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The allure of nanosilver

August 04, 2008|Margaret Woodbury | Special to The Times

A Remington electric shaver says nanosilver will decrease redness and irritation. The company AgActive touts that the SilverSure coating on its bedsheets will "fight against cross infection of superbugs such as MRSA [methicillin-resistant Staphylococcus aureus]." A website selling plastic food containers imbued with nanosilver reminds consumers that "a typical [hospital] infection can cost as much as $47,000 per patient to treat."

The website asserts that nanosilver will "improve blood circulation and metabolism" and "adds immeasurably to your well-being." And Helix curling irons are touted as a "natural bacteriostat" without any explanation of why bacteria on a curling iron may be problematic.

In September, the Environmental Protection Agency, concerned about a large number of nanosilver products claiming antimicrobial abilities, ruled that any device using silver to generate ions for the express purpose of killing organisms must go through a vetting process to determine that it poses no unreasonable risk to people and the environment.

At face value, the EPA ruling would seem to include any product using nanosilver as an antimicrobial; however, the EPA says that as a practical matter, only products that overtly claim to kill, destroy or mitigate pests will be targeted, requiring registration and vetting for hazard as a pesticide.

In March, the EPA fined a Southern California company, IOGEAR, $208,000 for making unsubstantiated antimicrobial claims about its nanosilver-coated computer mice and keyboards. The company has since stopped marketing the product as an antimicrobial or containing nanosilver, but it is under no obligation to stop putting nanosilver into its products. (IOGEAR declined to state if nanosilver was still an ingredient.)

A December 2006 report on nanoscale materials, prepared by the Food and Drug Administration, noted the proliferation of products using nanoscale silver and called for increased testing.

While the government and companies struggle to find a balance on this issue, the consumer is left with the option to buy nanosilver products or not.

"There are some pretty amazing claims that are being made, that these products will essentially cure anything," says Dr. Michael Bell, associate director for infection control at the federal Centers for Disease Control and Prevention. He says he is happy to have another weapon in the arsenal against bacteria. "But we need to do the studies to show benefit, and for whom -- and what downsides, if any, [there are] to using this [technology] on a wider scale."

If nanosilver is present in these products -- and no regulatory authority is testing them for content -- then it probably will kill 99.9% of germs present, says Dr. David Weber, an infectious disease physician and public health expert at the University of North Carolina in Chapel Hill. But no one has proved these consumer products cut infection rates, he adds. "MRSA primarily lives on skin and is mostly transmitted by direct touching. I've not seen any data that suggests if silver is sprayed onto a surface such as a computer or bedsheet that the risk of MRSA is reduced."

Normal silver metal is largely innocuous to people, says Sam Luoma, a researcher at John Muir Institute of the Environment at UC Davis who has studied nanosilver. It is commonly used in hospital water systems as an agent against Legionella, the culprit in Legionnaires' disease, and is bonded to hospital medical devices such as catheters that enter directly into arteries, cutting infection rates in patients. Even when it's ingested, silver readily reacts with chemicals in the body such as sulfur and is deposited harmlessly in cells' basement membrane, a supportive layer of collagen that also acts as a mechanical barrier.

"The big question with nanosilver is: Does it behave like regular silver?" Luoma says. Scientists don't yet know, because human studies on the substance are in their infancy.

Nanosilver, Luoma says, has a vastly increased surface area that may alter its ability to react and combine with other body chemicals, which in turn may allow it to bypass deposition in the basement membrane of cells.

Researchers also wonder if the nanosilver that is added into products such as computer mice and keyboards stays put in the devices or slowly sloughs off onto our skin. "Exposure might not necessarily be a bad thing, but I don't know that because I've yet to see a full characterization and assessment of risk," says Kristen Kulinowski, director of the International Council on Nanotechnology at Rice University in Houston.

In April, researchers from Arizona State University presented evidence at the American Chemical Society's national conference that nanosilver embedded into socks gradually released silver at rates that varied from product to product -- some socks gave up most of the silver in the first few wash cycles, others more gradually.

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