Burbot (Lota lota) as a bioindicator of microplastic pollution in the Tisza River: Multi-tissue contamination, polymer characterisation, and implications for ecological and human-health risks

Microplastic (MP) pollution poses a growing threat to freshwater ecosystems and human health, yet knowledge of its occurrence in European rivers remains limited. This study provides the first evidence of MP contamination in burbot (Lota lota) from the Hungarian upper Tisza River. MPs were detected in all sampled fish (n = 10), with an average of 24.6 ± 7.46 particles per individual. Most particles were fibres (83.3 %), predominantly blue and generally < 500 μm in diameter. A Kruskal-Wallis analysis showed significant differences in MP retention across tissues (p < 0.05), with gills (1.53 MPs g⁻¹) and the gastrointestinal tract (GIT; 1.54 MPs g⁻¹) containing higher loads than liver (0.89 MPs g⁻¹) and muscle (1.07 MPs g⁻¹). Correlation analysis indicated non-significant positive associations (p ≥ 0.05) between total MP load and retention in the GIT (r = 0.41), liver (r = 0.58), and muscle (r = 0.63), but a negative relationship with gills (r = -0.56). Raman spectroscopy confirmed 68 particles representing 17 polymer and copolymer types, grouped into three categories: anthropogenically modified cellulosic fibres (ACF), textile-derived MPs, and petroleum-derived MPs. Textile-associated materials, including ACF, PET-cotton blends, and indigo-dyed polyurethane, predominated, indicating strong inputs from domestic laundering and urban effluent. Estimated human exposure through burbot consumption ranged from 14.4 MPs/week in infants to 320.54 MPs/week in European adults (123.6 MPs/week in Hungary), highlighting a potential dietary exposure pathway. These findings show that inadequate upstream waste management drives contamination and provide a critical baseline for monitoring microplastic pollution in Central European freshwater systems. Given its ecological traits and tissue-specific retention patterns, burbot represents a valuable bioindicator for long-term riverine MP surveillance.