## 2 Materials and Methods
### Methods of Analysis of Physico-Chemical Characteristics and Tools
#### 2.2.1 Analytical Techniques--Analysing the Heavy Metals and Agrochemical Indicator Contents  
Limit values were applied to air-dried soil samples to determine the heavy metals analytically. Soil samples were processed as fine earth I (average particle size: 2 mm) and fine earth II (average particle size: 0.125 mm) for heavy metal determination measurements using the atomic absorption spectrometry method to ascertain agrochemical properties. Active and Exchange Reactions of Soils  
Soil pH, or the soil response, is a crucial factor affecting several different soil processes and qualities. It fundamentally impacts microbial activity, nutrient availability, and the solubility of Cd and Pb found in soil. The sorption and mobility of heavy metals, as well as the availability of vital nutrients for plant development, can all be strongly impacted by the pH of the soil. The measurement unveils crucial insights into the ecosystem's health and functionality. pH values were determined based on a water-to-soil ratio of 2.5:1, v:m [33]. The pH(H\({}_{2}\)O)--the active soil reaction--was gauged in distilled water, whereas the pH(KCl)--the exchange soil reaction--was appraised in a 1 mol.dm\({}^{-3}\) KCl solution (Centralchem, Ltd., Bratislava, Slovakia). A Unimax 2010 horizontal shaker (Heidolph Instrument GmbH, Schwabach, Germany) was used to ensure uniform suspension of the soil samples for 20 min. Subsequently, pH values were determined using an ino-Lab Multi 9310 pH meter (Labo SK, Ltd., Bratislava, Slovakia). We measured the total organic carbon content (_TOC_) in soil samples and the various separated fractions using the Nikitina-modified Tyurin method [34]. By utilising the Tyurin method modified by [PERSON] according to [PERSON] and [PERSON] for _TOC_ determination, this study ensured a standardised and reliable approach to quantifying the soil samples' levels of organic carbon. This information was crucial for understanding the soil's organic matter composition and its potential influence on heavy metal sorption and other soil properties. Components of Humans--Isolation of FA and HA Fractions  
Humus was extracted into Na\({}_{4}\)P\({}_{2}\)O\({}_{7}\) with c = 0.1 mol dm\({}^{-3}\) and NaOH to get the pH down to 13 (c = 1.0 mol dm\({}^{-3}\)). Soil samples were infused for 24 h. A spectrum analyser (Specord 50 Plus, Analytik Jena, Germany) was used to examine UV/Vis spectra from 300 nm to 700 nm. We calculated the content of humus using Equation (1) [35]:  
\[Hum=TOC\times 1.724 \tag{1}\]  
_Hum_ (%) = the humus content in the soil  
_TOC_ (%) = the total organic carbon  
1.724 is the valid conversion coefficient, assuming that the humus contains 58% carbon (e.g., 100/58 = 1.724)  
The group composition of humus substances (HSs) was used to determine their content using the Belcikova-Kononova technique [36]. In general, HSs can be fractionated into three principal groups, depending on their solubility in an aqueous environment at various pHs. These fractions include humus (HUs)--generally insoluble at any pH, fulvic acids (FAs)--soluble in every pH [37; 38], and humic acids (HAs)--soluble in alkaline media, which precipitate at pH below 2.0 [39]. A Na\({}_{4}\)P\({}_{2}\)O\({}_{7}\) solution (c = 0.1 mol\(\cdot\)dm\({}^{-3}\)) was applied to extract the samples for a full day (24 h) at 22 \({}^{\circ}\)C with periodic shaking to measure metal concentrations bound to humic and fulvic fractions. In order to quantify the amounts of metals bonded to the humic and fulvic fractions, the samples were extracted for 24 h at 22 \({}^{\circ}\)C with intermittent shaking using the Na\({}_{4}\)P\({}_{2}\)O\({}_{7}\) mixture (c = 0.1 mol\(\cdot\)dm\({}^{-3}\)). Centrifugation at 3000 rpm was used to remove any undissolved material [36]. \(FA\) and \(HA\) were separated from the mixture by filtering and acidifying with H\({}_{2}\)SO\({}_{4}\). Thermal 0.05 mol\(\cdot\)dm\({}^{-3}\) NaOH was used to dissolve the remaining \(HA\).