Spatial distribution, potential sources and geochemical baseline of Fe and potentially toxic elements in stream sediments in Quadrilátero Ferrífero, Brazil

Abstract

This study investigates geochemical baselines and the spatial distribution of potentially toxic elements (PTE) in stream sediments of the Quadrilátero Ferrífero (QF), Brazil—an iron-rich province with complex geology and extensive mining activity. A total of 804 microcatchments were sampled and analyzed for 15 environmentally relevant elements (including Fe, As, Cd, Hg, Ni, and Zn), selected based on their ecological significance, toxicity, and geogenic occurrence in mineralized terrains. Geochemical baselines were calculated using median ±2 × median absolute deviation (mMAD) and Tukey's Inner Fence (TIF), with mMAD providing more conservative and robust thresholds. A compositional data analysis (CoDA) framework was applied using isometric log-ratio (ilr) transformation and robust principal component analysis (RPCA) to explore geochemical-lithological affinities. Results showed that metavolcano-sedimentary sequences, especially from the Rio das Velhas and Minas Supergroups, exhibit elevated concentrations of multiple PTEs, while metabasic and ultrabasic units are enriched in Cr, Ni, and Co. The TTGM unit also showed distinctive enrichment in Ba and Pb. Spatial patterns suggest that lithology is one of the main controls on PTE distribution and represents a valuable tool for interpreting geochemical variation in mineralized regions. These findings offer a solid basis for environmental monitoring and future integration with land use data to support contamination risk assessments and sustainable watershed management in areas such as the QF.