*3.1. Soil Analysis*

Based on the data (Table 1), the soil samples under study (SP1-SP6) were homogeneous with each other, with a CEC in the range of 16–20 Cmol(+) kg−<sup>1</sup> and an alkaline pH (~8.3 pH), which suggested a low Pb availability. Soil texture was also rather similar among the soil samples, with a predominance of the sandy fraction. The high conductivity values (on average 585 ± 54.5 μS cm<sup>−</sup>1) raised a particular concern initially due to possible effects on plant growth, which may have a different sensitivity to soil salinity. However, during the phytoextraction test, no growth problems due to the high salt content in the soil were observed.

**Table 1.** Chemical properties in individual samples collected at the site under investigation (SP1-SP6). Values are reported as mean (*n* = 3) ± SD.


Therefore, the homogeneity of the main characteristics of the sampled soils allowed the composition of a single sample of contaminated soil (Pb-soil) on which to perform the phytoextraction tests.

As reported in Table 2, the soils had significant amounts of Pb, with a mean value between samples SP1-SP6 of 108 ± 3.45 mg kg−1. The total Pb content in the Pb-soil was in the range of values found in the original samples. These values are higher than the limit of the values for public, private, and residential green use, established by the Italian legislation [25], thus implying a potential environmental risk.

**Table 2.** Pb content (mg kg−1) in individual samples collected at the site under investigation (SP1-SP6) and in the Pb-soil composite sample. Values are reported as mean (*n* = 3) ± SD.


bdl: below detection limit.

The sequential extraction procedure (SEP), which allowed the evaluation of potentially phytoavailable Pb samples, showed that most of the Pb was in a form not available for uptake by plants (Table 2). The Pb amounts solubilized by H2O and KNO3 were negligible, amounting to about 1% of the total Pb concentration. The results are ascribable to the basic pH of the soil, whereas the amount extractable in EDTA 1% was about 20%. Also, the extraction with 2 mM EDTA significantly increased the Pb phytoavailability, extracting on average 6.7% of total Pb.
