for National Geographic News
Microscopic organisms that get their energy by inhaling metals in the ground play a key role in the arsenic poisoning of drinking water for millions of people in Bangladesh and the Indian state of West Bengal, according to a new study.
Researchers hope that the finding will shed light on how the drinking water came to be so heavily laced with arsenicand that, in turn, it is hoped, could yield a way to reduce the level of the toxin.
Cited by the World Health Organization as the "worst mass poisoning in human history," as many as several million wells in India and Bangladesh became contaminated with the poison in the early 1990s. The poisoning remains a grave threat to those who continue to drink and irrigate with the water today.
Exposure to high levels of arsenic can cause cancers of the skin, bladder, kidney, and lung, and diseases of blood vessels of the legs and feet. It may also contribute to diabetes, high blood pressure, and reproductive disorders.
"Some researchers have estimated that two-thirds of the population in Bangladesh are at risk for chronic arsenic poisoning," said Willard Chappell, an emeritus professor of environmental sciences at the University of Colorado at Denver and expert on arsenic.
For the past decade, research teams from around the world have tried to determine why arsenic is present in such high concentrations in the Bangladesh and West Bengal aquifers. That knowledge would help them identify areas of high risk and develop appropriate remediation strategies.
Reporting in the July 1 issue of the science journal Nature, an international team of researchers indicts bacteria for the rising arsenic levels.
"When we found maximum rates of arsenic mobilization, we found signatures for known metal-reducing bacteria including a commonly found iron-reducing bacteria," said John Lloyd, a microbiologist at U.K.'s University of Manchester. Lloyd led the research team.
Metal-reducing bacteria "breathe" metals such as iron to get energy from their food, in the same way that we humans breathe oxygen to break down our food. The bacteria breathe by passing electrons onto metals, which changes the characteristics of the metals. Scientists refer to this as metal reduction.
Derek Lovley, a microbiologist at the University of Massachusetts, Amherst, said the University of Manchester-led study definitively shows what many scientists had suspected.
"The paper puts together components that were known individually, but nobody had done that experiment with material from the [Bengal] aquifer before," he said. "It's important in that way. To speculate is one thing, it's another to definitively show it."
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