COMPARATIVE ASSESSMENT OF THE CONTENT OF MOBILE FORMS OF HEAVY METALS IN FOREST SOILS WITH DIFFERENT LEVELS OF ANTHROPOGENIC LOAD

Abstract

The article presents the results of a comparative assessment of the content of mobile forms of heavy metals (Cu, Zn, Pb, Cd) in forest soils exposed to different levels and types of anthropogenic load. The study was carried out at three sites with identical soil type and forest-growing conditions, which enabled minimizing natural variability and focusing on the impact of external factors. Site No. 1 is located within a recreational zone near a highway and is subject to constant transport and human pressure. Site No. 2 represents a forest area affected by a medium-intensity wildfire that occurred one month prior to the first sampling campaign. Site No. 3, located within forest land and with little anthropogenic influence, was used as a control site. Soil samples were collected from the upper humus horizon (0–10 cm) after removing the forest litter layer. The determination of mobile metal forms was performed using extraction with an acetate-ammonium buffer solution (pH 4.8), followed by instrumental analytical measurements. The results revealed clear spatial and temporal differences in metal concentrations. In 2022, the highest levels of Pb (1.37 mg/kg) and Cd (0.18 mg/kg) were recorded at the post-fire site, reflecting short-term post-fire effects associated with the combustion of organic matter, ash accumulation, and disruption of organo-mineral complexes. Three years later, a decrease in Cu and Zn content at this site indicated gradual stabilization and redistribution of metals within the soil profile during ecosystem recovery. In contrast, the roadside site demonstrated increasing Pb (up to 1.51 mg/kg) and Zn (0.86 mg/kg) concentrations in 2025, confirming the cumulative and long-term character of traffic-related pollution. The control site maintained stable background values throughout the study period. Although the concentrations of mobile forms of Cu, Zn, Pb, and Cd in both years did not exceed established maximum permissible levels, the detected differences highlight the contrasting influence of extreme (wildfire) and chronic (transport) anthropogenic factors on heavy metal mobility in forest soils. The findings confirm the suitability of mobile metal fractions as sensitive indicators of ecological changes and emphasize the importance of long-term environmental monitoring in post-fire and roadside forest ecosystems.