Comprehensive Evaluation of Organic Micropollutants in the Miho River Watershed: Detection Characteristics, Environmental Fate, and Integrated Risk Assessment

Background:The Miho River, a major tributary of the Geum River in South Korea, receives multiple pollutant inputs from urban, agricultural, and industrial sources, creating complex contaminant mixtures that include pharmaceuticals, pesticides, and industrial chemicals.Although previous studies have primarily focused on managing conventional water quality parameters and controlling nutrient pollution, the comprehensive assessment of trace-level micropollutants across the entire Miho watershed remains limited.Objectives: This study aimed to comprehensively characterize and quantify organic micropollutants in the Miho River watershed using an integrated analytical approach combining non-target screening (NTS) and quantitative analysis.Given the watershed's exposure to multiple pollution sources, we applied an integrated risk assessment framework to evaluate the potential ecological and human health impacts of the detected micropollutants.Methods: Surface water samples were collected from a total of 30 sampling sites across the Miho River watershed (19 national monitoring stations and 11 point sources) between August and September 2023.Highresolution liquid chromatography-mass spectrometry (LC-HRMS/Orbitrap) was employed for both NTS and quantitative analyses.Environmental risks were assessed using a multi-level framework incorporating risk quotients (RQ), the frequency of predicted no-effect concentration (PNEC) exceedances, and prioritization indexes (PI).Human health risks for the general population were evaluated based on drinking water exposure scenarios, with uncertainty quantified via Monte Carlo Simulations.Results: NTS detected a total of 109 organic micropollutants, including 45 industrial, 41 pharmaceutical, 14 pesticide, and nine others.Quantitative analysis showed 12 substances with mean levels ranging from 0.031 to 1.067 g/L.Environmental risk assessments identified Carbendazim, Diazinon, and Carbofuran as high-priority substances, with risk quotients (RQ) significantly exceeding thresholds.Ten industrial chemicals (D-Camphor, Docosanamide, Erucamide, and others) were ubiquitously detected, indicating the continuous discharge of persistent and bioaccumulative substances from point sources.However, human health risk assessments showed hazard quotients (HQ) below unity (<1.0) for non-carcinogenic substances and carcinogenic risks (CR) below regulatory thresholds (<10 -6 ), indicating negligible population-level health risks.Conclusions: This study confirms the widespread occurrence of organic micropollutants in the Miho River watershed, with several pesticides posing potential risks to aquatic ecosystems.Future studies should utilize advanced AI-based analytical techniques to assess the mixture toxicity and integrated risk of emerging contaminants, and to precisely characterize the removal efficiency of wastewater treatment plants, seasonal variability, and the contribution of point and non-point pollution sources.Such preemptive data-driven comprehensive research will provide essential scientific evidence for establishing river-basin-specific pollution control and management strategies and protecting the aquatic ecosystem of the Geum River basin.