Intertidal seaweed as natural collectors of marine debris: Evidence of epibiont-mediated trapping of diverse anthropogenic particles in the Bahía Blanca Estuary (southwestern Atlantic)

This study investigated the abundance, composition, and interaction mechanisms of marine microdebris (MDs) in ten seaweed taxa, surface waters and sediments from the Bahía Blanca Estuary (BBE, southwestern Atlantic, Argentina). All macroalgal taxa retained diverse anthropogenic particles, including microplastics (MPs), paint-derived particles, and microbeads, among others. MP abundance in those seaweeds tested ranged from 0 to 1.81 items/g w.w., with significant differences among taxa. Whereas in surface waters and sediments, the concentration of MPs ranged from 3 items/L to 16 items/L and from 145.67 to 1668.30 items/kg d.w., respectively. Several interaction mechanisms were observed, including physical attachment and retention mediated by epibiont biofilms. Field Emission Scanning Electron Microscopy (FE-SEM) analyses confirmed that epiphytic microorganisms, together with extracellular polymeric substances (EPS), can trap microfibers on algal surfaces. Chemical characterization using μ-FTIR and FE-SEM/EDS revealed a diverse mixture of synthetic polymers as ABS, plasticized PVC, nylon, PES, PS, PP, CE, and CA, paint-derived resins (PUR-alkyd and alkyd), and other anthropogenic particles (black SiO 2 microbeads), reflecting local sources such as port activities and urban inputs. Additives such as CaCO₃ and TiO₂ were also identified in paint particles. Although pollutant levels were low according to the pollution load index (PLI), some seaweeds exhibited elevated hazard scores due to high-risk polymers (PHI) and polymer-based resins. These results highlight the role of seaweeds as temporary sinks and potential bioindicators of diverse anthropogenic particles in coastal ecosystems, emphasizing their relevance for monitoring marine microdebris in local estuarine environments.