Significant arsenic reduction by pond sediment microflora in arsenic affected Bengal Delta

Abstract

Biogeochemical reduction and mobilization of sediment-bound arsenic have triggered widespread groundwater arsenic contamination and public health emergency in Bengal Delta. The present study examines arsenic reduction ability of pond sediment microbiota and their diversity from arsenic-affected villages. Arsenic reduction ability of pond sediment microbiota and individual bacterial isolates were studied in sediment microcosm and in culture medium. Arsenic-reducing strains were identified from 16S rDNA sequences. Pond sediment microflora caused profuse arsenic reduction under anoxic and partial anoxic conditions, and under the influence of labile organic matter. Prominent arsenic-reducing strains were identified as Chryseobacterium sp., Pseudomonas sp., Acinetobacter sp., and Comamonas aquatica. The presence of partial-to-true anoxic conditions, typical of pond ecosystems in this region and labile organic matter, as well as organic manure applications in ponds for aquaculture, strongly favored arsenic reduction by sediment microflora. The Bengal Delta plain is bestowed with thousands of aquaculture ponds and floodplain wetlands which might act as important sites for microbial reduction and mobilization of arsenic to the groundwater hydrologic system in the region.