Environmental Factor, November 2011, National Institute of Environmental Health Sciences
Superfund study shows arsenic mitigation strategies effective
First author Kathleen Radloff is one of several NIEHS-supported scientists at Columbia University whose research is helping reduce arsenic poisoning in Bangladesh, by limiting exposure at the source through education and intervention. (Photo courtesy of Kathleen Radloff)
Contaminated water in a shallow aquifer can penetrate into the deeper aquifer. Limiting water usage can reduce arsenic concentrations, by letting natural remediation take its course and slowing intrusion. (Diagram courtesy of Kathleen Radloff)
The use of shallow wells with elevated arsenic concentrations in Bangladesh and other parts of South and Southeast Asia has led to large-scale arsenic poisoning. Here, drillers assist the research team with building sampling wells. Local crews have been working with the team for more than a decade. (Photo courtesy of Kathleen Radloff)
Water from deep wells can be made safer from arsenic contamination by limiting how much water is pumped. This important new finding is based on an investigation of well usage in Bangladesh, a country known for large-scale arsenic poisoning, and has relevance in the U.S. where millions depend on private wells for drinking water.
In a study(http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1283.html) funded by the NIEHS Superfund Research Program (SRP), lead author Kathleen Radloff, Ph.D.(http://gradientcorp.com/people/talent.php?last=Radloff) , and her co-authors at Columbia University, the University of Delaware, and the University of Dhaka, Bangladesh, found that when water demand in Bangladesh was restricted to household use, the risk of contamination was significantly less than when irrigation water was also pumped from the deep aquifer. Increased pumping of deep groundwater can lead to the intrusion of arsenic-laden water from a shallower aquifer above.
The need for better monitoring
Elevated arsenic concentrations are common in wells across South and Southeast Asia, and their role as a primary source of drinking water has led to extensive arsenic poisoning in the region. To lower exposure, the use of deep-water wells, often drilled to depths of 500 feet or greater, has increased considerably. However, Radloff is concerned that the additional strain on deep aquifers is leading to higher levels of contaminants.
“Increasing water demand, such as for irrigation purposes, means that the water that remains in the ground is more likely to become contaminated,” said Radloff in a press release(http://www.ldeo.columbia.edu/news-events/natural-processes-can-limit-spread-arsenic-water-says-study) issued by the Lamont-Doherty Earth Observatory at Columbia University. “Where water demands are increasing, monitoring of water supplies also needs to increase - not only in Bangladesh, but also in the U.S.”
Furthermore, the researchers discovered that arsenic concentrations in deep aquifers declined over time, in a process called adsorption, where the arsenic attaches to naturally occurring sediments. This was revealed when arsenic-rich water was injected into a deep aquifer in Bangladesh. Within 24 hours, the researchers found that arsenic concentration had fallen by 70 percent, and continued to decline over a nine-day monitoring period.
Implications for well water in the U.S. and elsewhere
“This research carries far-reaching public health significance, not just for the people of Bangladesh, but also for those affected globally by arsenic exposure,” said William Suk, Ph.D., director of the SRP. The United States Geological Survey reports that 43 million Americans depend on unregulated private wells for their drinking water, and nearly a quarter of this country's wells have at least one contaminant that exceeds levels considered safe by the U.S. Environmental Protection Agency (EPA), including arsenic. The EPA also reports that arsenic is the second most common contaminant at Superfund sites.
According to Radloff, the effects of this contamination are more apparent in Bangladesh, where the concentrations are higher, but the same processes can occur in the United States. “Our estimates can be applied to aquifers with similar geochemical characteristics here in the U.S.,” she said. She cited the Mahomet aquifer in east-central Illinois as an example. “Farming demands have drastically altered water flow conditions and there are good reasons to expect arsenic concentrations might change more than they have in the past.”
Radloff, who completed her doctorate in Earth and Environmental Engineering at Columbia University, is now an environmental engineer for the private consulting company Gradient.
Citation: Radloff KA, Zheng Y, Michael HA, Stute M, Bostick BC, Mihajlov I, Bounds M, Huq MR, Choudhury I, Rahman MW, Schlosser P, Ahmed KM, van Geen A(http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1283.html) . 2011. Arsenic migration to deep groundwater in Bangladesh influenced by adsorption and water demand. Nat Geosci; doi:10.1038/ngeo1283 [Online 9 October 2011].
(Rebecca Wilson is an environmental health information specialist with MDB, Inc., a contractor for the NIEHS Superfund Research Program and Worker Education and Training Program.)