Tiny silver particles in clothing may lead to pollution, research suggests

In the unknowns of emerging nanotechnology, researchers are wondering if the science behind trendy no-smell socks, underwear and hunting gear might create unintended consequences in the environment.

Just a few simulated washings, for example, can pull nanosilver out of new socks that rely on it for killing odors, researchers said Sunday. That action sets the substance free to travel into wastewater and perhaps into fertilizer.

That prospect underscores the importance of studying nanosized materials that are increasingly a part of clothing and medical, electronic, and other consumer products, said UC Davis professor Alexandra Navrotsky.

"As a society, we should be doing research on these effects ideally before products go to market, not after," said Navrotsky, who heads a campus nanomaterials research unit.

University of California, Davis, is competing for a five-year, $25 million National Science Foundation grant to create a center devoted to studying the environmental impacts of nanomaterials, so small they are measured in billionths of a meter.

The campus, which survived the first cut when 30 grant applicants where whittled to 10, could learn later this month whether it is among three semifinalists.

At nanoscale, the nature of things can change fundamentally; items can take on different shapes, colors, electrical charges – or toxicities.

UC Davis researchers want to explore what happens when such creations are released into the environment, and nanosilver is on the short list of substances the university would target first if it wins the grant, Navrotsky said.

In one study with mouse sperm stem cells, nanosilver was about 45 times more toxic than standard silver, said Jennifer Sass, a toxicologist with the Natural Resources Defense Council in Washington, D.C.

Nanosilver is more potent because, in proportion to its size, it has more surface area where chemical reactions can take place.

"There's more killing activity per less volume," Sass said.

For human health, though, she worries about cosmetics and lotions with nano-ingredients much more than the clothing that has incorporated scent-controlling nanosilver.

"Silver is not the most toxic thing to humans," Sass said. "If you're a microbe, you have to worry a lot about silver, and that goes to beneficial microbes on our skin that eat up dead cells and dead hair."

The fear is that once it is washed out of socks or other clothing, nanosilver might keep on killing, taking out beneficial microbes in soil, groundwater or streams.

"The reason it's in socks is it kills bacteria," said Troy Benn, an Arizona State University doctoral student who outlined his findings Sunday at the American Chemical Society's national conference in New Orleans.

Sock studies being done by Benn and professor Paul Westerhoff at Arizona State University are "going to be really helpful," Sass said, because some people have suggested nanosilver wouldn't wash out of clothing.

Andrew Maynard, who tracks emerging nanotech for the Woodrow Wilson International Center for Scholars, said the work sounded like "a very useful piece of research."

The Arizona State research appears to be the first effort to measure how much silver comes out in the wash and to simulate what might happen to it during wastewater treatment, both Maynard and Sass said.

Benn collected his research material by shopping online for socks whose makers claimed they contained nanosilver. He chose seven different types made by five companies.

Researchers soaked and sloshed the socks in distilled water for up to seven simulated washings and found big variations from brand to brand when they tested the water.

One sock released more than a milligram of silver after a few washings, in the form of both nanosilver and one of its better-understood relatives, ionic silver. Some released much less, and at least one sock left no silver at all in the water.

That might not be surprising, though, since Benn did other tests – breaking down a sock with acid and analyzing what was left behind – to establish that one "nanosilver" sock contained no silver when it reached his lab.

It's possible the material simply sloughed off during shipping and handling, he said in an interview before the conference, or it might never have been there at all.

The research, which is ongoing and hasn't been published, didn't stop with the wash.

Westerhoff and Benn then "spiked" the wash water with activated sludge from a wastewater treatment plant, in an attempt to roughly simulate what might happen next.

Almost all the silver settled into a clumpy mass of "biosolids," separated from liquid effluent during treatment.

More than half of the biosolids produced by California water treatment plants are spread as fertilizer, which can interact with soil microbes and runoff.

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