Mitigating translocation of arsenic from rice field to soil pore solution by manipulating the redox conditions

Abstract

Arsenic (As) is uptaken more readily by rice over wheat and barley. The exposure of As to humans being in the rice-consuming regions is a serious issue. Thus, an effective practice to reduce the translocation of As from soil to rice grain should be implemented. During a flooding period, the water layer greatly limits the transport of oxygen from atmosphere to soil, which provides favorable conditions for reduction of oxygen. The reduction of Fe in the soil during the flooding condition is closely related to the As mobility, which expedites the release of As to the soil pore solution and increases As uptake by rice plants. Therefore, the performance of oxygen releasing compounds (ORCs) was evaluated to lower the translocation of As from soil to soil solution. Specifically, in the simple system containing ORCs and water, the oxygen releasing capacity of ORCs was scrutinized. In addition, ORCs was applied to sea sand and arsenic bearing ferrihydrite to identify the contribution of ORCs to As and iron mobility. Especially, ORCs were introduced to the closed (completely mixed system) and open (static) systems to simulate the paddy soil environment. Introducing ORCs increased the DO in the aqueous phase, and CaO2 was more effective in increasing DO than MgO2. In the static system simulating a rice field, the dissolution of ORCs was inhibited. The pH increased due to the formation of hydroxide, but the increase was not significant in the soil due to the buffering capacity of the soil. Finally, the As concentration in the soil solution was lowered to 25-50% of that of the control system by application of ORCs in the static paddy soil system. All experimental findings signify that the application of ORCs can be an effective practice to lower the translocation of As from soil to pore solution.