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The (Nano)Silver Bullet

Your toothpaste may be a pesticide. So might your electric razor, your computer keyboard, and your child’s teddy bear. These products, and scores of others, combine one of the world’s oldest disinfectants--silver--with one of its hottest new industries: nanotechnology. The manufacturers of these products boast that they fight bacteria, molds, and fungus. Therefore, according to the U.S. Environmental Protection Agency (EPA), these products may be pesticides. Though this may sound like a Rush Limbaugh story line about paranoid eco-Nazis, the reality is that we’re lacing ordinary household goods with known toxins. And until scientific testing and federal laws catch up with this new technology, we may be exposing the environment--and our own bodies--to untold harm.

The new science of nanotechnology allows manufacturers to use materials that measure between 1 and 100 nanometers. (A nanometer is a billionth of a meter, or roughly 1/100,000 the width of a human hair.) While nanoparticles can occur naturally and by accident--in diesel soot, for example--it’s only in the past decade or so that scientists have widely learned to create and manipulate them. Many nanotechnologies use nano-versions of common materials, like carbon and silver. These tiny particles take on almost magical qualities: Insoluble materials can become soluble, nonconductive substances start conducting electricity. Nanomaterials can be orders of magnitude more powerful than the same substance at normal scale. Myriad green applications are in the works, and medical miracles are promised.

For now, though, nanotech is largely used in industrial and consumer products, from cosmetics to fleece to plastic food containers. Often, the benefits are more convenient than essential: White sunscreen turns clear on the skin; fabrics resist stains and static; leftovers stay fresh longer. There are over 600 nano consumer products on the market today--up from about 200 two years ago, when the Washington-based Project on Emerging Nanotechnologies (PEN) started keeping an inventory--with three to four new products added weekly.

But those products raise multiple health and environmental questions. Do nanoparticles stay put, or do they liberate themselves? What happens if they get into the human body or the environment? Silver, for example, will kill both harmful and beneficial microbes. But little is known about the effects of nanosilver--the most frequently cited nanoparticle in PEN’s consumer-products inventory, showing up in more than 20 percent of the entries. The same is true for other nanomaterials, even ones that are ordinarily harmless. Animal studies show that because nanoparticles are so small, they can travel deep into the lungs, passing into the bloodstream and other organs. They may be able to penetrate the skin. And they’re much more chemically reactive, often in unpredictable ways. While consumer industries are racing to develop uses, environmental and health research lags far behind.

Troy Benn, a doctoral candidate in environmental engineering at Arizona State University, recently conducted one of the first experiments to test the properties of nanoparticles in consumer products--with results that do not bode well for their safety. Benn and his professor, Paul Westerhoff, simulated washing seven varieties of socks advertised as using antimicrobial silver nanoparticles to help kill foot odor. When they tested the wash water, one pair--hunting socks from ARC Outdoors--lived up to the boast of its website: “It won’t wash out.” All the other nano-socks leaked silver.

That’s a bummer for the buyer who expected long-lasting fresh feet. But it may be even worse for the wildlife that literally lives downstream. For years, wastewater treatment plants have worked with industries to limit the silver they dump down the drain. “Now, all of a sudden, we see these consumer products with silver,” says Ben Horenstein, an official at an Oakland sewage treatment plant who is active in the National Association of Clean Water Agencies. “Our ability to treat the wastewater is in jeopardy because of these antimicrobial products. … The water bodies we discharge to have aquatic life, and silver can adversely impact that.”

The EPA, still struggling over how to regulate nanoparticles, ruled that equipment that generates ions to kill microbes is a pesticide, which must be registered under the Federal Insecticide, Fungicide, and Rodenticide Act. But the law applies only if companies advertise the products as having antibacterial or other public health advantages. This ignores the multitude of products that fall outside these lines--potentially including Benn's nanosilver socks, since they claim to prevent odors but not disease. The obvious weaknesses of using a farm-oriented law that originated in 1947 to regulate 21st-century technology illustrate the pressing need for policymakers to adopt nano-specific rules.

Given that nanosilver may be more toxic, molecule for molecule, than ordinary silver, it’s unclear whether existing pollution laws provide enough protection. Nationally, the only law specifically governing nanotechnology is in Berkeley, California, which requires industries to report on which nanomaterials they’re using. The EPA only has a voluntary reporting program. And while the National Institute for Occupational Safety and Health has issued recommendations for protecting people working with nanoparticles--who are the most likely to be exposed--it has has no enforcement power.

Through a spokesman, the EPA says it “takes any unverified public health claims”--nano or not--“very seriously and can pursue the appropriate action.” But Horenstein sees “a gap in terms of regulatory oversight. As more and more of these things are coming on the market,” he says, “how much understanding do we want to have in advance, versus playing catch-up?”

The regulation gap stems in part from the data gap. Proposed legislation, supported by the Project on Emerging Nanotechnologies and big industry players like Dupont, would require that at least ten percent of federal nanotech spending go toward environmental, health, and safety research--compared to less than five percent currently. Some environmental groups would go further. Friends of the Earth, for example, calls for a moratorium on personal-care products containing engineered nanomaterials until they’re proven safe.

Benn and Westerhoff's findings provide scientific support for a cautious approach. And while nanotechnology could bring enormous benefits--from cheap, clean energy to better cancer treatments--their stinky-socks experiment suggests that some nanotech applications may not be worth the risk.

Carole Bass is a Connecticut-based journalist and a 2008 fellow of the Alicia Patterson Foundation, reporting on toxic exposures on the job.

By Carole Bass