## 3 Results and Discussion
### M. sylvestris Biomass Valorization Options
#### 3.5.2 Other Emerging Biomass Valorization Options for _M. sylvestris_  
In the scientific literature, many innovative biomass valorization options of _M. sylvestris_ have been discussed and might be integrated as a part of the dye production valorization chain. The remaining TE concentrations in the shoots were below the threshold set by the REGULATION (EU) 2019/1009 [60] (Cd 2 \(\upmu\)g g\({}^{-1}\), Cu 300 \(\upmu\)g g\({}^{-1}\), Pb 120 \(\upmu\)g g\({}^{-1}\), Zn 800 \(\upmu\)g\({}^{-1}\)), permitting the compost of this biomass to be used as a soil improve. As proposed in Section 3.1, _M. sylvestris_ biomass could be dried to separate flowers from leaves and stems. The remaining dried biomass of _M. sylvestris_ could be used as an alternative biomaterial for the production of activated carbon to remove metals such as Cu\({}^{2+}\) and Hg\({}^{2+}\) from water [32; 33]. As this would aim to saturate the biomaterial with metal, the initial metal concentration of this biomaterial might not be a problematic point as long as it does not leach out in the applied conditions. To consider the feasibility of this option, the removal capacity of multiple contaminants by biomass grown on TE-contaminated sites needs to be further investigated. The production of an environmentally friendly adsorbent for water remediation with _M. sylvestris_ could be a complementary valorization option. Based on the chemical composition of the remaining biomass, the extraction of high-value compounds could also be a valorization option. This extraction can, for instance, be performed by the hydrodistillation of the _M. sylvestris_ shoots to obtain essential oils (EO), as suggested in [34] or by water extraction [49]. EO or water extract have been reported as having antibacterial properties [34; 49]. Moreover, a wide variety of chemical properties, such as a fungicide, were reported and are currently being investigated [26]. In the case of EO produced from biomass from contaminated sites, the metal transfer in the end-products was reported to be extremely low [10; 17; 19; 61]. Concerning the water extract obtained with biomass grown on a contaminated site, TE transfer (Cd, Pb, Cu and Zn) could be expected but were reported to respect the recommended international limits [49]. The obtention of \begin{table}
\begin{tabular}{c c c c c} \hline  & **Cd** & **Cu** & **Pb** & **Zn** \\ \hline \multirow{6}{*}{Before dyeing} & Cotton unpretreated & 0.01 * & 0.16 & 0.04 & 2.67 \\  & Silk unpretreated & 0.01 * & 0.59 & 0.11 & 5.80 \\  & Cotton alum treated & 0.01 * & 1.08 & 0.06 & 1.67 \\  & Silk alum treated & 0.01 * & 4.18 & 0.11 & 2.60 \\  & Cotton iron treated & 0.01 * & 1.14 & 0.10 & 3.02 \\  & Silk iron treated & 0.01 * & 8.72 & 0.19 & 8.71 \\ \hline \multirow{6}{*}{After dyeing Area 1} & Cotton untreated & 0.01 * & 1.67 & 0.20 & 10.28 \\  & Cotton alum treated & 0.01 * & 2.35 & 0.10 & 6.17 \\  & Cotton iron treated & 0.01 * & 1.90 & 0.19 & 19.98 \\  & Silk untreated & 0.07 & 10.57 & 0.19 & 24.75 \\  & Silk alum treated & 0.06 & 9.74 & 0.31 & 29.27 \\  & Silk iron treated & 0.10 & 12.79 & 0.69 & 50.10 \\ \hline \multirow{6}{*}{After dyeing Area 2} & Cotton untreated & 0.03 & 0.21 & 0.45 & 6.44 \\  & Cotton alum treated & 0.02 & 0.28 & 0.38 & 5.86 \\  & Cotton iron treated & 0.03 & 0.29 & 0.56 & 8.56 \\  & Silk untreated & 0.10 & 0.51 & 0.36 & 11.45 \\  & Silk alum treated & 0.08 & 0.52 & 0.69 & 16.33 \\  & Silk iron treated & 0.09 & 1.03 & 1.34 & 18.48 \\ \hline \multirow{6}{*}{After dyeing Area 3} & Cotton untreated & 0.01 * & 1.44 & 0.17 & 9.57 \\  & Cotton alum treated & 0.01 * & 1.11 & 0.07 & 3.64 \\ \cline{1-1}  & Cotton iron treated & 0.03 & 1.96 & 0.26 & 17.40 \\ \cline{1-1}  & Silk untreated & 0.07 & 10.33 & 0.22 & 21.30 \\ \cline{1-1}  & Silk alum treated & 0.07 & 8.65 & 0.43 & 30.10 \\ \cline{1-1}  & Silk iron treated & 0.08 & 10.09 & 0.89 & 32.19 \\ \hline \end{tabular}  
* Limit of Quantification (LoQ).  
\end{table}