T178 Arsenic in Geologic Systems (Posters)

Tuesday, 2 November 2010
8:00 AM - 6:00 PM
Hall D

ARSENIC SPECIATION IN AQUIFER SEDIMENTS, WEST BENGAL, INDIA

Paper number: T178-12
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Arsenic concentrations in excess of the WHO drinking-water standard of 10 µg/L have been documented in groundwater from the Bengal basin of India and Bangladesh. The As is theorized to be released from iron (oxy)hydroxides under anoxic conditions and is heterogeneously distributed throughout the basin. Aquifer sediment samples were collected from four sites east and west of the River Bhagirathi-Hoogly, along the western margin of the basin in West Bengal state (India), for comparison of solid-phase As concentrations. Analyses of groundwater samples taken from the same area reveal low As concentrations west of the Bhagirathi-Hoogly, while As concentrations east of the river range from 2 µg/L - 4035 µg/L.

The sediment samples collected are currently undergoing grain size (hydrometer and sieve) analyses. Proportions of each major clast size, as well as the degree of sorting, may be interpreted using these analyses. The sediments will then undergo continuous-flow sequential extraction of solid-phase As, Fe, Mn, and Ca for analysis by atomic adsorption and infrared spectroscopy. We will examine relationships among these analytes in operationally-defined chemical “pools” (i.e., weakly adsorbed, strongly adsorbed or co-precipitated, and incorporated in mineral lattices). Mineralogical analyses via X-ray diffraction and thin-section petrography are pending. Understanding the texture and composition of the sediments from either side of the river will allow us to infer the extent to which depositional differences contribute to elevated As concentrations in Bengal basin groundwater.