## 3 Results and Discussion  
### Soil Characterization  
The values of SOC, SOM and pH for the investigated soils are shown in Table 2.  
Analyses of CA soil evidence higher contents of SOC and SOM in surface layer than on deeper layers. These results are not surprising, as they are generally higher in the first decimeters of the soil [24]. SOC and SOM content is grater for NOB soil compared to CA soil. SOC accomplishes \begin{table}
\begin{tabular}{c c c} \hline \hline
**Technique** & **Model** & **Features** \\ \hline \multirow{2}{*}{ICP-OES} & Perkin Elmer Optima & Mira Mist nebulizer, cyclonic spray chamber, dual echelle \\  & 7000 DV & monochromator, dual CCD detector \\ \hline \multirow{2}{*}{HR-ICP-MS} & Thermo Finnigan & Conical nebulizer, cyclonic spray chamber, magnetic and \\  & Element 2 & electric sector, SEM detector \\ \hline \multirow{2}{*}{GF-AAS} & \multirow{2}{*}{Perkin Elmer Aanalyst 600} & Transversely Heated Graphite Atomizer (THGA) furnace \\  & & assembly, longitudinal Zeeman-effect background correction, \\ \cline{1-1}  & & enhanced STPF technology, True Temperature Control (TTC), \\ \cline{1-1}  & & solid-state detector \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Models and technical specification of instrumental techniques used for the analyses. an essential positive function on many soil properties; it promotes the aggregation and stability of soil particles and it binds effectively with numerous substances, improving soil fertility, microbial activity, and nutrient availability such as nitrogen and phosphorus [25]. SOM is largely constituted by high-molecular-weight organic materials such as polysaccharides, proteins, sugars, amino acids and humic substances. Humic and fulvic acids can be present in a dissociated form, and thus are negatively charged (the main sources of these charges are carboxylic and phenolic groups in which hydrogen can be replaced by metal ions). The source of negative charges in soil colloids is strongly pH-dependent, and so the sorption of heavy metals in soils with relatively high organic content is strongly affected by pH as well as the ion properties of metals, like charge and ionic radius [26]. Moreover, the pH influences the availability of the nutrients for plants that reaches the maximum in the range 6-7 for P, 6.5-8 for macronutrients (K, Ca, Mg), and 5-7 for micronutrients such Cu, Fe, Mn, Ni, and Zn. Therefore, neutral conditions appear to be optimal for crop growth and soil microorganisms' activity [27]. In our case, pH is close to neutrality for both terrains. Considering the sandy-loam texture of soils, the medium-high percentages of organic matter and organic carbon [25], which foster metals immobilization, and the neutral pH, marked metal availability and massive uptake by cultivated plants were not expected [28; 29]. The concentration of the 22 elements detected in the superficial and deep layer samples of CA site, as well as their mean values and limits set by Italian legislation [30] are reported in Table 3. Overall, high concentration of Cr, Zn, Ni, Pb and Co were found in the CA site that exceeded public green area limits but not industrial area limits. NOB soil presents concentration values below the legal limits for all elements, except for Co, Cr and Ni. It can be noticed that the content of some elements, namely Ba, Cd, Cu, P, Pb and Zn, was higher on the surface soil layer. The higher yield of P on the surface is not surprising as it is derived from decomposed organic material (leaves, insects) or from the addition of organic soil amendments or fertilizers [31]. The other results could be attributable to anthropogenic contamination, as these metals are commonly linked to urban pollution. For instance, Ba may derive from its widespread use in manufactured materials such as tiles, automobile clutch and brake linings, rubber, brick, paint, glass, and other materials [32].