Distribution Of Antibiotics In Different Phases Of Water And Their Interaction Mechanism With Humic Acid

In recent years,much more attention has been paid to the contamination of antibiotics in water.Usually,solid in water environment is an important carrier for the distribution of antibiotics in different phases of water,which is influenced by various environmental factors,such as temperature,pH,ionic strength,humus and so on.Exploring the distribution of antibiotics in different phases and the distribution regularities under the influence of various environmental factors are of great significance to understand the environmental behavior of antibiotics and evaluating the harm of antibiotics.In this study,the suspended particles was selected as the representative of solid,and two typical antibiotics of OTC and SD were subjected as the target pollutants,to discuss the distribution regularities of antibiotics in suspension and water phase as well as the influence of various environmental factors on the distribution of antibiotics.Based on that,the interaction between the humus and two of antibiotics was studied by three-dimensional fluorescence spectrometry and UV-Vis spectrum to describe the interaction mechanism and the effects of different environmental factors on the interaction mechanism,then the mechanism of the effects of humus on the distribution of antibiotics in water was further clarified.The main results have been gained as follows:1.Both of the equilibrium concentrations of OTC and SD in suspension and water phase increased with the increase of initial concentration,while the distribution was always as follows:aqueous phase>suspension phase?OTC,SD?,and the distribution coefficient was Kd_OTC>Kd_SD,which indicated that the tetracycline antibiotics were more easily assigned to the suspended phase than the sulfonamides.Thermodynamic analysis showed that the distribution of the two antibiotics in suspension phase was spontaneous endothermic process and high temperature was favorable.The neutral and slight alkaline environment was beneficial to the distribution of two antibiotics in suspension phase.Within the experimental range,the high ionic strength?0.05⁰.08mol/L?was more suitable for OTC and SD from aqueous phase to suspension phase.Low concentration of HA can obviously promote the distribution of OTC and SD in suspension phase,the promotion effect gradually slowed down with the increase of concentration.2.The fluorescence analysis showed that HA is a natural macromolecule with fluorescence characteristics and has abundant functional group structures,which can provide the attachment sites for antibiotics and interact with each other.The fluorescence intensity of HA could be apparently quenched by OTC and SD due to static quenching with forming complexes,and the order of quenching constants K_SVV was as follows:Ksv_OTC>Ksv_SDD and Kb_OTC>Kb_SD,indicating that HA can promote the distribution of two kinds of antibiotics in suspension phase,especially the promoting effect of HA on tetracyclines was more obvious.The interaction between two kinds of antibiotics and HA belonged to spontaneous exothermic process,which illustrated that low temperature enhanced the facilitating effect of HA distribution on antibiotics in suspension phase.pH affected the structure of HA so that indirectly affected the interaction between HA and antibiotics,and then affected the distribution of antibiotics in suspension phase.The biggest quenching constant?Ksv?and the binding constant?Kb?appearing at pH=8.0 explained that neutral and slight alkaline condition was beneficial to the combination of HA with OTC and SD,and thus there was the most obvious effect on the residual distribution of antibiotics in the suspension phase.3.The UV Vis spectra analysis suggested that HA contained more aromatic groups and was easily associated with antibiotics.As the concentration of HA increased,E4/E6 increased,the degree of polymerization of C cytoskeleton or the conjugated degree of carbonyl group decreased,which was beneficial to its interaction with antibiotics and the promotion for the distribution of antibiotics in the suspension phase.With the increase of the concentration of OTC,there was obvious absorption peaks in the range of 230²60 nm and 330³60 nm,and the absorption band of the HA ultraviolet spectrum occurred slightly blue shift and the absorption intensity increased,this demonstrated that a new ground state complex generated.While with the increase of SD concentration,an absorption peak for aromatic structure appeared in the range of 190²20 nm,and the peak value increased and the absorption band happened with red shift,and the aromatization of HA decreased,which enhanced the interaction between antibiotics and HA.It was indicated that HA could promote the distribution of antibiotics in suspension phase.The temperature was insensitive to the UV characteristics of HA,HA-OTC and HA-SD systems.With the increase of pH,the absorption band of HA,HA-OTC and HA-SD ultraviolet spectrum occurred blue shift,the degree of polymerization of HA molecules decreased,the number of adsorption binding sites increased,at the same time,the interaction of antibiotics was enhanced.Therefore,neutral and slight alkaline environment could improve the promoting effect of HA on the distribution of antibiotics in the suspension phase.The absorption band of HA,HA-OTC and HA-SD happened with red shift,with the increase of ionic strength,which indicated that the repulsion between HA particles was weakened and the molecular polymerization was strengthened.Therefore,the interaction between antibiotics and HA was inhibited,and resulting the weakening of the promoting effect of HA on the distribution of antibiotics in the suspension phase.