## 4 Discussion
### Phytoremediation Properties of Hydrocharis morsus-ranae
#### 4.3.2 Comparison of Potential Cadmium Uptake by _Hydrocharis morsus-ranae_ with Other Pleustophytes
[106] found it to  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Plant Species**} & \multirow{2}{*}{**Cd Form**} & \multirow{2}{*}{**Cd Level**} & \multirow{2}{*}{**Duration** **(Days)**} & \multirow{2}{*}{**Nutrient**} & \multirow{2}{*}{**Efficiency of Removal (\%)**} & \multirow{2}{*}{**Reference**} \\  & & & & & & & Removal (\%) \\ \hline \multirow{6}{*}{_Pistia stratioides_} & \multirow{6}{*}{n.i.} & \multirow{6}{*}{\(<\)LOD} & \multirow{6}{*}{60} & \multicolumn{2}{c}{1 pond: 0.29 P-PO3\({}^{-}\) mg dm\({}^{-3}\)} & \multirow{6}{*}{50} & \multirow{6}{*}{[105]} \\  & & & & & 0.08 N-NO3 [FOOTNOTE:3]Footnote 3: \(\mathrm{P}\mathrmdemonstrate almost 81% efficiency at removing cadmium from mine waters after 10 days (Table 14). 3.3 The Advantages and Disadvantages of Using Hydrocharis morsus-ranae in the Phytoremediation of Cadmium-Polluted Waters  
When assessing phytoremediation capabilities, it is important to consider the biological factors and habitat conditions of a given plant species [22,100]. Since Hydrocharis morsus-ranae is a floating plant, bearing short roots with long hairs immersed in the water, it is better suited for the treatment of waters contaminated with cadmium than bottom sediments. The rosettes of the plant have dense leaf cover and also accumulate metals, although to a lesser extent than the roots (leaves to roots = 0.18) [44]. In natural conditions, the plant is only available for phytoremediation during the growing season, i.e., between May and September; however, under artificial conditions, with good insolation and optimal temperature, metal uptake can take place in any required period. The limitation in the use of frogbit is the short life of the leaves (14-17 days). As such, it must soon be removed from the polluted environment, preferably after two to three weeks. Although frogbit is characterized by low biomass, our findings confirm that it demonstrates highly efficient cadmium removal from water (Figure 4) under conditions of neutral water pH and low nutrient availability. 3.4 Proposal for the Use of Hydrocharis morsus-ranae Together with Other Pleustophyte Species for the Treatment of Cadmium-Polluted Waters  
Pleustophytes are well suited for phytoremediation of waters contaminated with cadmium, including municipal and industrial sewage. All species demonstrated different tolerances to toxic elements (Tables 13 and 14). This fact can be used to construct a technological line based on various types of sorption sites [22]. Frogbit is highly efficient at removing metals, including cadmium; however, it requires a longer time for vegetative development compared to other limnids in Europe and Asia, which limits its phytoremediation potential. In addition, the optimal growth environment for this species is associated with low concentrations of biogenic compounds, limiting its use in the treatment of municipal and mine wastewater. This species appears to be particularly suitable for use in the final stage of phytoremediation, under which conditions it demonstrates very high cadmium removal efficiency and can thoroughly clean the water or sewage treated in stages (Table 15). The process would have to run for three weeks and remove the biomass from the containers. This effect results from the plant's development cycle. Extending the time of exposure of the frogbit effluent to dissolved cadmium in the aquatic environment will be accompanied by the decomposition of organic matter and the release of metals accumulated in biomass, including toxic cadmium. The number of rosettes of this pleustophyte should be adjusted to the volume of sewage and the concentration of biogenic compounds (2 rosettes per 2 dm\({}^{3}\), for example, in the present study). is processed, e.g., in existing facilities together with municipal waste, the costs of this operation will be negligible. During the composting of plants, the by-product will be the collected leachate, which, depending on their chemical composition, may be subjected to further processing.