“…Through root adsorption of mobile Cd, rice grains may accumulate Cd, up to 10 mg/g, causing great threats to human health. − Fe(III) (oxyhydr)oxides are abundant redox-active components in soils, acting as the major sorbents for reducing Cd mobility. − Agricultural soils usually undergo anoxic–oxic oscillations due to rainfall and irrigation, affecting the transformation of Fe(III) (oxyhydr)oxides and consequent Cd retention. − Under anoxic conditions, Fe(III) (oxyhydr)oxides can be reduced by serving as terminal electron acceptors for microbial respiration, resulting in the dissolution of Fe(III) (oxyhydr)oxides . The produced Fe(II) either precipitates with anions (e.g., PO 4 3– ) or reacts with short-range ordered Fe(III) (oxyhydr)oxides (e.g., ferrihydrite), producing a wide range of secondary Fe minerals such as vivianite (Fe 3 (PO 4 ) 2 ·8H 2 O), goethite (α-FeOOH), and magnetite (Fe 3 O 4 ), depending on geochemical conditions. − During reductive dissolution of Fe(III) (oxyhydr)oxides, associated Cd will be released into solution due to the loss of adsorption sites, while the newly formed secondary Fe minerals can re-adsorb Cd in solution but typically exhibit lower retention of Cd due to the decrease in the specific surface. − Shift of the environment from anoxic to oxic conditions leads to Fe(II) oxidation and Fe(III) precipitation, which will enhance the immobilization of Cd through adsorption or coprecipitation, but oxidation and hydrolysis of Fe results in the decrease of pH, reducing Cd adsorption on Fe(III) (oxyhydr)oxides. − Transformation of Fe(III) (oxyhydr)oxides play a great role in the fate of Cd; however, existing studies were conducted only under anoxic or oxic conditions, only a few studies have looked into anoxic–oxic redox cycles and their effect on the transformation of Fe(III) (oxyhydr)oxides on Cd retention.…”