## 3 Results and Discussion
### Accumulation and Translocation of PTEs
Specifically, they can be built into the cell wall or transported into the vacuole [51,52]. However, they can be also transported into the above-ground body organs. This transport is conducted mainly via xylem, which belongs to the apoplast route [52]. This process is on the one hand highly dependent on the genetic makeup, but also on the environmental condition in which the plant grows. In our study, the highest TF values were found in Hg (1.764). The results suggest that _M. albus_ can be used for the phytoextraction of Zn and Pb as well (TF values). However, the ability of _M. albus_ to phytoremediate Zn and Hg was disputed by [PERSON] et al. [53], where TF factors of _M. albus_ for Hg were 0.56 and 0.51 in wet and dry seasons, respectively. These values suggests that _M. albus_ is not suitable for phytoextraction of Hg. In another study, crops capable of the phytoremediation of Pb and Cd fodder mallow (_Malva verticillata_ L.), rye (_Scale cereale_ L. var. _multicaule_ METZG. ex ALEF. ), and white sweet clover (_Melilotus albu_ MEDIC.) were determined [54]. White sweet clover showed the lowest ability to accumulate these PTEs in its tissues. In contrast, the present study shows that white sweet clover is suitable for lead phytoextraction according to TF values. Similarly, our study shows a suitability of white sweet clover for phytoextraction of Zn, which is not in agreement with [PERSON] et al. [55], where yellow sweet clover (_M. officialis_) showed a low TF for Zn (0.516). These differences in results can be attributed to the quality of the soil, because the ability of plants to translocate PTE to the above-ground parts of plants may depend on the soil fertility [1] and on the presence of organic acids [55]. Native plants of India grown on a highly polluted dumping site showed a higher TF rate than the reference plants [46]. However, the suitability of _M. albus_ for phytoremediation and phytoextraction processes is questioned by the low BCF and BAC values in case of Pb, Hg, and Zn. The present results suggest that these PTEs are sufficiently transported from roots to shoots, but on the other hand, the low values of BCF and BAC indicate the low rate of their accumulation in roots and shoots. These results are in agreement with [PERSON] et al. [17] who reported the fact that many legumes are tolerant to the presence of PTEs because they belong to the group of heavy metal excluders which do not accumulate PTEs in shoots. Therefore, legumes are suitable for being grown on fields polluted by PTEs. For example, _M. officialis_ (species related to _M. albus_) also did not show a capacity to accumulate Cu in its above-ground biomass ([4]; Table 4). When the values of BCF, TAC, and TF are compared between the individual plant species, legumes apparently show the lowest ability to bind HM in their biomass (Table 4). In contrast, representatives from the families of _Asteraceae_ and _Amaranthaceae_ exhibit the values of BCF, TAC, or TF more than two times higher (Table 4). This is a very important precondition for growing legumes in soils with a higher content of PTEs to produce biomass for ensiling because when the plants of this family have a lower capacity to bind HM in their biomass, then the risk of HM getting into silage is lower, and the risk that the process of methanogenesis will be stopped or inhibited during silage degradation in the biogas plant is eliminated. _M. albus_ is not able to accumulate the same amount as a hyperaccumulator, i.e., more than 10 ppm Hg; 100 ppm Cd and Se; 1000 ppm Co, Cr, Cu and Pb; 10,000 ppm Mn and