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Article

Flushing History as a Hydrogeological Control on the Regional Distribution of Arsenic in Shallow Groundwater of the Bengal Basin

Supporting Info

A. van Geen*^†, Y. Zheng^†^‡, S. Goodbred, Jr.^§, A. Horneman^†, Z. Aziz^†, Z. Cheng^†, M. Stute^†, B. Mailloux, B. Weinman^§, M. A. Hoque, A. A. Seddique, M. S. Hossain, S. H. Chowdhury and K. M. Ahmed

Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, Queens College, City University of New York, Flushing, New York 11367, Earth & Environmental Sciences, Vanderbilt University, Nashville, Tennessee 37235, Barnard College, Columbia University, New York, New York 10027, and Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh

Environ. Sci. Technol., 2008, 42 (7), pp 2283–2288

DOI: 10.1021/es702316k

Publication Date (Web): February 27, 2008

* Corresponding author e-mail: avangeen@ldeo.columbia.edu.

†

Lamont-Doherty Earth Observatory of Columbia University.

‡

Queens College, City University of New York.

Earth & Environmental Sciences, Vanderbilt University.

Barnard College, Columbia University.

Department of Geology, University of Dhaka.

Abstract

Whereas serious health consequences of widespread consumption of groundwater elevated in As have been documented in several South Asian countries, the mechanisms responsible for As mobilization in reducing aquifers remain poorly understood. We document here a previously unrecognized and consistent relationship between dissolved As concentrations in reducing groundwater and the phosphate-mobilizable As content of aquifer sediment for a set of precisely depth-matched samples from across Bangladesh. The relationship holds across nearly 3 orders of magnitude in As concentrations and suggests that regional as well as local patterns of dissolved As in shallow groundwater are set by the solid phase according to a remarkably constant ratio of 250 µg/L dissolved As per 1 mg/kg P-mobilizable As. We use this relationship in a simple model of groundwater recharge to propose that the distribution of groundwater As in shallow aquifers of the Bengal Basin could primarily reflect the different flushing histories of sand formations deposited in the region over the past several thousand years.