Ionomic analysis reveals the mechanism of mercaptosilane-modified palygorskite on reducing Cd transport from soil to wheat.

Mercaptosilane-modified palygorskite (MP) can immobilize Cd in acid soil and reduce the enrichment of Cd in rice. However, the immobilization effect and its durability on alkaline field were unclear. Meanwhile, whether MP could reduce Cd in different wheat parts at different stages also needs further exploration. Here, we determined the dynamic change of Cd in soil and wheat at different periods, studied the interaction mechanism at key organs, and calculated the contribution of coexisting metals on the reduction of Cd to study the effect of MP on the transfer of Cd in soil-wheat system. Results showed MP was highly effective to immobilize Cd in alkaline farmland and could take effect during the whole growing season but not change pH values. DTPA-Cd and EXE-Cd of soil were reduced by 34.88-49.71% and 49.36-84.81%, respectively, while OX-Cd was increased by 34.61-43.60% at the whole stages. Cd in grains at maturity stage was reduced from 0.118 to 0.069 mg/kg, lower than the limit standard of the China and Codex Alimentarius Commission (0.1 mg/kg). Root and nodes were critical organs influenced by MP to reduce Cd in grains, and the reduction efficiency on wheat was relatively weak at flowering and filling stage. MP regulated the antagonism or synergy effects of coexisting elements on Cd to modulate the Cd accumulation in grains. Besides, the contributions of different elements on Cd were also evaluated by path models. This will provide an important basis for the precision remediation of Cd-polluted alkaline wheat fields.