Distribution Characteristics And Risk Assessment Of Antibiotics In Lancang And Yarlung Zangbo Rivers

In recent years,antibiotics have received extensive attention as emerging environmental pollutants due to their increasing consumption and contamination incidents in the environment.In view of the special importance of rivers in the Southwestern region as the “Chinese Water Tower”,it is necessary to carry out systematic and in-depth study on antibiotic distribution characteristics and risk assessment in a timely manner.Here we select six classes antibiotics most frequently detected in China's waters as target compounds,including Sulfonamides(SAs),Quinolones(QNs),Tetracyclines(TCs),Macrolides(MLs),Beta-lactamases(?-Ls)and Others,with a total of 81 antibiotics.The pollution characteristics of antibiotics in water and sediments of Lancang River and Yarlung Zangbo River as well as their spatial and temporal distribution characteristics were studied in combination with the characteristics of low temperature,high illumination and low population density in the plateau.The concentration of antibiotics in main stream of Lancang River ranged from 3.27-53.08 ng/L and 0.64-12.91 ng/g in sediments.The concentrations range in Yarlung Zangbo River were 2.89-94.12 ng/L and 0.68-19.28 ng/g,respectively.Compared with other rivers(ND-2260 ng/L)at home and abroad,the antibiotic concentrations in Lancang and Yarlung Zangbo rivers were much lower.Because of differences of antibiotic consumption patterns in the plateau,the high detection frequency and concentrations of antibiotics in Lancang and Yarlung Zangbo rivers were sulfamethoxazole(SMX),sulfaguanidine(SGD),trimethoprim(TMP),roxithromycin(RTM),clarithromycin(CTM),azithromycin(AZM)and Anhydroerythromycin(AETM),which were different from other rivers in China,especially QNs antibiotics.The concentration of antibiotics in the waters of Lancang and Yarlung Zangbo rivers had obvious temporal and spatial differences.The seasonal variation of antibiotic concentration in Lancang River was mainly caused by the change of flow rate.Seasonal variation of antibiotic concentration in Yarlung Zangbo River was closely related to the number of tourists in Tibet.The concentration of antibiotics in Lancang River showed an increasing trend from upstream to downstream,which was caused by the increase of population distribution and the decrease of photolysis efficiency of antibiotics from upstream to downstream as well as dam interception.The photolysis efficiency of antibiotics in the lower water was weakened due to the development of cascade reservoir,which leads to the accumulation of sulfamethoxazole in the lower water because of its strong hydrophilicity and stability.In order to meet the demand of power generation,except Nuozhadu,the intake of the seven-stage reservoir was designed to divert deep water.Therefore,the deeper water with higher concentration was discharged to the subordinate reservoir and accumulated step by step.Nuozhadu intake was designed to take the upper water,so this accumulation phenomenon disappears in its subordinate reservoir.Shiga was the main source of antibiotic pollution in Yarlung Zangbo River.The concentration of antibiotics in water and sediment was the highest in Shigaze and Lhasa sampling sites.There is no big city distribution in the tributary of Yarlung Zangbo River,so the concentration of antibiotics was lower.Population,urban distribution and cascade reservoir development was the main factors affecting the spatial distribution of antibiotics in Lancang and Yarlung Zangbo rivers.The results of risk assessment showed that the environmental risk and health risk of antibiotics in Lancang and Yarlung Zangbo rivers were lower than those in other rivers in China.