Phytomanagement options with woody or herbaceous species represents a relevant option from an ecological and economic point of view for the management of large areas contaminated by potentially toxic trace elements such as trace metals and metalloids (PTTE) (Algreen et al. 2013; Bart et al, 2015; Malá et al. 2010; Toillon et al. 2013). However the long-term stability of immobilized PTTE in soils undergoing phytoremdediation should be predicted for various environmental scenarios (Cornelis et al, 2008). Moreover the PTTE ecodynamicshould be explored under rhizospheric processes rather than bulk soil. Rhizospheric soil corresponds to a geochemical micro-environment influenced by plants (root exudates composed of organic acids and siderophores, respiration) (Cadwell 2005) and microorganism activities (Hiltner 2004). These biological activities locally influence the ecodynamic of PTTE, either directly (precipitation, complexation, adsorption) or indirectly (effects of the rhizosphere on pH and redox potential, dissolution of minerals). Globally biological and soil processes may be strongly impacted by phytomanagement options.

Risks of PTTE in terrestrial ecosystems are currently evaluated on the basis of the soil total concentration although it does not well predict toxic effects in soil organisms and plants (Crommentuijn et al., 1997). However an accurate assessment of bioavailability must consider both speciation of PTTE in the rhizopshere as well as the biological receptors they can reach. Speciation in solution is unequivocally considered to be an effective way to estimate the bioavailability and toxicity of PTTE to soil organisms. Conversely, simultaneous investigations of PTTE ecodynamic in rhizospheric soil pore waters (SPW) and ecotoxicological effects have several advantages. The aim of this work was thus to assess the speciation, phytoavailability and potential remobilization of PTTE such as Zn, Pb, Cd, As and Ba in contaminated mine soils with selected laboratory experiments based on concentrations of the different metal(loid)s in both rhizospheric (SPW) and in plant tissues in a context of assisted phytoremediation together with speciation modelling in the SPW. Effects of Salix viminalis (willow) and Lolium perenne (ray grass) together with biochar (BC) amendment on the ecodynamic (characterization, speciation, mobility and phytoavailability) of these PTTE under rhizosphere influence were investigated in a pot experiment over 2 months. Results showed that soluble concentrations of Pb and Zn were decreased through time in contrast to As and Cd while Ba was increased. Experimental data from these time series were modelled with the humic ion-binding model included in the Windermere humic aqueous model (WHAM) to predict their speciation and compared with concentrations and mineralomasses of PTTE in plant organs. BC combined with plants modified the phytoavailability of Pb, Zn, Pb and Ba in SPW while it only slightly influenced As and Cd. BC could indeed act on PTTE accumulation inplant rhizosphere and sorption on soil phases and thus provide a mechanism for PTTE retention in the soil in combination with plant roots.