*3.4. Chemical Form*

According to the standard for the Tolerance of Heavy Metals in Plant Origin of Taiwan for leafy vegetables, 0.2 mg/kg·FW, most of the Cd concentrations in the edible parts of lettuce and pak-choi were beyond this standard if the water content of them was 90%. Whether treating with BC or not, Cd was mainly compartmentalized in the FE chemical form in the shoots of lettuce and pak-choi. Approximately 94–98% and 82–98% of the Cd accumulated in the shoots of lettuce and pak-choi, respectively, were compartmentalized in the FE at D42–D49 (Figure 3).

**Figure 3.** Effect of husk biochar treatment on the chemical form of Cd in the shoots of pak-choi and lettuce. The meanings of treatments are the same as in Table 1. FE, FW, FNaCl, FHAc, FHCl, and FR are inorganic, water-soluble, pectate- and protein-integrated, undissolved phosphate, oxalate, and residual chemical forms, respectively.
