Establishment of baseline values for fluvial sediments in the Paraopeba river basin (Brazil), prior to the Brumadinho dam failure

The establishment of standardized procedures for defining geochemical reference values is critical to ensure consistency, robustness, and reliability in environmental assessments, particularly in mining-affected regions where natural geochemical backgrounds commonly overlap with anthropogenic inputs. In these settings, the determination of reliable baseline values is essential for differentiating natural variability from contamination and for supporting informed environmental management and regulatory decisions. This study provides a detailed characterization of the geochemical composition of fluvial sediments from the upper and middle sectors of the Paraopeba River Basin (PRB), southeastern Brazil, with the aim of defining representative baseline values for potentially toxic elements (PTEs). The basin has been subject to prolonged environmental pressures associated with mining, culminating in the failure of the B1 tailings dam in Brumadinho. Notably, the sediment dataset used in this investigation was obtained prior to the dam collapse, allowing the characterization of pre-disturbance geochemical conditions. A total of 717 fluvial sediment samples were collected and analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Given the pronounced lithological diversity of the PRB, baseline were determined separately for each lithotype using multiple statistical techniques, including TIF, mMAD, and percentile-based approaches (75th and 98th percentiles). The results reveal a dominant geogenic control on the spatial distribution of several elements, particularly Ni, Cr, Co, Cu, and V, which are strongly linked to mafic and ultramafic lithologies of the Rio das Velhas Supergroup and the Santo Antônio do Pirapetinga Complex. Conversely, Fe and Mn show higher concentrations in areas associated with iron formations of the Minas Supergroup. Spatial mapping and multivariate analyses further indicate the combined effects of lithological controls and anthropogenic activities especially mining on sediment geochemistry. In some instances, the established baseline exceeds average upper continental crust concentrations and those reported for other mining-impacted river basins worldwide, underscoring the distinctive geochemical character of the Paraopeba River Basin. In summary, this study establishes the first regional geochemical reference framework for fluvial sediments in the Paraopeba River Basin, providing a robust scientific basis for environmental monitoring, contamination assessment, and the formulation of management and remediation strategies in watersheds influenced by mining activities.