Arsenic incorporation into authigenic pyrite, Bengal Basin sediment, Bangladesh

Authors

Heather A. Lowers, U.S. Geological Survey, MS 973, Denver, CO, USA
George N. Breit, U.S. Geological Survey, MS 973, Denver, CO, USA
Andrea L. Foster, U.S. Geological Survey, MS 901, Menlo Park, CA, USA
John Whitney, U.S. Geological Survey, MS 980, Denver, CO, USA
James Yount, U.S. Geological Survey, MS 980, Denver, CO, USA
Md. Nehal Uddin, Geological Survey of Bangladesh, Segenbagicha, Dhaka, Bangladesh
Ad. Atual Muneem, Geological Survey of Bangladesh, Segenbagicha, Dhaka, Bangladesh

Date of this Version

2007

Comments

Published in Geochimica et Cosmochimica Acta 71 (2007) 2699–2717.

Abstract

Sediment from two deep boreholes (~400 m) approximately 90 km apart in southern Bangladesh was analyzed by X-ray absorption spectroscopy (XAS), total chemical analyses, chemical extractions, and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the Bengal Basin. Authigenic framboidal and massive pyrite (median values 1500 and 3200 ppm As, respectively), is the principal arsenic residence in sediment from both boreholes. Although pyrite is dominant, ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment-bound arsenic between approximately 20 and 100 m, which is the depth range of wells containing the greatest amount of dissolved arsenic. The lack of pyrite in this interval is attributed to rapid sediment deposition and a low sulfur flux from riverine and atmospheric sources. The ability of deeper aquifers (>150 m) to produce ground water with low dissolved arsenic in southern Bangladesh reflects adequate sulfur supplies and sufficient time to redistribute the arsenic into pyrite during diagenesis.