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Arsenic filter developed at IIT-Madras triggers debate

A water filter for removing arsenic developed at IIT-Madras received much publicity recently, but some experts are sceptical about the claims made.

They urge decision-makers to become aware of the limitations of these devices before hastening to install them on a massive scale using public funds.

Arsenic is toxic even at very low doses. Millions of people in India and Bangladesh are exposed to high levels of arsenic through groundwater used for drinking.

Indian Institute of Technology-Madras (IIT-M) chemist Thalappil Pradeep has claimed that his filter delivers arsenic-free water at five paise per liter. It uses a purification system that employs silver nanoparticles trapped in tiny “cages” made of chitosan — a biomaterial derived from the shells of crabs and lobsters.

“The claims made in the press articles are amazing,” Ashok Gadgil, Distinguished Chair of Safe Water and Sanitation, and Professor of Civil and Environmental Engineering at the University of California-Berkeley, told this correspondent in an email.

Sabyasachi Sarkar, a former chemistry professor at IIT-Kanpur, whose team had developed and patented such a filter in 2009, agreed. “Initially it may work for a few liters of water but sustaining it for days and safe disposal of the used filter are big challenges,” Sarkar said.

Assuming a modest arsenic concentration of three milligrams in one liter of ground water, the IIT-M “community filter” daily supplying 10,000 liters of drinking water will be loaded with three kg of arsenic in around three months, clogging it, Sarkar said. “Where will the used filter loaded with arsenic be dumped?”

If smaller versions of the filter, distributed to households, are randomly thrown away after use (like people now do with used batteries) they will pollute the local soil with more arsenic. “This will be consumed by people via vegetables grown in such infected soil,” Sarkar said.

“Undoubtedly, disposal of sludge rich in arsenic is a big problem,” noted Dipankar Chakraborti, former Director, the School of Environmental Studies at Jadavpur University, who has studied the arsenic problem for three decades. “I do not know how the IIT-Madras project is taking care of it.”

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