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High in the Himalaya
In the 1990s, scientists identified the source of the arsenic contamination: the Himalaya mountain range, where arsenic-laden rocks and sediments are carried downstream along four major river systems—Ganges-Brahmaputra, Mekong, Irrawaddy, and Red.

This naturally occurring arsenic is harmless until it reaches the river basins. There, bacteria in surface and subsurface sediments release arsenic from the solids to a soluble, toxic form that slowly works its way into the shallow aquifers below.

This process has been occurring for millennia—a discovery made by Fendorf and colleagues in Cambodia in 2008—but had little impact on human health until recently when people began tapping groundwater to avoid pathogen-laden surface water.

Deep contamination
That same year, Michael demonstrated that in Bangladesh, an uncontaminated domestic well more than 500 feet (150 meters) deep could remain arsenic-free for at least 1,000 years. But Michael projected an entirely different scenario for deep irrigation wells, which use mechanized pumps instead of hand pumps to bring groundwater to the surface.

“Holly showed that if you start drawing high volumes of water from an irrigation well, you create flow conditions that bring arsenic-contaminated water from above into the deep aquifer below,” Fendorf says.

While many Bangladeshis are justifiably concerned about the accumulation of arsenic in rice paddies, the amount that actually ends up inside a rice grain is small compared with exposure from drinking water, he adds. “For that reason, we recommend that deeper wells only be used by individual households for drinking water and not for crop irrigation.”

In 1999, Bangladesh launched a major nationwide campaign to test well water quality. Since then, thousands of households have drilled deeper wells, some reaching depths of 1,500 feet (450 meters).

“Most people would say that deep wells are a good option,” Fendorf says. “They’re not that expensive, and the water often has a similar temperature and taste. For all intents and purposes, it’s the same water, except deep aquifers aren’t poisonous.

“However, because water-flow patterns below ground are constantly altered by irrigation and other land-use changes, the authors recommended that all existing deep wells in Bangladesh be retested on a regular basis.”

Other solutions
Aside from Bangladesh and India, the majority of affected countries have aquifers that only reach depths of 300 feet (100 meters). Therefore, deep-water wells are not an option. In Cambodia, people have turned to filtration to remove arsenic from shallow groundwater.

“Many arsenic filters are quite effective at removing arsenic over the short term,” Fendorf says. “However, they should be tested regularly, which doesn’t always happen, and replaced when they begin to fail from disturbance or exhaustion.”

Some governments in the region recommend piping water directly to villages or homes, but that solution raises other health issues, Fendorf says. “Piped water usually comes from a surface source, like a river,” he explains. “The problem is that it often contains bacteria and other pathogens. It might go through a sand filtration system, but that’s often ineffective.

“We need to be thinking broadly about water options that are available and not focus on a single solution,” he adds. “In one village, a deep well might work great, in another village maybe it’s rainwater harvesting or water filtration. As scientists studying groundwater, we can help people most by predicting where wells should be placed, and whether those wells will remain clean over time, particularly as a result of irrigation and other land-use changes.”

Support for the study was provided by a Woods Institute Environmental Venture Projects grant and the Stanford Environmental Molecular Science Institute, American Geophysical Union, European Union Asia-Link CALIBRE Project, U.S. Geological Survey, U.S. Agency for International Development, U.K. Department for International Development, UNICEF, and the U.S. National Institutes of Health.

More news from Stanford: http://news.stanford.edu/

We can get a hint of the power coming from longer-term nanotech by seeing what is being discovered today on how to use some of the new materials becoming available.  Many of us have been intrigued with graphene, a one-atom-thick planar sheet of bonded carbon atoms.  It’s no surprise that exciting applications are being found already, such as Nanotechweb’s report on work in South Korea:

…Kwang Kim, In-Cheol Hwang and colleagues at Pohang University of Science and Technology have synthesised a new type of magnetite composite based on reduced graphene oxide (RGO). The hybrid material, which is superparamagnetic at room temperature, can remove over 99.9% of arsenic in a sample, and reduce its concentration to below 1 ppb – as measured by inductively coupled plasma (ICP) techniques.

The magnetite-RGO composite can be dispersed in water. Once it has adsorbed arsenic, it can quickly be removed from a sample using a permanent hand-held magnet (with a strength of 20 mT) within a fraction of a minute.

Probably you already known that arsenic is a natural contaminant in water in parts of the western U.S. and in south Asia.  This is a huge problem and causes very serious health problems.  Let’s hope this helpful use of graphene is just the start of a great career for this nanomaterial, first in simple applications like this one, and later as part of more complex molecular machine systems. (HT to Meridian Nanotechnology and Development News)  —Chris Peterson