## 1 Introduction  
Soil pollution is a major global concern that occurs after industrial activities on a site have ceased and a variety of heterogeneously distributed pollutants remain. Commonly found contaminants include complex organic compounds such as polycyclic aromatic hydrocarbons and petroleum hydrocarbons, as well as trace elements (TEs). There are 650,000 registered sites where polluting activities took/are taking place in the EU, most of them in need of remediation [1]. TEs are frequently occurring soil contaminants (35%) [2], and most commonly among them Pb, Cr, As, Zn, Cd, Cu, and Hg [3]. The fact that TEs are not degraded overtime means that they persist in the soil, thereby threatening the quality of the environment with potentially detrimental effects on the health of humans and other organisms [4]. Most current decontamination methods for TE pollution have particular technical limitations and often a prohibitive cost that ranges from several hundred euros for deposition in a secure landfill to approximately EUR 1000 per ton for incineration. A promising alternative is phytoextraction, a technique which is applied in situ and can address multiple contaminants simultaneously at costs that are competitive with conventional methods [5]. With phytoextraction, two main strategies can be adopted: using either hyper-accumulators or moderate accumulators, the latter of which may remove a considerable amount of contaminants from the soil due to their high growth rate and biomass production despite their lower uptake rates [6]. Hyperaccumulator plants have the potential to accumulate very high amounts of one or more TEs in their biomass. They show TE concentrations in their dry biomass that may be 100 times higher than non-hyperaccumulators growing on the same site. Most hyperaccumulator plants are able to concentrate TE over a threshold of 100 mg g\({}^{-1}\) (0.01% dry weight) for Cd, As, 1000 mg g\({}^{-1}\) (0.1% dry weight) for Co, Cu, Cr, Ni, and Pb and 10,000 mg g\({}^{-1}\) (1% dry weight) Mn and Ni [7]. The most common plant species reported in the literature in phytoextraction are _Pteris vittata_ (As), _Alyssum bertolonii_ (Ni), _Brassica juncea_ (Cd), _Thlaspi caerulescens_, _Arabidopsis halleri_, _Sedum alfredii_ (Zn) _Elshotzia splendens_, and _Commelina communis_ (Cu) [8]. Unfortunately, hyperaccumulators do not show very high biomass rates and are very difficult to manage at the field scale (e.g., harvesting the biomass). The second group of plant species commonly used for phytoextraction do not accumulate TE in excessive amounts relative to their weight, but their phytoextraction capacity is compensated by their high biomass yield, making them very attractive for this purpose [9]. Fast-growing species commonly used in phytoextraction, like poplar and willow, are often a valuable choice to address mixed (inorganic and organic) environmental pollution [10]. On a field scale, these species, which are managed as short-rotation coppice stands, have been proposed for the phytoextraction of TEs and other pollutants from different media, including soil [11], municipal sewage sludge [12], landfill leachate [13], and municipal wastewater [14]. Despite the large number of benefits associated with this technique including cost effectiveness [15], high social acceptability [16] and ecological restoration [17], one of the main drawbacks when addressing soil pollution is represented by the long time frame required to reduce pollution below safety thresholds. While the time frame depends on the targeted contaminant(s), the adopted strategy and plant(s) used, studies report that a reasonable estimate for the effectiveness of TE phytoextraction from soil ranges between a few years to more than one century [5]. The undoubtedly long and unpredictable process often discourages stakeholders and policymakers from adopting this approach.