Organic Micropollutants in Waterways of a Large-Scale Water Diversion Project: Insights from Nontarget Screening and “Community” Analysis

Large-scale water diversion projects are essential for meeting the needs of water-stressed regions, necessitating an evaluation of their impact on water quality and aquatic ecosystems. This study provides the first snapshots of organic micropollutants (OMPs) along the 1466 km Eastern Route of China's South-to-North Water Diversion Project. Using nontarget analysis with ultrahigh-performance liquid chromatography and high-resolution mass spectrometry, we identified and quantified 357 OMPs from water samples collected during the water diversion period (WDP) and the nonwater diversion period (NWDP). The OMPs included 136 household compounds, 112 agricultural compounds, 102 industrial compounds, and 7 traffic markers. Significant regional variations in OMP concentrations and compositions were observed during the NWDP due to diverse local pollution sources along the route. However, such differences were reduced during the WDP, likely due to water transfer. OMP diversity varied substantially during the NWDP but was more stable with less distance decay during the WDP. Network analysis indicated closer relationships between the OMPs during the WDP, suggesting a more consistent spatial distribution. The source water overwhelmingly influenced the water quality along the diversion route. These findings underscore the need for ongoing assessments of the impact of water diversion on regional water quality and ecosystems.