A threat beneath the surface: Microplastic contamination in the groundwater of one of Europe's largest wetland complexes

The widespread use of plastic has contributed to a significant accumulation of plastic waste in the environment, much of which is deposited on land. Microplastic (MP) from this waste can infiltrate the soil and reach groundwater, leading to accumulation in subsurface environments. Although MP contamination in soils and groundwater has only recently drawn scientific attention, our study investigates this issue within the Biebrza Valley, one of Europe's largest and most ecologically significant wetland areas. We collected samples from 102 wells distributed across the valley to provide comprehensive coverage and establish baseline MP levels in the groundwater of lowland Europe. MP particles were detected in 101 wells, with concentrations up to 14.1 particles/L and a mean value of 1.3 ± 2.1 particles/L. No significant relationship was found between MP contamination and population density across the valley. Instead, our results suggest a patchy distribution of MP, potentially influenced by the immediate surroundings of each well. Polyurethane and polyamide were the most common polymers identified, suggesting agricultural sources of contamination. Importantly, our study underscores the need for reliable verification techniques, as only 3 % of suspected particles were confirmed as MP through Raman spectroscopy.