Microplastic Pollution in High-Elevation Water Bodies of the Serra da Estrela Mountain Range, Portugal

Abstract Microplastics—synthetic particles ranging in size from 1 μm to 5 mm—are now widely recognised as an emerging environmental issue due to their ubiquity across ecosystems. While most research has focused on marine environments, important knowledge gaps remain regarding their occurrence in freshwater systems, particularly in remote and high-altitude ecosystems. Given the increasing human use of these environments, understanding potential sources and drivers of contamination is crucial. This study assessed and characterised microplastic pollution in high-elevation water bodies from Serra da Estrela during two sampling campaigns (June and November 2023). Eight water bodies were sampled, with surface water and sediment collected. Suspected particles were isolated, quantified, and characterised according to size, shape, colour, and polymer type using micro-FTIR and FTIR-ATR spectroscopy. Differences between sampling periods and the influence of human presence were also evaluated. Microplastics were detected in all sampled water bodies. A total of 1338 particles were identified, with average concentrations of 0.35 particles L⁻ 1 in water and 48.2 particles kg⁻ 1 dry weight in sediments. Most particles were larger than 300 μm, with a detection limit of 100 μm. Spectroscopic analyses showed that polypropylene (PP) and polyethylene (PE) were the dominant polymers. Concentrations were higher in June than in November and were associated with proximity to areas of greater anthropogenic activity, likely reflecting the residual impact of winter recreational activities during the snow period. This is the first report on microplastic pollution in the highest mountain range in continental Portugal. Further monitoring is needed to preserve water quality and support conservation of these high-altitude ecosystems.