## 3 Results
### Mercury Removal Performance of NbSs
#### 3.3.2 Hg Removal Through Plant Uptake
crussipes_ showed the highest THg accumulation, achieving up to 74.4% and 50.9% removal, respectively. Root systems played a crucial role in uptake, and evapotranspiration and sediment deposition were also quantified to track Hg distribution across the system. The meta-analysis by [PERSON] et al. [39] synthesized data from over 30 studies and confirmed that root uptake is the dominant pathway for mercury absorption in aquatic phytoremediation systems. Root retention and cell wall precipitation were highlighted as major mechanisms limiting Hg translocation to aerial tissues. The effectiveness varied by plant family, with species from _Aracae, Hydrochariaceae_, and _Salviniaceae_ showing strong uptake potential. Environmental factors like water pH and plant lifeform also significantly influenced Hg absorption outcomes. The alluvial diagram in Figure 5 visualizes the relationship among NbS types, plant species, and mercury uptake levels categorized by concentration. The data used to construct this figure were extracted and synthesized from peer-reviewed studies included in this review, which reported plant-based Hg uptake values across different NbS systems. Uptake values were classified into four categories: very high (>100 mg/kg), high (20-100 mg/kg), medium (2-20 mg/kg), and low (<2 mg/kg). Non-constructed wetland systems, primarily comprising pilot-scale and experimental setups, showed strong associations with plants exhibiting very high Hg uptake. For instance, _Salvinia natanus_ and _Lenna minor_ achieved elevated bioaccumulation under controlled mesocosm conditions with continuous water column Hg exposure and nutrient availability [39; 49]. These systems typically used spiked water inflows and maintained ideal redox conditions for metal bioavailability, which likely enhanced uptake. _Eichhornia crussipes_ and _Ludivgia helminthhorriiza_ also showed high uptake values (58.8 and 51.89 mg/kg, respectively) in pilot-scale systems with shallow water columns and high organic content, potentially facilitating Hg mobility [50]. In contrast, most species in full-scale constructed wetlands were associated with low Hg accumulation. Studies by [PERSON] et al. [46] and [PERSON] et al. [51] documented that plants such as _Phragmites australis, Elodea densa_, and _Sagittaria montevidensis_ were grown in wetland substrates characterized by high clay content or residual organic soils with slightly acidic to neutral pH levels, which are known to bind mercury and reduce its bioavailability. However, _Typha domingensis_ exhibited very high Hg uptake, possibly due to its presence in a tropical wetland with fluctuating water levels and organic-rich peaty sediments that favor Hg methylation and plant assimilation. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**NbS Type** & **Plant Species** & **Removal Efficiency** & **Reference** \\ \hline Constructed wetland & _T. latifolia, T. angustifolia, T. domingensis_ & 14\% removal of THg; 11\% increase in TMeHg & [40] \\ \hline Pilot-scale constructed wetland & _Limmocharis flava_ & 90\% & [44] \\ \hline Constructed wetland with pyrrhotite and zero-valent iron & _Acorus calamus_ & 98.9\% & [38] \\ \hline Free water surface constructed wetland & _Aquarius palifolius_ & 91.8\% & [45] \\ \hline Pilot-scale constructed wetland & _Scripus californicus; Potamogeton pusillus_ & \(\sim\)50\% THg removal; 8\% increase in TMeHg & [41] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of the plant species and mercury treatment performance by constructed wetlands in the reviewed studies. The synthesis of the articles on the mercury removal performance of NbSs revealed that constructed wetlands and non-constructed systems both rely on plant uptake and sediment interaction for mercury removal, with root absorption and retention being key mechanisms in both.