其在氯化消毒过程中的转化规律具有重要意义。本研究选择一种典型的PPCPs类有机物双氯酚酸（DCF）作为目标污染物，研究其在氯化反应中动力学、机理及遗传毒性变化趋势。天然水体中存在大量的离子（氯离子和溴离子等），腐殖质和其它微污染物，均与氯化过程紧密相关。因此在研究DCF单独氯化反应的基础之上，进一步研究其在共存体系中的氯化过程。同时，高锰酸钾作为一种常见的预氧化手段，本文同样对其关于DCF的降解过程进行研究。主要研究结果如下。 Cl-和Br-是天然水体中重要的阴离子，可以与活性氯直接反应。DCF氯化反应速率随着Cl-浓度的增加而线性升高，主要归因于Cl2的生成；而低剂量的Br-可以显著提高DCF氯化反应速率。使用液相色谱-质谱联用技术检测出多种中间产物，据此推测两条主要反应路径。一是在DCF芳环上的亲电取代反应，生成氯取代或羟基取代产物；二是攻击氨基，首先生成Cl-N中间体，进而发生进一步氧化。DCF氯化产物的遗传毒性随活性氯浓度的增加而升高。Cl-的存在对DCF氯化产物的分布和遗传毒性没有明显的影响，而微量Br-的存在会导致溴代产物的生成从而使遗传毒性增强。 腐殖酸（HA）作为水体中常见的大分子有机物可以与活性氯和DCF相互作用。HA的存在能有效提高DCF氯化反应速率。HA分子具有复杂的空间结构，可以与DCF分子之间相互作用，改变DCF氯化反应的微环境从而加速反应。HA的存在对DCF氯化产物的分布以及反应路径无明显影响。HA自身氯化产物不具有遗传毒性效应，但其可以通过与DCF竞争活性氯使混合体系遗传毒性降低。 曲马多（TRA）是一种常见的镇痛药，有研究表明TRA与DCF共同使用情况下有助于更好地缓解疼痛。TRA氯化反应速率随pH值上升而升高。在碱性条件下，HOCl选择氨基作为优先攻击位点。而在酸性和中性条件下，存在两种可能的反应路径。一是芳环上的亲电取代；二是攻击氨基。遗传毒性测试表明TRA氯化产物的遗传毒性随着活性氯浓度的增加而升高，主要是由于一些氯代和多氯代产物的生成。 TRA与DCF复合氯化体系中，二者属于竞争关系，反应速率降低，反应路径保持不变，复合体系遗传毒性略有升高。 高锰酸钾作为一种常见的氧化剂被广泛用做预氧化。高锰酸钾氧化DCF遵循二级反应动力学规律，反应速率随pH的升高而降低。使用液相色谱-质谱联用技术分析出一系列降解产物，并提出一种开环反应机理。高锰酸钾首先亲电攻击氨基，生成初级中间产物2,6-二氯苯胺和5-羟基-双氯芬酸，后者可以被进一步氧化发生开环反应，脱羧酸反应等。Pharmaceuticals and personal care products (PPCPs) have received increasing attention in recent years. Although these micro-pollutants are present in low concentrations, they are potentially harmful to the environment and may pose a threat to human health. Due to the low removal efficiency of PPCPs during conventional water treatment processes such as coagulation, sedimentation and filtration, PPCPs are widly detected in the water, including in groundwater and drinking water. Chlorine disinfection is the most used disinfection method. Taking into account its potential toxicity, the study of PPCPs chlorination process is of great significance. In this study, a typical PPCPs compound diclofenac (DCF) was selected as the target contaminant, to study its kinetics, mechanism and toxicity during chlorination process. Natural water contains a large number of ions (chloride and bromide ions, etc.), humus and other micro-pollutants, which are closely related to chlorination process. Therefore, on the basis of the study of DCF chlorination process, we further study it in complex system. In addition, because of permanganate is widly used for pre-oxidation, the degradation of DCF by permanganate was studied. The main research results are as follows. Cl- and Br- are important anions in natural water, which can react with chlorine directly. The chlorination rate of DCF increased linearly with increasing Cl- concentration, mostly attributting to the formation of Cl2. In the prescence of trace amout of Br- could significantly increase DCF chlorination rate. A variety of intermediates were detected with liquid chromatography-mass spectrometry (LC-MS), whereby two major reaction paths were deduced. One is an electrophilic substitution on the aromatic ring leading to the formation of chlorinated or hydroxyed products, and another one is an electrophilic attack on the amino, leading to the formation of halogenated-N intermediate which can be further oxidized. The potential genotoxicity of DCF chlorination products increased with increasing chlorine concentration. The presence of Cl- has no significant effect on the distribution and genotoxicity of DCF chlorination products, whereas the presence of Br- leads to the formation of brominated products and increases the toxicity. Humic acid (HA), as a common macromolecular compound in water, can interact with chlorine and DCF. The presence of HA can effectively enhance the DCF chlorination rate. Due to its complex structure, HA interacts with DCF to change the microenvironment of DCF chlorination reaction. The presence of HA has no significant effect on the distribution of DCF chlorination products and the reaction pathway. Although HA chlorinated products do not show a genotoxicity effect, but HA can compete with DCF to reduce the toxicity of complex chlorination products. Tramadol (TRA) is a common analgesic, when co-use with DCF could be useful for relief the pain. The TRA chlorination rate increases with increasing pH. Under alkaline conditions, HOCl selects the amino as primary attack site. In the acidic and neutral conditions, there are two possible reaction pathways. One is electrophilic substitution on the aromatic ring; another is electrophilic attack on the amino. The genotoxicity of TRA chlorination products increased with increasing chlorine concentration, mainly due to the formation of some chlorinated products. During chlorination of TRA and DCF simultaneously, the reaction rates are reduced because of competition reaction. The reaction pathways remain the same, while the toxicity of complex system increased slightly. Permanganate as a common oxidant is widely used for preoxidation. Permanganate oxidize DCF followed the second order reaction kinetics, and the reaction rate decreased with increasing pH. A series of degradation products were analyzed by LC-MS, and a ring-openging reaction mechanism was proposed. Permanganate electrophilic attack of amino firstly, with the formation of the primary intermediate 2,6-dichloroaniline and 5-hydroxy-diclofenac, which can be further oxidized through ring-opening and decarboxylation reaction