Combined effects of land use and geology on potentially toxic elements contamination in lacustrine sediments from the Araguaia River floodplain, Brazilian Savanna

Freshwater ecosystems play a fundamental role in maintaining biodiversity and supporting human societies; however, the mobilization of potentially toxic elements (PTEs) poses a significant threat to their integrity. Here, we characterized the elemental composition of the bottom sediments of 72 lakes in the Araguaia River floodplain, a region that has been undergoing large-scale environmental degradation due to the advance of anthropogenic activities. The objectives of this study were to assess the degree of Cr, Cu, Ni, Pb, and Zn contamination in bottom sediments, identify critically contaminated areas, and evaluate the contribution of anthropogenic and natural factors to the distribution of PTEs in the floodplain. The contamination and enrichment factors followed the order of Ni > Cr > Pb > Cu > Zn. Notably, Ni and Cr showed the highest proportions of samples with moderate and significant enrichment, respectively, with a considerable and very high degree of contamination. Critical areas of PTE contamination have been identified in lakes with intense anthropogenic land use and igneous and metamorphic rocks derived from mafic parent materials. All PTEs were strongly correlated with the Mg concentrations in the sediments, which were used here as a proxy for regional geology characterization. Land-use intensity was positively associated with higher Cr and Ni concentrations in sediments. Organic matter content significantly influenced the accumulation of PTEs in sediments (except for Cr). This study offers valuable insights into the sources, distribution, and control of PTE contamination in floodplain lakes, underscoring the importance of sustainable land use management in mitigating contamination risks.