April 9, 2008 -- The smell from your socks might not be the only toxic thing around. Silver nanoparticles, used for years to kill bacteria and eliminate odors in socks, food containers, medical dressings and even teddy bears, might be a threat to the environment, according to new research.
"People might not even be aware they are buying these things," said Troy M. Benn, an environmental engineer at Arizona State University in Tempe. Benn and his colleagues presented their findings this week at a meeting of the American Chemical Society.
Among an estimated 600 consumer products that contain nanomaterials, at least 20 percent contain silver nanoparticles.
The treated products can be effective since silver is known to have odor-fighting and antibacterial properties. But little is known about how these particles affect waterways once they pass through laundry drains.
To find out, the researchers bought six pairs of commercially available silver nanoparticle-treated socks. They soaked them in water and put them in a washing machine.
After as little as one washing, virtually all of the nanoparticles from two brands of the socks washed out. After four washings, two other brands lost just 1 percent of the silver nanoparticles. That suggested to researchers that it is the manufacturing process of the socks, not the nanoparticles themselves, that caused the silver to disappear down the drain.
The researchers tested waterways for two types of silver: reportedly harmless nanoparticle silver and harmful ionic silver. They found both.
Ionic silver in waterways kills fish and other aquatic creates when it enters their gills, but is harmless to humans.
The scientists raised concern about the overall level of silver, noting that the sludge and wastewater from the manufacturing plants is often sold to farms as fertilizer or dumped into waterways.
Increased silver concentrations could render bacteria used in water treatment plants less effective. Silver concentrations could also pose its own risks.
"With increased silver in waste water it could become so concentrated with silver that it could be classified as a hazardous waste," said Benn.
A hazardous level would be as much as 20 times what their results suggest.
The findings will be published in the journal Environmental Science and Technology.
Nanoparticles, silver or otherwise, should be treated like any other chemical, according to Challa Kumar, a nanotechnology researcher at Louisiana State University.
"They could be dangerous, you never know," said Kumar. "But we don't want to blame the nanoparticles for being toxic when it's not the nanoparticles but the manufacturing process that is the problem.
"But if the silver is getting leeched out then it is a matter of concern."
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