Degradation Products Identification And Biotoxicity Analysis Of Cephalosporins By The Ultrasonic/Fenton Process

Cephalosporins,a typical antibiotic,were widely used,which also caused serious pollution problems.At present,the existing treatment technology of sewage treatment plants cannot remove cephalosporins effectively,and the presence of cephalosporin antibiotics can inhibit the metabolic activity of microorganisms.Therefore,it is quite necessary to identify the characteristic pollutants of cephalosporins in the degradation process,so as to determine the causes of the refractory and high-toxicity in the water environment,and provide reference for evaluation of ecological environment and treatment measures for cephalosporins in the future.This study selected three common cephalosporin antibiotics:cefadroxil,ceftriaxone,and cefradine for research.The dissertation elucidated the degradation process and degradation products.The main conclusions of this study are as follows:?1?This dissertation studied the behavior of three cephalosporin antibiotics during ultrasound,Fenton degradation process.First,the cephalosporins were degraded by ultrasound and Fenton respectively.The degradation was studied from several aspects including pH,ultrasonic power,and ultrasonic time under ultrasonic conditions.Fenton's experiments investigated the following degradation conditions:dosage of ferrous sulfate,the ratio of H₂O₂ to ferrous sulfate,and the reaction time.Based on the above experiments,the best degradation conditions can be determined for cephalosporins.In addition,through data screening,UV scanning,GC-MS,and so on,the degradation products can be identified and characterized.The degradation of cefadroxil,ceftriaxone,and cefradine can be achieved by ultrasound and Fenton.Ultrasound can achieve rapid degradation of cefadroxil,ceftriaxone,and cefradine,but the degradation rate is less than 45%;in the Fenton degradation experiments,when C(Fe²⁺)=0.036 mmol/L,C?H₂O₂?:C(Fe²⁺)=6:1;C(Fe²⁺)=0.054 mmol/L,C?H₂O₂?:C(Fe²⁺)=12:1;C(Fe²⁺)=0.036 mmol/L,C?H₂O₂?:C(Fe²⁺)=6:1,the three cephalosporin antibiotics all have the best degradation rates.the best degradation rate of them can reach up to 97.1%,84.1%,and 80.7%,respectively.?2?The toxicity of ceftriaxone is higher than cefadroxil,cefradine among the three cephalosporin antibiotics.The EC50 values of ceftriaxone measured by luminescent bacteria and dehydrogenase activity were 12.1 mg/L and 25.36 mg/L,respectively.Evaluating the biological toxicity of cefadroxil,ceftriaxone,and cefradine in the degradation process:the toxicity of cefadroxil,ceftriaxone,and cefradine were reduced by the Fenton process.However,there is a phenomenon that the toxicity is higher than the parent compound during the reaction.?3?GC-MS Analysis of cephalosporins'degradation products concludes that cefadroxil can transform into three fragments of P1?P2?P3 through the removal of–OH group and the opening of?-lactam ring;Ceftriaxone sodium can transform into three fragments of P4?P5?P6 through dounle-bond isomerism and the opening of?-lactam ring;Cefradine can transform into four fragments of P3?P7?P8?P9 through the removal of–OH and COOH—groups and the opening of?-lactam ring.The specific structure of the fragments can be further deduced by mass spectrometry combined with the structure of cefadroxil,ceftriaxone sodium and cefradine,and their degradation paths can be predicted respectively.?4?7-ACA,as degradation products,may appeared the degradation process of cephalosporin antibiotics.The toxicity of 7-ACA compounds may be even higher than the parent compounds,resulting in higher toxicity during degradation.P1,P4,and P7 all belong to 7-ACA compounds and may be the main cause of increased toxicity of cefadroxil,ceftriaxone,and cefradine during degradation process.