Distribution and hydrogeochemical behavior of arsenic-enriched groundwater in the sedimentary aquifers: Comparison between Datong Basin, China and Kushtia District, Bangladesh

High arsenic (As) groundwater has become a major global concern due to its widespread occurrence. A comparative hydrogeochemical study was performed on the As -enriched groundwater in Datong Basin, China and Kushtia District, Bangladesh. The elevated As concentrations of Datong Basin ranged from 0.31 to 452 g L-1. As enriched groundwater is mainly Na-HCO3 type water, and characterized by higher pH value, high Nat, low Ca2+, S02,- and NO3along with moderate TDS. The release of As in aquifers resulted from the reduction of As -carrying crystalline iron (Fe) oxide/hydroxides and oxidation of organic matter. The aquifers of Kushtia District, Bangladesh are unconsolidated, alluvial in nature, and developed from Holocene floodplain and Pleistocene deposits. High As (6.04-590.7 g L-1) groundwater occurs mainly in shallow aquifers. The Ca-HCO3 type groundwater is distinguished by circum-neutral pH, medium-high EC, high HCO, and low content of K and Cl-. The reductive suspension of MnOOH increased the dissolved As loads and redox responsive elements such as SO4- and pyrite oxidation acted as the main mechanisms for As release in groundwater. The weak loading of Fe suggests that the release of Fe and As was decoupled in sedimentary aquifers of Kushtia District.