# Screening of Plants and Indigenous Bacteria to Improve Arsenic Phytoextraction
## 4 Conclusions  
Through numerous microcosm tests organized in three successive campaigns, the efficacy of potassium hydrogen oxalate versus phosphate as an arsenic mobilizing agent and of two different consortia of PGPR bacteria was evaluated. The tests confirmed that the use of oxalate led to a significant increase in the bioavailability of arsenic in soils, and that the addition of PGPR bacteria improves the absorption of As, although the effect is more evident at the level of the roots (probably due to the short growth times at the microcosm scale). This effect was confirmed by the improvements in terms of total uptake obtained with a second set of PGPR bacteria, as demonstrated by the direct comparison between the second and third series of microcosms.  
After treatment with 0.2 M KHC2O4 and the second set of PGPR bacteria (third microcosm set), the total uptake of arsenic in the aerial part of the plants increased from 0.19 to 3.11 (S2) and from 0.06 to 4.25 (SW) for _Z. mays_ compared to the treatment with KH2 PO4 and the first consortium of bacteria (first microcosm set). Similarly, the absorption of _C. sativa_ increased from 0.04 to 1.53 (S2) and from 0.02 to 0.48 (SW). Overall, the pot experiments revealed that _Z. mays_ performed better than _C. sativa_.  
The concentration of arsenic in plants confirms the validity of the Italian legislation (Legislative Decree No. 152 of 2006), which prohibits the placing on the agricultural market of vegetables from reclaimed areas. In this specific case, since the site is intended for industrial use, there is no possibility that any part of the area under study is intended for agriculture. The possibility of people coming into contact with the contaminated plants, as well as that of arsenic transfer into the food chain, can therefore be excluded. An interesting possibility, alternative to disposal and in line with the provisions of the European Union, is the exploitation of biomass for energy purposes. This is allowed only for the energy self-production of the company but allows to increase the sustainability of the remediation activity. In the case of hemp, there are also numerous constraints that govern its cultivation.  
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.; 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.  
Figure 10: Arsenic total uptake comparison in shoots of _Z. mays_ and _C. sativa_ grown on soil control (CT) and As-contaminated soil samples treated with oxalate (O): (**a**) S2 soil, (**b**) SW soil. PGPR bacteria (second set of isolates) were added to all soil samples, as indicated by the “++” sign. The values are the mean of three replicates, and the error bars show the standard deviation. Values with different letters are significantly different at the 5% probability level (Tukey’s test).  
**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 photoremediation experiments.  
**Conflicts of Interest:** The authors declare no conflict of interest.