Author(s): Quyen. Do Thi Thuy; Avner. Vengosh; Brittany Merola; Hien. To Thi
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Keywords: Rsenic; Dong Thap; Groundwater; Release mechanism; Source
Abstract: This study investigated the source, release mechanism and speciation of geogenic Arsenic in shallow aquifers in Dong Thap Province, Mekong delta, Vietnam. The rural areas in Thanh Binh isle and Tan Hong border district were chosen since drilled wells remain the major fresh water source for drinking and irrigating at these areas. A total of 60 groundwater samples were collected in February and March, 2012. Field parameters (pH, temperature, DO, EC, Eh) were measured on sites using portable devices. Water samples were analyzed in laboratory for major ions, total As, As speciation, Fe, Mn and stable isotopes. The analysis result showed the entirely difference between groundwater chemistry of Thanh Binh and Tan Hong. Water type in Thanh Binh was Ca (Mg) -HCO 3 while the composition in Tan Hong water samples showed variety of types but mostly Na-Cl. Groundwater in Thanh Binh was predominantly reducing, contrary to the oxidizing condition of Tan Hong aquifer. Arsenic concentrations also showed spatially heterogeneous distribution over the whole study area. Groundwater from the shallow aquifers in Thanh Binh was far exceeding the permissible WHO Standard limits as well as the Vietnam Standard limit of 10μg/L for As. As (III) species was dominant and made up 70%of total As concentration. In contrast, 100%water samples in Tan Hong contained less than 10μg/L As. Stable isotopeδ2H andδ18O analysis technique firstly introduced in this area also provide valuable evidence for the difference recharges for groundwater in two research sites. The reducing condition, high concentration of Fe and HCO 3 - and the depletion of SO 4 2- indicated reductive dissolution of the Fe oxyhydroxide as the significant mechanism that released As to Thanh Binh groundwater.
Year: 2014