## 3 Results and Discussion
### Pot Experiments  
This section reports the results obtained from the analyses carried out on the plants used for phytoextraction and the soil in which they were grown. The effect of the soil improver FW was also assessed. Statistically significant differences between fresh weights (reported in Table 4) of plants grown in soils treated with soil improver or without were always found, indicating a growth stimulation by the amendment due to its content in organic substances and macronutrients and probably to its protective action against microbial pathogens [23]. Reported data refer to results obtained from one of the experiments, established that they did not differ significantly from the others. PTE concentration values (reported in Tables S2 and S3, Supplementary Materials, as an average of the data obtained from the three replications) were processed using a chemometric treatment aimed to evaluate the uptake efficiency of the plants towards the different elements. BF and TF were calculated as well to assess the plant mineral uptake and the transport from roots to the aerial part, respectively. In Figure 2a,b, the score and loading biplots resulting from the principal component analysis (PCA) on the autoscaled data relating to the element concentrations in aerial parts (leaves and stems) and roots of the plants are reported. Figure 2a presents a close correlation between _P. vittata_ and arsenic, i.e., epigeal levels of As in _P. vittata_ are higher when plants are grown in the two soils added with FW. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{_Helianthus annuus_} & \multicolumn{3}{c}{_Zea mays_} & \multicolumn{3}{c}{_Brassica juncaea_} & \multicolumn{3}{c}{_Pteris vittata_} \\ \hline CA & 22.2 & \(\pm\) & 2.6 & 34.4 & \(\pm\) & 3.5 & 7.1 & \(\pm\) & 1.4 & 10.6 & \(\pm\) & 1.5 \\ CA + FW & 52.8 & \(\pm\) & 6.8 & 68.3 & \(\pm\) & 8.6 & 62.2 & \(\pm\) & 6.4 & 12.0 & \(\pm\) & 1.4 \\ NOB & - & & & - & & 13.6 & \(\pm\) & 1.7 & 7.0 & \(\pm\) & 1.6 \\ NOB + FW & - & & & - & & 70.5 & \(\pm\) & 8.0 & 10.6 & \(\pm\) & 1.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Total fresh weight (aerial parts + roots) (g/plant) \(\pm\) SD of the plants. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**NOB with FW**} & \multicolumn{3}{c}{**CA with FW**} & \multicolumn{3}{c}{**FW**} \\ \hline Al & 22,367 & \(\pm\) & 865 & 22,075 & \(\pm\) & 6571 & 16,534 & \(\pm\) & 1014 \\ As & 9.23 & \(\pm\) & 2.05 & 12.3 & \(\pm\) & 0.4 & 3.75 & \(\pm\) & 0.12 \\ Ba & 133 & \(\pm\) & 15 & 369 & \(\pm\) & 16 & 170 & \(\pm\) & 7 \\ Ca & 20,031 & \(\pm\) & 1481 & 31,311 & \(\pm\) & 8496 & 52,258 & \(\pm\) & 3084 \\ Cd & 0.24 & \(\pm\) & 0.02 & 0.55 & \(\pm\) & 0.04 & 0.48 & \(\pm\) & 0.02 \\ Ce & 43.0 & \(\pm\) & 1.8 & 47.6 & \(\pm\) & 13.9 & 17.3 & \(\pm\) & 0.1 \\ Co & 20.6 & \(\pm\) & 1.8 & 15.6 & \(\pm\) & 1.4 & 6.42 & \(\pm\) & 0.47 \\ Cr & 271 & \(\pm\) & 39 & 142 & \(\pm\) & 24 & 70.7 & \(\pm\) & 0.9 \\ Cu & 51.6 & \(\pm\) & 6.1 & 87.6 & \(\pm\) & 3.1 & 95.4 & \(\pm\) & 2.7 \\ Fe & 30,309 & \(\pm\) & 320 & 28,704 & \(\pm\) & 2326 & 16,211 & \(\pm\) & 995 \\ K & 8469 & \(\pm\) & 632 & 7935 & \(\pm\) & 2164 & 13,920 & \(\pm\) & 470 \\ La & 19.2 & \(\pm\) & 1.4 & 20.9 & \(\pm\) & 9.5 & 9.25 & \(\pm\) & 0.82 \\ Mg & 26,175 & \(\pm\) & 7400 & 13,220 & \(\pm\) & 2424 & 11,746 & \(\pm\) & 1624 \\ Mn & 814 & \(\pm\) & 20 & 837 & \(\pm\) & 64 & 506 & \(\pm\) & 15 \\ Na & 871 & \(\pm\) & 59 & 909 & \(\pm\) & 341 & 2900 & \(\pm\) & 82 \\ Ni & 235 & \(\pm\) & 55 & 138 & \(\pm\) & 22 & 53.0 & \(\pm\) & 3.1 \\ P & 2383 & \(\pm\) & 194 & 3275 & \(\pm\) & 82 & 9271 & \(\pm\) & 635 \\ Pb & 34.4 & \(\pm\) & 0.8 & 267 & \(\pm\) & 3 & 49.9 & \(\pm\) & 1.3 \\ Sr & 54.3 & \(\pm\) & 7.4 & 112 & \(\pm\) & 5 & 192 & \(\pm\) & 5 \\ Ti & 903 & \(\pm\) & 101 & 950 & \(\pm\) & 145 & 733 & \(\pm\) & 41 \\ V & 44.4 & \(\pm\) & 1.4 & 50.3 & \(\pm\) & 9.8 & 24.4 & \(\pm\) & 1.8 \\ Zn & 116 & \(\pm\) & 6 & 229 & \(\pm\) & 10 & 225 & \(\pm\) & 23 \\ \hline \hline \end{tabular}
\end{table}