POTENTIALLY TOXIC AND ESSENTIAL ELEMENTS, AND ENZYMATIC BIOMARKERS IN TWO NATIVE FISH SPECIES FROM THE MIDDLE TOCANTINS RIVER, MARANHÃO, BRAZIL: INSIGHTS INTO ECOSYSTEM AND HUMAN HEALTH

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INTRODUCTION: The interface between the Cerrado and Amazon biomes is increasingly exposed to environmental stressors, yet few studies have addressed contaminant bioaccumulation and biological responses in native ichthyofauna. Understanding the presence of toxic elements and their effects on fish health is essential for ecological risk assessment. OBJECTIVE: This study provides a first comprehensive ecotoxicological evaluation of potentially toxic and essential elements (PTEs and EEs) in two native fish species, Branquinha (Psectrogaster amazonica) and Branquinha-cascuda (Caenotropus labyrhinthicus), from the middle Tocantins River, Maranhão, Brazil. MATERIALS AND METHODS: Specimens were collected from two contrasting sites: the urban riverside zone of "Beira Rio" and a fluvial beach near the rural community of “Embiral”. PTE and EE concentrations were analyzed in liver and muscle tissues, while biochemical stress was assessed using enzymatic biomarkers (AChE, AST, ALT, and ALP). To estimate potential human health risks from fish consumption, several indices were applied, including bioconcentration factor, risk quotient, risk index, and estimated daily intake. RESULTS AND CONCLUSION: In P. amazonica from urban area, concentrations of As (muscle: 1.83 mg/kg; liver: 1.6 mg/kg), Pb (liver: 3.90 mg/kg), and Se (muscle: 9.30 mg/kg; liver: 13.91 mg/kg) exceeded national and international safety thresholds. In contrast, C. labyrhinthicus from rural zone showed no detectable Pb or Zn, suggesting lower local contamination, although elevated levels of As (muscle: 2.85 mg/kg) and Se (muscle: 15.94 mg/kg) remain concerning. Bioaccumulation of Fe and Se was observed in both species. Biomarker analyses revealed significant enzymatic alterations associated with urban pollution, indicating physiological stress. These findings highlight potential public health risks and underscore the importance of continued biomonitoring. They also provide critical baseline data for environmental management, public health strategies, and regional conservation planning in the Cerrado–Amazon ecotone.