Interactions Of Cyanobacterial Blooms-derived Dissolved Organic Matter And Antibiotics

The presence of residual antibiotics in environment is of great concern due to their ecotoxicity effects and ecological risks.The anbitiotics can promote the development of antibiotics-resistant genes among bacterial populations.Occurrence of cyanobacterial harmful algal blooms(CyanoHAB)in freshwater ecosystems has expanded worldwide in recent decades because of the dual pressure from increasing anthropogenic activity and global climate change.The overgrowth of cyanobacteria releases a considerable part of their phtotsynthetic products as dissolved organic matter(DOM),which is of vital importance to the environmental behaviors,including complexation,sorption,degradation,and accumulation,of contaminants in waters.However,the complex interactions between the occurrence of CyanoHAB and the fate of antibiotic,which is of vital importance to the assessment and control of combined pollution in eutrophic lakes,has yet to be elucidated.Accordingly,the present study focused on the typical CyanoHAB derived-DOM from the eutrophic Lake Taihu(China),investigated the complexations of DOM and antibiotics,and revealed the roles of critical factors in regulating the sorption of antibiotics.Results of this work provide deeper insights toward understanding the migration,elimination,and ecotoxicity of antibiotics in eutrophic lakes,being of great significance to the sustainable development of ecology and human health.The main results are listed as following:(1)Complexations of antibiotics with CyanoHAB-derived DOM were studied using multi-spectroscopic techniques.The three fluorescent components,tyrosine-,tryptophan-,and humic-like component,were identified in DOM by excitation emission matrix spectra with parallel factor analysis(EEM–PARAFAC).Their fluorescence were quenched at different degree by tetracycline(TTC)titration through static quenching.Conformational changes in DOM fractions in the complexation of TTC was indicated by UV–Vis spectra.Synchronous fluorescence spectra combined with two dimensional correlation spectroscopy(2D–COS)further suggested that the formation of TTC–DOM complexes occurred on the sequential order of tryptophan-> tyrosine-> humic-like component.The associated complexing constants(logK)of three components with TC were in the range of 5.05-5.85,followed the order of C2 > C3 > C1.Therefore,the binding ability of protein-like substances to TTC were stronger than that of humic-like substances.(2)Roles of CyanoHAB-derived DOM components in the sorption of antibiotics onto sediment minerals were investigated.The presence of DOM promoted the adsorption of SMT on goethite(?–FeOOH).The adsorptive fractionation of DOM on goethite indicated that the affinity sequence of the four fluorescent PARAFAC components followed the order of: tryptophan-> tyrosine-> long emission wavelength(LEW)humic-> and short emission wavelength(SEW)humic-like component.Meanwhile,tyrosine-like components can strongly form complexes with SMT with a large binding constant,followed by tryptophan-and SEW humic-like components.However,LEW humic-like component did not effectively react with SMT.This result indicated that protein-like substances in DOM were favorable to SMT adsorption by acting as a bridge to form complexes with both goethite surface and SMT molecules,whereas humic-like substances played secondary roles in the DOM–goethite–SMT ternary system.(3)Effects of biodegradation on the functional components in DOM-antibiotics complexation were studied.A total 79% dissolved organic carbon loss over time accompanied after the 4-day biodegradation in a laboratory 4-stage plug-flow bioreactor.EEM–PARAFAC analysis showed that the protein-like components were preferentially degraded by microorganisms as compared to the humic-like components.With the combination of high performance liquid chromatography-EEM and 2D–COS,the bioavailiability of relatively hrdrophilic protein-like components was suggested to be stronger than hydrophobic ones.However,hydrophilic humic-like components were more bioresistant than hydrophobic ones.Therefore,although CyanoHAB-derived DOM can stabilize antibiotics temporarily,the significant biodegradation of DOM in the later period of CyanoHAB may decrease the binding affinity of antibiotics to DOM.