April 7, 2008

Also appeared in print Apr. 14, 2008, p. 10

ACS Meeting News

Toxic Socks

Silver nanoparticles intended to control odor release in the wash

Rachel Petkewich

Arizona State University researchers have found that socks impregnated with odor-fighting silver nanoparticles release the nanoparticles when washed. This study, the first to examine how nanoparticles are released from commercially available clothing raises concerns about silver particles leaching into wastewater and the environment.

Troy M. Benn, a graduate student at ASU, presented these results in the Division of Environmental Chemistry at this week's ACS national meeting in New Orleans. Details of the work, which Benn carried out with ASU professor of civil and environmental engineering Paul Westerhoff, will soon appear in Environmental Science & Technology.

Various nanoparticles are increasingly used to make clothing free of wrinkles and resistant to stains, but little is known about what happens to nanoparticles in the laundry. The study is significant because it examines whether such products release nanoparticles during use, Mark R. Wiesner, an environmental engineer at Duke University, said.

Benn and Westerhoff reasoned that the sock manufacturing process may control how much silver is released during washing because the amounts varied widely among the socks they tested.

Juan P. Hinestroza, assistant professor of fiber science at Cornell University, agrees. He said the varying amounts and morphologies of the silver released are indeed functions of different processes used to deposit the silver onto the textile material and the properties of the textile substrate. He hopes this study will motivate scientists to develop synthetic routes that take advantage of the properties of silver nanoparticles in textiles while preventing leaching into wastewater streams.

The ASU researchers shook six brands of socks each in one-half liter of distilled water with no detergent for one hour and then analyzed the effluent with electron microscopy. The socks contained up to 1,360 µg of silver per gram of socks, and released as much as 650 µg of silver as both ionic and colloidal forms. "In the environment, both ionic and nanosilver exhibit adverse effects to aquatic organisms, although through what appears to be different biological mechanisms," Westerhoff said.

The ASU researchers' model indicated that both kinds of silver would be trapped in biosolids in wastewater treatment facilities. They said increased use of nanoproducts could produce increased amounts of silver in these biosolids, which could limit the use of such biosolids as agricultural fertilizer. Benn added that the Environmental Protection Agency doesn't currently regulate silver levels in biosolids from wastewater treatment but does, for example, list maximum concentrations for drinking water. And in 2006, EPA officials announced that the agency would begin regulating as a pesticide the silver ions released in a washing machine that are intended to kill bacteria (C&EN, Dec. 4, 2006, page 14).

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