Environmental background in Amazonian rivers near the industrial pole, northern Brazil

). While Al and Fe concentrations are linked to regional geology and exhibited negative temporal trends, Cd and Pb require particular attention due to their association with rising anthropogenic pressures. Overall, the study successfully identified environmental thresholds, generating the first 41-year background reference for the region. This contribution is crucial for distinguishing natural variability from long-term contamination and significantly strengthens environmental monitoring and impact assessment in Amazonian aquatic ecosystems.