The World Health Organization (WHO) has referred to the situation in Bangladesh, where an estimated 60 million people are affected, as "the largest mass poisoning of a population in history."

In the May 28 issue of the journal Science, researchers from Stanford University, the University of Delaware, and Columbia University review what scientists understand about this groundwater contamination crisis and offer solutions for the region, which spans Bangladesh, Cambodia, China, India, Myanmar, Nepal, Pakistan, and Vietnam.

Holly Michael, assistant professor of geological sciences in the College of Earth, Ocean, and Environment at the University of Delaware, is a co-author of the article, with Scott Fendorf from Stanford and Alexander van Geen from Columbia University. Fendorf received his doctorate from UD in 1992 and is now chair of environmental and Earth system science at Stanford.

Michael earned her doctorate from the Massachusetts Institute of Technology and joined the UD faculty in 2008. She traveled to Bangladesh to study the groundwater contamination problem firsthand during her postdoctoral training with the U.S. Geological Survey.

Arsenic occurs naturally in the Earth's crust. Tasteless, odorless, and colorless in solution, the element is a known carcinogen and can be detected in water only through testing.

The source of South Asia's arsenic contamination is the Himalaya Mountains. Minerals from rocks, eroding coal seams, and sediments contain arsenic and are carried into the major rivers that flow out of the mountains, including the Indus, Ganges, Brahmaputra, Irawaddy, Meghna, Mekong, and Red rivers. The flat, low-lying floodplains of these major rivers are the areas affected by groundwater contamination.

A logical solution is to dig deeper wells to reach uncontaminated aquifers for supplying safe drinking water. However, farmers also want access to this water to irrigate their rice paddies. And that's a problem, according to Michael's research.

In 2008, Michael showed through numerical modeling of groundwater flow in the Bengal Basin that an uncontaminated domestic well more than 500 feet (150 meters) could remain arsenic-free for at least a thousand years.

However, she projected an entirely different scenario for deep irrigation wells, which use mechanized pumps instead of hand pumps to bring groundwater to the surface. The high volumes of water drawn by these irrigation systems induced a much faster downward migration of arsenic-contaminated surface water into the deep aquifer.

"To protect drinking water from arsenic contamination, we recommend that deeper wells only be used by individual households for drinking water and not for crop irrigation," Michael says.

In addition to preserving deep wells specifically for drinking water, she and her co-authors also recommend these measures:

+ Reinvigorating well-testing campaigns by governments and international organizations.

+ Better use of existing geological data and the compilation of test results to target zones that are low in arsenic for the installation of community wells.

+ The re-testing of tens of thousands of deep wells, particularly those that have been used for both domestic and farming purposes.

+ The choice of mitigation option can be situation-dependent: filters or other alternatives may be the best choice in some areas.

"Obviously, arsenic-contaminated drinking water is a huge problem from a human health perspective," Michael says. "We've shown that there are some viable options in South Asia, but there is much more that we need to understand."

Currently, Michael is working to model arsenic transport, how it may move in the future in the aquifer system in Bangladesh. She also is working with the World Bank on a study of groundwater sustainability in Bangladesh related to water supply and vulnerability of coastal groundwater to sea-level rise.

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