【作者】 葛林科；

【导师】 陈景文；

【作者基本信息】 大连理工大学 ， 环境工程， 2009， 博士

【摘要】 抗生素作为一类新兴污染物在环境水体中不断被监测到。这类污染物因具有“假”持久性并能引起环境菌群的抗药性而受到广泛关注。氯霉素类与氟喹诺酮类抗生素广泛应用于水产养殖,是环境中特别是在水产养殖区及附近水域中普遍存在的两类抗生素,研究其环境转化、归趋和生态风险具有重要意义。表层水体中,光化学降解是抗生素类污染物的主要消减方式。因此,本论文选取2种氯霉素类抗生素与8种氟喹诺酮类抗生素（FQs）,研究其光解动力学、光解产物、路径和机理,并着重考察重要水环境因子对光解的影响与作用机制,旨在深入理解其环境光化学行为。考察了纯水中氯霉素类抗生素甲砜霉素和氟甲砜霉素的光降解,结果表明:这两种化合物在太阳光或模拟日光（λ＞290 nm）照射下不发生光解,而在UV-vis（λ＞200 nm）照射下发生了光解,其光解反应遵循准一级动力学,表观量子产率分别为0.022±0.002和0.029±0.002。运用电子顺磁共振（EPR）技术及活性氧物种（ROS）淬灭实验,确定了甲砜霉素和氟甲砜霉素的光解反应涉及直接光解和单线态氧（¹O₂）参与的自敏化光解。利用HPLC-MS/MS和离子色谱（IC）,鉴定了甲砜霉素和氟甲砜霉素的光降解产物,据此推测的光降解路径包括自敏化光氧化、光致水解、脱氯及氯化。考察了甲砜霉素和氟甲砜霉素在不同水中的光解动力学差异,发现:UV-vis照射下,它们在海水中光解最快,纯水中次之,淡水中最慢;而在太阳光或模拟日光照射下,仅在淡水中发生了光解。这表明水中溶解性物质对光解的作用依赖于光源发射光谱。为揭示这种依赖效应,深入研究了不同光源照射下海水的优势成分Cl^-、淡水中重要的光活性物质腐殖酸（HA）以及其他溶解性物质（Fe（Ⅲ）、NO₃^-、HCO₃^-等）对甲砜霉素和氟甲砜霉素光解的作用,并用EPR技术检测了ROS。结果表明,在UV-vis照射下,Cl^-促进了¹O₂的生成并加快了自敏化光解;而在模拟日光照射下,即使存在Cl^-,光解也没有发生。在UV-vis照射下,HA通过光掩蔽效应抑制了光解;而在模拟日光照射下,HA光敏化生成¹O₂,引发了甲砜霉素和氟甲砜霉素的降解。与其他溶解性物质的作用相比,Cl^-和HA对光解的作用较为显著,据此可以有效解释不同光源照射下甲砜霉素和氟甲砜霉素在海水、淡水和纯水中光解动力学的差异。为进一步揭示水中溶解性物质对抗生素光解的影响规律,研究了沙拉沙星等8种FQs的环境光化学行为。模拟日光（λ＞290 nm）照射下,纯水中FQs的光解符合准一级反应动力学,量子产率为（0.47～7.0）×10^-2。通过ROS淬灭实验和产物鉴定得知,FQs发生了直接光解及·OH和¹O₂参与的自敏化光降解,光解路径依赖于母体结构,主要为N⁴-烷基脱除、光致脱羧和羟基化脱氟。发光菌（Vibrio fischeri）毒性实验表明,FQs光降解生成了具有较高环境风险的中间产物,对Vibrio fischeri表现出光修饰毒性。与纯水中相比,淡水、海水中FQs表现出了相似或较弱的光降解能力。为理解FQs在不同环境水体中的光化学行为,以沙拉沙星和加替沙星为模型化合物,分别考察了pH、Cl^-和HA对光解的作用,并运用中心组合实验,系统评估了Fe（Ⅲ）、Cl^-、HA和NO₃^-的复合效应。结果表明,淡水、海水中FQs相似或较弱的光降解能力归因于pH与水中溶解性物质对光解的综合作用。在pH 5～11范围内,FQs在其等电点附近光解最快。Cl^-没有显著影响FQs的光解动力学（p＞0.05）,其他溶解性物质HA和NO₃^-等对FQs光解均表现为抑制作用,其不仅通过光掩蔽效应减慢光解,而且能够捕获·OH和¹O₂,抑制自敏化光解。综上,氯霉素类与氟喹诺酮类抗生素均可以发生直接光解和自敏化光解,其光降解动力学受到水中溶解性物质的影响。本研究所揭示的溶解性物质对光解的作用机制,对于理解抗生素类污染物的环境光化学行为具有重要意义。更多还原

【Abstract】 Antibiotics have been increasingly detected in environmental waters as emerging contaminants.These pollutants are pseudopersistent and have been proved to induce bacterial resistance,making them of acute concern.Phenicol and fluoroquinolone antibiotics（FQs） are commonly used in aquaculture and ubiquitous in the environment,especially in fish farms and ambient waters,so it is of great significance to investigate their environmental transformation, fate and ecological risk.In surface waters,photochemical degradation is a central factor in determining the fate of antibiotics.Therefore,the present study selected 2 phenicols and 8 FQs as model compounds,investigated their photodegradation kinetics,photoproducts,pathways and mechanisms,and elucidated the effects of main aqueous environmental factors on the photodegradation so as to better understand their environmental photochemical behavior.Photodegradation experiments on thiamphenicol and florfenicol were performed in pure water under irradiation of different light sources.The two phenicols did not photodegrade under solar or simulated solar irradiation（λ＞290 nm）,but photolyzed quickly when exposed to UV-vis irradiation（λ＞200 nm）.The UV-vis photodegradation reactions followed the pseudo-first-order kinetics,and their quantum yields were 0.022±0.002 and 0.029±0.002, respectively.Electron paramagnetic resonance（EPR） measurements and scavenging experiments indicated that the phenicols underwent direct photolysis and self-sensitized photodegradation via singlet oxygen（¹O₂）.The photodegradation intermediates were identified by HPLC-MS/MS and IC,and the proposed degradation pathways involve self-sensitized photo-oxidation,photoinduced hydrolysis,dechlorination and chlorination.Photodegradation kinetics of the two phenicols in different waters were investigated.It was found that under UV-vis irradiation,they photodegraded the fastest in seawater,followed by pure water and freshwater,whereas under solar or simulated sunlight,they photodegraded in freshwater only.The effects of Cl^-（the dominant seawater constituent）,humic acids（HA, main constituents in freshwater） and other water constituents（Fe（Ⅲ）,NO₃^-,HCO₃^-,etc.） on the photodegradation of the antibiotics as a function of different light sources were studied so as to interpret the light-source-dependent effects of different waters.Under UV-vis irradiation,Cl^- was found to promote ¹O₂ formation and accelerated the photodegradation of the two phenicols,whereas the phenicois did not photolyze under simulated solar irradiation, irrespective of Cl^-.In contrast,the presence of HA inhibited phenicol photolysis under UV-vis irradiation through competitive photoabsorption,but HA photosensitized degradation under simulated solar irradiation.Assessing the role of all the water constituents showed that the light-source-dependent effects of Cl^- and HA on the photodegradation explained most of the different photolytic kinetics in natural waters and pure water.To further understand the effects of aqueous dissolved matter on photodegradation of antibiotics,we explored the environmental photochemical behavior of eight FQs,such as sarafloxacin,gatifloxacin,etc.These FQs were exposed to simulated solar irradiation（λ＞290 nm） and their photodegradation followed apparent first-order kinetics.The quantum yields ranged from 4.7×10^-3 to 7.0×10^-2.Scavenging experiments revealed that the FQs underwent direct photolysis and self-sensitized photodegradation via·OH and ¹O₂.Product studies indicated that three main photodegradation pathways co-occurred and were highly parent-structure dependent.The three pathways are piperazinyl N⁴-dealkylation,photoinduced decarboxylation,and hydroxylated defluorination.The photodegradation solutions of the FQs exhibited photomodified toxicities to luminescent bacterium Vibrio fischeri,indicative of the formation of some hazardous products.The FQs exhibited a similar or less photodegradable potential in freshwater and seawater, compared to that in pure water.In order to elucidate the photochemical behavior in natural waters,sarafloxacin and gatifloxacin were selected as model compounds to examine the individual role of pH,HA and Cl^- on the photodegradation kinetics of the two FQs.Moreover, the multivariate effects of Fe（Ⅲ）,HA,NO₃^- and Cl^- were investigated by a four-factor central composite design.It was observed that the FQs photodegraded the fastest around their isoelectric points.The photodegradation kinetics were not affected by Cl^-（p＞0.05）.HA and NO₃^- inhibited the photodegradation for they acted mainly as radiation filters and had an important role in scavenging reactive oxygen species.These results suggested that the similar or less photodegradable potential of FQs in natural waters was attributed to the integrative effects ofpH and the different aqueous dissolved matter.In conclusion,both the phenicols and the FQs underwent direct photolysis as well as self-sensitized photodegradation.Their photodegradation kinetics were affected by the aqueous dissolved matter.The study revealed the mechanisms for the aqueous dissolved matter affecting the photodegradation,which are of great significance to better understand the environmental photochemical behavior of the antibiotics.更多还原