Spatio-temporal dynamics and risk assessment of microplastics in water, sediment and fish from a critical wetland ecosystem: Arial Beel, Bangladesh

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Global attention toward microplastics (MPs) arises from their pervasive presence in aquatic systems and harmful effects on the ecosystem, biota, and human wellness. Since the detection of MPs in Arial Beel has not yet been studied, therefore, this investigation aimed to examine MPs abundance, seasonal variation, physical attributes, and polymer types in water, sediment, and five small indigenous species (SIS; n = 150) with a risk assessment. Samples from five sites were isolated through a series of laboratory methods: chemical digestion, density separation, and filtration, polymer identification through FT-IR and risk assessment using standardized methods. Results showed that MPs occurred in the intestine, gills, and muscle of all species studied, were notably higher in the benthopelagic fish Anabas testudineus (1–1.90 MP/ind.) across all seasons. Besides, sediment (12.33–127.33 MPs/kg) showed significantly greater mean levels of MPs compared to water (11–31.67 MPs/L), with levels varying ( p < 0.05) by location and season. Fish tissues were dominated by smaller particles (101–300 µm); water and sediment contained larger particles (601–900 µm), particularly in winter and dry seasons. The shape of MPs was mostly fibrous, followed by fragments and foams. Polymeric profile analysis found that PE, PS, and PP were the most prevalent types detected in all samples. Furthermore, risk assessment metrics identified notable seasonal pollution risk. In sum, our results indicate that MP contamination in the Arial Beel occurs at concerning levels. By elucidating the seasonal dynamics of MPs, this study provides a key reference and practical guidance for agencies seeking to assess pollution levels with seasonal precision.