Microplastics in tropical freshwater carnivorous fish: edible tissue contamination and an exploratory Fillet Risk Score (FRS) framework

Microplastic contamination in freshwater fish is an emerging concern for ecosystem health and food safety, yet exposure in edible tissues remains insufficiently characterized. This study investigated microplastic accumulation in three tropical freshwater carnivorous fish species from the Selangor River, Malaysia, with emphasis on organ-specific distribution, edible fillet contamination, particle size–shape composition, polymer identity, and screening-level dietary exposure relevance. Microplastics were quantified in gills, stomach, intestine, and fillet tissues, classified by morphology, and evaluated using principal component analysis, the Pollution Load Index (PLI), and an exploratory Fillet Risk Score (FRS). Microplastics were detected in all analysed organs, confirming that contamination extended beyond the gastrointestinal tract into edible tissue. Smaller particles dominated the observed burdens, particularly the <0.5 mm fraction, while inclusion of the <0.1 mm category revealed contamination that would likely be underestimated in conventional assessments. Fibres, films, fragments, and beads showed organ- and species-specific variation, indicating distinct exposure and retention pathways associated with feeding behaviour and tissue function. Raman analysis identified polyethylene, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, and poly(methyl methacrylate), reflecting mixed anthropogenic inputs from packaging waste, fishing-related materials, and urban infrastructure. Together, these findings show that direct quantification of edible fillets, combined with morphology-sensitive exposure screening, provides a more comprehensive framework for evaluating microplastic contamination and potential dietary exposure in tropical freshwater systems.