Concentrations and forms of heavy metals in Slovak soils

The risk assessment of heavy-metal contamination in soils requires knowledge of the controls of metal concentrations and speciation. This study aimed to explore the relationship between soil properties (pH, CEC, C org, oxide concentrations, texture) and land use (forest, grassland, arable) concerning the partitioning of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn among the seven fractions of a sequential extraction procedure in 146 A horizons from Slovakia. A cluster analysis identified 92 soils representing background metal concentrations, while the remaining 54 soils exhibited anthropogenic contamination. Forest soils displayed the lowest heavy-metal concentrations among background soils, except for Pb, which was highest due to the organic layer's shielding effect. Conversely, arable soils contained elevated concentrations of Cr, Cu, and Ni, indicating agrochemical inputs. Grassland soils showed high Cd and Zn concentrations likely stemming from geogenic factors. The study findings suggested that the parent material influenced metal concentration thresholds, with podzols indicating metal depletion in E horizons caused by pedogenic eluviation processes. Crucially, pH levels were found to predominantly control bioavailable fraction contributions of all metals, alongside Fe oxide-associated metal contributions influencing total concentrations. These insights enhance understanding of heavy-metal dynamics and inform soil management practices.