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With ultra-tiny silver particles turning up in everything from toothpaste to plastic food containers, researchers are eager to understand any potential impacts on people, animals or the environment. But can they get there when the substance itself is so dynamic?
Robert MacCuspie, a research chemist at the National Institute of Standards and Technology, is exploring how even minor changes in the dilution, preparation or storage of nanosilver can make a big difference in how the material behaves. Understanding those changes — and characterizing their differences — is a crucial step in vetting the substance for safety.
MacCuspie spoke about those challenges recently to students at the University of New Haven’s Tagliatela College of Engineering. He reminded them to, above all, “do good science” when working with newfangled materials.
For example, his team found that storage conditions made a big difference in the condition of the super-small nanosilver, which has a tendency to agglomerate, or clump together into larger particles. When stashed away in the dark, MacCuspie said, only 3 percent of the nanoparticles were lost over a three-month period.
But when the nanoparticles were stored in “regular light,” he said, up to 40 percent were lost.
These changes could make a big difference in trying to suss out whether and how nanosilver might pose a danger. While silver has been used for centuries — and studies suggest nanosilver has been around just as long—there are concerns about the growing use of nanosilver, typically as an antimicrobial agent.
Studies show that when clothes impregnated with nanosilver are washed, some of the substance comes out in the water. Nanosilver has also been found in end-stage sewage sludge.
Late last year, the U.S. Environmental Protection Agency approved the first nano-based pesticide, which uses nanosilver. While that approval is time-limited and requires additional safety testing in the interim, the Natural Resources Defense Council filed suit in January to force the EPA to take the product off the market. Several other advocacy groups recently filed their own brief of support in the case.
Nanotechnology leverages the often-unique properties of super-small particles (a nanometer is a billionth of a meter) to create products with amazing qualities. These materials can make better batteries or lighter and stronger bike frames, as well as new medical instruments and medicines that can save lives. They’re increasingly common in consumer products, from “mineral-based” sunscreens to stain-repellent pants to boat paints that resist algae growth.
Nanomaterials are believed to hold great promise for a wide variety of applications. Their ultra-tiny size also gives them different properties; scientists are struggling to figure out whether that can make them dangerous in the process, and how and why it happens.
MacCuspie said the debate among nanosilver safety researchers right now is between “hypothesis testing,” which is basically exploring the worst-case scenario by using massive amounts of the substance, and testing that’s aimed at simulating real-world conditions.
“As a field, we’re really trying to do our best to meet in the middle,” he said.
Obviously, MacCuspie said, understanding the potential risk of a product — which is basically balancing the toxicity of a substance against the level of exposure — is crucial. If the exposure is the equivalent of a thimbleful of nanosilver in a railroad car full of another, safe, substance, that much less of a concern.
But given limited time and resources, it’s unlikely that researchers and regulators can test every consumer product.
Working from a common sense of what nanosilver is would make evaluating toxicity questions easier, MacCuspie said. If policymakers within federal agencies see 20 papers saying nanosilver is toxic, and 20 papers saying it’s not, they’re left with a muddle.
“It might help to have some insight,” he said. “So then, that helps the regulators, too.”
