Hydrogeochemistry of Surface Waters in the Iron Quadrangle, Brazil: High-Resolution Mapping of Potentially Toxic Elements in the Velhas and Paraopeba River Basins.

Abstract

The assessment of sediment contamination is a critical component in understanding the dynamics of potentially toxic elements (PTEs) in aquatic ecosystems, particularly in regions with intensive mining activities. This study focuses on the Rio das Velhas basin, located in the Iron Quadrangle (IQ), one of the most important mining provinces in the world, characterized by extensive anthropogenic pressures and rich geological diversity. A comprehensive evaluation of sediment contamination in this region was conducted, applying multiple univariate and multielement indices, including the contamination factor (CF), enrichment factor (EF), modified contamination degree (mCd), pollution index (PI), modified pollution index (MPI), and ecological risk index (RI). A high sampling density (1 sample per 15 km2) enabled the creation of geochemical maps and the identification of contamination hotspots. The results revealed that As and Cd are the most concerning elements, with concentrations exceeding regional background levels. While EF provided a more sensitive and comprehensive spatial distribution of contamination, MPI emerged as a robust index for capturing geochemical trends in complex environments. The study also highlighted that over 20% of the samples exceeded guideline values for sediment quality, posing ecological risks. Elevated concentrations of PTEs, particularly As and Cd, raise concerns about their potential mobilization and bioaccumulation, threatening aquatic ecosystems. These findings underscore the urgent need for enhanced monitoring and targeted management strategies in mining-impacted basins. This work not only advances the understanding of sediment contamination dynamics in the IQ but also establishes a methodological framework for evaluating sediment quality in heavily impacted mining regions worldwide.