Effectiveness of pre-processing interventions for microplastic reduction in freshwater and coastal bivalves: Insights for seafood safety and pollution mitigation

Microplastic (MPs) contamination in aquatic ecosystems poses escalating ecological and food safety concerns, with bivalves serving as effective sentinel organisms for pollution monitoring. However, data on tropical species and the effectiveness of commonly applied post-harvest pre-processing interventions remain limited. This study quantified MPs abundance, characteristics, and removal efficiency in three commercially important tropical bivalves Lamellidens marginalis, Meretrix casta, and Perna viridis collected from freshwater, estuarine, and coastal habitats in Maharashtra, India (n = 540). Specimens were analyzed in untreated and sequentially treated states, including depuration (24-72 h), surface cleaning of edible tissues, and gill removal. Depuration durations were selected to reflect typical short-term post-harvest holding practices relevant to consumer exposure. MPs concentrations in fresh samples ranged from 3.8 ± 0.41 to 12.4 ± 1.15 items/g wet tissue, dominated by fibres and fragments, with polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) as the most prevalent polymers. MPs abundance declined progressively with depuration across all species, reaching approximately 50-60% reduction after 72 h (L. marginalis: 6.87 to 2.75 items/g; P. viridis: 10.61 to 5.03 items/g; M. casta: 9.32 to 4.66 items/g). Surface cleaning and gill excision produced additional, species-specific reductions, with combined interventions achieving up to 69.4% removal in P. viridis. Treatment and species effects were statistically significant (p < 0.05). Despite these reductions, fine MPs (<100 μm) persisted across all interventions. Morphotype and polymer profiles shifted following treatment, with fibres preferentially removed during gill excision, while smaller fragments showed greater resistance to elimination. These findings demonstrate that conventional depuration and anatomical pre-processing can substantially reduce, but not eliminate, MPs contamination in tropical bivalves. The persistence of fine and polymer-specific MPs highlights the need for integrated mitigation strategies and standardized monitoring frameworks to safeguard seafood safety in tropical aquatic and aquaculture systems.