## 3 Results and Discussion  
### Phytoremediation of Cd and Zn by Taracum officinal  
Effect of EDDS on the Adsorption of Cd and Zn  
The concentrations of heavy metals in the shoots or roots of _Taraxacum officinal_ (mg/kg plant) in all pots by adding various concentrations of EDDS after 3 weeks of growth are shown in Figure 2a for Cd and Figure 2b for Zn. By comparing the data in Figure 2a, it can be found that adding more EDDS (i.e., Pot Nos. 6 and 7 when adding 5 or 7 mmol kg\({}^{-1}\) of EDDS) significantly enhanced the concentrations of Cd both in the shoot and in the root. On the other hand, the concentrations of Zn are not largely varied, although those in Pot No. 5 when adding 3 mmol kg\({}^{-1}\) EDDS is the highest. The translocation factor (TF) from root to shoot was calculated by dividing the metal concentration of the shoot by that of the root:  
\[\text{TF}=\text{C}_{\text{shoot}}/\text{C}_{\text{root}} \tag{1}\]  
The TFs of Cd and Zn in _Taraxacum officinal_ are shown in Figure 3. As can be observed in Figure 3, the TF increased by adding EDDS, which is particularly remarkable in the case of 1 mmol kg\({}^{-1}\) of EDDS for Cd. However, as for Zn, a large increase in TF was not observed, although the value was high when adding 0.5-3 mmol kg\({}^{-1}\) of EDDS compared to no addition. This suggests that _Taraxacum officinal_ is more tolerant toward low concentrations (0.5 or 1 mmol/kg soil) of EDDS, as well as heavy metals (Cd and Zn), considering the biomass of each shoot or root under the presence of EDDS, as shown in Table S2, although high concentrations of EDDS may result in a decrease of biomass. It is known that the biomass decreases by adding a chelating agent such as EDTA for the phytoremediation of Cd, Pb, and Cu [33]. This may be due to the increase in heavy metal solubility, as well as the toxicity of EDTA. In this work, the amount of Cd uptakeen increased as the concentration of EDDS increased. Therefore, it is considered that the biomass or TF showed small values under high EDDS concentrations in this study. [PERSON] et al. [34] described that the interaction pattern of Cd and Zn shows an antagonistic behavior under the combined treatment of low concentrations of Cd and Zn (while it shows a synergistic behavior under the combined treatment of high concentrations of Cd and Zn). It is known that the pathways of the uptake and transport of Cd and Zn in plants are similar in nature because of the similarities in their physical and chemical characteristics. However, plants have cleverly developed to react to Cd and Zn stresses adequately enough to prevent the damage induced by Cd and to maintain Zn homeostasis [35]. However, these reactions have been found to depend on the species, external bioavailable metal concentration, tissue type, and developmental stage. It has been suggested that Zn and Cd homeostasis mechanisms in plants consist of a common pathway. When heavy metals present in equal amounts in the geochemical background of soil systems, they do not disrupt the soil metabolism or plant growth. Moreover, Zn has been used in the biochemistry of land plants and its homeostasis is maintained by a tightly regulated network of low-molecular-weight ligands, membrane transport, Zn-binding proteins, and regulators. In its oxidized form, Zn functions as a catalytic or structural cofactor in a large number of enzymes and regulatory proteins [36]. In contrast, Cd is a non-essential and non-metabolic heavy metal, and its proper functioning in the soil system has not been proven yet. Plants cultivated on soil with elevated amounts of heavy metals generally show signs of inhibited growth, limited germination of seeds, and deformation of roots. These effects can be clearly observed during the early stage of plant development. When the concentration of metals in the soil system increases, synthesis of phytochemicals in the plants is induced. The main function of these proteins is to sustain the homeostasis of metals in the cell.