Abstract:

       Geogenic high As groundwater has been found worldwide with more than 100 million people being at risk. Mechanisms of As enrichment have received much attention at both scientific and governmental levels. Intact sediments and indigenous bacteria were sampled from high As aquifer of the Hetao Basin, Inner Mongolia. Bacteria leaching experiments were conducted by using deionized water and two artificial water solutions in different nutrient conditions (including 2% glucose as carbon source and glucose-free). Results show that glucose has stimulated indigenous bacteria activities, which has resulted in a continuous decrease in suspension pH and a distinct increase in As concentration of glucose-amended suspensions.Chemical compositions(especially As species)affect As enrichment in suspensions.Reduction of sulfate was evidently observed after 9 d of incubation amended with glucose, which is slightly affected by chemical compositions of solution. Indigenous bacteriamediated release and transformation of As are believed to include release of sediment As(V), reduction of solution As(V) and release of sediment As(Ⅲ). Therefore, solution As(Ⅲ) would promote As mobilization from sediment. During As release, concentrations of Fe and Mn concomitantly increase in suspensions. Concentration of suspension As exhibits a good linear relationship with that of Fe, with a correlation coefficient of 0.967,1.It implies that indigenous bacteria-mediated reduction of Fe/Mn oxides would greatly contribute to As mobilization in aquifer sediments.

Key words: groundwater, reductive environment, enrichment, biogeochemistry, Inner Mongolia