Presence of Micropollutants and Transformation Products During Subsurface Irrigation with Treated Wastewater Assessed by Non-Target Screening Analysis

While wastewater treatment plant (WWTP) effluent offers a potential alternative source for irrigation, the fate of organic micropollutants (OMPs), including transformation products (TPs), in effluent-irrigated fields remains largely unknown. Using non-target analysis (NTA), we investigated OMPs in WWTP effluent and their distribution throughout a full-scale subsurface irrigation (SSI) field where effluent was used for irrigation. Our results indicate that TPs accounted for approximately 80% of the detected effluent OMPs. Weather and SSI hydrology seem to influence OMP distribution and transformation. Wetter conditions promoted deeper leaching of OMPs in soil, and drier conditions favored their capillary rise and biotransformation, as shown by the detection of 37% more TPs in the rhizons during a dry year. On average 45 OMPs, at least 50% with a logD <3, were detected at −2.3 m depth, highlighting their potential to reach groundwater and the importance of including TPs in further risk assessment. This approach demonstrates how NTA and subsequent data analysis tools can support the identification of (unknown) OMPs and contribute to understanding OMP fate under field conditions, which is the first step in an exposure-driven environmental risk assessment. Overall, our study emphasizes the importance of carefully considering (unknown) OMPs for more responsible effluent reuse.