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Arsenic in shallow groundwater of Bangladesh: investigations from three different physiographic settings
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering. (KTH-International Groundwater Arsenic Research Group)
Department of Geology, University of Dhaka.
Institute of Geological Sciences, Faculty of Science, Masaryk University.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering. (KTH-International Groundwater Arsenic Research Group)ORCID iD: 0000-0003-4350-9950
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2007 (English)In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 15, no 8, 1507-1522 p.Article in journal (Refereed) Published
Abstract [en]

Occurrences of arsenic (As) in the Bengal Basin of Bangladesh show close relationships with depositional environments and sediment textures. Hydrochemical data from three sites with varying physiography and sedimentation history show marked variations in redox status and dissolved As concentrations. Arsenic concentration in groundwater of the Ganges Flood Plain (GFP) is characteristically low, where high Mn concentrations indicate redox buffering by reduction of Mn(IV)-oxyhydroxides. Low DOC, HCO3-, NH4+ and high NO3- and So(4)(2-) concentrations reflect an elevated redox status in GFP aquifers. In contrast, As concentration in the Ganges Delta Plain (GDP) is very high along with high Fe and low Mn. In the Meghna Flood Plain (MFP), moderate to high As and Fe concentrations and low Mn are detected. Degradation of organic matter probably drives redox reactions in the aquifers, particularly in MFP and GDP, thereby mobilising dissolved As. Speciation calculations indicate supersaturation with respect to siderite and vivianite in the groundwater samples at MFP and GDP, but groundwater in the GFP wells is generally supersaturated with respect to rhodochrosite. Values of log P-CO2 at MFP and GDP sites are generally higher than at the GFP site. This is consistent with Mn(IV)-redox buffering suggested at the GFP site compared to Fe(III)-redox buffering at MFP and GDP sites.

Place, publisher, year, edition, pages
2007. Vol. 15, no 8, 1507-1522 p.
Keyword [en]
arsenic; alluvial and deltaic aquifers; hydrochemistry; redox-buffering; Bangladesh
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-9344DOI: 10.1007/s10040-007-0203-zISI: 000251144400005Scopus ID: 2-s2.0-36549055242OAI: oai:DiVA.org:kth-9344DiVA: diva2:113539
Note
QC 20100809Available from: 2008-10-21 Created: 2008-10-21 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Arsenic in Alluvial Aquifers in the Meghna Basin, Southeastern Bangladesh: Hydrogeological and Geochemical Characterisation
Open this publication in new window or tab >>Arsenic in Alluvial Aquifers in the Meghna Basin, Southeastern Bangladesh: Hydrogeological and Geochemical Characterisation
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

 Elevated levels of arsenic (As) in Bangladesh groundwater has emerged as a massive calamity exposing a large population to the risk of As toxicity from drinking water sources and agricultural products. Holocene alluvial aquifers in the delta- and flood-plains of the Ganges-Brahmaputra- Meghna (GBM) river systems are severely affected by high levels of As in groundwater. Groundwaters abstracted from Holocene alluvial aquifers of shallow depth (<150 m) contain As at concentrations mostly above WHO provisional drinking water guideline value of 10 μg/l whereas groundwater from the Holocene deeper aquifers (usually >150 m) and the Plio- Pleistocene aquifers contain low-As (<10 μg/l) water.The study reveals that the local and regional scale variations in groundwater composition, levels of As concentrations and the redox conditions are governed by the geological attributes of the aquifers. Groundwater in the grey to dark grey argillaceous sediments where organic matter and micas are abundant contain high concentration of dissolved As. Concentrations of As is generally low in the groundwater abstracted from the light grey to yellowish brown arenaceous sediments. A major proportion of As in the dark grey sediments is bound to poorly crystalline and amorphous metal-oxyhydroxides, particularly Fe-oxyhydroxides, that are readily mobile. On the other hand, As concentrations in the light grey to yellowish brown sediments are low and predominantly bound to less mobile stable crystalline phases. Redox reactions linked to the degradation of organic matter are the potential mechanism of As mobilisation through reductive dissolution of Fe-oxyhydroxides in grey to dark grey sediments in the Holocene shallow aquifers. This is reflected in groundwater compostion that is characterised by high concentrations of As, HCO3 -, Fe and dissolved organic carbon (DOC). However, concentration of dissolved Fe is probably controlled by the precipitation of secondary Fe-minerals like siderite (FeCO3), vivianite [Fe3(PO4)2 8H2O] and pyrite (FeS2). Weathering of biotite [K (Fe, Mg)3 AlSi3O10 (F, OH)2] is one of the major sources of Fe-oxyhydroxides in the sediment and thus plays a significant role in the processes of As mobilisation in groundwater.High concentrations of As and salinity are the major constraints for groundwater development in the Holocene alluvial aquifers of the Meghna basin. The Holocene shallow aquifers (<150 m) are high in dissolved As and salinity, while the Holocene deeper aquifers (>150 m) are low in As but contains pockets of saline groundwater. Molar ratios of Cl-/HCO3 - and Na+/Cl- indicate mixing of relict seawater with the freshly recharged water in these aquifers. Groundwater abstracted from the Pliocene Dupi Tila aquifer located at relatively higher elevations along the eastern part of the Meghna basin is not affected by As and salinity. Stable hydrogen (δ2H) and oxygen (δ18O) isotopes indicate relatively fast groundwater recharge rate with insignificant evaporation effect in the Meghna basin. The groundwater samples from shallow aquifers show relatively wider variations in isotopic composition than the deeper ones indicating multiple recharge regimes. Abstraction of groundwater from the Holocene deeper low-As aquifers for drinking purposes should thus be be properly guided to minimise the risk of cross-contamination and installation of high-capacity irrigation wells in the deeper aquifers must be avoided for sustainable drinking water supplies.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xii, 26 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1047
Keyword
Alluvial aquifer, groundwater, arsenic mobilisation, geology, Meghna basin, Bangladesh
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-9348 (URN)
Public defence
2008-11-05, F3, KTH, Lindstedtsvägen 26, Stockholm, 14:15 (English)
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Note
QC 20100809Available from: 2008-10-22 Created: 2008-10-21 Last updated: 2010-08-09Bibliographically approved

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