Iron fractionation and iron plaque-mediated effects of woody peat and its humate on cadmium and arsenic behavior in a ricesoil system

Cadmium and arsenic (Cd / As) pose dual threats to food safety and human health. The efficacy of woody peat and its humate as heavy metal(loid) immobilizers is influenced by the presence of metal (hydro) oxides, yet their synergistic regulation of Cd / As mobility and their accumulation in rice remains unexplored. Hence, we systematically investigated the effects of those amendments on Cd / As behavior in rice-soil system using incubation and pot experiments. The results showed that CaCl2-Cd decreased by 14.40–95.75%, while KH2PO4-As increased by 21.95–64.11% on 60th day of incubation. The fractionation of Fe oxides effectively affected the Cd / As availability, and the low Eh playing a critical regulatory under flooding conditions. The grain Cd reduced by 40.85–69.41% and grain As enhanced by 13.10–37.20% in early and late rice. The FeIP / MnIP in iron plaque decreased, of which simultaneously reduced Cd retention while enhancing As sequestration. The distinct variations in availability Cd / As and CdIP / AsIP play key roles in influencing uptake of Cd / As by rice. This study provides novel insights into Fe fractionation and Fe plaque-mediated regulation of Cd / As behavior by woody peat and its humate in rice-soil system.