Exposure to toxic metals induces biochemical and histological alterations in the liver of native fish from a lacustrine area in the eastern Amazon, northern Brazil

The accumulation of toxic metals threatens biodiversity and poses significant risks to human health. The aim of this study was to determine environmental quality of Lake Açu, located in Conceição do Lago Açu, Maranhão, Brazil, utilizing biochemical and histopathological biomarkers in <i>Prochilodus lacustris</i> exposed to toxic metals. Samples were collected from three sites: S1 - urbanized area impacted by domestic sewage and fishery waste; S2 - intermediate location; and S3 - site furthest from the urban area, during dry and rainy seasons. Water, sediment, and fish liver samples (<i>n</i> = 80) were analyzed. Elevated concentrations of aluminum (33,204.87 mg/kg at S2 during the dry season), copper (22.89 mg/kg; limit ≤0.2 mg/kg at S3 during the rainy season), and manganese (1,621.57 mg/kg at S1 during the dry season) were detected in sediments, with copper exceeding Brazilian safety limits (CONAMA Resolutions 420/2009 and 2012). Mercury concentrations (0.05 mg/kg) reached the maximum established limit (≤0.05 mg/kg). These elevated metal levels correlated with hepatic lesions in fish, including cytoplasmic vacuolization (100%) and cellular degeneration (90%), mainly in S1 and S2 sites. Glutathione S-transferase (GST) activity averaged 4 U/mg protein, while catalase (CAT) activity was close to 400 U/mg protein. Seasonal and spatial variations did not significantly influence enzymatic responses. Data demonstrate that contamination by toxic metals in Lake Açu compromises hepatic integrity and fish physiology, emphasizing the urgent need for mitigation measures and environmental management to protect aquatic biodiversity.