Transformation pathways of arsenic species: SRB mediated mechanism and seasonal patterns

Sulfate reducing bacteria (SRB) mediated reduction plays a key role in the biological cycling of As, which inherently associates with the transformation of As species. However, the potential pathways of As species transformation, the predominant driving process and their explanatory factors regulating seasonal As mobility mediated by SRB remains poorly understood. This study explored the possible pathways of seasonal As species transformation mediated by SRB, and identified the predominant driving process and key environmental factors in response to As mobilization in different seasons. SRB-mediated reduction governed the seasonal mobilization of As, significantly promoted reduction of As (V) and endogenous release of As, and exhibited strong seasonal variability. The flux of As(III) and TAs in group SRB in summer were 1.92-3.53 times higher than those during the ice-bound period. The results showed two distinct stages namely release and re-immobilization both in summer and ice-bound period. While As was easier to be gradually transformed into a more stable state in SRB reduction process during ice-bound period. Both in summer and ice-bound period, SRB presented significant regulating effects on As behavior by influencing loosely adsorbed As, pyrite and As sulfides in sediments as well as the formation of sulfide during the process of SRB reduction. The main effecting pathways on As mobilization were the direct effects of SRB, S^2- and Fe²⁺ in summer, but IP was also an important pathway affecting As mobility during ice-bound period. This work provides new insights into mechanisms responsible for seasonal As mobilization.