Degradation Of Typical Quinolones By UV/PDS And Preliminary Study On Cytotoxicity Of The Products

In recent years,although the Animal Husbandry and Veterinary Bureau of Ministry of Agriculture and Rural Affairs has strictly controlled the use of drugs in aquaculture,and some antibacterial drugs have been restricted or prohibited,some small and medium-sized aquaculture companies still use various antibacterial drugs unreasonably to promote the growth of aquatic organisms and prevent diseases.Because antibacterial drugs are highly chemically stable and difficult to degrade,and the low concentration of antibacterial drugs can pose a threat to the lives and health of organisms and humans,the problems of antibacterial drugs residues in aquaculture water bodies have attracted more and more attention.Ultraviolet（UV）/Peroxydisulfate（PDS）combined process is an advanced oxidation technology based on sulfate radical（·SO₄^–）.The redox potential of·SO₄^–is as high as 2.5～3.1 e V,which can effectively degrade the residual antibacterial drugs in freshwater.However,there are relatively few studies on the degradation of antibacterial drugs in marine aquaculture water.In this paper,UV/PDS advanced oxidation technology was used to study the degradation of ofloxacin（OFL）and flumequine（FLU）,the main content of this study is the reaction kinetics of OFL and FLU,and the reactive active site of OFL and FLU,product composition and production pathway,and preliminary biotoxicity analysis of the product.The results of the study are as follows:（1）The effects of different water bodies,inorganic anions,initial p H and initial concentration of PDS on the degradation of OFL and FLU by UV/PDS system were studied.OFL and FLU can be degraded by UV/PDS in fresh water,marine aquaculture water and seawater,but the reaction rate constants were different in different water bodies.The reaction rate constants of OFL in different water bodies was in the following order:seawater>marine aquaculture water>freshwater,while flumequine followed freshwater>marine aquaculture water>seawater.The difference in reaction rate was mainly caused by the different concentration of inorganic anions in the water.Br^–and HCO₃^–can promote the degradation of OFL by UV/PDS system,while Cl^–can inhibit the degradation of OFL by UV/PDS.Br^–,Cl^–and HCO₃^–all can inhibit the degradation of FLU by UV/PDS.In addition,the change of p H value will also affect the degradation of OFL and FLU in the UV/PDS system.Over-acid and over-alkali will inhibit the degradation of OFL by UV/PDS,and the reaction rate was the largest when the initial p H=7,while the degradation rate of FLU decreased as the p H value increases.The increase of the initial perdisulfide concentration will promote the degradation of OFL and FLU.（2）Based on density functional theory,the frontier molecular orbital and charge distribution characteristics of OFL and FLU were analyzed,and the reactive sites of OFL and FLU were inferred.The reactive sites of OFL were mainly located in the piperazine group and the quinolone group.The N1,N2,C6and C7 atoms on the piperazine ring had higher negative charges,which were the best attack sites for electrophiles;C21,O24,O25 and O26 on the quinolone group also had higher negative charges and were the best attack site for nuclear reagents.The electron cloud of HOMO and LUMO of FLU was mainly distributed in the quinolone group.The quinolone group was not only the best attack site for electrophiles but also the best attack site for nucleophiles.According to the energy band gap(E_HOMO-E_LUMO)results,FLU was more stable than OFL.The product analysis showed that OFL was degraded mainly through decarboxylation,defluorination,deoxygenation and hydrogenation reactions in the UV/PDS system,and seven final products were observed,including two halogenated products,but only one non-halogenated product was identified in the FLU degradation system.（3）The preliminary cytotoxicity analysis showed that the degradation products obtained by the reaction of UV/PDS and OFL showed slight toxicity to Chlorella pyrenoidosa and Priacanthus tayenus.The product had a maximum inhibition rate of 9.72%on Chlorella pyrenoidosa,and caused slight damage to the liver cells of Priacanthus tayenus,reducing the species richness and diversity of intestinal microbes.However,compared with the traditional method UV/Na Cl O,the cytotoxicity of the products was obviously much lower;according to the analysis results of EPI Suite,compared with FLU（Logkow=1.6,Log BCF=0.579）,the intermediate products of FLU（Logkow>1.6,Log BCF>0.579）were more likely to accumulate in organism,while the Logkow and Log BCF of the final product P100 were both less than 0,indicating that after UV/PDS treatment,the bioaccumulation of the final product P100 of FLU was relatively low,and it was not easy to accumulate in the organism.In summary,studying the degradation process of OFL and FLU under the action of the UV/PDS system provided a theoretical basis for the removal of antibacterial drugs in the aquatic environment（fresh water,marine aquaculture water and sea water）.