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Coastal hydrodynamics drive microplastic retention in filter-feeders
Summary
Mussels and clams pick up more microplastic pollution when they live in coastal waters that trap debris close to shore, but the good news is these shellfish can naturally flush out those particles when moved to cleaner, offshore waters. This suggests that giving farmed shellfish time in open water before they're harvested could be a simple way to reduce the amount of microplastic people eat when they enjoy seafood.
Microplastic retention in filter-feeders is strongly associated with land-derived inputs, whereas the contribution of hydrodynamic processes to microplastic contamination in coastal systems remains poorly understood. In this study, carried out in the central Tyrrhenian Sea (Gulf of Gaeta, Italy), microplastic retention in bivalves was analyzed in relation to coastal circulation patterns. The composition of microplastics within bivalve tissues was consistent with the interplay of inland inputs with coastal currents. When water-masses remained nearshore, microplastic concentrations in filter-feeder bivalves increased. Conversely, offshore water inflows coincided with a significant decrease in retained particles, consistent with natural depuration. Overall, these patterns suggest that microplastic contamination is closely linked to circulation regimes influencing water-mass exchange and particle residence times. Although filter-feeding bivalves are highly exposed to microplastic contamination because of their trophic mode, this study highlights their ability to eliminate retained particles, rather than supporting a progressive long-term bioaccumulation. When applied to aquaculture practices, these findings raise the possibility that self-depuration periods in offshore waters before commercialization could contribute to reducing human exposure to microplastics through shellfish consumption.