## 4 Conclusions  
Biochar and activated biochar were tested individually as a soil amendment and they demonstrated good potential for heavy metal immobilization from contaminated soil. The current work tested the dual effect of biochar/activated biochar amendment with _Pileum_ sp. species for the remediation of Se in the soil. Activated biochar enhanced soil characteristics, mainly pH and organic matter, and reduced Se mobility in soil. In comparison with pristine biochar, activated biochar demonstrated better performance due to its developed porous structure which was able to sequester Se via possible different mechanisms. In the absence of biochar and activated biochar, Se presented high accumulation potential in plant tissues (BAF of 8.8), showing that _Pileum_ specie could be considered as a good accumulator to be  
Figure 4: Bioaccumulation factors of heavy metals in plants at different Se concentrations (1, 2, and 3 mg/kg) using different quantities of materials: 10 and 50 g of activated biochar and 10 g of pristine biochar collected at the end of the greenhouse experimental device.  
Figure 5: Bioaccumulation factors of cations in plants at different Se concentrations (1, 2, and 3 mg/kg) using different quantities of materials: 10 and 50 g of activated biochar and 10 g of pristine biochar collected at the end of the greenhouse experimental device.  
used for Se phytoremediation under cold climate. _Phleum_ plants could also be used for the phytoremediation of some heavy metals, mainly Cr and Ni, showing high bioaccumulation factors (almost 2.0 and 3.3, respectively). Se uptake is also influenced by soil factors, mainly Se concentration, pH, redox potential, organic matter, cations, anions, and metals (Al, Cr, Fe, Mn, Co, Pb). Se levels in plants were also significantly correlated with anion concentrations (Cl\({}^{-}\), SO\({}_{4}\)\({}^{2-}\), NO\({}_{3}\)\({}^{-}\)) but not to heavy metals and cations levels. However, in the presence of biochar or activated biochar, Se plant uptake and accumulation were reduced. This confirmed that the use of pristine and activated biochar hindered the phytoextraction of Se levels. This solution combining activated biochar and _Phleum_ plant species could be upscaled and applied by managers for the restoration of Se-contaminated mine soils in a cold environment.  
Conceptualization, S.E.; methodology, S.E. and F.B.; software, S.E.; validation, S.E., F.B., E.R., S.K.B. and J.-F.B.; formal analysis, S.E.; investigation, S.E. and F.B.; resources, S.E., F.B. and E.R.; data curation, S.E.; writing--original draft preparation, S.E.; writing--review and editing, S.E., F.B., S.K.B. and J.-F.B.; visualization, S.E.; supervision, S.M., S.K.B. and J.-F.B.; project administration, F.B., S.M., S.K.B. and J.-F.B.; funding acquisition, S.E., F.B., S.K.B. and J.-F.B. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Mitacs-Acceleration Postdoctoral Research Fellowship (Ref FR46934), the Quebec's Ministry of Economy, Science and Innovation (Ministere de l'Economie, de la Science et de l'Innovation du Quebec) that financed the project through the Program for College Research (2020-2021) 2021-CO-285724.  
Not applicable.  
All data are available in the article.  
The authors express their great appreciation to researchers and laboratory personnel of the Centre Technologique des Residus Industriels (CTRI) for technical assistance.  
The authors declare that they have no conflicts of interest to report regarding the present study.