Effect of biochar amendments on As and Pb mobility and phytoavailability in contaminated mine technosols phytoremediated by Salix

Abstract

Mining activities lead to widespread environmental pollution of terrestrial ecosystems due to the presence of metal(loid)s in tailings. These contaminated areas present a health risk and hence need to be rehabilitated. Ex situ methods for soil remediation have been used for a long time but are expensive and disruptive to soil. Phytoremediation techniques for the stabilization or extraction of metal(loid)s could be an efficient alternative as they provide a low-cost and environmentally friendly option. However, due to the often poor nutrient content of these contaminated soils, amendments must be added to enhance plant growth and to improve phytoremediation efficiency. Biochar, a pyrogenic product, is a promising amendment for assisted phytoremediation. The aims of our study were (i) to evaluate the effect of a pinewood biochar on the physicochemical properties of a former mine contaminated technosol, (ii) to assess the mobility and phytoavailability of As and Pb and (iii) to investigate the remediation potential of three willow species (Salix alba, Salix viminalis and Salix purpurea). A greenhouse experiment was conducted with contaminated technosols amended with biochar and garden soil, single or combined, revegetated with the 3 willow species. The physicochemical properties of soil pore water (SPW) as well as metal(loid) concentrations were determined. Plant growth, Salix organ dry weight and metal(loid) uptake were determined in order to evaluate the phytoremediation potential of the three Salix species studied. Biochar increased the pH and electrical conductivity of SPW. Biochar addition had no effect on As mobility but decreased SPW Pb concentration by 70%. For the three Salix species investigated, biochar addition to the polluted soil induced a better growth and a higher dry weight production. In most modalities tested, the metal(loid) content in the Salix organs increased due to the biochar application. Globally, a positive effect of biochar was noticed on the soil qualities (pH and electrical conductivity increase) and plant growth. Metal(loid)s were mostly confined to the roots. Among the species tested, Salix alba presented the lowest metal(loid) concentrations in the aerial parts, making it a particularly suitable tool for Pb soil phytostabilization.