Nature of arsenic enrichment in groundwater and to assess the main geochemical factors controlling arsenic mobilization in Pabna, Bangladesh

摘要

Arsenic (As) in the groundwater of Bangladesh is a serious natural calamity and a public health hazard. Groundwaters (to a depth of 70 m) from the study area of Pakshi Union in the southwestern part of Bangladesh were collected to determine arsenic concentration and geochemical analyses. Groundwater geochemical conditions changed from oxidized form to a successively more reduced form. Groundwater is characterized by circum-neutral pH with a moderate to strong reducing nature. The analysis reveals that groundwater arsenic concentrations in the uppermost aquifer (10-70 m of depth) range from 7.0 to 168.2 mgL~(-1). The dominant groundwater type is Ca-Mg-HCO_(3) type with high concentrations of As, Fe and Mn but low levels of NO_(3)~(-) and SO_(4)~(2-), and other parameters were also below the desirable limit. Correlation analysis shows that As is closely associated with Fe and Mn which suggest that reductive dissolution of MnOOH and FeOOH mediated by anaerobic condition represents an important mechanism for releasing arsenic into the groundwater from arsenic rich sediments. Poor correlation of Mn and Fe suggests that siderite and rhodochrosite were precipitated on the surface of sediments.