Microplastics ingested by freshwater fish in rivers of the Syr Darya basin and associated ecological risks

Studies on the ingestion and accumulation of microplastics (MPs) by river fish in various regions worldwide are crucial for a deeper understanding of MP cycles and for assessing food safety. This paper presents data on the quantitative assessment of MP and viscose fiber (0.15-5 mm) ingestion by several fish species inhabiting the rivers of the Syr Darya basin in the Republic of Uzbekistan and an ecological risk assessment based on the polymer hazard index (PHI). The average MP concentration in fish gastrointestinal (GI) tracts (n = 61) attained 2.61 ± 4.38 items/ind, or 11.5 ± 43.8 μg/ind. The MP concentration normalized to total body weight was 86.3 ± 130 items, or 241 ± 636 μg/kg. Particles were predominantly fibers. Microplastic ingestion by fish from the Kara Darya and Chirchiq rivers did not differ significantly. No differences were observed between species, and between fish of different sexes and juveniles. Furthermore, no correlation was found between MP ingestion by fish and their trophic level. However, a significant (p < 0.05) correlation was revealed between the MP concentration in GI tracts and linear-weight parameters of fish. MP polymers predominant in fish from the Syr Darya basin included mainly PE, PET, PP, and polyethersulfon (PES) plastics. In addition to PES, "minor" polymers, such as PAN, PUR, and PVC, contributed to the ecological risk associated with polymer toxicity. The ecological risk for MPs extracted from the collected fish specimens was assessed based on the PHI and categorized as moderate (hazard category III). The study provides the first experimental evidence of MP ingestion by freshwater fish in the rivers of the Syr Darya basin. The data obtained can be used for the quantitative assessment of global plastic pollution and its threat to environmental components, including living systems, as well as for the ecological risk assessment.