Transformation And The Associated Toxicity Of Penicillin Antibiotics In Natural Water And Soil Mineral Environments

With the increasing consumption of antibiotic drugs,numbers of researchers have paid more attentions to the problems of environmental resistance bacteria and resistance gene.However,understanding of the complex relationship between resistance bacteria(gene)and antibiotics in soil and water environments need further investigations based on amounts of theoretical knowledges involving migration and transformation rules of antibiotics,environmental relevant concentration and persistence,metabolic process,degradation pathway of antibiotics and their products.The migration,transformation and degradation mechanisms of penicillin antibiotics,which are the most widely used antibiotic,have been widely reported.However,these studies mainly focused on the degradation kinetics of penicillin antibiotics,and the quantitative and qualitative analysis of degradation products in simulated solutions in laboratory.The transformation and degradation mechanisms of penicillin antibiotics in natural water and soil medium are still poorly understood.In addition,previous studies indicate the toxicity variation of penicillin and cephalosporin antibiotics during hydrolysis and photolysis,but the mechanism of the product toxicity is also still unclear.To overcome these problems,four class penicillin antibiotics were chosen as the model antibiotics including 6-aminopenicillanic acid,penicillin G,ampicillin and amoxicillin.The contents about(i)photolysis and hydrolysis of penicillin G in natural waters,(ii)degradation of penicillin antibiotics in simulated soil system and(iii)toxicity of penicillin products after hydrolysis and photolysis were all investigated.The main factors and mechanisms of penicillin antibiotics in soil and water environments and the toxicity mechanisms of penicillin degradation products were predominantly focused.The main conclusions were illustrated as follows:(1)Hydrolysis and photolysis are the two main degradation pathways of penicillin G in natural water.Ca2+ ions in natural water are the main factors in controlling the hydrolysis rate of penicillin G,and the soluble biological metabolic organic matter can also promote this hydrolysis.A large number of Ca2+ions can coordinate with the carbonyl and carboxyl groups in penicillin G molecule,which stabilize the reaction intermediate of hydrolysis.This accelerates the hydrolysis rate of penicillin G.The amino and sulfhydryl groups in soluble biological metabolic organic matter can also act as a strong nucleophile to facilitate the rapid hydrolysis of penicillin G.The direct photolysis is the main process in natural water,and the photolytic rate is not affected by pH,salt concentration and organic matter in surface water.The hydrolysis pathway of penicillin G in natural water mainly contains the destruction of ?-lactam bond,decarboxylation,hydrolysis of branched amide bond,etc.The photolytic pathway involves hydroxylation of benzene ring and the oxidation of ?-lactam ring in PG molecule.(2)Under neutral condition,goethite and Zn2+ in soil can synergistically catalyze the rapid hydrolysis of penicillin antibiotics,and the hydrolysis rates in goethite/Zn system are hundreds of times higher than that in the presence of sole goethite or Zn2+ion.The coordination between penicillin and goethite surface was characterized by Fourier transform infrared spectroscopy(FTIR)in ternary penicillin/goethite/Zn2+system.The specific complex among penicillin,goethite and adsorbed Zn is responsible for the rapid hydrolysis process.The hydrogen bond between surface hydroxyl groups and carbonyl group in penicillin,and the bidentate complex between surface ion and carboxyl groups in penicillin can stabilize the reaction intermediate in hydrolysis reaction.The fitting results of Zn-K-edge X-ray near-edge absorption spectrum showed that under the neutral and weak alkaline conditions,the adsorbed Zn2+on goethite surface was dominantly in the form of Zn hydroxides,and Zn(OH)2 can as act the main nucleophile to catalyze the penicillin hydrolysis.PO43-and F-ions were utilized to modify different hydroxyl groups on goethite surface,and we found bidentate and tridentate hydroxyl groups on goethite surface were the main active sites involved in penicillin hydrolysis reactions.(3)During the photolysis,the significantly increasing toxicity of penicillins and cephalosporins was observed,and the toxicity of photolysis products was higher than hydrolysis products.Four penicillin antibiotics(6-aminopenicillanic acid,penicillin G,ampicillin and amoxicillin)have the different basic structures,but the similar toxicity level,indicating that the photolytic products of the ?-lactam structure part of penicillin were the main active composites for increasing toxicity.Meanwhile,the photolysis volatile products such as benzene and toluene were also partly attributed to the toxicity.Different advanced oxidation processes of penicillin antibiotics have different toxicity effects.No remarkable toxicity effects of products were observed in ·OH oxidation processes including UV+H2O2 and Fenton reactions,and the toxicity of intermediate products increased with the increase of SO4-· concentration in oxidation(UV+S2O82-)system.According to the results of MS analysis,the sulfoxide intermediate products and low molecular weight organic acids were detected,which was responsible for the increase toxicity of antibiotics during the photolytic process.Generally,the degradation process,factors and reaction mechanism of penicillin antibiotics were systematically investigated in natural water and simulated soil minerals(goethite/metal system).It provides reliable theoretical basis for risk assessment of penicillin antibiotics in water and soil environments.The toxicity variation and mechanism of penicillin antibiotics in simulated environmental water and industrial wastewater oxidation treatment are also observed,which is the key step to evaluate the ecological risk of penicillin antibiotics.