A subject that we have returned to on several occasions, arsenic-contaminated drinking water, could one day become a thing of the past thanks to the unexpected discovery of the magnetic properties of rusty nanoparticles.
Researchers at Rice University’s Center for Biological and Environmental Nanotechnology (CBEN) have developed a low-cost technology that can extract arsenic from drinking water. The discovery could save millions of people from untold suffering across India, Bangladesh, and other developing countries where thousands of wells are poisoned by arsenic salts. This issue was first brought to light by Dipankar Chakraborti of the University of Jadavpur whom I interviewed for The Guardian in 1995.
“Arsenic contamination in drinking water is a global problem, and while there are ways to remove arsenic, they require extensive hardware and high-pressure pumps that run on electricity,” explains Rice’s Vicki Colvin, “Our approach is simple and requires no electricity.” It involves nanoparticles of iron oxide that can be produced cheaply by “cooking” nothing more sophisticated than rust and vegetable oil. The resulting particles are smaller than a virus and have unique magnetic properties, says Colvin.
“Magnetic particles this small were thought to only interact with a strong magnetic field,” she explains, “Because we had just figured out how to make these particles in different sizes, we decided to study just how big of a magnetic field we needed to pull the particles out of suspension. We were surprised to find that we didn’t need large electromagnets to move our nanoparticles, and that in some cases hand-held magnets could do the trick.”
Iron can form bonds with arsenic, and Colvin’s group reasoned that they could extract arsenic from drinking water by simply adding their rusty nanoparticles, letting the iron gather up the arsenic ions and then removing the particles with a magnet. They have demonstrated that they can extract arsenic from water to well within the US EPA’s threshold for safe drinking water.
Colvin’s graduate student, Cafer Yuvez, has been working for several months to refine a method that villagers in the developing world could use to prepare the iron oxide nanoparticles. The primary raw materials are rust and fatty acids, which can be obtained from olive oil or coconut oil, Colvin said.
Chakraborti is less enthusiastic about the long-term outcome of arsenic clean-up technology of this kind. “Undoubtedly, this is one of the approaches for removing arsenic from contaminated water, like aluminum, hydrated ferric oxide, membrane, and ion exchanger. However, on the lab scale many techniques work but difficulties arise when it is applied in the field.”
Chakraborti is only too familiar with the political and bureaucracy that can stymie any technological development. “Development of such technology is only possible when a combination is made between bureaucrats, technocrats, and villagers with proper village level participation,” he adds.
In West Bengal alone there are more than 3 million treatment plants that were purchased from German and US companies. Chakraborti asserts that 92% of these plants lie inactive in the street unused. “To apply this technique in the field I want to be optimistic,” he says, “but my past experience is not sweet.”
Yavuz, C., Mayo, J., Yu, W., Prakash, A., Falkner, J., Yean, S., Cong, L., Shipley, H., Kan, A., Tomson, M., Natelson, D., & Colvin, V. (2006). Low-Field Magnetic Separation of Monodisperse Fe3O4 Nanocrystals Science, 314 (5801), 964-967 DOI: 10.1126/science.1131475