Arsenic reduction and mobilization cycle via microbial activities prevailing in the Holocene aquifers of Brahmaputra flood plain

Abstract

Arsenic mobilization and immobilization are primarily controlled via hydrogeological and microbiological activity in an alluvial flood plain. In this study, two distinctly different high (HAsCR) and low (LAsCR) arsenic contaminated regions were selected. Morphological analysis of sediment samples showed the presence of authigenic (viz. magnetite) in HAsCR whereas detrital minerals (viz. flaky muscovite) morphology observed in the LAsCR study area. Indigenous arsenic-reducing microbes were isolated from groundwater samples of both study areas. The identified microbial species are Lysinibacillus sphaericus,Acinetobacter nosocomialis,Pseudomonas aeruginosa and Bacillus licheniformis showed a significant As tolerance limit and depicted their capability to enhance the dissolved arsenate [As(V)] concentration in the study area groundwater aquifers. This collective study for sediment color and microbiology analysis of two representative alluvial regions, suggested that the redox aquifer condition is favorable for the reductive dissolution mechanism of iron along with arsenate-reducing microorganism, which found main cause for the heterogeneous distribution of dissolved arsenic. This study bridges the knowledge gap between causes for heterogeneous concentration distribution of As in alluvial aquifer and the role of arsenate reducing bacteria in high and low As contaminated groundwater regions.