# Improvement of Arsenic Phytoextraction Using Indigenous Bacteria and Mobilizing Agents
## 4 Conclusions  
Microosm (300 g of soil per test) and mesocosm (4 kg of soil per test) tests were carried out to evaluate the leaching efficacy of dilute solutions of potassium hydrogen oxalate and ascorbic acid in different ratios. All trials were conducted in the presence of a consortium of arsenic-resistant PGPR.  
The tests confirmed that the combined use of the two organic compounds allows a significant increase in the bioavailability of arsenic in the soils under study and, therefore, absorption by plants. Following treatment with 0.2 M oxalate and 0.01 M ascorbic acid, the arsenic contents in the aerial parts of the plants increased almost tenfold (from 1.23 to 10.41 mg kg\({}^{-1}\) in \(Z\). _mays_ and from 1.05 to 8.12 mg kg\({}^{-1}\) in \(C\). _sativa_). All trials in pots revealed that \(Z\). _mays_ performed better than \(C\). _sativa_.  
Despite the greater bioavailability of arsenic in the soils treated with the leaching solution, no percolation phenomena were observed.  
Although the plants used are particularly suitable for the geographical and climatic conditions of the area, the results obtained confirm that the assisted phytoremediation approach (a nature-based solution) is effective and sustainable in dealing with arsenic contamination.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multicolumn{2}{c}{_Z. **mays**} & \multicolumn{2}{c}{_C. **sativa**_} \\ \cline{2-5}  & **Volume** & **As** & **Volume** & **As** \\ \hline CT & 770 \(\pm\) 59 b & 0.26 \(\pm\) 0.03 a & 640 \(\pm\) 70 a & 0.12 \(\pm\) 0.01 a \\ Ox 0.2/AA 0.01 & 553 \(\pm\) 50 a & 0.25 \(\pm\) 0.02 a & 648 \(\pm\) 45 a & 0.09 \(\pm\) 0.01 a \\ \hline \hline \end{tabular}
\end{table}
Table 4: Volume of leachates formed (mL) and concentrations of As (mg L\({}^{-1}\)). The values are the means of three replicates and the error bars show \(\pm\) standard deviations. The different letters within the same column represent different significance levels at \(p<\) 0.05 (Tukey’s test).  
**Author Contributions:** Conceptualization, E.F. and G.P.; methodology, E.F., M.B. and G.P.; validation, E.F., G.P. and M.V.; formal analysis, M.B. and M.V.; investigation, E.F. and M.B.; resources, E.F., G.P. and M.V.; data curation, S.F. and M.V.; writing--original draft preparation, E.F. and M.V.; writing--review and editing, S.F. and M.V.; visualization, M.V.; supervision, M.V.; project administration, G.P.; funding acquisition, E.F. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by Eni S.p.A, Research & Technological Innovation Department, San Donato Milanese (Italy), and fully funded by Syndial S.p.A. (now Eni Rewind S.p.A.), agreement number 3500038857.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained within the present article.  
**Acknowledgments:** The authors thank [PERSON], IRET-CNR, for technical assistance in the phytoremediation experiments.  
**Conflicts of Interest:** The authors declare no conflict of interest.