Microbial reduction and migration of As/Fe mediated by electron shuttle: Differences between incorporated and adsorbed As(V)

Abstract

Metal-reducing bacteria play a central and important role in the biogeochemical cycle of arsenic (As) and iron (Fe). Research on As/Fe migration from arsenic-containing iron minerals mediated by electronic shuttles is of significance to groundwater protection and human health. Further, the redox activity and bioavailability of goethite with differing occurrence and distribution of arsenic have not been studied clearly. In this study, the function of electron shuttle AQDS in Fe(III) bioreduction was determined. It was found that acidic conditions were conducive to the growth and reproduction of strain D2201, which was beneficial to the reduction of As(V)/Fe(III). The OD600nm value of the bacteria at pH 6 exceeded twice that at pH 8. Then, three types of goethite, namely pure goethite (Gt), coprecipitated As(V)-goethite (Gt-As), and adsorbed arsenic-goethite (Gt∗As), were compared for microbial reduction reactivity. X-ray photoelectron spectroscopy analysis illustrated the proportion of OH- content in Gt-As was much lower than that of Gt and Gt∗As, indicating Gt-As carried more surface defects and had higher bioavailability. The Fe(II) content released from AQDS-mediated bioreduction of Gt-As was two-fold higher than that of Gt and Gt∗As at pH 7. In addition, pH significantly affected goethite bioreduction efficiency and arsenic migration degree. The dissolved Fe(II) concentration for Gt-As was 0.98, 0.133, and 0.139 ​mM at pH 6, 7, and 8, respectively; corresponding to dissolved As(T) content of 3.51, 1.48, and 1.31 ​μM within 9 days of culture. This study highlights the significant influence of AQDS and mineral structure on the As/Fe biochemical cycle, which will help further develop the bioremediation of arsenic-contaminated sediments.