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

Abstract

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 O 2 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.

Activated Carbon Application Simultaneously Alleviates Paddy Soil Arsenic Mobilization and Carbon Emission by Decreasing Porewater Dissolved Organic Matter

“…11−13 To inhibit soil As release, strategies such as adsorptive removal of As by Fe/Mn/Ti oxides were applied. 14,15 Also, competitive inhibiting reductive dissolution of As-bearing Fe(III) (oxyhydr)oxides by intermittent irrigation and amending manmade oxygen release tissues, 16 calcium peroxide, 17 and nitrate fertilizer 18 was studied. To reduce GHG emissions, amendments of Fe(III) (oxyhydr)oxides, SO 4 2− , and biochar have been reported in peat and paddy soils as well as coastal sediments.…”

“…During soil anaerobic respiration, soil organic carbon decomposition typically couples with microbial reduction processes that sequentially use NO 3 – , Mn­(IV), Fe­(III), and SO 4 2– as electron acceptors, accompanied by GHG emission . Ferric Fe­(III) (oxyhydr)­oxides and SO 4 2– reduction and CH 4 emission were strongly associated with As transformation in flooding paddy fields, leading to the occurrence of arsenite (As­(III)), methylated, and thiolated As species in porewater. − To inhibit soil As release, strategies such as adsorptive removal of As by Fe/Mn/Ti oxides were applied. , Also, competitive inhibiting reductive dissolution of As-bearing Fe­(III) (oxyhydr)­oxides by intermittent irrigation and amending manmade oxygen release tissues, calcium peroxide, and nitrate fertilizer was studied. To reduce GHG emissions, amendments of Fe­(III) (oxyhydr)­oxides, SO 4 2– , and biochar have been reported in peat and paddy soils as well as coastal sediments. − Both reductions of As release and GHG emission involve Fe­(III) since it is recognized as the dominant electron acceptor in flooding soils. , Oxygen and NO 3 – are competitive electron acceptors for both Fe­(III) reduction and CH 4 production, while Fe­(III), SO 4 2– , and biochar are competitive electron acceptors only for CH 4 production.…”