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Arsenic (As) is a priority environmental pollutant in paddy field. The coupling of arsenate (As(V)) reduction with anaerobic methane (CH 4 ) oxidation was recently demonstrated in paddy soils and has been suggested to serve as a critical driver for As transformation and mobilization. However, whether As(V)-dependent CH 4 oxidation is driven by distinct methanotrophs under different pH conditions remains unclear. Here, we investigated the response of As(V)-dependent CH 4 oxidation to pH shifts (pH 5.5-8.0) by employing isotopically labelled CH 4 . Furthermore, the underlying mechanisms were also investigated in well-controlled anoxic soil suspension incubations. Our results showed that As(V)-dependent CH 4 oxidation is highly sensitive to pH changes (1.6-6.8 times variation of arsenite formation). A short-term (0-10 d) pH shift from near-neutral pH to acidic conditions (i.e., pH 5.5, -85% arsenite formation) had an inhibitory effect on As(V)-dependent CH 4 oxidation. However, prolonged acidic conditions (i.e., >15 d) had no significant influence on As(V)-dependent CH 4 oxidation. The microbial analyses indicated that As reduction in paddies can be driven by anaerobic CH 4 oxidation archaea (ANME) and methanotrophs. And, methanotrophs may serve as a critical driver for As(V)-dependent CH 4 oxidation. Moreover, type I methanotrophs Methylobacter were more active in oxidizing CH 4 than type II methanotrophs Methylocystis when the pH ≥ 6.5. However, Methylocystis had a higher tolerance to soil acidification than Methylobacter. This study illustrates that As(V)-dependent CH 4 oxidation could be dominated by distinct methanotrophs along with pH shifts, which eventually enhances As release in paddy soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The increase in toxic heavy metal pollutants in rice paddies threatens food safety. There is an urgent need for lnow-cost remediation technology for immobilizing these trace metals. In this study, we showed that the application of the soil microbial fuel cell (sMFC) can greatly reduce the accumulation of Cd, Cu, Cr, and Ni in the rice plant tissue. In the sMFC treatment, the accumulation of Cd, Cu, Cr, and Ni in rice grains was 35.1%, 32.8%, 56.9% and 21.3% lower than the control, respectively. The reduction of these elements in the rice grain was due to their limited mobility in the soil porewater of soils employing the sMFC. The restriction in Cd, Cu, Cr, and Ni bioavailability was ascribed to the sMFC ability to immobilize trace metals through both biotic and abiotic means. The results suggest that the sMFC may be used as a promising technique to limit toxic trace metal bioavailability and translocation in the rice plants., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Arsenic (As) behavior in paddy soils couples with the redox process of iron (Fe) minerals. When soil is flooded, Fe oxides are transformed to soluble ferrous ions by accepting the electrons from Fe reducers. This process can significantly affect the fate of As in paddy fields. In this study, we show a novel technique to manipulate the Fe redox processes in paddy soils by deploying soil microbial fuel cells (sMFC). The results showed that the sMFC bioanode can significantly decrease the release of Fe and As into soil porewater. Iron and As contents around sMFC anode were 65.0% and 47.0% of the control respectively at day 50. The observed phenomenon would be explained by a competition for organic substrate between sMFC bioanode and the iron- and arsenic-reducing bacteria in the soils. In the vicinity of bioanode, organic matter removal efficiencies were 10.3% and 14.0% higher than the control for lost on ignition carbon and total organic carbon respectively. Sequencing of the 16S rRNA genes suggested that the influence of bioanodes on bulk soil bacterial community structure was minimal. Moreover, during the experiment a maximum current and power density of 0.31 mA and 12.0 mWm -2 were obtained, respectively. This study shows a novel way to limit the release of Fe and As in soils porewater and simultaneously generate electricity., (Copyright © 2018 Elsevier Ltd. All rights reserved.)