The Characteristics Of Antibiotics And Antibiotic Resistance Genes Pollution In The Main Rivers Of Chongqing City

In this study,the occurrence and spatiotemporal distribution of 14 antibiotics（6Sulfonamides（SAs）:Sulfadiazine（SDZ）,Sulfathiazole（STZ）,Sulfamerazine（SMR）,Sulfamethazine（SMZ）,Sulfamethoxazole（SMX）and Sulfadimethoxine（SDM）;4Fluoroquinolones（FQs）:Ofloxacin（OFL）,Norfloxacin（NOR）,Enrofloxacin（ENR）and Ciprofloxacin（CIP）;2 Tetracyclines（TCs）:Oxytetracycline（OTC）and Tetracycline（TC）;2 Macrolides（MLs）:Erythromycin（ETM）and Roxithromycin（RTM））,4 corresponding antibiotic resistance genes（sul I of sulfonamides,qnr S of fluoroquinolones,tet M of tetracyclines and erm B of macrolides）,1 integron integrase gene（int I）and 2 fecal source indicators（human:HF183;pig:Pig-2-Bac）were analyzed in water and sediment of 12 sampling sites from two rivers（Yangtze River:from Xi Peng to Feng Du;Jialing River:from Bei Bei to Chao Tianmen）of Chongqing city,southwest China.In addition,the bacteria community structure in sediments and the potential influence of antibiotics on bacterial community were obtained.The main results and conclusions are following:（1）The results of antibiotic distribution presented that all target antibiotics were detected except for SDM,which indicated that there were multiple antibiotic residues in this area.OFL and ETM were the predominant antibiotics in both seasons.The antibiotic concentration in water and sediment in March ranged from 0 to 1.49×10³（ETM）ng L^-1 and from 0 to 1.52×10⁴（NOR）μg kg^-1,respectively,while in September they were from 0 to 1.22×10²（SMZ）ng L^-1 and from 0 to 1.6×10¹（SMZ）μg kg^-1,the remarkably higher concentration of antibiotics（especially SMX,OFL,ENR and RTM）in sediments of these two rivers than those in other domestic and foreign rivers were found.The detection frequency of most antibiotics were higher in samples collected in September but concentrations were lower,fluoroquinolones is dominant in downtown while in county it was macrolides.Flow rate,illumination intensity,antibiotic application type and the difference of physical and chemical properties of water are the possible causes of the difference of spatial distribution.Risk assessment found that SMX,OFL,CIP and ETM posed high risk toward some sensitive algaes.Hechuan（HC）,Beibei（BB）,Tong Jiaxi（TJX）and Chao Tianmen（CTM）reaches harbor more antibiotics of high risk.（2）The results of ARGs distribution showed that the absolute abundance of the four ARGs ranged from 0 to 1.96×10⁸ copies L^-1 and from 0 to 6.26×10⁸copies g^-1 in water and sediment in March,while in September they were from 0 to 5.61×10⁶ copies L^-1 and from 0 to 8.07×10⁷copies g^-1,respectively.SulⅠis dominant among the four target ARGs,whose detection frequency is up to 100%and absolute abundance is 1-2order of magnitude higher than other ARGs.Of the twelve sampling sites,CTM,JGS and TJT possess higher ARGs abundance,indicating that large amount of daily sewage treatment capacity and frequent human activities may lead to the increase of ARGs abundance in the environment.Overall,the relative abundance of the four target ARGs is higher in water than those in sediment,and it is higher in the Yangtze River than those in the Jialing River of sediment samples.（3）Correlation analysis indicated that antibiotics is not the exclusive selective pressure for ARGs,and intⅠmay play a vital role in the dissemination of selected ARGs due to the strong positive correlations between them（p<0.01）.In addition,environmental factors such as the temperature,p H,oxidation-reduction potential,total organic carbon and nitrite of water,the organic matter,sediment water content,total organic matter and dissolved organic matter of sediment could affect the distribution of target antibiotics and ARGs.Most selected antibiotics and ARGs in this study showed significant positive correlation with human fecal indicator,indicating that human feces is a potential source of antibiotics and ARGs.（4）Sediment bacterial community structure analysis indicated that,samples collected in September possess significantly higher bacterial richness and diversity than samples collected in March.In Mach and September,JGS and FD were found with the highest bacterial richness,FD and YZ were with the highest bacterial diversity,respectively.The dominant phyla were affiliated to Chloroflexi,Firmicutes,Proteobacteria,Acidobacteria,Actinobacteria and Bacteroidetes,which account for more than 73%in each corresponding sampling site.Among of them,significant seasonal variations were found in Proteobacteria,Firmicutes and Acidobacteria.（5）The correlation analysis showed that almost all of the SAs（STZ,SMR and SMZ）had a significant positive correlation with the related bacteria（p<0.05）,probably because the concentration of SAs in the sediment of this study area was relative low,so they had no inhibitory effect on these bacteria.Only SMZ was negatively correlated with weissella（p<0.05）,indicating that weissella may be a SMZ sensitive bacterium.OFL and RTM had a significant correlation with a variety of bacteria.The higher detection frequency and concentration of them in this study area may be one of the reasons for this result.In addition to antibiotics,other environmental factors include p H,sediment water content,total organic carbon,dissolved organic carbon,inorganic carbon,nitrate nitrogen,ammonia nitrogen of sediment,heavy metals like Cd,Cr,Eu,Mo,Pb,Sn,V,Ti and Mn may also have some relevance to the bacterial community structure of sediment in this area.