Sustainable Immobilization of Arsenic by Man-Made Aerenchymatous Tissues in Paddy Soil

Arsenic (As) is a major environmental pollutant and poses a significant health risk to humans through rice consumption. Elevating the soil redox potential (Eh) has been shown to reduce As bioavailability and decrease As accumulation in rice grains. However, sustainable methods for managing the Eh of rice paddies are lacking. To address this issue, we propose a new approach that uses man-made aerenchymatous tissues (MAT) to increase soil Eh by mimicking O₂ release from wet plant roots. Our study demonstrated that the MAT method sustainably increased the soil Eh levels from −119 to −80.7 mV (∼30%), over approximately 100 days and within a radius of around 5 cm from the surface of the MAT. Moreover, it resulted in a significant reduction (−28.5% to −63.3%) in dissolved organic carbon, Fe, Mn, and As concentrations. MAT-induced Fe(III) (oxyhydr)oxide minerals served as additional adsorption sites for dissolved As in soil porewater. Furthermore, MAT promoted the oxidation of arsenite to the less mobile arsenate by significantly enhancing the relative abundance of the aioA gene (130% increase in the 0−5 cm soil zone around MAT). The decrease in As bioavailability significantly reduced As accumulation in rice grains (−30.0%). This work offers a low-cost and sustainable method for mitigating As release in rice paddies by addressing the issue of soil Eh management.