| Bacterial resistance has become a public health problem worldwide.Antibiotic resistance genes（ARGs）have been detected in many media such as lakes,surface rivers,soil and sediments.As the interaction of surface water and groundwater,the Hyporheic Zone（HZ）has a pollution interception function.Contaminants such as antibiotics and ARGs will reach the HZ and even groundwater through water flow.Therefore,a comprehensive investigation of antibiotics and ARGs to clarify the risk level and evolution process is of great significance for protecting the safety of drinking water.This article takes the Zaohe-Weihe confluence as the research area,takes oxytetracycline（OTC）,sulfamethoxazole（SMZ）,norfloxacin（NOR）and ARGs as the target pollutants.Conducted a comprehensive pollution survey in the HZ（surface water,groundwater and sediment）,summarized its distribution characteristics and environmental leading factors,explored the transfer mechanism of ARGs in different media,and simulated the evolution of ARGs under different environmental factors,revealing the characteristics of host bacteria of ARGs.The specific conclusions are as follows:1.Distribution characteristics of media and antibiotics in the HZ（1）The distribution of antibiotics in surface water and groundwater is similar,and the concentration levels are NOR>OTC>SMZ,and in sediments,it is OTC>SMZ>NOR.Antibiotics showed an attenuation trend along the river,but did not show an obvious decay law in the horizontal direction.The correlation between antibiotics and environmental factors is not significant,the properties of sediment particles have a greater impact,and the relationship between clay and TOC is extremely significant.（2）OTC shows a significant correlation between surface and groundwater,indicating that OTC in groundwater is carried by surface water replenishment.OTC and SMZ in sediments and groundwater have reached a dynamic equilibrium after adsorption-desorption exchange.The partition coefficient of the three antibiotics in the sediment-water phase is SMZ>OTC>NOR.2.Distribution characteristics and resistance mechanism of ARGs in HZ（1）In the HZ of Zaohe-Weihe Rivers,of the 271 ARGs of 9 types of antibiotics,228 ARGs were detected,with a total detection rate of 84%.The higher detection rate indicates the diversity of ARGs in the interaction zone.The concentration ratio of the first 150 ARGs was analyzed,and the specific performance was Aminoglycosides>Lactams>Sulfonamides>Tetracyclines.（2）Among the three media,sulfonamides and aminoglycosides are the most common ARG types.The abundances top 6 of ARGs and MGEs are tnp A-04>cep A>sul1>aad A2-03>sul2>int I1.The distribution levels are 8.38×10-2,3.04×10-2,2.61×10-2,2.22×10-2,1.84×10-2 and1.35×10-2,respectively.The abundance of ARGs in the water samples were mainly concentrated at S2,S3,and the sediments were mainly concentrated at S2,S3 and S5.The distribution characteristics are related to the location of the Zaohe sewage outlet and the nature of the sediment.The high abundance of MGEs is conducive to the horizontal transfer of ARGs.（3）Principal component analysis shows that the distribution characteristics of ARGs are related to the medium.There are similarities between water phases,and differences between water phases and sedimentary phases.Differential gene analysis showed that aac（6’）-Ib-3 was more present in groundwater,and tnp A-04,cat B3,tet G-02,tet M-01 and msr（D）were more present in sediments.（4）The resistance mechanism of ARGs in the interaction zone is:target site replacement or change>inactivation>efflux pump action>ribosome protection.The two mechanisms of target replacement or change and inactivation are dominant.3.Correlation between environmental factors,movable genetic elements and ARGs（1）Redundancy analysis shows that the main controlling factors affecting the distribution of ARGs in different media are different.In surface water,the p H has a contribution rate of65.4%and express significantly correlated;In groundwater,TN and COD contribute the most;In sediments,the TOC and clay have contribution rates of 32.8%and 13.5%respectively.（2）The correlation between MGEs and ARGs is that ARGs in water bodies are significantly related to int I1 and tnp A-03,ARGs in sediments are significantly related to int I1and tnp A-04,and overall ARGs are significantly related to int I1 and tnp A-03.Different media environments depend on different transposase genes,which accelerate the transfer of ARGs between different media.（3）The heavy metal concentrations of the 10 sampling points showed similar characteristics.From the average point of view,they were all at the mg/Kg level,in order:Zn>Cr>Cu>Pb>Ni>Cd;in the residue state and the organic matter combined state It is mainly combined with iron and manganese oxide.Among them,aad A-01,sul1,sul2,tet X are significantly positively correlated with Cr,indicating that Cr can promote the production and proliferation of ARGs.The degree of influence of the six metals on ARGs can be roughly divided into Cr>Pb>Cd>Ni>Cu>Fe.Ni in the residue state has a significant positive correlation with a variety of ARGs.4.The time kinetic process and microbial analysis of ARGs under different factors（1）Under the simulated conditions of the HZ,the addition of antibiotics increases the abundance of most ARGs,and the sterilization conditions have certain restrictions on the proliferation of ARGs.The abundance of ARGs is anaerobic>aerobic-anaerobic interaction>aerobic.（2）The cluster correlation heat map shows that there are some bacterias that affect tetracycline and sulfonamide ARGs.At the phylum level,they mainly concentrated on Proteobacteria,Firmicutes and Bacteroidetes.At the genus level,the four genera under the phylum Proteus,Micromycobacterium,Brevundomonas,Neospirillum,and Sphingomonas all have a strong positive correlation with tet G-02,which may be host strain of tet G-02.The other10 species of bacteria significantly affected the abundance of ARGs.（3）Under anaerobic conditions in the HZ,the abundance of ARGs and MGEs is higher than that of aerobic conditions.And 7d after the addition of antibiotics,the abundance of ARGs increased,where 25℃>15℃>5℃.Most ARGs showed higher abundance under the treatment of 0.2%Na Cl concentration.Compared with the control group,low salinity may promote the production and proliferation of ARGs,and the high salinity of 2%Na Cl has a certain inhibitory effect on the growth and reproduction of resistant bacteria.Different environmental factors（oxygen,temperature and salinity）have significant effects on the abundance of single ARG and tnp A-04 in the evolution process. |
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