*2.3. Analysis of PTEs*

Thirteen heavy metals and trace elements were determined: arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), titanium (Ti), vanadium (V), zinc (Zn), and mercury (Hg). Pseudo-total and available elements were determined for each soil horizon (91 samples). PTEs associated with noncrystalline Al and Fe were determined only in surface horizons.

The determination of pseudo-total PTEs was performed by microwave-assisted digestion, with concentrated HNO3 and HCl (HCl:HNO3 ratio 1:3), according to the EPA 3051A method [23]. The metals were determined in the digestate by ICP-MS. The limits of detection, calculated as 3 times the standard deviation of blank values, in mg kg<sup>−</sup>1, were: As, 0.09; Cd, 0.006; Co, 0.03; Cr, 4.6; Cu, 1.1; Fe, 8.3; Mn, 1.0; Ni, 0.32; Pb, 1.0; Ti, 2.0; V, 2.8; Zn, 6.1; and Hg, 0.01.

Available PTEs were extracted by Mehlich 3 reagent [24] and determined by ICP-MS.

PTEs associated with noncrystalline Al and Fe were extracted by ammonium oxalate/oxalic acid at pH 3 [25] and determined by ICP-MS.
