## 4 Discussion  
The As, Cr, and Ni concentrations in soil samples were below the maximum permissible levels adopted in national legislation [52]. The Cd content in one of the soil samples (sample 27) with pH = 6.6 exceeded almost three times the maximum permissible level of 2.5 mg/kg. In the same soil sample, the concentration of Pb was very close to the maximum permissible one of 130 mg/kg. In several locations with pH levels ranging from 6.0 to 7.4, the Zn content was discovered to be near the maximum permissible limit of 390 mg/kg but remained below the intervention levels. As expected, Cu was identified as the primary cause of soil contamination. The copper levels were below the maximum permissible level (for pH < 6.0) of 80 mg/kg at only two studied sites. At all of the other examined sites, the concentration of Cu was significantly elevated, ranging from 2 to 16 times higher than the maximum permissible level and reaching values as high as 1288 mg/kg. The concentrations of potentially toxic elements in other open-pit copper mines in Bulgaria such as Asarel-Medet, which have the same origin as \"Isar Asen\", were analyzed in [PERSON] et al. (2018) [55]. The observed concentrations of Cu in this study also exceeded 2 to 10 times the maximum permissible concentrations, reaching 2400 mg/kg. In addition, compared with other areas exposed to copper mining and smelting, the determined concentrations of Cu in our study were significantly higher than those reported in Germany--420.9 mg/kg [18], in Spain--642 mg/kg [56] and in China--1990 mg/kg [57]. The obtained concentrations for Cd, Co, Cr, Cu, Fe, Mn, Sb, Sn, and Zn of _Taraxacum officinal_ exceeded the background levels typical for Bulgaria and published in [PERSON] et al. (2014) [54]. In the area of the \"Isar Asen\" mine, the determined concentration for Cr was twice the background level. Co, Cu, Fe, Mn, and Zn were three times higher than the background levels. The Sb and Sn concentration levels were five times higher than in the background regions. The highest value compared to the background concentrations of 0.04 to 0.30 mg/kg was found for Cd, with a value of 5.31 mg/kg. [PERSON] et al. (2012) [58] analyzed dandelion leaves sampled from a mining area located in the mountain district of Belluno (NE Italy) and found concentrations of Cu, Cr, and Zn close to those determined in this study. Regarding Cd, the concentration found in the plant samples from \"Isar Asen\" was five times higher than those found by [PERSON] at al. [58]. The very good discrimination obtained between the sandy and clay sampling locations resembled their different element soil profiles, which should be considered when the transfer and accumulative factors are analyzed (Figure 2). The PLS-DA model results for the sand and clay groups based on the element concentrations of the soil samples showed that the elements responsible for the grouping of the samples (VIP score above 1) were Be, Mg, Al, K, Ca, Ti, V, Fe, Ni, Cu, Zn, Mo, Sn, Sb, Ba, TI, and Bi. The soils falling into the sand group were characterized by high concentrations of Na, P, Ti, Mn, Ni, Zn, As, Se, Sn,  
Figure 8: PC1 factor loadings (**a**) and factor scores (**b**) of the element accumulation factor dataset. Sb, Pb, and U, in contrast to the other group. The clay group included soils with higher concentrations of the elements Mg, Al, K, Ca, V, Cr, Fe, Co, Cu, Rb, Mo, Ag, Cd, Ba, La, Tl, Bi, and Th. The wide range of the soil samples' pH and CEC could be explained by the different soil and rock materials used during the remediation activities in the sampling region. In order to explore the relationships between TFs and AFs with pH in water, pH in KCl, and CEC, correlation analysis was performed (Figures S1 and S2). The TF correlation map showed a larger similarity of CEC with the TFs of the elements, which could be explained by the fact that CEC also reflects the soil texture and content of soil organic matter.