## 4 Results and Discussion  
The soil organic matter is characterised by significant sorption capacity, consisting of binding various components, including heavy metals, which limits their migration in the soil environment and their toxicity. The results of the content of humus in the samples indicated that the vast majority of soils were characterised by medium and high humus content (Table 3). Very high and low humus soils were of minor importance (in the order of a few percent). The pH value is a very important parameter characterising the soil's ability to retain heavy metals. The results of the pH in KCl for soil samples are presented in Table 4. The general pH of the analysed soils was mostly neutral and slightly acidic. The concentrations of heavy metals in soil samples depend on many factors and are time-varying. The assessment of heavy metals accumulation and the self-cleaning ability of the soil environment as a heavy metal storage medium is a complex issue. The process of migration of pollutants can be divided into two stages. The first one is related to the direct supply of pollutants as a result of increased anthropoppressure and their accumulation in the environment. The second stage is the duration of the operation of the processes to which the stored pollutants are subject after the anthropoppressure has ceased or markedly diminished. Due to the slow migration of some pollutants, such as the heavy metals considered, the system can naturally reduce the mass, toxicity, concentration and mobility of pollutants without human intervention. Such entrusting to nature of some or all of the self-cleaning processes has been defined by the Office of Solid Waste and Emergency Response (OSWER) of the EPA as Natural Attenuation (also known as intrinsic remediation or natural restoration) [52]. Soil air is characterised by an increased content of CO\({}_{2}\), which, by changing the gas balance of infiltrating waters, leads to an increase in the content of HCO\({}_{3}\)- ions in the waters percolating through the unsaturated zone [53]. Solid phases, usually amorphous and/or cryptocrystalline, are also formed in the soil zone. For this reason, they are more \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**pH (in KCl)**} & **\textless{}4.5** & **4.6–5.5** & **5.6–6.5** & **6.6–7.2** & **\textgreater{}7.2** \\  & **Very Acid** & **Acidic** & **Slightly Acidic** & **Neutral** & **Alcaline** \\ \hline percent of samples \% & 9.2 & 17.2 & 26.4 & 34.6 & 12.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: pH values in soil samples. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Content of Hummus \%**} & **\textless{}1.0** & **1.01–2.00** & **2.01–3.50** & **\textgreater{}3.51** \\  & **Low** & **Medium** & **High** & **Very High** \\ \hline percent of samples \% & 9.2 & 40.2 & 47.2 & 3.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Content of humus in soil samples. soluble than the crystalline phases. In general, the soil also experiences a radical change in pH and Eh conditions, which affects the migration capacity of many elements along with infiltration waters. Water migration of elements in the soil zone is also dependent on the amount and nature of the organic substance, which creates various types of complex compounds, protective colloids, etc. In the area covered by the research, brown soils and chernozems, characterized by a high degree of enrichment in organic matter, predominate. Sorption processes take place in the soils, in which colloids, clay minerals and organic matter participate. This study focuses only on the physicochemical processes occurring in the soil, with the omission of biological processes. However, it is worth noting their significant role in modifying the chemistry of the soil.