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Arsenic enrichment in groundwater of the alluvial aquifers in Bangladesh: an overview
Univ Dhaka, Dept Geol.
KTH, Superseded Departments, Land and Water Resources Engineering.ORCID iD: 0000-0003-4350-9950
Univ Dhaka, Dept Geol.
Univ Dhaka, Dept Geol.
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2004 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 19, no 2, 181-200 p.Article in journal (Refereed) Published
Abstract [en]

Arsenic in the groundwater of Bangladesh is a serious natural calamity and a public health hazard. Most groundwater from the shallow alluvial aquifers (<150 m), particularly in the Holocene plain lands, are vulnerable to As-enrichment. Delta plains and flood plains of the Ganges-Brahmaputra river system are moderately to severely enriched and more than 60% of the tube wells are affected. Shallow aquifers in the Meghna river basin and coastal plains are extremely enriched with more than 80% of the tube wells affected. Aquifers in the Pleistocene uplands and Tertiary hills are low in As. The vertical lithofacies sequence of the sediments from highly enriched areas of the country show two distinct lithofacies associations-a dominantly sandy channel-fill association and a fine-grained over bank association. The sediments can be grouped into 4 distinct lithofacies, viz. clay, silty clay, silty sand and sand. Thin section petrography of the As-enriched aquifer sands shows that the sands are of quartzolithic type and derived from the collision suture and fold thrust belt of the recycled orogen provenance. Groundwater is characterized by circum-neutral pH with a moderate to strong reducing nature. The waters are generally of Ca-Mg-HCO3 or Ca-Na-HCO3 type, with HCO3- as the principal anion. Low SO42- and NO3-, and high dissolved organic C (DOC) and NH4+ concentrations are typical chemical characteristics of groundwater. The presence of dissolved sulfides in these groundwaters indicates reduction Of SO4. Total As concentration in the analyzed wells vary between 2.5 and 846 mug l(-1) with a dominance of As(III) species (67-99%). Arsenic(III) concentrations were fairly consistent with the DOC and NH4+ contents. The HNO3 extractable concentrations of As (As-NO3) in the sediments (0.5-17.7 mg kg(-1)), indicate a significant positive correlation with Fe-NO3, Mn-NO3, Al-NO3 and P-NO3. The concentrations Of S-NO3 (816-1306 mg kg(-1)) peaked in the clay sediments with high organic matter (up to 4.5 wt.%). Amounts of oxalate extractable As (As..) and Fe (Fe x) ranged between 0.1-8.6 mg kg(-1) and 0.4-5.9 g kg(-1), respectively. Arsenic(ox) was positively correlated with Fe-ox, Mn-ox, and Al-ox in these sediments. Insignificant amounts of opaque minerals (including pyrite/arsenopyrite) and the presence of high As contents in finer sediments suggests that some As is incorporated in the authigenically precipitated sulfides in the reducing sediments. Moreover, the chemical extractions suggest the presence of siderite and vivianite as solid phases, which may control the aqueous chemistry of Fe and PO43-. Reductive dissolution of Fe oxyhydroxide present as coatings on sand grains as well as altered mica (biotite) is envisaged as the main mechanism for the release of As into groundwater in the sandy aquifer sediments.

Place, publisher, year, edition, pages
2004. Vol. 19, no 2, 181-200 p.
Keyword [en]
Aquifers; Arsenic; Channel flow; Concentration (process); Floods; Health hazards; Sand; Sediments; Water wells; Flood plains; Natural calamity
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-9343DOI: 10.1016/j.apgeochem.2003.09.006ISI: 000188550600003Scopus ID: 2-s2.0-0842280797OAI: oai:DiVA.org:kth-9343DiVA: diva2:113538
Note

QC 20100730

Available from: 2008-10-21 Created: 2008-10-21 Last updated: 2015-06-01Bibliographically 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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Supervisors
Note
QC 20100809Available from: 2008-10-22 Created: 2008-10-21 Last updated: 2010-08-09Bibliographically approved

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