Factors and pathways regulating the release and transformation of arsenic mediated by reduction processes of dissimilated iron and sulfate

Highlights: • DFeRB and SRB present significant effects on reduction of As (V) and endogenous As release. • The mechanism and pathways of As mobilization were obviously differently mediated by DFeRB and SRB. • Fe³⁺, Fe²⁺ and S²⁻ play the key roles in regulating As mobility, intrinsically linked with DFeRB and SRB. • Two main pathways for Fe³⁺ and Fe²⁺ to influence As mobility were found in DFeRB mediated reduction. • The risk of As mediated by DFeRB and SRB could give more attention during the ice-bound period. The driving process and explanatory factors regulating the transformation and migration of arsenic (As) mediated by dissimilatory iron reducing bacteria (DFeRB) and sulfate reducing bacteria (SRB) remain poorly understood. The novelty of this study is to explore the driving process and key environmental factors governing As mobilization mediated by DFeRB and SRB based on continuous As speciation and environmental parameter monitoring in a sediment-water system. The results illustrate the reduction process mediated by DFeRB and SRB significantly promotes the reduction of As(V) and the endogenous release of As. However, in the DFeRB and SRB mediated reductions, the main driving process and key explanatory factors that dominate the As mobility are significantly different. DFeRB has significant effects on the reductive dissolution and re-distribution of Fe(III) oxyhydroxides and As-containing Fe(III) minerals and on adsorption-desorption, which in turn influenced the transformation of iron species and the release and ecotoxicity of As. Meanwhile, the environmental factors that affect As mobility depend on Fe²⁺ and Fe³⁺ in DFeRB-induced reduction, presenting two main pathways: the process of As mobilization mediated by DFeRB, and the process influenced by the inorganic phosphorus involved in the competitive adsorption and anion exchange. Significantly different from DFeRB, the effects of SRB on As behavior mainly occur by influencing the adsorbed As, pyrite, and As sulfides in the sediments and through the formation of sulfides during the sulfate reduction. The main pathways of As mobilization reflect the direct effects of SRB, S²⁻, and Fe²⁺. In addition, the role of NH₄⁺-N in the driving process of As mobility is more pronounced in SRB-induced reduction. NO₃⁻-N is an essential factor affecting As mobility, but the effects of NO₃⁻-N on As lead to non-significant pathways. This work provides insights into the environmental effects of DFeRB and SRB on the biogeochemical cycle of As.