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。以恩诺沙星(ENR)为目标抗生素,这项研究调查了ENRCl-DBPs在人工湿地(CWs)中的降解和转化。结果表明,ENR及其Cl-DBPs在初步阶段影响了CW的生物降解,但不影响植物根系的吸附,基材,和生物膜。ENR的哌嗪基团具有很大的电负性,容易发生亲电反应。ENR的喹诺酮基团上的羧基具有较强的亲核性,并且容易发生亲核反应。喹诺酮基团芳香结构上带显著负电荷的C原子容易发生卤化。在ENR氯化过程中,一个途径是喹诺酮组的反应,其中氯的亲核取代反应发生在羧基上的C26原子上,然后在芳香环上C17位点的Cl+作用下发生卤化;另一个途径是哌嗪基团的反应,其中N7原子首先被HOCl攻击,导致哌嗪环裂解,然后是脱酰基,脱烷基化,和卤化。在ENRCl-DBPs的生物降解过程中,哌嗪结构的反应性强,尤其是在N6、N7、C13和C14位点,喹诺酮类的环结构相当稳定,并且仅在N5位点发生癸环丙基。总的来说,ENRCl-DBPs在CWs中的生物降解经历了包括哌嗪环裂解的过程,叔胺裂解,脱烷基化,以及在辅酶作用下的醛氧化,其中代谢物如酮,醛类,羧酸,酰胺,伯胺,仲胺,生产叔胺和乙醛酯。大多数ENRCl-DBPs比它们的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,CWs通过吸附和生物降解的协同作用有效降低了ENRCl-DBPs的环境风险。
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.