Arsenic alleviation in rice by using paddy soil microbial fuel cells

Background and aims: Rice (Oryza sativa L.) consumption is a major route of dietary exposure to arsenic (As) in humans. One main reason for the high accumulation of As in rice grain is the high bioavailability of As in porewater of flooded paddy soil. Recently, it has been shown that the application of soil microbial fuel cell (sMFC) can significantly reduce soil porewater As concentration, however, the effect of sMFC on As accumulation in rice is unknown. Hence, this study was aimed at reducing the As uptake in rice grown in As contaminated soil by sMFCs. Methods: A pot experiment was performed to investigate As distribution in rice tissues and the functional microbial communities in soil when the sMFC was installed. The As in the soil porewater and rice plant parts were analyzed. 16S rRNA sequencing and Quantitative PCR were used to examine the microbial community and to quantify the relative abundance of As resistance genes in the rhizosphere, respectively. Results: The results suggest that the sMFC can simultaneously work as an electricity generator and As mitigator. The total As concentrations in the stems, leaves, husks, and rice grains were significantly decreased by 53.4%, 44.7%, 62.6%, and 67.9%, respectively in the plants with sMFC compared to the control. This decrease in As accumulation in the sMFC treatment may be explained by the decrease in the soil porewater dissolve organic matter content and abundance of As reducing gene (arsC). Moreover, known As reducing classes such as Clostridia, Bacilli and Thermoleophilia were significantly enhanced in the control treatment. Conclusions: Integrating the sMFC in rice paddy soil offers a promising way to mitigate As accumulation in rice tissue and reduce dietary As exposure, while simultaneously producing electricity.