Geochemical mechanisms of natural arsenic mobility in the hydrogeologic system of Lower Katari Basin, Bolivian Altiplano

•Hydrochemistry of water bodies is strongly influenced by the water/sediment interaction.•Seasonal variation of water/sediment causes a high flooding risk downstream of basin.•The hydrogeology shows the groundwater flow direction of southeast to northwest.•BCR Sequential extraction indicates the As adsorption on iron and aluminum oxides/hydroxides minerals.•Spatial distribution of As shows higher values in the northern region (alluvial sediments).