Biological Fe(II) and As(III) oxidation immobilizes arsenic in micro-oxic environments

Abstract

Fe(III) oxyhydroxides play critical roles in arsenic immobilization due to their strong surface affinity for arsenic. However, the role of bacteria in Fe(II) oxidation and the subsequent immobilization of arsenic has not been thoroughly investigated to date, especially under the micro-oxic conditions present in soils and sediments where these microorganisms thrive. In the present study, we used gel-stabilized gradient systems to investigate arsenic immobilization during microaerophilic microbial Fe(II) oxidation and Fe(III) oxyhydroxide formation. The removal and immobilization of dissolved As(III) and As(V) proceeded via the formation of biogenic Fe(III) oxyhydroxides through microbial Fe(II) oxidation. After 30 days of incubation, the concentration of dissolved arsenic decreased from 600 to 4.8 μg L-1. When an Fe(III) oxyhydroxide formed in the presence of As(III), most of the arsenic ultimately was found as As(V), indicating that As(III) oxidation accompanied arsenic immobilization. The structure of the microbial community in As(III) incubations was highly differentiated with respect to the As(V)-bearing ending incubations. The As(III)containing incubations contained the arsenite oxidase gene, suggesting the potential for microbially mediated As(III) oxidation. The findings of the present study suggest that As(III) immobilization can occur in microoxic environments after microbial Fe(II) oxidation and biogenic Fe(III) oxyhydroxide formation via the direct microbial oxidation of As(III) to As(V). This study demonstrates that microbial Fe(II) and As(III) oxidation are important geochemical processes for arsenic immobilization in micro-oxic soils and sediments.

Arsenic biomineralization by iron oxidizing strain (Ochrobactrum sp.) isolated from a paddy soil in Hunan, China

“…Biological remediation is widespread appreciated as a low‐cost and environmentally friendly approach in contaminated soils. Recently, biological mediated ferrous iron [Fe(II)] oxidation is shown to be able to trigger the transformation of As speciation (Tong et al, 2019; Xue et al, 2020; Zhang et al, 2020). Fe oxidizing bacteria (FeOB) play a dominant driving role in Fe(II) oxidation under neutral anaerobic environment (Chen et al, 2018; Li et al, 2016), followed by the formation of poorly soluble iron(hydrogen) oxides (Zhao et al, 2013).…”

“…Fe oxidizing bacteria (FeOB) play a dominant driving role in Fe(II) oxidation under neutral anaerobic environment (Chen et al, 2018; Li et al, 2016), followed by the formation of poorly soluble iron(hydrogen) oxides (Zhao et al, 2013). The generated iron(hydrogen) oxides are characterized by large specific surface area and positive surface charge (Ackermann, Vetterlein, Kuehn, Kaiser, & Jahn, 2010), which exhibit specific adsorption capacity for anions such as AsO 4 3− and AsO 3 3− since the inner‐sphere bidentate binuclear bonding surface complexes are formed (Bowell, 1994; Tong et al, 2019; Zhang et al, 2020). The inoculation of FeOB in paddy soils could promote the formation of Fe plaque (Xiao, Li, & Ye, 2020) which is composed mainly of ferrihydrite, goethite and siderite, facilitating the adsorption of As (Wu et al, 2016).…”

“…The inoculation of FeOB in paddy soils could promote the formation of Fe plaque (Xiao, Li, & Ye, 2020) which is composed mainly of ferrihydrite, goethite and siderite, facilitating the adsorption of As (Wu et al, 2016). Moreover, the co‐precipitation of As is effectively enhanced during anaerobic microbial Fe(II) oxidation and biogenic iron(hydrogen) oxides formation (Jia, Huang, Chen, & Zhu, 2014; Park, Han, & Ahn, 2016; Tong et al, 2019). Recent studies have concluded that the incorporation of As into iron(hydrogen) oxides promote the formation of ferric arsenate or scorodite (Chen et al, 2018; Tong et al, 2019), which trap more As in the mineral structure.…”

“…Moreover, the co‐precipitation of As is effectively enhanced during anaerobic microbial Fe(II) oxidation and biogenic iron(hydrogen) oxides formation (Jia, Huang, Chen, & Zhu, 2014; Park, Han, & Ahn, 2016; Tong et al, 2019). Recent studies have concluded that the incorporation of As into iron(hydrogen) oxides promote the formation of ferric arsenate or scorodite (Chen et al, 2018; Tong et al, 2019), which trap more As in the mineral structure. Furthermore, As oxidase genes ( aioA ) are confirmed to be encoded on some FeOB (Nitzsche, Weigold, Lösekann‐Behrens, Kappler, & Behrens, 2015), resulting in the conversion of As(III) to less toxic and mobile As(V), which reduce the As bioavailability.…”

“…Recently, biological process and chemodenitrification are illustrated to occur simultaneously (Chen et al, 2018; Li, Li, & Li, 2018). The rate of biological Fe(II) oxidation has been revealed to be 3–6‐times higher than the chemical oxidation by NO 2 − (Shelobolina et al, 2012), and the rates may ultimately affect the forms of the mineral products (Tong et al, 2019; Zhao et al, 2013). In addition, the presence of Fe(II) in turn affects the NO 3 − reduction.…”