Establishing iron-inspired barriers to combat abnormal arsenic accumulation in rice from soils within regulatory limits.

Rice cultivated in seemingly arsenic (As) uncontaminated soils may accumulate As levels exceeding food safety standards, a phenomenon often overlooked by current soil quality standards. This study investigated the effectiveness of iron (Fe)-inspired barriers in limiting As dissolution and translocation in uncontaminated paddy fields, addressing the need for safe rice production under global warming and extreme weather pressures. We hypothesized that Fe-based materials could inspire Fe barriers in the soil-rice system. Our experiments demonstrated that application of 0.25 % (w/w) FeSO and 1 % (w/w) ferrihydrite reduced inorganic As in brown rice grains by 29.8 % and 37.1 %, respectively, under the conventional water management practice, which included both flooded and intermittent drainage periods. Path analysis revealed a negative correlation between increased soil amorphous Fe oxide content and bioavailable As. Mössbauer spectroscopy confirmed microcrystalline Fe oxide enrichment in soil clay-sized fractions due to FeSO application, activating the soil matrix Fe barrier. Ferrihydrite reduced As translocation through adsorption and lattice sequestration. Iron plaques on rice roots were also inspired as a second Fe barrier: FeSO application increased total Fe content on iron plaques by 35.1 % and As proportion in high-crystallinity Fe oxide fraction by 11 %, thus limiting As uptake by white root. However, combining FeSO with organic fertilizer application resulted in excess As release from the soil matrix, and dissolved organic carbon encroached on the adsorption sites of the Fe barrier, nullifying the barriers' effectiveness. Our results demonstrate the potential of Fe-inspired barriers in the soil-rice system as an effective solution to As anomalies in rice from uncontaminated areas.