The spheres of Posidonia oceanica, very common on Mediterranean beaches, reveal microplastic pollution in the seas: more than one in three is contaminated with plastic. This is according to a study undertaken by ENEA (National Agency for New Technologies, Energy, and Sustainable Economic Development) in 13 locations along the Lazio coast and published in the international journal Environments (MDPI). The study examined the structure and content of 1,300 of these spheres, known as Aegagropile, or "sea balls". The findings demonstrate that 34.9% of the spheres include plastic fragments, accounting for a total of 1,415 detected particles and an average of 3.1 elements per sphere. Microplastics (less than 5 millimeters) account for 48.7% of the materials collected, followed by mesoplastics (29.6%) and macroplastics (21.9%). One of the most significant findings is a strong link between the presence of microfibers in the spheres and proximity to wastewater treatment plants: these purification systems only partially retain synthetic microfibers released during home laundry, which then reach the sea and settle on the bottom of the ocean.