Wang Xiaoou, Xue Ming, Wang Meiyan, Zhang Changping, Li Jiayin, Xie Haijiao
Key Laboratory of Clean Energy Utilization and Pollutant Control in Tianjin, School of Energy and Environmental Engineering, Hebei University of Technology, China.
Key Laboratory of Clean Energy Utilization and Pollutant Control in Tianjin, School of Energy and Environmental Engineering, Hebei University of Technology, China.
Chemosphere. 2024 Mar;352:141404. doi: 10.1016/j.chemosphere.2024.141404. Epub 2024 Feb 9.
Antibiotic residues and their chlorinated disinfection by-products (Cl-DBPs) have adverse effects on organisms in aquaculture water. Taking enrofloxacin (ENR) as target antibiotic, this study investigated the degradation and transformation of ENR Cl-DBPs in constructed wetlands (CWs). Results showed that, ENR and its Cl-DBPs affected the biodegradation of CWs at the preliminary stage, but did not affect the adsorption by plant roots, substrates, and biofilms. The piperazine group of ENR had great electronegativity, and was prone to electrophilic reactions. The carboxyl on quinolone group of ENR had strong nucleophilicity, and was prone to nucleophilic reactions. C atoms with significant negative charges on the aromatic structure of quinolone group were prone to halogenation. During the chlorination of ENR, one pathway was the reaction of quinolone group, in which nucleophilic substitution reaction by chlorine occurred at C26 atom on carboxyl group, then halogenation occurred under the action of Cl at C17 site on the aromatic ring; the other pathway was the reaction of piperazine group, in which N7 atom was firstly attacked by HOCl, resulting in piperazine ring cleavage, then followed by deacylation, dealkylation, and halogenation. During the biodegradation of ENR Cl-DBPs, the reactivity of piperazine structure was strong, especially at N6, N7, C13, and C14 sites, while the ring structure of quinolone group was quite stable, and only occurred decyclopropyl at N5 site. Overall, the biodegradation of ENR Cl-DBPs in CWs went through processes including piperazine ring cleavage, tertiary amine splitting, dealkylation, and aldehyde oxidation under the action of coenzymes, in which metabolites such as ketones, aldehydes, carboxylic acids, amides, primary amines, secondary amines, tertiary amines and acetaldehyde esters were produced. Most ENR Cl-DBPs had greater bioaccumulation potential and stronger toxicity than their parent compound, fortunately, CWs effectively reduced the environmental risk of ENR Cl-DBPs through the cooperation of adsorption and biodegradation.
抗生素残留及其氯化消毒副产物（Cl-DBPs）对水产养殖水体中的生物具有不利影响。本研究以恩诺沙星（ENR）作为目标抗生素，调查了人工湿地（CWs）中ENR Cl-DBPs的降解和转化情况。结果表明，ENR及其Cl-DBPs在初始阶段会影响人工湿地的生物降解，但不影响植物根系、基质和生物膜的吸附作用。ENR的哌嗪基团具有很强的电负性，易于发生亲电反应。ENR喹诺酮基团上的羧基具有很强的亲核性，易于发生亲核反应。喹诺酮基团芳香结构上带有显著负电荷的碳原子易于发生卤化反应。在ENR氯化过程中，一条途径是喹诺酮基团的反应，即羧基上的C26原子发生氯的亲核取代反应，然后在Cl作用下芳香环上的C17位点发生卤化反应；另一条途径是哌嗪基团的反应，即N7原子首先被HOCl攻击，导致哌嗪环裂解，随后发生脱酰基、脱烷基和卤化反应。在ENR Cl-DBPs的生物降解过程中，哌嗪结构的反应活性较强，尤其是在N6、N7、C13和C14位点，而喹诺酮基团的环结构相当稳定，仅在N5位点发生去环丙基反应。总体而言，人工湿地中ENR Cl-DBPs的生物降解经历了哌嗪环裂解、叔胺分裂、脱烷基和在辅酶作用下的醛氧化等过程，其中产生了酮、醛、羧酸、酰胺、伯胺、仲胺、叔胺和乙醛酯等代谢产物。大多数ENR Cl-DBPs比其母体化合物具有更大的生物累积潜力和更强的毒性，幸运的是，人工湿地通过吸附和生物降解的协同作用有效降低了ENR Cl-DBPs的环境风险。
