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Quantification of geogenic arsenic in clay-plug sediment of Holocene floodplains

Shallow aquifers in Holocene flood basins around the world are loci for the pollution of arsenic, which poses a severe health threat to millions of people. Groundwater is the prime source of water for consumption and irrigation in densely-populated areas of developing countries. Arsenic concentrations are conditioned by the meandering-river geomorphology of the Holocene flood basins, and show a high spatial variability. The combination of high organic carbon deposition rates and the presence of solid-state arsenic constitutes a potential locus for pollution in clay-filled clay plugs. After the reductive dissolution in anoxic conditions, the mobilized arsenic migrates to adjacent sandy point-bar aquifers, and accumulates in high concentrations by stratigraphic entrapment. In this paper the pollution threat is quantified through the calculation and analysis of solid-state arsenic in clay plug sediment. To assess the arsenic volume in clay-plug sediment, the bulk sediment volume of twenty clay plugs on the Middle Ganges Plain of Bihar (India) was calculated by combining surface area analysis of Sentinel-2 satellite data with side-scan sonar depth profiling of oxbow lakes, and with sedimentological data from four cored shallow wells. Arsenic concentrations in the clay-plug sediment, obtained elemental analysis (ICP-MS based) of 18 core sub-samples and complemented with published concentration data, yielded an average arsenic content of 28.75 mg/kg sediment in the 12 m thick clay plugs, and a total arsenic weight of 0.07 – 3.13 . 106 kg per clay plug. Arsenic and iron concentrations in the sediment decrease with depth, and this testifies to the increased dissolution.


Santosh Kumar (1), Devanita Ghosh (2), Marinus Eric Donselaar (1,3), Floortje Burgers (1) & Ashok Kumar Ghosh (4)
Department of Applied Geoscience and Engineering, Delft University of Technology, The Netherlands(1); Laboratory of Biogeochem-mystry, Centre for Earth Sciences, Indian Institute of Science, Bengaluru, Karnataka, India (2); Department of Earth and Environmental Sciences, Division of Geology, Leuven, Belgium (3) Mahavir Cancer Sansthan and Research Centre, Patna, India (4)
GeoUtrecht 2020