Study On The Degradation Of Chloramphenicol In Water And Sediment Based On Stable Isotope Analysis

Chloramphenicol antibiotics,as a kind of typical antibiotics,is widely used in medical and aquaculture,especially present in waters near the hospital and aquaculture areas.The environmental pollution caused by chloramphenicol can not be ignored.Chloramphenicol is mainly studied in pollution distribution,residue detection,degradation mode and influencing factors.There are few reports on the mechanism of degradation and the variation of stable isotope characteristics.In recent years,compound-specific isotope analysis(CSIA)developed gradually and has been applied to the field of environment,the limitation of traditional research methods is solved.Based on chloramphenicol as the research object,this study uses the CSIA technology to establish the concentration of chloramphenicol monomer and carbon hydrogen isotope analysis method.Then we study the degradation of chloramphenicol hydrolysis and the photodegradation process of hydrogen and carbon isotopic composition of changes with the presence of the sediment.The carbon and hydrogen isotope fractionation and the correlation between carbon and hydrogen isotopes in different chloramphenicol degradation processes were revealed.The apparent kinetic effects of chloramphenicol were further analyzed based on the previous research results to provide more theoretical basis for the degradation mechanism.The main research results are summarized as follows:(1)The detection method of chloramphenicol concentration and carbon hydrogen monomer isotope analysis was established.The suitable concentration range of chloramphenicol concentration and molecular carbon and hydrogen isotope analysis was established,ranging from 1 to 5 mg/L.The recovery rate of the method was 82.0%～93.1%,and the RSD value was between 0.53%～6.71%.The precision of this method is better.(2)The degradation kinetics of chloramphenicol in different degradation processes were analyzed.The hydrolysis and photodegradation of chloramphenicol in different media(aqueous phase and granular phase)were in accordance with the first-order reaction kinetics,and the correlation coefficients were all above 0.97.The degradation rate of chloramphenicol in the photodegradation process was about 2 times that of the hydrolysis process,indicating that the photodegradation process was the main one in the natural water environment.The degradation rate of chloramphenicol in the granular phase was about 1.3～1.5 times that in the aqueous phase,indicating that chloramphenicol degrades more quickly and to a greater extent in the granular phase of sediment.(3)The effect of sediment adsorption on chloramphenicol was studied.The adsorption of sediment on chloramphenicol gradually reached the adsorption equilibrium after 3 hours.In the adsorption process,the carbon and hydrogen isotopic composition of chloramphenicol did not change significantly,indicating that the adsorption process did not affect the isotopic fractionation effect of chloramphenicol,and the degradation reaction was the main cause of the isotope fractionation effect.(4)The influence of sediment on chloramphenicol degradation process was studied.In the presence of sediment,the fitting results of isotopic fractionation degree and degradation degree of chloramphenicol in different media were better,and the fitting coefficients were above 0.96,show that the degradation process of water phase and particle phase in chloramphenicol molecular carbon isotope fractionation follow Rayleigh fractionation model.Isotope enrichment coefficient of particle phase chloramphenicol photodissociation process carbon isotope enrichment coefficient was about 1.7 times in the aqueous phase,the hydrolysis process of carbon isotope enrichment coefficient of about 1.3 times in the aqueous phase and particle phase hydrogen isotope enrichment coefficient of about 1.2～1.4 times of water phase,show that the degree of isotope fractionation in the particle phase was greater than in the water phase and photodegradation process of isotope fractionation degree was greater than the hydrolysis process.In other words,the photodegradation degree of chloramphenicol in particle phase was greater and the degradation was more complete.(5)Using two-dimensional carbon-hydrogen isotopic composition of the relative changes of identification to distinguish the different degradation process of chloramphenicol,Λvalue of chloramphenicol hydrolysis was 27.08 to 27.71,the photolysis processΛvalue was 4.69 to 6.11,Λvalue can effectively distinguish between chloramphenicol hydrolysis and photodegradation reaction.The AKIE_C value of chloramphenicol hydrolysis reaction was 0.996-1.008,which conformed to the KIE value range of nucleophilic substitution reaction(SN1)C-N bond fracture,indicating that chloramphenicol produced amide hydrolysis.During the photodegradation process,the AKIE_C value of the photodegradation reaction of chloramphenicol in the aqueous phase was 1.025-1.030,which was in line with the KIE range of the nucleophilic substitution reaction(SN1)of C-Cl bond fracture.The AKIEC value of the photodegradation reaction of chloramphenicol in the granular phase was 1.042,which was close to the KIE value of the oxidation of C-C bond,which may be the photooxidation and condensation reaction process of C-C bond fracture.In this paper,through the establishment of chloramphenicol stable isotope analysis method,analysis and research the different degradation process of carbon and hydrogen isotopic composition of chloramphenicol characteristics,isotopic fractionation for perfecting chloramphenicol degradation process database,the chloramphenicol degradation mechanism provides a theoretical basis and technical support,is of great significance to the further study of environmental behavior of chloramphenicol.