Microplastics detection and characterisation in the urban water cycle of Geneva, Switzerland: Assessing the supply...

Microplastics (MPs) are increasingly detected in aquatic environments and are a growing concern due to their persistence, mobility, and potential risks to ecosystems and human health. This study aims to investigate the presence of MPs (>20 μm) across the urban water cycle of Geneva (Switzerland). The scope of the assessment includes large water volumes (50-2000 L) of raw water sources (groundwater and surface water), drinking water treatment, water supply network, and effluents of three wastewater treatment plants. MPs concentrations, size distributions, and chemical compositions were determined across these interconnected systems. Sampling and analysis followed a strict quality assurance protocol aligned with current MP analysis guidelines and standards. Fourier-transform infrared spectroscopy (FTIR) was used to characterise MPs. Geneva's main conventional drinking water treatment plant (serving approximately 500,000 consumers) showed high removal efficiency, reducing MPs concentrations from 640 ± 292 MP/m³ in raw water to 10 ± 6 MP/m³ after treatment (including coagulation, sand filtration, ozonation and granular activated carbon filtration), demonstrating a removal efficiency of 97 ± 3 %. Groundwater samples showed low concentration of MPs (8 ± 7 MP/m³). However, the drinking water supply network (DWSN) contributed to an increase of MPs concentration, with values equal to 27 ± 37 MP/m³ in the eastern section and 23 ± 19 MP/m³ in the western section. Effluents from wastewater treatment plants (WWTPs) exhibited the highest concentrations, averaging 5829 ± 5108 MP/m³. This study highlights the importance of full-cycle monitoring and supports the need for improved mitigation strategies across all stages of the urban water cycle.