Arsenic in drinking water with Lex van Geen

Tens of millions of people in South and Southeast Asia are drinking water from wells naturally contaminated by arsenic, an element that causes cancers. But testing wells for arsenic could help end the health crisis.

Lex van Geen: Someone drinking water containing 500 micrograms per liter arsenic – which is 50 times the WHO guideline – that person has a one in ten chance of dying from cancer of lung, liver, or bladder. It’s comparable to smoking your whole life.

Lex van Geen, of Lamont-Doherty Earth Observatory, co-authored a May 2010 paper on this subject in the journal Science. He told EarthSky arsenic is naturally released from sediment in the aquifer that feeds the wells. He said the first health symptoms were discovered in the mid 1980s. When scientists looked at the geology, they found that the distribution of arsenic is patchy. That means if your well is contaminated, it’s likely you live within walking distance of an uncontaminated well.

Lex van Geen: Some people are drinking water that’s high in arsenic without knowing it, and others are not aware that a neighbor may have a well that is actually low in arsenic.

Van Geen said that in the early part of this century, 5 million wells were tested in Bangladesh, the most heavily affected country. Approximately a third of the people who were drinking contaminated water before testing are no longer drinking it today, he said.

Lex van Geen: Testing wells, documenting the patchiness, and then encouraging people to go to those sources of water that are low in arsenic – that’s what has had biggest impact so far. But there still is a long way to go.

Van Geen told EarthSky that arsenic is an element that’s naturally released into the groundwater, when soil dissolves under certain conditions.

Lex van Geen: By and large, people think these are natural processes related to the reductive dissolution of ion oxides – rust, essentially – that coats sand grains. And the reason that’s a factor is because arsenic has strong affinity for that rust. As that dissolves, it releases the arsenic.

He said that although the issue has been studied for about 25 years, there are still lots of unknowns about how and why arsenic appears in the aquifer. But scientists do know that its presence varies widely.

Lex van Geen: If you consider villages individually, if you keep drilling, you will eventually reach a layer that is low in arsenic. Arsenic distribution varies with depth.

That means that deep wells, rather than the more common shallow wells, are less likely to contain arsenic, said Van Geen. His paper also makes the recommendation that farmers be discouraged from irrigating their rice fields with deep groundwater, as it may lead to the contamination of the deeper aquifers.

June 28, 2010

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