Research On The Features Of Sorption And Desorption For Fluoroquinolones And Sulfonamides On Purple Soil

Antibiotics for the function of disease prevention,curing of non-virus infection,promoting cell growth,and so on,are used as drugs and feed additives,which are widely used throughout the world.But after entering the animal body,the majority of antibiotics can't used by the body but discharged as bioactive metabolites form or the matrix form,and as agricultural fertilizer into the soil environment,causing potential pollution.Soil is a natural adsorbent and carrier,which provides adsorption point for pollutants.Adsorption is the first step in the introduction of antibiotics into the soil environment,controlling the subsequent transfer and regression,and studying the adsorption behavior of antibiotics is conducive to controlling antibiotic pollution from the source.Desorption is the inverse process of adsorption,which can be used to determine the firmness of pollutants in soil.The purple soil is widely distributed in southwest China,and the purple soil in the southwest region accounts for 51.53%of the total purple soil in China,which is one of the most important agricultural soils in Chongqing area.Given the use and abuse of antibiotics and may cause the environmental risk effect,this study selected the typical purple soil of soil in Chongqing as the tested soil,two common veterinary antibiotics fluoroquinolone antibiotics?FQs?and sulfanilamides antibiotics?SAs?of norfloxacin?NOR?,ofloxacin?OFL?,sulfadiazine?SD?and sulfamethazine?SMZ?as text drug,the adsorption test design was carried out in accordance with the OECD batch balance test,the effects of NOR,OFL,SD and SMZ on the adsorption-desorption characteristics of purplr soil under different experimental conditions were studied.The results of the study are as follows:Adsorption of four antibiotics in purple soil can be divided into began rapid adsorption process and then the slow adsorption process of two stage,FQs and SAs antibiotics choose 6 h and 16 h respectively as adsorption equilibrium time.The initial concentration of FQs antibiotics increased from 1mg/L to 10mg/L,and the adsorption equilibrium quantity of NOR and OFL rose to 195.7 mg/kg and 191.9mg/kg respectively from 19.8 mg/kg and 19.3 mg/kg respectively.After adsorption equilibrium,the average of the adsorption coefficient K_d of NOR in the three concentrations was1133 L/kg,OFL was 417 L/kg.The initial concentration of SAs antibiotics increased from 1mg/L to 10mg/L,and the adsorption equilibrium quantity of SD and SMZ rose from 2.29mg/kg and 2.52mg/kg respectively to 21.2 mg/kg and 33.0 mg/kg respectively.After reaching the adsorption equilibrium,the adsorption coefficient K_d of SD at three concentrations was 4.74 L/kg,and SMZ was 5.71 L/kg.The kinetics of four antibiotics were fitted by the first order kinetics,the second-order kinetics and the Elovich model.In the three dynamic models,the fitting results are indicated as follows:second-order kinetics>Elovich model>first-order kinetics and the correlation coefficients?r?of the three dynamics models are all significantly correlated?p<0.01?.Freundlich,Langmuir and D-R model were adopted to fit the adsorption and desorption isotherm of the four antibiotics,and all of the fitting results were pretty good,r of the three adsorption thermodynamic models reached the significant correlation level?p<0.01?.According to the relationship between adsorption energy gibbs free energy??G?and adsorption energy?E?range and adsorption mechanism,the adsorption of four antibiotics in purple soil are mainly physical adsorption.The desorption of FQs is more weak than SAs'desorption,meanwhile,desorption is also a process of slow release and a quick release.Adopting Freundlich and Langmuir thermodynamic model to simulate the desorption of four antibiotics,the fitting results of the two models were both good,and r reached the most significant correlation level?p<0.01?.Two kinds of antibiotics have different degrees of desorption hysteresis,but they all belong to the positive hysteresis phenomenon,and the mean values of the hysteresis index of NOR,OFL,SD and SMZ are 0.0222,0.0332,0.157 and 0.124 respectively.The effects of different environmental factors?ionic strength,pH value and organic matter content?on the adsorption of four antibiotics were discussed.In general,with the increase of pH value,the adsorption of antibiotics was inhibited,adjust the concentration of the background electrolyte CaCl₂ to change the ionic strength.The increase of ionic strength inhibited the adsorption of antibiotics.The content of organic matter can promote the adsorption of SAs antibiotics in purple soil,but the promotion of FQs antibiotics is less.Some of antibiotics will be preserved in the soil after adsorption,selecting agricultural soils near the farms of Tongnan,Dazu,and Qijiang county three areas,adopting the solid phase extraction-HPLC instrument to measure the capacity of NOR,OFL,SD and SMZ in the soil.Tongnan,Dazu county detection rate showed 100%,while Qijiang county showed 95%.According to the international coordinating council?VICH?pointed out that when antibiotics capacity in the soil is more than 100?g/kg,there will be a larger environmental risk impact on soil microbial community structure and function,as well as the European commission?EM?define risk quotient?RQ?to evaluate the potential of antibiotics in soil environment risk,in the investigation of antibiotic,risk impact of antibiotics on soil mainly comes from the FQs antibiotics,and the soil samples were median risk level.