| Antibacterial agents are widely used in livestock and poultry production as preventives and therapeutics against bacterial infections.After application,only a small amount of drug residues in animals,and most of these agents(60%-90%)are excreted as prototypes or metabolites through feces and urine which pollute soil,groundwater,surface water and sediments,etc.leading to environmental drug-resistant bacteria and drug residues in agricultural products.Finally,antibacterial agents' residues are consumed by people through meal and threaten human's health.Fluoroquinolone antibiotics(FQs)are widely used in human medicine and aquaculture in recent years due to their advantages of wide antibacterial spectrum,strong antibacterial activity,wide distribution in vivo,high tissue concentration,etc.A large amount of drug-containing contaminants are discharged into the environment,resulting in high enrichment of fluoroquinolone drugs in the environment.FQs in the environment will eventually be eaten by human beings by migrating to the food chain,endangering human health.Therefore,how to accelerate the degradation of FQs in livestock and poultry manure and reduce FQs pollution in the environment are attracting great attention from scholars all over the world.In this study,HPLC methods for the determination of Mabaoshaxing(MBF)and Salashaxing(SAR)residues in pig excrement were established through the selection of sample extracts.The effects of MBF and SAR concentrations and environmental light,temperature and fermentation on the degradation of the two drugs in pig excreta were studied by this method,so as to provide support for the safe use of pig excreta containing drugs.(1)The results of the Establishment of HPLC method for simultaneous detection of Marboftoxacin(MBF)and Sarafloxacin(SAR)in pig excreta showed: the extraction solutions of methanol acetate,ammoniated methanol,methanol,concentrated acetic acid and deionized water were investigated in the screening of sample pretreatment methods.It was found that the extraction effects of MBF and SAR from pig excrement were better when methanol: concentrated acetic acid: deionized water =6:1:3.The mobile phase detected by HPLC is 0.05mol/L citric acid and methanol solution,flow rate is 1ml/min,column temperature is 35°C,fluorescence detectorwas used,fluorescence excitation wavelength was 278 nm,emission wavelength was 495 nm.The minimum detection limit of MBF was 0.0105 ?g/ml,the recovery rates were 72.99% ~ 89.16%,the minimum detection limit of SAR was 0.0438 ?g/ml,and the recovery rates were 72.34% ~80.42%.(2)The results of the effects of initial concentration of drugs on degradation showed that: the degradation rates of MBF and SAR were obviously affected by concentrations.The higher the initial concentration of drug,the slower the degradation rate would be when compared with the degradation rate of lower concentration.When the initial concentration of the drug is 20 ?g/mL,50 ?g/mL and 100 ?g/mL respectively,the degradation rates of MBF were 17.25%,13.58% and11.85%,the half-lives were 239 d,266.54 d and 301.3d.While the degradation rates of SAR were14.95%,12.06% and 10.49%,and the degradation half-lives were 315 d,330d and 364.74 d.(3)The results of the effect of light conditions on the degradation showed that: light promoted the degradation of drugs.MBF and SAR were relatively stable and got a long half-lives in the dark.However,the degradation rates of MBF increased to 75.60%,58.18% and 45.19%under light.The degradation half-lives were 11.75 d,16.12 d and 16.9d respectively.While,the degradation rates of SAR increased to 69.45%,53.96% and 40.83%,and the degradation half-lives were 11.36 d,15.75 d and 17.1d respectively.(4)The results of the effects of temperature on degradation showed that: the initial concentrations of MBF were 20 ?g/mL,50 ?g/mL and 100 ?g/mL at 25?.After 29 days of degradation,the degradation rates were 29.90%,25.10% and 23.49%,and the degradation half-lives are 53.31 d,69.3d and 77 d.However,the degradation rate increased slightly at 45?,40.80%,34.66% and 29.05% respectively,and the half-lives of degradation were 34.65 d,36.47 d and 43.31 d respectively.At 25?,the initial concentration of SAR were 20 ?g/mL,50 ?g/mL and100 ?g/mL.After 29 days,the degradation rates were slightly higher than that of MBF,which were 32.05%,27.96% and 26.21%.The degradation half-lives were 33 d,43.31 d and 49.5d.However,the degradation rates at 45? were the same as that of MBF.The degradation rates were45.10%,31.64% and 29.45%,and the half-lives of degradation were 23.1d,34.65 d and 40.76 d.(5)The results of the effects of lactic acid bacteria fermentation on the degradation showed that lactic acid bacteria fermentation had little effect on the degradation of these two drugs.After adding exogenous fermented lactic acid bacteria into pig excrement for 29 days,the degradationrates of MBF and SAR with initial concentrations of 20 ?g/mL,50 ?g/mL,100 ?g/mL were38.70%,31.38%,25.73% and 41.10%,33.74%,26.25%,and the degradation half-lives were 33 d,46.2d,57.75 d and 26.65 d,31.5d,43.31 d.(6)The results of investigations on the two FQs pollution contents in pig excreta of some large-scale pig farms in southern Guizhou showed that: MBF was not detected,and the pollution concentrations of SAR were 0.022-0.2?g/g/g.Conclusion: The degradation rates of MBF and SAR in pig excreta are lower and the residual time is longer.The higher the drug concentration is the lower the degradation rate would be.Light,high temperature and fermentation can promote the degradation of the two drugs,and Lighting effects is the best.However,the harm to the environment caused by the discharge of pig excreta containing drugs within 29 days and agricultural usage of these pig excreta needs further investigation. |
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