Mining activities have a long history of impacting aquatic environments, such as the Doce River Basin (DRB), in Brazil. After the collapse of the Fundão dam (MG), high concentrations of metals in water and sediments from DRB were reported, and some remain above legal standards even after 4 years. Wastewater, industrial effluents, and pesticide runoff from agricultural landscapes have released organic chemicals into this waterbody, resulting in complex mixtures with metals. No previous study has investigated the co-occurrence of organic contaminants and their potential toxicological effects in the DRB. Besides, their mechanisms of toxicity in aquatic organisms are obscure, making it difficult to distinguish effects triggered by organic contaminants from those induced by metals. For unveiling mechanisms of toxicity, LC-HRMS metabolomics can be a powerful approach in field-scale monitoring studies, helping to comprehend biological responses to environmental stressors. This study aims to investigate mechanisms of toxicity of environmental chemicals from DRB using a comprehensive LC-HRMS metabolomics approach in fish embryos (Rhamdia quelen) exposed to chemical mixtures, in order to distinguish responses induced by inorganic and organic chemicals. Fish embryos will be exposed for 96h to 6 treatment groups, considering mixtures of inorganic chemicals (same concentrations detected in DRB), organic chemicals extracted from sediments from DRB and complex mixtures of both inorganic and organic chemicals. Exposures will occur in Brazil and samples will be transported to Spain for LC-HRMS analysis to elucidate mechanisms of toxicity, including oxidative stress and possible endocrine disruption pathways. The results will help to identify and distinguish effects of different classes of environmental chemicals when combined as complex mixtures, not only in the DRB but also in other aquatic ecosystems.
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