Microplastic retention by cultivated Betaphycus gelatinus and its washing-based removal: Implications for biocarrier...

Microplastics (MPs) have become ubiquitous contaminants in marine ecosystems; however, their interactions with tropical macroalgae remain insufficiently understood. In this study, the abundance, size distribution, and polymer composition of MPs in seawater and on the surface of the cultivated macroalga Betaphycus gelatinus and wild Sargassum polycystum were investigated in Qizi Bay, Hainan, China. The mean MP abundance in seawater was 3.5 ± 0.69 items·L^-1, with fibers being the dominant morphology and polyethylene (PE), polyamide (PA), and polypropylene (PP) identified as the major polymer types. Both macroalgal species exhibited relative MP enrichment potential, with Rm/Rs values of 184 and 244 for B. gelatinus and S. polycystum, respectively, indicating their capacity to retain MPs compared with surrounding seawater. Decontamination experiments further showed that combined dehydration-washing treatment significantly improved the removal of surface-associated MPs, achieving a maximum desorption efficiency of 92.21%. Orthogonal analysis indicated that washing time exhibited the strongest main effect among the tested parameters, with optimal desorption achieved under 8 h washing time, 40 mL washing volume, and 50 rpm shaking speed. Overall, cultivated B. gelatinus functions as a biological retention surface for MPs and provides opportunities for reducing the MP burden associated with harvested seaweed biomass through optimized processing strategies.