<p style="text-align:justify">All aquatic species in the river mouths flowing into the Mediterranean Sea and Atlantic Ocean are contaminated with microplastics, with molluscs being the most affected due to their ability to filter water. Rivers are one of the main sources of pollution by microplastics (5 to 0.0001 mm in size) and nanoplastics (smaller than 0.0001mm) in the oceans. Estuaries, as transition zones between rivers and the sea, are major hotspots for the accumulation of these particles, which are retained in sediments. They pose a threat to aquatic ecosystems given their ability to capture harmful chemicals from the surrounding environment, enter the food-web through ingestion, and bioaccumulate towards higher trophic levels, including valuable commercial species.</p>