Amendment of Husk Biochar on Accumulation and Chemical Form of Cadmium in Lettuce and Pak-Choi Grown in Contaminated Soil

(1) Background: Cadmium (Cd) accumulated in vegetables not only affects their growth but can also enter the human body via food chains and lead to various illnesses. Plants can decrease the toxicity by changing the chemical forms of Cd, which include inorganic (F-E), water-soluble (F-W), pectate- and protein-integrated (F-NaCl), undissolved phosphate (F-HAc), oxalate (F-HCl), and residual forms (F-R). Among them, F-E and F-W chemical forms show higher mobility to translocate upward from roots to shoots compared with the others. (2) Methods: Different varieties or cultivars of lettuce and pak-choi were grown in Cd-contaminated soils amended with husk biochar (BC) to replenish nitrogen to the recommended amount and also to raise the soil pH value. (3) Results: More than 73% of the accumulated Cd in the edible organs was compartmentalized in F-E chemical form in both leafy vegetables regardless of treatments. In comparison with control, the application of BC decreased the Cd concentrations and bioconcentration factors in the roots and shoots of two leafy vegetables at different growth periods in general. The chemical form and bioaccessible fraction of Cd in the edible blanching tissues were used to calculate the risk of oral intake. The vegetable-induced hazard quotients of lettuce and pak-choi were acceptable, except for pak-choi grown in control without applying BC.