Tissue-specific accumulation and species-level variability of microplastics in four freshwater fish from the Dez River, Iran

Microplastics (MPs) are emerging contaminants of global concern due to their persistence, bioaccumulation potential, and implications for both aquatic ecosystems and human health. This study explored MP contamination in four economically important freshwater fish species—Carasobarbus luteus, Arabibarbus grypus, Luciobarbus barbulus, and Oreochromis niloticus—collected from the Dez River in southwestern Iran. A total of 120 specimens (30 per species) were sampled near the Dez Dam using gill nets. Edible (muscle) and inedible (skin and gastrointestinal tract) tissues were analyzed separately for MP content following alkaline digestion with 10% KOH and vacuum filtration. Visual identification under a stereomicroscope was used to quantify and categorize MPs by color. Microplastics were detected in all species and tissue types, with significant interspecific variation. Carasobarbus luteus exhibited the lowest MP burden, significantly lower than O. niloticus and L. barbulus. No significant differences were found among tissue types, suggesting widespread tissue distribution. Color composition varied across species, with black MPs being the most abundant. Notably, green MPs were only observed in O. niloticus and L. barbulus. These findings highlight the impact of ecological traits, including feeding behavior and habitat use, on the risk of MP exposure. The detection of MPs in edible tissues highlights potential food safety concerns and underscores the need for routine monitoring of freshwater fish in affected river systems. This study reports the first evidence of MP contamination in fish from the Dez River and contributes to the growing body of data on freshwater plastic pollution in understudied regions.