The Fate Of Veterinary Antibiotics In System Of Soil And Plants And Their Mechanism

Widely used as feed additives and continuously introduced into the soil environment,veterinary antibiotics?VAs?are regarded as the false persistent pollution and result in inestimable environmental effects,which have aroused widespread concern in the society.In this paper,five typical veterinary antibiotics in China,are used as test drugs,such as chlortetracycline?CTC?,sulfamethoxazole?SMZ?,sulfathiazole?ST?,tylosin?TYL?and gentamycin?GM?.Under with high concentration and low concentration of antibiotics,a series of experiments were conducted to investigate the machenism of VAs uptake and translocation by plants.The specific results of the survey as follows:?1?HPLC-MS/MS detection methods for single-antibiotics were established,which were on the basis of the extraction and detection original methods of 11 antibiotics in the plants.The detection and quantification limits were 0.006-0.014?g/kg and 0.01-0.048?g/kg,respectively.The extraction method of gentamycin from plants and its detection method in HPLC-MS/MS were established,which were based on the method of extracting gentamycin from dregs.The recoveries were about 93.3%-95.2%,and the limit of quantitation were 0.001-0.002?g/kg and 0.003-0.006?g/kg,respectively.This method is simple and practical,and it can used in the rapid quantitative determination of gentamicin residues in plants.?2?Through the study of mixed antibiotics on maize,it was found that different antibiotics distributed in different zone of root tips,and mixed antibiotic would make a difference in the uptake and transfer of antibiotics by plants.CTC and SMZ were mainly concentrated at 0.5-2.0 mm zone of root tips,ST was mainly concentrated at 4.0-6.0 mm zone of root tips.Under the influence of mixed antibiotics,the values of RCF and TF were fluctuant in different level:The RCF values of the CTC are between 0.01-0.73 and the RCF values of the SMZ are between 0.01-0.28;the TF values of the CTC are between 0.01-2.5,and the TF value of SMZ are between 0.01-2.8.Through the study of antibiotics in an enclosed maize hydroponic system,the percentage of metabolized antibiotics by maize was about10.32%-18.34%,and the percentage of natural degradation was about 0.15%-0.91%,which confirmed that the biodegradation of antibiotics in maize is the main route of antibiotics'degradation.Through the combination of different respiratory inhibitors?NaN₃,malonate,Salicylhydroxamic Acid,Salicylhydroxamic Acid+NaN₃?,it was showed that the absorption of chlortetracycline and sulfamethoxazole in maize roots treated with 10 mg/L chlortetracycline and sulfamethoxazole were the active absorption process dominated by cyanide-resistant respiration;the TF values of both antibiotics in maize treated the aquaporin inhibitor HgCl₂ were falling,which indicated that the transport processes of antibiotic in maize were associated with the transport of water.?3?The higher the initial concentration of antibiotics in the soil,the higher the concentration of residual antibiotics in the soil environment.The addition of antibiotic-degrading bacteria will increase the removal efficiency of antibiotics to some extent,but with the growth of plants,the difference in antibiotic residual percentage among the treatments become smaller.The residual concentrations of antibiotics in soil were 0.022-0.063 mg/kg,0.115-0.367 mg/kg,and 0.265-1.385 mg/kg,respectively;the antibiotic concentrations in the roots of Chinese cabbage were 0.010-0.077 mg/kg,0.0174-0.0822mg/kg and 1.118-3.551 mg/kg,respectively,while the initial concentrations of antibiotics were 1,10,and 50 mg/kg in soil.The results indicated that the higher the initial concentration of antibiotics in soil,the higher the residual antibiotic concentration in the soil and the cabbage.In the spinach-pot experiment,the gentamicin residual percentage in CGF treatment?spiked with gentamycin and its degrading-fungi FZC3?were reduced by approximately 3.3%compared with the CG treatment?spiked with gentamicin?after 7 days.The residual rate of tylosin in CTW treatment with?spiked with tylosin and its degrading-bacteria?was reduced by 4.1%compared with the CT treatment?spiked with tylosin?.All above indicated that the antibiotic-degrading microbe could improve the removal of the two antibiotics in the soil;but as time went by,the differences in the residual rates of antibiotics among all the treatments gradually decreased.?4?Exogenously antibiotics?tylosin and gentamicin?and their degrading bacteria?tylosin-degrading bacteria achromobacter,gentamicin-degrading fungi FZC3?were added in spinach-pot experiment,then found that GM and tylosin-degrading bacteria have an impact on soil bacteria,while TYL and GM-degrading fungi have an impact on soil gungi.We also found that the addition of GM and TYL both produced antagonistic effects.According to the results of high-throughput sequencing,there were significant differences on the bacterial richness and diversity in the three treatments of CG,CTW and CMM compared with that in the blank treatment?CC?.There were significant effects on the richness and diversity of the fungi in the soil in the three treatments of CGF,CT and CMM compared with that in the CC treatment.Analysis and comparison of the bacterial community structure in each treatment,it revealed that at the first and second week,under the phylum and genus classification levels,the community structure of the three treatments of CG,CTW,and CMM was significantly different from that of the CC treatment,showing in Proteobacteria,Actinomyces,and Firmicutes in phylum,and in Sphingomonas,Arthrobacter,Achromobacter,and Lactobacillus under genus classification level.All above indicated that FZC3 and Achromobacter have a greater impact on bacterial communities.Analysis of the fungal community structure among all the treatments showed that there was a significant difference in the fungal community structure of CGF and CMM treatments compared with the CC treatment at the first week,showing in Ascomycota and Zygomycota under the phylum classification level,and in Aspergillus and Mortierella under the the genus classification level.At the second week,there was a significant difference in fungal community structure of the CGF,CT and CMM treatments compared with CC treatment.They were showed in Ascomycota,Basidiomycota and Zygomycota under the phylum classification level,and in Fusarium and Guehomyces under the genus classification level.All indicated that gentamicin-degrading fungus FZC3 and tylosin had a greater impact on soil fungi.There were no significantly different of the community richness and diversity of fungi and bacteria,bacterial and fungal community structure between the CM treatment and the CC treatment,which confirmed that GM and TYL were antagonistic.