Groundwater is widely used for irrigated farming. In this study, arsenic (As) contamination in groundwater and surface soil of agricultural fields irrigated with groundwater in Mekong Delta in Vietnam was investigated. Total As concentration and arsenite-As (As(III)) concentrations of 16 groundwater samples and total As concentration of 16 surface soil samples from agricultural fields where the groundwater was used for irrigation were measured. Mekong river water samples and surface soil samples from agricultural fields where the Mekong river water was used for irrigation were also analyzed as reference soil samples. As concentration of all measured groundwater samples were higher than the Vietnamese standard for As concentration of irrigation water (50 μg/L), and As(III) was the most abundant form of As in the groundwater. Total As concentrations of 10 of 16 soil samples exceeded the Vietnamese standard for As concentration of soil (12 mg/kg) and a positive correlation between As concentrations of groundwater samples and of soil samples was observed. Water-soluble and phosphate-exchangeable As fractions in the soil samples were more than 16 % of total soil As content. These data suggest that irrigation with groundwater in Mekong Delta area increases the As concentration of agricultural field soil, and that countermeasure technology to remove As from the contaminated groundwater should be needed to keep sustainable irrigation agriculture in Mekong Delta area.
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