Bacterial Sulfate Reduction Facilitates Iodine Mobilization in the Deep Confined Aquifer of the North China Plain

Abstract

Bacterial sulfate reduction plays a crucial role in the mobilization of toxic substances in aquifers. However, the role of bacterial sulfate reduction on iodine mobilization in geogenic high-iodine groundwater systems has been unexplored. In this study, the enrichment of groundwater δ34SSO4 (15.56 to 69.31‰) and its significantly positive correlation with iodide and total iodine concentrations in deep groundwater samples of the North China Plain suggested that bacterial sulfate reduction participates in the mobilization of groundwater iodine. Similar significantly positive correlations were further observed between the concentrations of iodide and total iodine and the relative abundance of the dsrB gene by qPCR, as well as the composition and abundance of sulfate-reducing bacteria (SRB) predicted from 16S rRNA gene high-throughput sequencing data. Subsequent batch culture experiments by the SRB Desulfovibrio sp. B304 demonstrated that SRB could facilitate iodine mobilization through the enzyme-driven biotic and sulfide-driven abiotic reduction of iodate to iodide. In addition, the dehalogenation of organoiodine compounds by SRB and the reductive dissolution of iodine-bearing iron minerals by biogenic sulfide could liberate bound or adsorbed iodine into groundwater. The role of bacterial sulfate reduction in iodine mobilization revealed in this study provides new insights into our understanding of iodide enrichment in iodine-rich aquifers worldwide.

Abiotic and Biotic Reduction of Iodate Driven by Shewanella oneidensis MR-1

“…Laboratory studies on their sorption behavior have shown that IO 3 – has greater sorption than I – on iron-bearing minerals such as hydrous ferric oxide and goethite, as well as natural soils and sediments. − Thus, the reduction of IO 3 – to I – could have an important influence on the mobility of iodine in natural systems. A previous study showed that the Fe­(II) solution was able to reduce IO 3 – , which was often cited to support that Fe­(III)-reducing bacteria residing in iodine-rich environments could facilitate iodine mobilization through abiotic IO 3 – reduction by biogenic Fe­(II). ,− However, the intermediates and stoichiometries of the abiotic reaction between Fe­(II) and IO 3 – have not been thoroughly investigated.…”