Effects of organo-mineral complexes on Cd migration and transformation: from pot practice to adsorption mechanism

Cadmium (Cd) contamination in agricultural soil challenges food security and threats human health. Although it has been demonstrated that organo-mineral complexes (OMCs) are capable of adsorbing heavy metals in a stable medium, the practice of using OMCs to stabilize Cd in soil, and the crop response to OMCs are not yet clear. In this study, two separate but interrelated experiments were carried out using artificial OMCs made from modified palygorskite and compost. Compared with the recommended fertilization treatments (NPK+ chicken manure), OMCs increased the biomass, root development, and seed quality of Brassica napus. Moreover, the OMC treatment transformed the bioavailable Cd to Fe–Mn oxide-bound Cd in the rhizosphere, resulting in a significantly reduction in Cd accumulation in Brassica napus. Further tube experiments revealed that Cd adsorption by OMCs was heterogeneous chemical adsorption, and the Cd2+ was stabilized as CdCO3 and CdFe2O4 crystals on the surface of palygorskite. The presence of phenols, aldehydes, hydroxyls, and hydrocarbons in OMCs enhanced the Cd stabilization. From pot to tube, this research demonstrated the practical application of OMCs in stabilizing Cd at various scales, and described the potential of OMCs in increasing agricultural yields while limiting Cd migration.