## 3 Results and Discussion
### Mescosm Tests  
The average values of the fresh biomass of the root and aerial part of _Z. mays_ related to mesoccosm tests are given in Table 4.  
As the experimentation scale increases, the contamination effect is observed more. Plants grown on the contaminated soils produced less biomass, reducing by more than 20 percent for the root system and more than 60 percent for the aerial part compared to the control. The concentrations of hydrocarbons in _Z. mays_ plants for the mesocosm tests are also shown in Table 4. It should be noted that PAHs were always below the limit of quantification for both the aerial and root parts in all samples. Figure 6 shows the concentration trends of C \(\leq\) 12 and C > 12 in the soil at initial conditions (beginning of the mesocosm test Ss) and at the end of mesocosm test in the non-vegetated (Snv) and vegetated case (Sv C). It is worth pointing out that the observable deviations in this further experimentation from the microcosm Ss and Snv values shown in Figure 4 are within the estimated experimental uncertainty and are, therefore, consistent. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{_Zea mays_} \\ \hline  & **Shoots** & **Roots** & **C \(\leq\) 12** & **C > 12** \\ \hline A & 31.3 \(\pm\) 1.43 & 8.65 \(\pm\) 1.32 & 1.16 \(\pm\) 0.56 & 250 \(\pm\) 53.0 \\ B & 33.8 \(\pm\) 1.72 & 9.15 \(\pm\) 1.22 & 1.06 \(\pm\) 0.58 & 202 \(\pm\) 70.0 \\ C & 31.4 \(\pm\) 1.55 & 8.50 \(\pm\) 1.25 & 2.4 \(\pm\) 0.89 & 300 \(\pm\) 52.0 \\ D & 30.7 \(\pm\) 1.32 & 8.71 \(\pm\) 1.82 & 2.3 \(\pm\) 0.76 & 320 \(\pm\) 60.0 \\ CT & 83.8 \(\pm\) 2.10 & 11.1 \(\pm\) 1.70 & — & — \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Fresh weight (g) and concentration (mg kg\({}^{-1}\)) of hydrocarbons (C \(\leq\) 12 and C > 12) contained in _Z. mays_ plants grown in different soils (A–D) during mesocosm tests. Data reported as the mean of replicates with the related standard deviation. Figure 6: Variation of C \(\leq\) 12 (**a**) and C > 12 (**b**) hydrocarbon content in the soil (mg kg\({}^{-1}\)d.m.) for different soils (A–D) during mesocosm tests. Data reported as the mean of replicates with the related standard deviation. Ss = starting soil, Snv = non-vegetated soils; Sv = vegetated soil; C denote _Z. mays_ (Corn). Figure 6 confirms a trend of decreasing concentration values related to natural soil attenuation mechanisms (Snv) as time passes, but this trend is accentuated using plants (Sv C). Indeed, considering C > 12 hydrocarbons (the most relevant portion of the contamination), a 15-18% increase in degradation from non-vegetated to vegetated soils is observed. However, it should be noted that given the considerable variability in the analyses, the results are not always statistically significant. The resulting concentration of PAHs compared to the beginning (Ss) of the mesocosm experimentation is presented in Table S3. Also, in the specific case of pyrene (Figure 7), as with other PAHs (Table S3), the trend observed in the mesocosm tests is similar to that found in the microcosm, although the effect of plants is proportionally less pronounced due to contamination-related distress, which was found to be more pronounced than in the microcosm. Therefore, it is likely that the appropriate selection of PGPB can significantly improve the degradation yield at the mesocosm scale. In general, it is confirmed that relying just on the biological synergy of chosen plants and PGPB is possible, especially for treating soils intended for agricultural use. In addition, compared to traditional remediation techniques such as landfill disposal, it is a cost-effective and low-impact approach, which results in a lessening of CO2 equivalent emissions by whole orders of magnitude [12]. Furthermore, it is possible to dispose of the produced biomass through waste-to-energy solutions such as electricity production through incineration or bio-oil production through pyrolysis, increasing overall efficiency and further reducing the remediation environmental impact by roughly 30% [12].