Bioaccumulation of toxic and essential elements and enzymatic responses in native fish from the middle Tocantins River.

This study provides the first ecotoxicological evaluation of potentially toxic elements (PTEs), essential elements (EEs), and enzymatic biomarkers in two native fish species, Branquinha (Psectrogaster amazonica) and Branquinha-cascuda (Caenotropus labyrhinthicus), from the middle Tocantins River, Brazil. Specimens were collected from the urban riverside zone of Beira Rio (P1) and a fluvial beach near the rural community of Embiral (P2). PTEs and EEs concentrations were measured in liver and muscle tissues, and biochemical biomarkers included acetylcholinesterase (AChE), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP). Human health risks associated with fish consumption were assessed using the bioconcentration factor (BCF), risk quotient (RQ), and estimated daily intake (EDI). In P. amazonica (urban zone), arsenic (As) exceeded limits by 83–266% in muscle and 60–220% in liver, lead (Pb) in liver by 95–1850%, and selenium (Se) by up to 4537%. In C. labyrhinthicus (rural zone), As and Se in muscle exceeded limits by 185–470% and 5–200%, respectively, while Pb and zinc (Zn) were not detected. BCF values indicated moderate bioaccumulation of sulfur (S) (2867.29) and iron (Fe) (2641.30). Risk assessment revealed a high level of concern, with an RQ for Se reaching 53.13 and As intake exceeding child safety thresholds sevenfold, highlighting significant food safety risks.