Water quality in S. Asia Scientists solve puzzle of arsenic-poisoning

The World Health Organization has blamed the arsenic for high rates of cancer in India, Bangladesh, Myanmar, Cambodia, and Vietnam.

In a news report on March 24 by Stanford News Service, Fendorf has solved the puzzle of how and why the natural arsenic was somehow working its way into the groundwater more than 100 feet below the surface, instead of remaining chemically trapped in the river sediments. Solving that mystery could have significant implications for policymakers trying to reverse the mass poisoning, said Stanford University soil scientist Fendorf maintains.

The culprits responsible for dissolving the arsenic turned out to be bacteria that live in the soil and sediment of the river basin, Fender and his team found. Arsenic flowing down the river from the Himalayas sticks to rust particles called iron oxides.

Upon reaching the river delta, these arsenicladen particles are buried by several layers of soil, creating an oxygen-free, or anaerobic, environment, the researchers found. Normally, bacteria use oxygen to breathe.

But in an anaerobic environment, they can use other chemicals, including rust and arsenic.

As the bacteria metabolize the iron and arsenic, they convert it to a form that readily dissolves in water.

Epidemiologists first identified arsenic poisoning in the 1980s in the Ganges-Brahmaputra Delta in Bangladesh. The sudden occurrence of the disease was linked to the increased use of wells for drinking water.

Fendorf suspected that the arsenic actually dissolved at a much higher depth, very close to the surface. Using a site on the Mekong River in Cambodia, digging wells at three different depths in a 20 square mile site, suspicions were confirmed.

"We found out that, sure enough, within the first 2 to 3 feet from the surface, arsenic was coming out of the solids-that is, the sediments transported down from the Himalayas-and into the water, and then it migrated down into the aquifer," Fendorf said. Aquifers are the source of drinking water for people who use wells throughout Cambodia, Bangladesh, Myanmar, India and Vietnam, the report says.

"As these sediments get buried very rapidly, the bacteria go through an anaerobic metabolism that dissolves the iron minerals and the arsenic with it," Fendorf said. "The arsenic goes into the water and the problem starts."

A team of scientists led by Stanford University soil scientist Scott Fendorf says bacteria cause the absorption of high levels of natural arsenic into groundwater in South Asia from the natural arsenic flowing down from the Himalayan mountains. The results are pub- lished in the latest issue of the journal Nature. The World Health Organization has blamed the arsenic for high rates of cancer in India, Bangladesh, Myanmar, Cambodia, and Vietnam. In a news report on March 24 by Stanford News Service, Fendorf has solved the puzzle of how and why the natural arsenic was somehow working its way into the groundwater more than 100 feet below the surface, instead of remaining chemically trapped in the river sedi- ments. Solving that mystery could have signifi- cant implications for policymakers trying to reverse the mass poisoning, said Stanford University soil scientist Fendorf maintains. The culprits responsible for dissolving the arsenic turned out to be bacteria that live in the soil and sediment of the river basin, Fender and his team found. Arsenic flowing down the river from the Himalayas sticks to rust particles called iron oxides. Upon reaching the river delta, these arsenic- laden particles are buried by several layers of soil, creating an oxygen-free, or anaerobic, environ- ment, the researchers found. Normally, bacteria use oxygen to breathe. But in an anaerobic environment, they can use other chemicals, including rust and arsenic. As the bacteria metabolize the iron and arsenic, they convert it to a form that readily dissolves in water. Epidemiologists first identified arsenic poi- soning in the 1980s in the Ganges-Brahmaputra Delta in Bangladesh. The sudden occurrence of the disease was linked to the increased use of wells for drinking water. Fendorf suspected that the arsenic actually dissolved at a much higher depth, very close to the surface. Using a site on the Mekong River in Cambodia, digging wells at three different depths in a 20 square mile site, suspicions were confirmed. "We found out that, sure enough, within the first 2 to 3 feet from the surface, arsenic was coming out of the solids-that is, the sediments transported down from the Himalayas-and into the water, and then it migrated down into the aquifer," Fendorf said. Aquifers are the source of drinking water for people who use wells throughout Cambodia, Bangladesh, Myanmar, India and Vietnam, the report says. "As these sediments get buried very rapidly, the bacteria go through an anaerobic metabo- lism that dissolves the iron minerals and the arsenic with it," Fendorf said. "The arsenic goes into the water and the problem starts."