Bangladesh: ponds ’caused arsenic’ contamination, MIT study says

Man-made ponds may be responsible for widespread arsenic contamination of ground water affecting millions of people in Bangladesh, a new study says [1].

Rebecca Neumann hangs off the end of bamboo scaffolding built at the field site. Assisted by a man hired from a nearby village, she is connecting a tube that will run from the surface water in the rice field up to a higher point on the scaffolding. Photo: Sarah Jane White, MIT

Researchers in MIT’s Department of Civil and Environmental Engineering believe they have pinpointed a pathway by which arsenic may be contaminating the drinking water in Bangladesh, a phenomenon that has puzzled scientists, world health agencies and the Bangladeshi government for nearly 30 years.

The research suggests that human alteration to the landscape, the construction of villages with ponds, and the adoption of irrigated agriculture are responsible for the current pattern of arsenic concentration underground.

In 2002, a research team led by Charles Harvey, the Doherty Associate Professor of Civil and Environmental Engineering at MIT, had determined that microbial metabolism of organic carbon was mobilizing the arsenic off the soils and sediments, and that crop irrigation was almost certainly playing a role in the process. But the exact sources of the contaminated water have remained elusive, until now.

Around 25m people in the country have been exposed to arsenic through water. Experts have described the situation as the worst mass poisoning of a population in history.

Man-made ponds – often dug with the help of international aid agencies – were originally created to protects villagers from unclean water.

The arsenic enters water supplies from agricultural and industrial waste or from natural deposits in the ground.

A Bangladeshi farmer shows the effects of arsenic poisoning. Photo: BBC

Around two million people in Bangladesh suffer from arsenic poisoning. Chronic ingestion of small doses has been linked to cancer of the bladder, kidney, lung or skin, while large doses can kill immediately.

Arsenic contamination of ground water is a global problem and has occurred in other countries such as Argentina, Chile, China, India, Mexico, Taiwan, Thailand and the United States.

But the gravity of the contamination in Bangladesh is unprecedented. Millions of Bangladeshis knowingly poison themselves because there is often no alternative water source. Harvey estimates that the incidence of death from arsenic-induced cancer will rise to approximately 3,000 cases per year if consumption of contaminated water continues.

Scott Fendorf, a professor at Stanford University who studies arsenic content in soils and sediments along the Mekong River in Cambodia, says Harvey’s previous research, published in 2002, “transformed the scientific community’s outlook on the problem.”

The current work, he adds, has two big ramifications: “It shows that human modifications are impacting the arsenic content in the groundwater; and that while the rice cropping system appears to be buffering the arsenic, the ponds excavated to provide fill to build up the villages are having a negative impact on the release of arsenic.”

Harvard scientist and co-author of the study Rebecca Neumann said that arsenic contamination could be avoided by digging deeper drinking water wells below the ponds.

Charles F. Harvey. Photo: MIT

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. There they would combine continual testing of the well water and hydrogeological modeling of the groundwater system with a study of how the clean water effects the villagers’ health, placing special emphasis on the neurological development of children.

“There are all sorts of studies to show how arsenic hurts people. We’re trying to turn it around and show how removal of the arsenic will help them,” says Harvey.

[1] Neuman, R.B. … [et al.] (2009). Anthropogenic influences on groundwater arsenic concentrations in Bangladesh. Nature Geoscience. Published online: 15 November 2009 | doi:10.1038/ngeo685

Source: BBC, 15 Nov 2009 ; ScienceDaily, 15 Nov 2009; MIT, 15 Nov 2009