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Baseline assessment of suspended microplastics: Spatial distribution, polymer composition, and ecological risk in two Central Portuguese rivers
Summary
Scientists found tiny plastic bits called microplastics in every water sample they tested from two major rivers in Portugal, mostly in the form of super-small fibers from things like plastic packaging and textiles. These plastics were small enough (less than 1mm) to pose meaningful risks to river ecosystems, and since these same rivers can be sources of drinking water and support fish we eat, this adds to growing evidence that microplastics are working their way into the water and food we consume daily.
Microplastics (MPs; 1–5000 µm) are an emerging environmental concern due to their persistence and ubiquity in aquatic ecosystems; although while marine environments have been widely studied, freshwater systems remain comparatively less explored. This study investigates the occurrence, abundance, characteristics and associated ecological risks of MPs in the upper water column (5–15 cm depth) of the Mondego and Vouga rivers, two major river systems in Central Portugal. The results indicated that MPs were detected at all sampling sites in both rivers, with concentrations ranging from 156 to 1667 items/m³ , confirming their widespread occurrence. Both rivers exhibited similar MP characteristics, with comparable dominance in colour, shape, size and polymer type. Morphological analysis identified four colours, with black MPs dominating (67.9% in Mondego; 57.2% in Vouga), five size categories, with the 100–1000 µm fraction prevailing (54.8% in Mondego; 63.3% in Vouga). Among the three observed forms, fibres were predominant (86.9% in Mondego; 93.9% in Vouga). Five distinct polymer types were identified, with polyethylene (36.9% in Mondego, 24.7% in Vouga) and polypropylene (45.2% in Mondego, 47% in Vouga) emerging as the most common. Risk assessment based on the pollution load, polymer hazard, and potential ecological risk indices revealed that several sites fell within index-based risk categories ranging from low to danger, despite overall moderate MP concentrations. This study uniquely demonstrates that the predominance of sub-millimetre (<1000 µm; within the detectable size range, ≥100 µm). MPs in the upper water column can significantly drive moderate to high index based ecological risks categories, highlighting their critical role in freshwater pollution.