Arsenic toxicity of groundwater in parts of the Bengal basin in India and Bangladesh: the role of Quaternary stratigraphy and Holocene sea-level fluctuation |
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Authors: | S K Acharyya S Lahiri B C Raymahashay A Bhowmik |
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Institution: | (1) Geological Survey of India, 27 Jawaharlal Nehru Rd. Calcutta, 700016, India e-mail: skacharyya@yahoo.com Tel.: +249-6976(0), 466-0215(R) Fax: +249-6956, IN;(2) Department of Civil Engineering, Indian Institute of Technology, Kanpur 208016, India, IN |
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Abstract: | Arsenic toxicity in groundwater in the Ganges delta and some low-lying areas in the Bengal basin is confined to middle Holocene
sediments. Dissected terraces and highlands of Pleistocene and early Holocene deposits are free of such problems. Arsenic-rich
pyrite or other arsenic minerals are rare or absent in the affected sediments. Arsenic appears to occur adsorbed on iron hydroxide-coated
sand grains and clay minerals and is transported in soluble form and co-precipitated with, or is scavenged by, Fe(III) and
Mn(IV) in the sediments. It became preferentially entrapped in fine-grained and organic-rich sediments during mid-Holocene
sea-level rises in deltaic and some low-lying areas of the Bengal basin. It was liberated subsequently under reducing conditions
and mediated further by microbial action. Intensive extraction of groundwater for irrigation and application of phosphate
fertilizer possibly triggered the recent release of arsenic to groundwater. This practice has induced groundwater flow, mobilizing
phosphate derived from fertilizer, as well as from decayed organic matter, which has promoted the growth of sediment biota
and aided the further release of arsenic. However, the environment is not sufficiently reducing to mobilize iron and arsenic
in groundwater in the Ganges floodplains upstream of Rajmahal. Thus, arsenic toxicity in the groundwater of the Bengal basin
is caused by its natural setting, but also appears to be triggered by recent anthropogenic activities.
Received: 23 August 1999 · Accepted: 16 November 1999 |
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Keywords: | Arsenic in groundwater Bangladesh Bengal basin Deltaic sedimentation Holocene sea-level rise West Bengal |
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