Limited roles of anthropogenic activities on arsenic mobilization in groundwater from the Yinchuan Basin, China

Arsenic (As) pollution in groundwater is an extremely concerning issue all over the world, because it has brought many negative health effects on people. However, the impact of anthropogenic activities on the formation of high As groundwater is poorly understood. Seventy-nine groundwater samples and seven surface water samples were taken along two transects in the Yinchuan Basin, China, to trace effects of anthropogenic activities on distri-bution of high As groundwater by using artificial sweeteners. The sampling campaign showed that, in 47% of samples, As concentrations exceeded the WHO drinking water guideline (10 mu g/L). Both acesulfame and sucralose were detected in the groundwater samples, and concentrations in samples from the transect of the upper stream of regional groundwater were generally higher than those from the transect of the middle stream. Both acesulfame and sucralose in all studied groundwater samples had the detection rate (DR) > 7 and the detection frequency (DF) > 90%, indicating that they can be used as tracers to reflect anthropogenic activities. Higher As groundwater samples generally had lower concentrations of the artificial sweeteners and vice versa, showing that the influence of anthropogenic activities on high As concentration was limited. Geological pro-cesses are the main reason for the formation of high As groundwater. High As groundwaters were characterized by moderate reducing conditions, and the reductive dissolution of Fe(III) hydroxides led to the release of the adsorbed As into groundwater. Additionally, As desorption was another process to mobilize As under the con-ditions of elevated pH and/or high HCO3?. This study provides an insight into relative contribution of anthro-pogenic activities and hydrogeochemical conditions to As enrichment in groundwater, and highlights the necessity in protecting low As groundwater highly vulnerable to human activities in high As-groundwater areas.