Biochar addition decreases the mobility, bioavailability and phytotoxicity of potentially toxic elements in an agricultural contaminated soil

The aim of this study was to assess the influence of a biochar added at 3% w/w (Bio) and its combination with a municipal solid waste compost (MSWC), on the mobility, bioavailability and phytotoxicity of several potentially toxic elements (PTE), such as As (55 mg•kg−1), Sb (84 mg•kg−1), Ni (176 mg•kg−1) and Cr (214 mg•kg−1) present in a Lebanese contaminated soil (TS). Sequential extraction procedures showed that Bio and its combination with MSWC decreased soil labile PTE, with Bio increasing remarkably their residual fraction compared to the untreated soil (+ 47, 59, 4 and 9% for As, Sb, Cr and Ni respectively). Amendments addition also favoured an increase of the metabolic potential and catabolic versatility of soil microbial communities, as well as soil functionality. Dehydrogenase, β-glucosidase and urease activities in TS+Bio showed a significant increase (+ 45, 16 and 21% respectively, with respect to control). Results from a pot experiment showed that all treatments enhanced green bell pepper and wheat yield significantly, and reduced PTE transfer from root to shoot. Overall, the results obtained suggested that biochar addition at 3% rate can be an effective environmental friendly strategy for the in situ remediation of PTE-polluted Eastern Mediterranean soils.