Remediation pathways and mechanism of Fe-Zn-supported biochar on Cd accumulation in wheat: wheat tissues and coexisting elements

Cadmium (Cd)-contaminated wheat grains seriously threaten human health. Here, a novel iron/zinc-supported biochar (Fe/Zn-BC) was prepared and applied to investigate the remediation effects of alkaline soil and wheat contaminated with Cd, focusing on the influence mechanism on the Cd and coexisting elements accumulation in wheat.

We performed various doses of BC and Fe/Zn-BC treatment in the winter wheat pots. The available Cd content and Cd fraction in the soil, and Cd, Fe, Zn, Mn, Cu, Ni, and Pb contents in wheat tissues were determined.

The results showed that the contents of DTPA-Cd and DTPA-Pb were significantly reduced by 33-54% and 10-27% in the Fe/Zn-BC treated soil, respectively. The reduction rates of Cd in wheat root, straw, node, flag leaf, and grain in Fe/Zn-BC treatments were better than those of BC treatments. Furthermore, Zn, Fe, and Mn contents increased significantly in root, straw, node, flag leaf and grain. Both the bioaccumulation factor (BF) and transfer factor (TF) of Cd were decreased with the addition of Fe/Zn-BC, expect for the TF_leaf/root. Structural equation model fitting results showed that inhibition of Cd uptake by root and promoting Cd transport from root to flag leaf were the main pathways to reduce grain Cd content. Increasing the coexisting elements of Zn and Mn to reduce the accumulation of Cd in grains through antagonism was another important mechanism in the Fe/Zn-BC treatments.

Fe/Zn-BC was an amendment that efficiently reduced Cd accumulation in wheat grains and had great potential for remediation of Cd-contaminated soil.