Harmonisation-Oriented Monitoring of Microplastics in Reclaimed Water for Agricultural Irrigation: Loads and Polymer Composition

Microplastics (MPs) in water treatment plants (WTPs) represent a critical environmental concern, particularly when treated effluent is reused for agricultural irrigation. This study investigates the occurrence, removal efficiency, and characterization of MPs in tertiary-treated wastewater destined for agricultural reuse in water-scarce regions. Additionally, the study examines the influence of sample volume on extrapolated MP concentrations. Despite advanced treatment processes including ultrafiltration achieving removal efficiencies of 89%, substantial quantities of MPs remain in final effluents at concentrations ranging from 89 to 399 MPs/m3 (equivalent to 0.1–0.4 MPs/L) with a mass load of 2 µg/L at the outlet. Morphological analysis revealed a shift from fragment-dominated influent (~50%) to film-dominated effluent (~51%), with blue particles being most prevalent. Size distribution analysis showed distinct peaks: 50–100 µm for fragments, 100–250 µm for films, and 250–500 µm for fibres. Polytetrafluoroethylene (PTFE) emerged as the dominant polymer across all morphotypes. Finally, converting particle counts to mass loads indicated an average decrease from ~11 µg/L at the inlet to ~2 µg/L at the outlet, underscoring that number- and mass-based metrics provide complementary information for risk assessment.