The allure of nanosilver
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 www.nanosilverproducts.com 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.
If traces of nanosilver do slough onto our skin, it isn’t clear if they would then have the ability to penetrate deeper, perhaps entering our circulatory system. “At this point, there is no consensus,” says Vladimir V. Murashov of the National Institute for Occupational Safety and Health in the U.S. Department of Health and Human Services. “In some studies, nanoparticles do not penetrate beyond the top-most layer of skin; other studies show that nanoparticles . . . can penetrate.”
In one of the few human studies to date, a case report published in 2006 in the Journal of Trauma: Injury, Infection and Critical Care looked at using nanosilver in the wound dressings of a burn patient. It found some risk of liver toxicity from the dressings, which were applied to a 17-year-old boy who had suffered burns on 30% of his body.
After one week of treatment, the boy’s liver enzymes were elevated and he’d developed a grayish discoloration of his skin that is associated with silver toxicity. Blood and urine silver levels were elevated. When nanosilver treatment was aborted, his clinical symptoms retreated but blood levels of silver remained elevated for weeks.
Another 2006 study conducted in the burn unit of Wenzhou Medical College in China reported significant benefit to using nanosilver in wound dressings. A group of 191 patients with second-degree burns was randomly divided into three groups -- those treated with silver nanoparticle dressings; those treated with an antibacterial topical cream containing sulfa antibiotics and a standard-sized silver compound; and those with petroleum jelly gauze dressings.
Wound-healing time was significantly shorter for patients treated with nanosilver dressings and whose burns were more superficial. Patients with deep second-degree wounds had similar healing rates if treated with either nanosilver or topical antibacterial cream. (Those who received petroleum jelly gauze dressings fared the worst.)
The majority of studies have been conducted in animals -- finding, for example, that rat liver cells in culture show higher toxicity to nanosilver particles than other types of nanoparticles such as titanium dioxide or iron oxide, and that female rats, after oral exposure to nanosilver, had a twofold increase over male rats in tissue accumulation of nanosilver in their kidneys.
“We’re just beginning to understand how nanosilver will interact with living organisms,” Kulinowski says. “I would like to see more studies that are directly applicable to human health.”
If risks of nanosilver are unclear, it’s worth asking if adding it to products is necessary -- if we need to so scrupulously sanitize our environment.
Microbiologist Charles Gerba of the University of Arizona says he finds the idea of nanosilver coatings tantalizing. “We’re in an era where the development of self-sanitizing surfaces would be good,” he says. MRSA, he adds, tends to collect on vending machine buttons, which are rarely cleansed, so coating those and other high-touch areas with nanosilver might make good sense.
Other microbe specialists aren’t convinced.
“The entire planet is covered quite richly with infectious material,” says the CDC’s Bell. “Are there things we can do to reduce the burden of infectious matter and, frankly, does it matter?”
Adds Weber, “Do I think putting silver on the handle of a household telephone will decrease infection rates? The answer is, probably not.”
So perhaps having a knife coated with nanosilver might cut the chance of cross-contamination of salmonella if lazy kitchen practices take root and the knife is not washed thoroughly between chopping the raw chicken and the salad. And if you share a computer, then you may increase your risk of illness if there’s a flu outbreak.
But until the safety and efficacy studies come in on nanosilver, perhaps, Kulinowski and Weber suggest, it’s best to whip out an alcohol wipe and swab that keyboard and mouse. After all, Weber says, there are 100 years of safety data on using alcohol as an antiseptic.
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