Study On The Characteristics Of Antibiotics In Poyang Lake And The Adsorption And Degradation Of Typical Antibiotics

Since the mid-1990s,with the continuous popularity of new environmental analytical instruments and methods,the focus on environmental pollutants has gradually extended from traditional and typical pollutants,like heavy metals,persistent organic pollutants(POPs)and eutrophication,to trace emerging pollutants such as antibiotics.While antibiotics play a positive role,they also have negative effects that cannot be ignored.Nearly 20 years of research shows that,due to its frequent use on human,livestock and aquaculture,the constant presence of antibiotics in the environment has resulted in a persistent state;More seriously,these low concentrations of antibiotics pose selective pressures on environmental microorganisms,leading to death of sensitive ones and dominance of resistant ones,and further causing inestimable potential threat to human lives.As a new type of pollutants,antibiotics have gradually raised extensive concerns in public and among environmentalists.Poyang Lake is the largest freshwater lake in China,multiple types of aquacultures and livestocks distribute in the surrounding areas.Meanwhile,the regions surrounding Poyang Lake are densely populated areas,antibiotics from domestic sewage and medical wastewater,which are inadequately treated by the sewage disposal plant or even without any treatment,are directly discharged into nearby canals or rivers and eventually flow into the Poyang Lake,threatening its ecological system.At present,research on the environmental monitoring,risk assessment and environmental fate of antibiotics in Poyang Lake area is basically blank.As the largest freshwater lake in China and a representative region of well-established ecological water environment,it is necessary to carry out relevant researches in Poyang Lake.It is also necessary to develop antibiotic degrading and removing technologies to control the contamination and their induced resistant gene pollution.This study systematically conducts continuous monitoring of antibiotic residues in the surface water in Poyang Lake.The research illustrates the characteristics,temporal and spatial distribution in Poyang Lake,urban lakes and aquaculture waters around Poyang Lake;the risk quotient methods(RQs)are used to evaluate the ecological risk of antibiotics in the above types of water;the adsorption and photodegradation of typical antibiotics in Poyang Lake areas are studied by indoor simulation experiments.Finally,the degradation and removal for a variety of antibiotics(4 kinds of tetracycline class,5 kinds of sulfonamides and 5 kinds of quinolones)by adsorption of typical red soil in Jiangxi province coupled with laccase oxidation is carried out,and the degradation mechanism is preliminarily expounded.This research could provide scientific basis and technical support for the water environmental protection and environmental management of emerging pollutants in Poyang Lake basin.The main achievements of this research include:(1)For three consecutive years from 2014 to 2016,this project systematically carried out monitoring of antibiotics in Poyang Lake,including the characteristics,temporal and spatial distribution of antibiotics in Poyang Lake.The aquaculture water surrounding Poyang Lake and lake water from a nearby city were also monitored.Meanwhile,this study also discussed the impact of "Five River" flow on the temporal distribution of antibiotics in Poyang Lake.The results showed that the residual content of antibiotics during our monitoring period in Poyang Lake was low,and the concentration was in ng/L level.Tetracyclines(TCs),sulfonamides(SAs)and macrolide antibiotics(MLs)are the main types of antibiotics detected in Poyang Lake.Compared with other lakes and waters,the detection concentration of five target antibiotics in Poyang Lake was moderate or below average.The concentration of sulfamethoxazole(SMX)in certain aquaculture water body around Poyang Lake was close to 300ng/L.Compared with other lakes in our country,the concentrations of antibiotics in five urban lakes in Nanchang were generally at moderate levels,except for the enrofloxacin(EFX).(2)This research adopts the RQs presented in the EU technical guidance documents as environmental risk assessment method to evaluate the ecological risk of typical antibiotics in Poyang Lake area.The acute and chronic toxicity data of organics on three typical species(fish,daphnia,and algae)in aquatic ecosystem was collected from the Ecological Structure Activity Relationships Program(ECOSAR,v1.1)model developed by USEPA.RQs classification method is proposed for ecological risk classification.The research indicates that,during our monitoring period,the antibiotic pollution level in the water body of Poyang Lake and its surrounding cities is virtually risk-free,but the risk attains a medium level at individual aquaculture point.(3)In this paper,the sediment adsorption and photodegradation behaviors of four typical antibiotics(two quinolones and two sulfonamides)in Poyang Lake area were studied by indoor experiment.The results showed that the adsorption process of four antibiotics was in accordance with the pseudo second-order kinetics model,and the adsorption was mainly chemical adsorption.Two kinds of sulfonamide antibiotics are difficult to be adsorbed on sediments in Poyang Lake water,while two quinolones can be adsorbed quickly on sediments in lake water.The photodegradation rates of four antibiotics were sequenced as follows:ciprofloxacin>enrofloxacin>sulfadiazine>sulfamethoxazole.Sediment adsorption is the main fate of two quinolone antibiotics in sediment and lake water environment.However,the two sulfonamide antibiotics are difficult to be adsorbed on the sediment,and the photodegradation rate is also very slow.Therefore,they are easy to stay in the water environment or migrate with the water flow.(4)This study developed a method for the removal of multiclass antibiotics(4 tetracyclines,5 sulfonamides and 5 quinolones)by typical Jiangxi red soil coupled with laccase from Trametes versicolor.The optimum parameters of the coupling system were as follows:syringaldehyde(SA)was chosen to be a mediator in the laccase mediator system,the reaction concentration of SA was 0.5 mmol/L,pH=6,reaction temperature was 25?,laccase concentration was 0.5 mg/mL,and red soil concentration was 50 g/L.The results showed that the removal rates of all kinds of antibiotics were over 70%and 90%respectively in 15 min and 60 min,and nearly 100%in 180 min in the coupling system.Most of the antibiotic removal occured in the first 15 min,showed that the coupling system can effectively remove three kinds of antibiotics at the same time.Tetracycline and sulfonamide antibiotics can be oxidized and degraded by laccase-SA catalytic oxidation,and tetracyclines and quinolones can be adsorbed by red soil.However,in the coupling system,laccase-SA oxidation was the main mechanism for the removal of tetracycline antibiotics.