## Materials and Methods
### Plants, Growth Conditions and Phytoextraction Assessment  
Studies on the accumulation of PTEs in plants were carried out in pots. Plants were grown in standard plastic nursery pots (diameter, 12 cm; capacity, 600 mL) arranged as follows: at the bottom of each pot, 60 mL of coarse-grained quartz sand (sterilized at 150 \({}^{\circ}\)C in a stove for 48 h) were placed in order to facilitate drainage. The pots were then filled with unaltered soil or soil mixed with the soil improver FW (70% soil and 30% soil improver (_v/v_)).  
_Brassica juncea_ (L.) Czern. ISC199, _Helianthus annuus_ L. Nano semplice and _Zea mays_ L. Panna plants were obtained from seeds (the first provided by Arcoiris, Modena, Italy; sunflower and corn by [PERSON], Udine, Italy). Since preliminary experiments showed a reduction in germination induced by the presence of the soil improver, we sowed 100 seeds per species in trays containing the CA soil without amendment in order to get plants as uniform as possible. After germination, uniformly grown plants were transplanted, three per pot, in the CA soil, with or without amendment. About two weeks from transplanting, they were thinned to one per pot.  
_P. vittata_ plants were obtained from spores collected from plants growing at the Botanical Garden of Torino (Italy) and dispersed on the CA soil that was kept constantly humid. About three monthsafter spore germination, evenly developed sporophytes were transplanted into pots containing CA soil tests.  
Five plants per treatment were cultivated under controlled conditions in a growth chamber under the following conditions: 16/8 h light/dark photoperiod, and 23 \(\pm\) 1 \({}^{\circ}\)C/20 \(\pm\) 1 \({}^{\circ}\)C light/dark thermoperiod. The light source consisted of four GreenPower LED production modules (Certhon, Poeldijk, The Netherlands) per shelf with a 2:1 red (626 nm peak) and blue (470 nm peak) emission. Plants were watered three times a week with deionized water, provided to limit leaking from the pots, and the experiment was carried out according to a randomized design, changing the position of each pot during the experiment in order to avoid the effect of position on plant growth.  
Based on the results obtained from this first experimental trial, two more experiments were carried out on the four plants including, for _P. vittata_ and _B. juncea_, the cultivation in the NOB soil, with and without amendment, following the same methodology described above.  
The sampling took place at early flowering, eight weeks from souring for _B. juncea_ and _P. vittata_ and fifteen weeks for _H. annuus_ and _Z. mays_. For each plant, the fresh weight was determined.  
Harvested plants were washed to eliminate soil residues and epigeal and hypogeal parts were separated. Then, they were weighed, freeze-dried and ground to obtain samples as homogeneous as possible.  
Leaves and stems or roots were pretreated through a microwave-assisted acid digestion [27], and three replicates were prepared for each sample.  
In all, 20 elements (V, Cr, Co, Ni, Cu, As, Cd, Pb, Zn, P, Mg, K, Ca, Al, Ti, Mn, Ba, Sr, Fe and Na) were determined by ICP-AES or HR-ICP-MS depending on the concentration range. Bioconcentration factor (BF) was calculated in order to assess the amount of PTEs that were transferred from the soil to the plant. It was calculated according to the following formula [28; 29]:  
\[\text{BF }=\ \frac{\text{PTE concentration in plant biomass}\left(\text{mgkg}^{-1} \text{ dry weight}\right)}{\text{PTE concentration in soil}\left(\text{mgkg}^{-1} \text{ dry weight}\right)} \tag{1}\]  
Moreover, to evaluate in which part of the plant the PTEs were preferentially accumulated, the translocation factor (TF) was calculated using the following relationship [28; 29]:  
\[\text{TF }=\ \frac{\text{PTE in leaves and stems}\left(\text{mgkg}^{-1} \text{ dry weight}\right)}{\text{PTE concentration in roots}\left(\text{mgkg}^{-1} \text{ dry weight}\right)} \tag{2}\]