Plastic pollution in brackish waters: Macroalgae as collectors of plastic debris

Transitional waters, like the Capo Peloro lagoon, are ecologically and commercially valuable but particularly vulnerable to plastic pollution. This study investigates, for the first time, how two bloom-forming macroalgae, Chaetomorpha aerea and Hypnea cornuta, trap plastic debris in Ganzirri lake (Capo Peloro lagoon). Both species acted as natural traps for plastics, ranging from macroplastics (> 25 mm) to microplastics (< 5 mm). C. aerea captured more macroplastic (4.91 items/kg) than H. cornuta (2.19 items/kg). The average abundance of microplastics on C. aerea (0.35 items/g) and H. cornuta (0.51 items/g) was more than 100 times higher than surrounding waters (0.003 items/ml). FTIR and Raman analysis identified 16 synthetic polymers, 3 elastomers, and 2 anthropogenic microfibers, revealing a great polymer diversity. A wider spectrum of anthropogenic microparticles was isolated from macroalgae, with 11 different materials identified in C. aerea and 14 in H. cornuta, compared to 7 found in the water. Wastewater from domestic laundry, dumping activities, mollusc farming, and fisheries were identified as the main sources of plastics. While algae removal may help reduce plastic pollution, it must be managed sustainably to prevent biodiversity loss or secondary pollution. The results highlight the importance of integrat macroalgae management with broader conservation strategies to protect these vulnerable ecosystems.