Arsenic bioavailability to rice plant in paddy soil: influence of microbial sulfate reduction

Abstract

Purpose High arsenic (As) mobility in anaerobic paddy soil due to microbial Fe-and As-reducing processes results in As accumulation into rice plants. Sulfur (S) also undergoes microbial reducing processes in the anaerobic paddy soil, while this process interacts with the Fe-and As-reducing processes, forms secondary minerals, and thus influences As mobility in paddy soil. This work was carried out to investigate the role of sulfur and sulfate-reducing bacteria (SRB) in As redox transformation and bioavailability to rice plant in an anaerobic paddy soil. Materials and methods Anaerobic incubation experiments with or without sulfate (SO 4 2− ) and SRB were carried out to monitor S and iron (Fe) dynamics and their relations to As speciation and release to soil solution. Rice cultivation in pot experiment was then carried out to check the SO 4 2− amendment in bioavailability and uptake into rice plants.Results and discussion The inoculation of an enriched SRB community into the sterilized paddy soil increased reduction and release of As to the soil solution after flooding, showing its ability in arsenate (As(V)) as well as SO 4 2− reduction to arsenite (As(III)) and sulfide (S 2− ), respectively. Sulfate addition (2 and 100 mM) into the anaerobic paddy soil increased the reduction of SO 4 2− and ferric iron (Fe 3+ ) and resulted to lower dissolved As in the soil solution, which limited As mobility in the paddy soil. Application of SO 4 2− (100 mg kg −1 ) into paddy soil finally decreased the concentration of dissolved As in the soil solution by 23.5 % and also decreased As content in rice roots and iron plaque by 22.6 and 30.5 %, respectively. Conclusions The results revealed the important role of sulfur and the SRB activity in As speciation and mobility in anaerobic paddy soil, implying a lower As bioavailability to rice plants under sulfur-enriched anaerobic paddy soil, and an efficient way to reduce As accumulation in rice plants by sulfur fertilization in paddy soils.

Effects of Iron Amendments on the Speciation of Arsenic in the Rice Rhizosphere after Drainage

“…The increased As-S contents under anaerobic soil incubation with 1 wt % of ZVI was consistent with the results observed by Suda et al [15]. Jia et al [40] showed that the application of sulfate to paddy soil resulted in the decreased concentration of As in the soil solution, and they concluded that microbial sulfate reduction had a role in immobilizing the As in anaerobic soil by facilitating the precipitation of immobile arsenic sulfide. Sulfate reduction followed by the formation of arsenic sulfide can be further enhanced by the addition of ZVI, which was used in this study.…”

Relevance of Reactive Fe:S Ratios for Sulfur Impacts on Arsenic Uptake by Rice

“…The soils contained 15.4 and 11.0 mg As per kg soil, respectively, which is within the range of natural As contamination levels reported for paddy soils from this region [48,49] (also SI, Table S2). The S content of the soils (330 and 363 mg per kg soil, respectively) represents the high end of the distribution for paddy soils within this region (disregarding acid sulfate soils, see SI, Table S2) and matches that of other paddy soils used in pot trials [47,50]. We intentionally chose soils with a high (but not extreme) total S content in order to avoid an S deficiency effect in the control treatment, as the aim was to examine the effect of adding excess S. Soil was air dried and disaggregated to <4 cm aggregate size before transporting to Stanford University, where it was stored in room temperature in the dark until the start of the experiment.…”

Effects of Sulfate Application on Inhibiting Accumulation and Alleviating Toxicity of Arsenic in Panax notoginseng Grown in Arsenic-Polluted Soil

“…Hu et al (2007) reported that the application of sulfate significantly decreased As uptake by rice seedlings because of the overall effect of enhancement of formation of iron plaques on the root surface and soil, the desorption of arsenate from iron plaque, and the competitive transport into cells. Jia et al (2015) reported that sulfate and sulfate-reducing bacteria (SRB) helped to reduce the As bioavailability in paddy soil and consequently reduced As accumulation in rice. In the anaerobic soil, SRB can reduce SO 4 2− to S 2− , and the reduction of As(V) to As(III) may result in the formation of indiscerptible As 2 S 3 .…”

“…In the anaerobic soil, SRB can reduce SO 4 2− to S 2− , and the reduction of As(V) to As(III) may result in the formation of indiscerptible As 2 S 3 . FeAsS is especially easily formed when large amounts of Fe(II) or FeS are available (Jia et al 2015;Porter et al 2004). S and As both exist in soil in the form of anion, and arsenate could be desorbed from the surface of iron oxides by sulfate (Lafferty and Loeppert 2005).Therefore, we speculated that sulfate could desorb the arsenate on the surface of P. notoginseng roots, which may be one of the reasons for the decrease of As level in P. notoginseng roots.…”