Polymer-specific hazard, more than particle abundance, shapes microplastic ecological and dietary risk profiles in a tropical mangrove estuary

Microplastic contamination of tropical mangrove fisheries remains poorly quantified, and polymer-specific ecological and dietary risks are rarely integrated for West African estuaries. This study assessed microplastic abundance, polymer composition, ecological risk, and human dietary exposure in commercially important finfish and crustacean species from the Escravos Estuary, Nigeria, using stereomicroscopy, FTIR identification, toxicity-weighted indices, and ingestion-based exposure modelling. Microplastics were detected in all taxa, with a mean abundance of 4.30 ± 0.76 particles g⁻¹. Surface water averaged 20.5 ± 0.7 particles L⁻¹ (n = 2 duplicate samples), and polymer and shape profiles broadly co-occurred between water and biota. Filaments (35%) and fibres (24%) dominated, while transparent and blue particles were most common, suggesting inputs from wastewater, fishing gear, and packaging materials, with possible pigment bleaching under tropical solar exposure. Detected polymers included polyvinyl alcohol, polyacrylamides, chlorosulfonated polyethylene, polystyrene, polymethyl methacrylate, and polyamides. Toxicity-weighted indices were calculated only for polymers with published hazard scores. The mean polymer ecological risk index for water indicated Class IV (7.4 × 103), and assemblage-level BALI exceeded one. Plastic Estimated Daily Intake values, derived from gastrointestinal concentrations as conservative upper-bound estimates, ranged from 1.35 to 2.24 particles kg⁻¹ bw day⁻¹ for adults and 6.31–13.59 particles kg⁻¹ bw day⁻¹ for children, reflecting gastrointestinal rather than edible-tissue exposure. Toxicity-weighted risk was more strongly associated with polymer hazard than particle abundance. Despite limited spatial replication from a single wet-season survey (May 2025), the findings support polymer-informed frameworks for environmental and human exposure assessment in tropical mangrove ecosystems.