Flood‑Driven Remobilisation of Legacy Metal Contaminants in Sovenian River Basins

The August 2023 floods in Slovenia exposed how extreme hydrological events can transform industrial and mining legacies into acute public health and agricultural crises. Heavy rainfall triggered mass wasting and river overflows across 183 municipalities - an area of approximately 17,203 km² ‑ resulting in roughly €9.9 billion in losses.

Slovenia’s rich mineral deposits historically fueled industrial development but left enduring environmental burdens. Beyond the physical devastation, these floods remobilized toxic sediments from historical hotspots, including the Mežica Pb–Zn mine, the Celje zinc smelter, and the Idrija mercury mine. Our study uses field measurements, geochemical analyses, and a comprehensive GIS framework to examine how flood deposits contaminate farmland and influence human exposure pathways across the nation’s river basins.

We conducted a GIS-based analysis that integrated national geochemical surveys, environmental monitoring data, hydrological records, historical & modern land-use maps, and flood-hazard assessments. This enabled us to identify zones where contamination sources overlap with flood-prone areas across four major river basins: Sava, Drava, Mura, and Soča. By overlaying these layers with current land use, we delineated agricultural and urban parcels most at risk of metal contamination.

Analyses reveal pronounced contamination gradients and significant overlap between polluted zones and cultivated floodplains. In the Sava basin, multiple hotspots (Celje, Jesenice, and Litija) coincide with intensively farmed floodplain terraces. Overbank sediments here show metal concentrations tens to hundreds of times above background levels; specifically, Celje’s topsoils contain Zn up to 8,600 mg kg⁻¹ and Cd often exceeding critical thresholds. GIS overlays indicate that a substantial portion of this farmland lies within high-hazard flood zones. In the Drava basin, spatial analysis highlights a narrow corridor where the Meža plume passes through cropland; floodplain soils downstream remain laden with Pb, Zn, and Cd from legacy mining. By contrast, the Mura basin, while largely agricultural, shows minimal overlap between contaminated zones and flood-prone areas, reflecting its predominantly geogenic background and lower industrial impact. In the Soča basin, we observed moderate overlap: heavy Hg contamination from Idrija (sediment averages 603 mg kg⁻¹ and floodplain soils 157.7–294.8 mg kg⁻¹) is largely confined to specific terraces, yet downstream agricultural parcels remain at risk.

Our findings show that Slovenian floodplains are disproportionately burdened by legacy pollutants that re-enter the environment during extreme events. As climate projections indicate more frequent and intense flooding in Alpine and Pannonian regions, it is urgent to integrate flood risk management with soil remediation, agricultural planning, and public health strategies to safeguard food security and human well-being.