Assessment of Elemental Geochemistry: Enrichment and Mobilisation in Acid Sulfate Soils in Southeast Brazil

Abstract

The spatial distribution of acid sulfate soils is influenced by coastal processes, and due to their location, these soils can accumulate significant amounts of trace elements. This study assesses the horizontal and vertical distribution of major elements (Ca, Mg, K, Al, Fe, S), minor elements (P, Ti, Mn), and trace elements (Ba Co, Cu, Cr, Mo, Ni, Pb, V, Zn) in acid sulfate soils of the interdistributary plain of the Doce River Delta, Espírito Santo, Brazil. The area, influenced by sulfidization and sulfurization processes, shows significant variations in the concentration of these elements due to interactions between chemical element characteristics, soil properties, and landscape features. Depth profile analysis revealed significant heterogeneity, particularly in Ti concentrations, suggesting that variations in soil element concentrations may result from both historical geological depositions and recent mobilisation processes. To assess contamination, the geo-accumulation index (Igeo) and enrichment factor (EF) were applied. The results varied significantly depending on the selected background reference. The discrepancy between indices highlights the critical importance of selecting an appropriate background for a realistic assessment of contamination by potentially toxic elements in estuarine soils. The conclusions emphasise that, in addition to absolute element concentrations, local pedogenesis and soil chemistry must be considered when interpreting contamination data. This study highlights the need to adapt environmental assessment methodologies to the specific geographic and environmental conditions of the studied areas. Ensuring that assessments accurately reflect environmental risks is essential for guiding decision-making and environmental management.