## 4 Discussion
The increasing dispersion of Pb in the environment and its known toxicity to plants and animals has led to a multiplication of studies on the presence of the element in soils and its migration dynamics. The anthropogenic sources of diffusion are industrial, craft and agricultural activities. The danger of Pb lies, in addition to its intrinsic toxicity for organisms, to the aforementioned tendency to stabilization, which makes its soil pollution practically irreversible. In fact, it is estimated that the natural removal of 10% of Pb from polluted soil takes about 200 years [62, 64]. Several health and environmental problems could be caused by metals depending on their way in food chains, concentrations and chemical status [13]. The Cd does not perform essential biological functions for plants and animals and is, on the contrary, highly toxic [12, 65, 66]. The plants, once having absorbed the element, are unable to eliminate it and, therefore, tend to accumulate it mainly in the roots and, to a lesser extent, in the aerial parts of the plant; this phenomenon fortunately limits the movement of the Cd through the food chain [67]. Concentrations detected in the environment hardly lead to acute poisoning, but the greatest risk for human health is given by chronic accumulation [68]. The main sources of soil contamination can be: use in agriculture of sewage sludge and phosphate fertilizers deriving from phosphorites, rocks naturally rich in this element; industrial sources such as mines, Pb and Zn foundries [9]. The metal Cd has a remarkable affinity with organic matter and being easily bioavailable can enter the food chain through plants or migrate deep into the soil with the risk of contaminating groundwater. The mobility of the Cd is strongly influenced by the pH, increasing when the soil has an acid reaction, although migrations of Cd have also been reported in the literature in neutral and alkaline soils [63]. The preliminary results, obtained during the first experimental year of hemp cultivation, showed the capability of plants to grow until seed maturity in soils containing high concentrations of Cd, Pb and Zn and during environmental and agronomic disadvantageous conditions. In the polluted site, some heterogeneities in crop emergence were observed due to an imperfect seedbed preparation and to failures in the irrigation system. Few studies have been realized to explore different phytoextraction capabilities among hemp varieties. Moreover, there did not exist a comparison using multi contaminated sites. In this study the differences in metal contents among varieties were significant. This result is in agreement with those observed by [PERSON] and [PERSON] [30] where 18 accessions tested for 45 days in soil contaminated by 25 mg kg\({}^{-1}\) of Cd showed interesting differences among varieties in Cd concentrations. According to [PERSON] et al. [69], which compared the phytoextraction results obtained from some hemp varieties by different authors, the metal extraction in specific Cannabis varieties may be explored. The metal distribution in different parts of the plants varied in the two sites. As can be observed in Table 2 the highest HMs values were observed for Cd and Zn in leaves and the values found for Site 3 were statistically higher than those of Site 5 (Table 2 and Figure 2). In the polluted soil, Zn in hemp was very higher than that observed by [PERSON] et al. [31] and [PERSON] et al. [29]: in leaves, the part of the plant with the highest values observed, Zn exceeded 950 mg kg\({}^{-1}\). Analyses revealed that Pb in tissues of plants collected in the polluted site has higher values for roots (17.79 mg kg\({}^{-1}\)) followed by leaves and stems with significantly lower values for seeds (about 1.5 mg kg\({}^{-1}\)). The Pb values described above are similar to those described by [PERSON] et al. [26] and [PERSON] et al. [31] for leaves. On the other hand, these latter authors reported lower contents in roots, stems, and seeds. Low contents of Cd and Pb were observed also by [PERSON] et al.