Spatial Patterns and Source Apportionment of Potentially Toxic Elements in Flood-Affected Fluvisol Soils of the Bosna River Alluvial Plain

This study quantifies the concentrations, spatial patterns, and sources of potentially toxic elements (PTEs) in Fluvisols from the Bosna River floodplain. Total As, Cr, Ni, Cu, Zn, Ba, V, and Co contents locally exceed national thresholds (e.g., As > 15 mg/kg, Cr > 80 mg/kg, Ni > 40 mg/kg), yet Ti-normalised enrichment factors mostly remain in the “no to minor” range (EF ≈ 1–3) and contamination factors in the “low to moderate” range (CF ≈ 1–3), indicating only slight to moderate enrichment even where absolute concentrations are high. Cr, Ni, Co, Ba, and V display similar spatial patterns, strong positive correlations with Mg and Fe, and consistently low EF values, confirming their predominantly geogenic origin linked to ultramafic and mafic parent rocks. In contrast, Cu, Zn, Pb, and Cd form coherent spatial clusters, share positive correlations, and show slightly elevated EF and CF values in flooded soils (typically EF and CF between 1 and 3), indicating diffuse industrial and agricultural inputs superimposed on a strong natural background. Flooding did not uniformly increase PTE concentrations but enhanced spatial heterogeneity and reorganised geochemical associations, particularly for Zn, As, and Cd, while the observed links between inorganic carbon (TIC), Ca, and Mg indicate that carbonate buffering and base cations help constrain metal mobility rather than exert a dominant control on all elements. The novelty of this work lies in integrating Ti-normalised EF and CF referenced to a local Fluvisol background with high-resolution GIS mapping and paired flooded versus control multivariate analysis, providing a quantitative, transferable framework to disentangle geogenic and anthropogenic signals and to prioritise post-flood monitoring of As, Cu, Zn, Pb, and Cd in naturally metal-rich floodplains.