## 3 Results and Discussion  
### Concentration of PTEs in the Soil and Plant Biomass  
Table 1 shows that the highest PTE concentrations in the aerial biomass were those of zinc (average 12.638 mg/kg) and copper (average 4.0 mg/kg). As is the case with other microelements, Cu is to a certain extent beneficial to plants and animals but its high concentrations cause damage to cells [3; 39; 40]. Cu is essential for the vital functions of organs, as no physiological and biochemical processes can take place without it. In animals, these processes are necessary for the formation of pigments, elastin, and collagen. Cu also helps the transfer of iron from liver to bone marrow by which it participates in the process of hematopoiesis [41]. One serious sign of a lack of Cu in animals, combined with other factors, is osteoporosis. This is a systemic disease of the skeleton, characterized by the focal or generalized loss of bone tissue with the ratio between organic and inorganic skeleton matter remaining preserved [42]. In plants, Cu represents an essential heavy metal, i.e., a microelement which most physiological processes could not do without. Cu in plants is a part of proteins, and is indispensable for the transfer of electrons and hence for the processes of photosynthesis and cellular respiration [3; 8; 43]. Plants can absorb it from the soil while humans and animals receive it in food [43]. [PERSON] et al. [44] experimented with red clover on plots contaminated with Cu and found that clover was able to absorb 4 mg/kg after two months, 12 mg/kg after four months, and 23 mg/kg after six months of being grown on the contaminated soil. The authors further tried to grow red clover on the soil contaminated with Zn. In this case, they found that clover absorbed 19 mg/kg after two months, 39 mg/kg after four months, and 47 mg/kg after six months of being grown on the contaminated soil. When we compare these values of Cu and Zn concentrations with values measured in the current research study (Table 1), _M. albus_ apparently exhibited markedly lower Cu and Zn concentrations in its biomass than red clover did. In contrast, the lowest HM concentration in the aerial biomass was observed in Hg, which reached on average 0.003 mg/kg. The second lowest concentration was detected in Cd (0.075 mg/kg). It follows from Table 1 that the highest concentration of microelement in the underground biomass was that of Zn (av. 10.560 mg/kg). Other high concentrations were those of Cu (av. 5.128 mg/kg) and arsenic (av. 0.848 mg/kg). [PERSON] et al. [4] informed that in sweet yellow clover (_Mellotus officinalis_), higher concentrations of Cu intensively accumulate in roots and lower concentrations are transported to the aerial biomass. However, conclusions of their study are not fully in line with the data (Table 1) presented in the experiment because the concentration of PTEs was demonstrably higher in the root compared to that in the shoot only in _M. albus_, whereas _M. officinalis_ probably deposited PTEs in its biomass evenly. The lowest concentration in the underground biomass was that of mercury (av. 0.002 mg/kg), and very low concentrations were observed also of cadmium (0.105 mg/kg). The difference between the highest concentration of zinc and the lowest concentration of mercury was more than 10.5 mg/kg. However, when we further compare the measured concentrations of HM in the plant biomass and in the soil with available permissible limits of HM concentration in water, soil, and plants according to WHO and FAO (Table A2), we find out that the concentration of measured HM was higher than limits for drinking water; this was expected as the limits are very strict. On the other hand, the soil content of HMs was slightly higher (by ca. 10-20%) in our experiment than the Hg and Zn limits set up by WHO. This indicates that the soil content of PTEs was slightly increased; the reason for this however was not found. When shoots and roots were compared separately, the contents of most HMs in plant biomass did not exceed the limits.