Pollution Characteristics And Risk Assessment Of Typical Antibiotics In Daxi Reservoir Basin

The Daxi reservoir basin is a"river-reservoir"complex system consisting of two different water bodies,a river and a reservoir,and the quality of water bodies in the basin is important for human health.This study takes the Daxi reservoir basin as the research object,analyzed the spatial and temporal distribution characteristics of water environmental factors and antibiotics in the basin,explored the influence of water environmental factors on the environmental behavior of antibiotics,identified the sources of antibiotics,and assessed the potential risks of antibiotics to ecology and human health,with a view to providing strong technical support for maintaining the ecological health and safety of the Daxi reservoir basin.The following conclusions were drawn:（1）During the four seasons,the water temperature ranged from 4.6 to 36.3^oC;DO concentrations ranged from 1.2 to 12.22 mg/L,and the average concentrations in four seasons was in theⅠ～Ⅱwater;p H value ranged from 6.05 to 8.95,which was in accordance with the surface water environmental quality standard;TN was dominated byⅢwater in the reservoir system andⅣwater in the river system;NH₃-N was dominated byⅡwater in both reservoir and river systems;TP was dominated by IV water in both reservoir and river systems;COD_Mnwas dominated byⅢ～Ⅳwater in the reservoir system andⅣwater in the river system.Temporally,TN,NH₃-N,NO₂^--N,TP,Chla and COD_Mn all showed significant seasonal differences,and all showed a trend of autumn>summer>spring>winter;NO₃^--N and DOC also showed significant seasonal differences,but the seasonal trends were different,with NO₃^--N showing a trend of spring>winter>autumn>summer,and DOC showing a trend of summer>autumn>spring>winter.Spatially,NH₃-N,TP,Chla and DOC were not significantly different in the"river-reservoir"system,but TN,NO₃^--N,NO₂^--N and COD_Mn showed significant spatial variability,and there was a certain spatial gradient from the river system to the reservoir system.According to the comprehensive nutritional status index（TSI）method to evaluate the eutrophication of water bodies,the Daxi reservoir basin was in a moderate to mild eutrophication state.（2）A total of 19 target antibiotics were detected in the Daxi reservoir basin.The contamination contribution of different classes of antibiotics was in the order of TCs>FQs>SAs>MLs>CPAs>β-Ls.SAs,FQs and TCs were the main types of antibiotic contamination in the waters of the basin.Temporally,antibiotic concentrations were highest in winter at 40.37ng/L and lowest in summer at 12.6 ng/L.The fugacity characteristics of different classes of antibiotics in different seasons were different,with SAs having the highest concentration in summer and the lowest concentration in winter,while FQs,TCs,RTMs and TAP all had the highest concentration in winter and the lowest concentration in summer,showing an opposite seasonal trend to SAs.In the four seasons,SMX,SMM and TMP were the main contamination components of sulfonamide antibiotics;NFX,EFC,OFX and DIF were the main contamination components of quinolone antibiotics;TC and DXC were the main contamination components of tetracycline antibiotics.RTM had high detection rates and relatively low detection concentrations in four seasons.LEX was only detected in the spring,with a detection rate of8.7%and detection concentrations of ND～5.0 ng/L.The detection rates of TAP ranged from8.7%to 52.17%in the four seasons,and the detected concentrations showed a seasonal trend of winter>autumn≈spring>summer.Spatially,there was no obvious pattern of variation in SAs,RTM was greater in the Zhucao river than in the reservoir bank zone,while FQs,TCs and TAP were greater in the reservoir bank zone than in the Zhucao river.Different types of antibiotics enter the reservoir after flowing into the river through various pathways,so that the total antibiotic concentrations showed the distribution pattern of the reservoir bank zone>Zhucao river>inflow tributary estuary.（3）Spearman correlation analysis showed that temperature,DO,p H,DOC,COD_Mn,Chla,TP,TN and NH₃-N were correlated with antibiotics,and DO had the greatest effect.The correlations between Shannon-Wiener diversity index,Margalef richness index,biomass and total abundance of plankton and some antibiotics were also found by linear fitting.（4）The results of PCA-MLR analysis showed that domestic and pharmaceutical wastewater、livestock breeding wastewater、agricultural wastewater and aquaculture wastewater were the main sources of antibiotics in the Daxi reservoir basin,and their pollution contributions rates were 36.75%,24.32%,27.32%and 11.61%,respectively.（5）Most antibiotics posed no ecological risk to the three aquatic organisms,and only a few posed medium to low ecological risk to algae and low ecological risk to invertebrates and fishes at some points.The cumulative ecological risk of antibiotics was mainly from SAs and FQs,and the average cumulative ecological risk of river system was lower than the average cumulative ecological risk of reservoir system.Antibiotics in the Daxi reservoir basin posed no potential health risk to human.