Simultaneous influence of indigenous microorganism along with abiotic factors controlling arsenic mobilization in Brahmaputra floodplain, India

In the dynamic cycling of oxic and anoxic aqueous alluvial aquifer environments, varying Arsenic (As) con centrations are controlled by both abiotic and biotic factors. Studies have shown a significant form of toxic As (III) being released through the reductive dissolution of iron-oxy/hydroxide minerals and microbial reduction mechanisms, which leads to a serious health concern. The present study was performed in order to assess the abiotic and biotic factors influencing As release into the alluvial aquifer groundwater in Brahmaputra floodplain, India. The groundwater chemistry, characterization of the sediments, isolation, identification and character ization of prominent As releasing indigenous bacterium were conducted. The measured solid and liquid phases of total As concentration were ranged between 0.02 and 17.2mgkg(-1) and 8 to 353 mu G L-1, respectively. The morphology and mineralogy showed the presence of detrital and authigenic mineral assemblages whereas pri mary and secondary As bearing Realgar and Claudetite minerals were identified, respectively. Furthermore, significant non-labile As fraction was found associated with the amorphous oxides of Fe, Mn and A1. The ob served groundwater chemistry and sediment color, deduced a sub-oxic reducing aquifer conditions in As-con taminated regions. In addition, 16S rDNA sequencing results of the isolated bacterium showed the prominent Pseudomonas aeruginosa responsible for the mobilization of As, reducing condition, biommeralization and causing grey color to the sediments at the shallower and deeper aquifers in the study area. These findings suggest that microbial metabolic activities are equally responsible in iron-oxy/hydroxide reductive dissolution, controlling As mobilization in dynamic fluvial flood plains.