Arsenic contamination in groundwater of Tan Hong and Thanh Binh District, Dong Thap Province

Abstract

A total of 55 groundwater samples were collected in February and March, 2012 to investigate the As contamination in groundwater at Thanh Binh and Tan Hong district, Dong Thap province, Vietnam. Field parameters (pH, temperature, DO, EC, Eh) were measured on sites using portable devices. Water samples were analyzed in laboratory for total As and Fe concentration. The analysis result showed the entirely difference between groundwater chemistry of Thanh Binh and Tan Hong. Groundwater in Thanh Binh was predominantly reducing (-93 mV, average), contrary to the oxidizing condition of Tan Hong aquifer (182.2 mV, average). 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 10 µg/L for As (average 408.16 µg/L). In contrast, 100% water samples in Tan Hong contained less than 10 µg/L As. Strong positive correlation was found between Fe and As concentration. The reducing condition and high concentration of Fe indicated reductive dissolution of the Fe oxyhydroxide as the significant mechanism that released As to Thanh Binh groundwater.