CAMBRIDGE, MA — Man-made ponds are a catalyst for arsenic contamination in Bangladeshi drinking water, according to a Massachusetts Institute of Technology (MIT)-led research team, MIT’s Department of Civil and Environmental Engineering reported in a November 16 news release.

The researchers said in a paper appearing online November 15 in Nature Geoscience that human alteration of the landscape, the construction of villages with ponds, and the adoption of irrigated agriculture have created a pathway for arsenic concentration underground.

Arsenic-contaminated drinking water has been poisoning and killing Bangladeshis over the last several decades. In 2002 MIT researchers studying what has been referred to by University of California professor of epidemiology Allan H. Smith as “the largest mass poisoning of a population in history” determined that microbial metabolism of organic carbon was mobilizing naturally occurring arsenic off soils and sediments, and that crop irrigation also was a contributing factor. However, the exact sources of the contaminated water had remained elusive until this latest research.

The research team, led by MIT Doherty Associate Professor of Civil and Environmental Engineering Charles Harvey and former MIT graduate students Rebecca Neumann and Khandaker Ashfaqu, has explained that ponds excavated to provide soil to build up villages for flood protection are the source of the organic carbon that now mobilizes the arsenic in their 6-square-mile test site. The carbon settles to the bottom of the ponds, then seeps underground where microbes metabolize it. This creates the chemical conditions that cause arsenic to dissolve off sediments and soils and into the groundwater.

The researchers also found that in their test area, which is flooded by annual monsoons, the rice fields irrigated with arsenic-laden water serve to filter out much of the arsenic from the water system, the MIT news release said.

It was in the 1980s that arsenic poisoning and its link to drinking water were first identified. That is about the time that a national effort was made in Bangladesh to switch from surface water sources for drinking and irrigation to groundwater sources to reduce the number of bacterial illnesses caused by drinking water. As a result, tube wells of about 100 feet were drilled, but it was found that the tube wells tapped into the arsenic-contaminated shallow aquifer.

According to Neumann, the findings suggest “that the problem could be alleviated by [drilling] deeper drinking water wells below the influence of the ponds or by locating shallow drinking wells under rice fields.” The researchers suggest that irrigation wells remain at the shallow level.

Harvey and a team of environmental scientists and physicians are making plans for a multi-year study that would provide deep wells for two villages in Bangladesh whose inhabitants suffer from arsenic poisoning, the release said, noting that the team would continue testing of the well water and hydrogeological modeling of the groundwater system. Data gathered there would be combined with a study of how the clean water affects the villagers’ health, placing special emphasis on the neurological development of children.

To read the full release, click here.

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