Study Shows Natural Processes Can Limit Spread of Arsenic in Water

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“Many people in Bangladesh and other parts of Asia have been poisoned by drinking groundwater laced with arsenic—not introduced by humans, but leached naturally from sediments, and now being tapped by shallow drinking wells. In recent years, to avoid the problem, deeper wells have been sunk 500 feet or more to purer waters—but fears have remained that when deep water is pumped out, contaminated water might filter down to replace it. Now, a study has shown that deep sediments can grab the arsenic and take it out of circulation—a finding that may help to keep wells safe elsewhere, including in the United States. The study, led by researchers at Columbia University’s Department of Earth and Environmental Engineering and the Lamont-Doherty Earth Observatory, appears in the current online edition of the journal Nature Geoscience.

“Lead author Kathleen Radloff and her colleagues injected arsenic-rich water into a deep aquifer in Bangladesh, then monitored arsenic levels over nine days. They found that arsenic fell by 70 percent after 24 hours, and continued to decline over the monitoring period. They attributed this to the arsenic sticking to the surfaces of deep sediment particles, in a process called adsorption.

“However, the process may have limits. The results were applied to a hydrological model of the Bengal Basin, the aquifer that serves most of Bangladesh and the neighboring Indian state of West Bengal. Using the model, the team found that the risk of arsenic contamination is limited when wells are restricted to household use, but increases significantly if they are also used for irrigation, even if much arsenic adsorbs to the sediment.”

Read more: EPonline