Publication details

Geochemical characterisation of shallow aquifer sediments of Matlab Upazila, Southeastern Bangladesh - Implications for targeting low-As aquifers

Authors

VON BROMSSEN Mattias LARSSON Sara Haeller BHATTACHARYA Prosun HASAN M. Aziz AHMED Kazi Matin JAKARIYA M. SIKDER Mohiuddin A. ŠRÁČEK Ondřej BIVEN Annelie DOUSOVA Barbora PATRIARCA Claudio THUNVIK Roger JACKS Gunnar

Year of publication 2008
Type Article in Periodical
Magazine / Source Journal of Contaminant Hydrology
MU Faculty or unit

Faculty of Science

Citation
Web https://www.sciencedirect.com/science/article/pii/S0169772208000727
Doi http://dx.doi.org/10.1016/j.jconhyd.2008.05.005
Keywords arsenic; groundwater; Bangladesh; redox; hydrogeochemistry; shallow sedimentary aquifer
Description High arsenic (As) concentrations in groundwater pose a serious threat to the health of millions of people in Bangladesh. Reductive dissolution of Fe(Ill)-oxyhydroxides and release of its adsorbed As is considered to be the principal mechanism responsible for mobilisation ofAs. The distribution ofAs is extremely heterogeneous both laterally and vertically. Groundwater abstracted from oxidised reddish sediments, in contrast to greyish reducing sediments, contains significantly lower amount of dissolved arsenic and can be a source of safe water. In order to study the sustainability of that mitigation option, this study describes the lithofacies and genesis of the sediments within 60 m depth and establishes a relationship between aqueous and solid phase geochemistry. Oxalate extractable Fe and Mn contents are higher in the reduced unit than in the oxidised unit, where Fe and Mn are present in more crystalline mineral phases. Equilibrium modelling of saturation indices suggest that the concentrations of dissolved Fe, Mn and PO43--tot in groundwater is influenced by 4 secondary mineral phases in addition to redox processes. Simulating As-[I] adsorption on hydroferric oxides using the Diffuse Layer Model and analytical data gave realistic concentrations of dissolved and adsorbed As-[I] for the reducing aquifer and we speculate that the presence of high PO43--tot in combination with reductive dissolution results in the high-As groundwater. The study confirms high mobility of As in reducing aquifers with typically dark colour of sediments found in previous studies and thus validates the approach for location of wells used by local drillers based on sediment colour. A more systematic and standardised colour description and similar studies at more locations are necessary for wider application of the approach.

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