| With the urge of population increase and economic development,sanitation improvement has been paid more attention by global society,the speed and scale of WWTPs construction boosted as well.Although WWTPs can dramatically eliminate contaminants such as organic matters,nutrients and fecal bacteria from wastewater,it was still inefficient to address all contaminants especially some emerging pollutants such as APIs.Thus,the effluent discharge from WWTPs has inevitably become concentrated point sources that inputting pollutants into surface water.Recently,water safety issues have arisen as a serious aftermath due to WWTPs’ effluent discharge.In particular,the ecological risk caused by APIs from effluent discharge has been emphasized by researchers.In this study,China’s most densely populated and fastest economically developed Yangtze River Basin was used as the research objective.Here,we present an Arc GIS-based APIs fate model,a spatially explicit model assessing the impact of unintended treated wastewater,estimating the concentrations of APIs and evaluating the ecological risks in river networks.The results demonstrated that one-third of the river segments in the basin were potentially influenced by the effluent through local or upstream inputs.Under average flow scenario,the fraction of unintended treated wastewater takes up less than 1% in water sources,with a mean traveling time of 0.26 days from discharge site to the nearest water source.Whereas under low flow scenario,the fraction of effluent discharges would increase drastically by 40?180% which imposes a higher environmental risk to the water source.In addition,the study indicated that both ERY and DIC discovered in water source have significant ecological risks,while the ecological risks from MET and LOR are negligible.The ecological risk of APIs in the river network gradually increases from upstream to downstream and reaching a peak value in the Yangtze River Delta.The study explored the relationship between DF value of river networks and ecological risk of APIs in water sources,and found that as the DF value increases,the RQ values of APIs would significantly reduce.Therefore,either increasing the emphasis of reusing wastewater or relocating dumping sites to river networks with larger natural flows could have remarkable effect on reducing risks from APIs.The study quantified the removal efficiencies of APIs at different transform processes,including human excretion,WWTPs removal,physical dilution,and instream decay processes.Instream API decays could also have some implications for the final concentration and environmental risk in water source,but the magnitudes of the impacts may largely depend on physicochemical property of target APIs.For example,the instream APIs loss was ～36% of MET,but for TRI was only 9%.Therefore,for the contaminants with high instream loss rates,environmental buffers could be an economical alternative to increase the retention time,and alleviate the potential environmental risks caused by APIs in water source.In summary,the study quatitatively evaluated the impact of effluent discharge on the drinking water sources in the Yangtze River Basin under the different flow scenarios,and estimated the concentration and RQs of APIs in the river networkd.Finally,we provide the targeted recommendations for the water environment management policies of the Yangtze River Basin. |
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