Influence of fish length and weight on microplastic accumulation in freshwater fish from the Kahayan river, Indonesia

Microplastics are pervasive in freshwater systems and can enter the human food chain via fish consumption. This study examined microplastic ingestion in 75 individuals (23 species) from upstream, midstream, and downstream sections of the Kahayan River (rainy season). Microplastics occurred in 65.2% of fish with a mean of 2.21 items/ind. Fibers dominated (80-90%), and most particles were in the 500-1000 µm and >1000 µm size classes, with polyethylene (PE) was the most common polymer. Correlation analyses showed moderate positive coefficients between fish length/weight and total microplastic counts. However, most correlations were not statistically significant (p > 0.05). Notably, fish length was significantly associated with fiber particles and particles >1000 µm, suggesting larger individuals tend to retain larger and fibrous particles. Because sampling occurred only during the rainy season and sample sizes per species were limited, results should be interpreted cautiously. These findings highlight the importance of ecological traits in explaining microplastic loads and point to potential human exposure through fish consumption, underscoring the need for targeted monitoring and improved waste management in riverine communities.