Effects of Simultaneous Application of Ferrous Iron and Nitrate on Arsenic Accumulation in Rice Grown in Contaminated Paddy Soil

The objective of this study was to investigate the effects of simultaneous application of ferrous iron [Fe­(II)] and nitrate (NO₃^–) on arsenic (As) accumulation in rice plants during the entire growth period. To this end, Fe­(II) and NO₃^– were simultaneously applied to As-contaminated soil in a pot experiment conducted under climate-controlled greenhouse conditions. In comparison to the control and sole treatments with Fe­(II), NO₃^–, or amorphous iron (Fe) oxides, the simultaneous application of Fe­(II) and NO₃^– significantly reduced As bioavailability by enhancing As­(V) immobilization in the soil and also significantly inhibited As accumulation in rice plants, especially that of iAs in the grain. The presence of Fe­(II) and nitrate can decrease As releasing via inhibiting reductive dissolution of iron minerals, and the Fe­(II) oxidation coupled with nitrate reduction can immobilize As via incorporating As into iron secondary minerals. Therefore, the simultaneous application of Fe­(II) and NO₃^– effectively decreased As accumulation in rice plants by enhancing As oxidation/immobilization mediated by abiotic/biotic Fe redox transformation and mineralization. These findings provided new insights into the Fe/N/As biogeochemical cycles and are also important from the view of agronomic management of As toxicity and mitigation in As-contaminated paddy fields