Arsenic adsorption by sediments could help to limit contamination of deep groundwater, according to a study published online this week in Nature Geoscience.
Increased concentrations of arsenic are common in shallow groundwater in many parts of South and Southeast Asia. But there is concern that pumping of deep groundwater could lead to the intrusion of arsenic-rich water from above. Kathleen Radloff and colleagues injected arsenic-rich water into a deep aquifer zone in Bangladesh, and monitored arsenic concentrations following withdrawal of the water. They found that the concentrations of arsenic in the withdrawn water declined by 70% compared with that injected after just 24 hours, whereas the concentration of a tracer remained constant. They attribute the decline in arsenic concentrations to adsorption on sediments.
The authors then use a model to simulate groundwater flow in the Bengal Basin, using the experimental data. The simulations suggest that adsorption of arsenic by sediments extends the area over which deep groundwater can be used with a low risk of arsenic contamination.