Mineralogia

Applied Geochemistry 26 (2011) 587–599

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Applied Geochemistry
journal homepage: www.elsevier.com/locate/apgeochem

Mineralogyand geochemistry of shallow sediments of Sonargaon, Bangladesh and implications for arsenic dynamics: Focusing on the role of organic matter
Ashraf Ali Seddique a,b,⇑, HarueMasuda b, Muneki Mitamura b, Keiji Shinoda b, Toshiro Yamanaka c, Shinji Nakaya d, Kazi Matin Ahmed e
a

Department of Petroleum and Mining Engineering, Jessore Science andTechnology University, Jessore-7408, Bangladesh Department of Geosciences, Osaka City University, Sugimoto-cho 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan Graduate School ofNatural Science and Technology, Okayama University, Okayama 700-8530, Japan d Department of Civil Engineering, Shinshu University, Nagano 380-0928, Japan e Department of Geology,University of Dhaka, Dhaka-1000, Bangladesh
b c

a r t i c l e

i n f o

a b s t r a c t
Mineralogy and geochemistry of modern shallow sediments (up to 5 m thick) within thezone of water table fluctuations were studied to determine the likely sources and processes responsible for releasing As into groundwater. Samples were collected from differentgeological settings with varying groundwater As concentrations during dry (December 2005) and wet (September 2006) seasons at Sonargaon, Bangladesh. Stratigraphic sequences ofthe studied sediments showed three distinct lithofacies, viz. clayey-silt, silty-clay, and silty-very fine sand, corresponding to fine-grained overbank associations. Total Asconcentrations of shallow sediments ranged from 80% of the As was fixed in insoluble and organic phases, while the amount of As in reducible and acid-soluble phases was very low (