Histopathological Damage and Mortality in Rainbow Trout Exposed to Microplastics from Disused Tires

This study evaluated the acute toxicity of end-of-life tire fragments (EDT) in juvenile Oncorhynchus mykiss, analyzing the relationship between digestive bioaccumulation, histopathological damage, and mortality.A completely randomized design was conducted following OECD Guideline 203, exposing 105 fish to five concentrations (0, 6.25, 12.5, 25, and 50 mg/L) for 96 h.Digestive density and particle count were used as indicators of bioaccumulation, reflecting the retention of tire-derived particles in the digestive tract and enabling the association between ingestion and toxic effects.The highest particle accumulation was recorded at 6.25 mg/L (1912 particles), which is attributed to stress-induced reductions in feeding activity at higher concentrations, limiting particle ingestion.Mortality showed a clear concentration-response pattern, reaching a maximum of 71.43% at 50 mg/L after 96 h, confirming acute toxicity.Histopathological analysis revealed sinusoidal congestion and cytoplasmic vacuolization, progressing to hepatic necrosis at concentrations ≥12.5 mg/L.These results demonstrate that exposure to EDT induces digestive bioaccumulation and dosedependent liver damage, even at low concentrations, representing an underestimated ecotoxicological risk for freshwater fish species.