Comparison of plant Cd accumulation from a Cd-contaminated soil amended with biochar produced from various feedstocks

The bioavailability of cadmium (Cd) in agricultural soils is a significant health concern due to the potential risk of human exposure via foods grown in Cd-contaminated fields. Biochar has been known to have a highly porous structure and high pH, as well as containing various functional groups; as such, it can immobilize heavy metals. Although it has found that biochar amendment in Cd-contaminated agricultural soils could be effective in reducing Cd bioavailability in previous studies, differences in plant Cd accumulation from Cd-contaminated soils amended with biochars produced from various types of biomass have not been fully discussed yet; we aimed to address this shortcoming in the present work. The soil investigated was an acid soil (pH 5.1) and had an elevated concentration of Cd (total Cd: 3.3 mg kg-DW⁻¹). Six kinds of biochar were produced, i.e., from woodchips (Japanese cedar [CE] and Japanese cypress [CY]), moso bamboo (MB), rice husk (RH), poultry manure (PM), and wastewater sludge (WS), at a pyrolysis temperature of 600 °C. Biochars were incorporated into the Cd-contaminated soil at 3% (w/w) and pot experiments using Brassica rapa var. perviridis were conducted for 28 days in a growth chamber. The Cd concentrations in the above-ground portion of the plants were significantly decreased as a result of the incorporation of all biochars compared to the unamended soil, with reduction ratios following the order PM (78%) > > WS (31%) ≈ RH (29%) ≈ MB (28%) ≈ CY (26%) > CE (19%). Among all biochar-amended soils, soil pH and shoot biomass were highest for those amended with PM-derived biochar. These results suggest that in Cd-contaminated soils, PM-derived biochar may offer significant potential in reducing plant Cd accumulation due to the immobilization of soil Cd and an effect of dilution resulting from enhanced plant shoot biomass.