U. OREGON (US) — Nanoparticles—long thought to be potentially hazardous to human health—have in reality been forming naturally for as long as humans have used silver, copper, and other metals for tools and jewelry.
Using high-powered transmission electron microscopes and a new approach that allows for the direct observation of microscopic changes in nanoparticles over time, researchers found that silver nanoparticles deposited on the surface of SMART Grids slides began to transform in size, shape, and particle populations within a few hours, especially when exposed to humid air, water, and light.
Similar dynamic behavior and new nanoparticle formation was observed when the study was extended to look at macro-sized silver objects such as wire or jewelry.
“Our findings show that nanoparticle ‘size’ may not be static, especially when particles are on surfaces,” says James E. Hutchison, professor of chemistry at the University of Oregon. “For this reason, we believe that environmental health and safety concerns should not be defined—or regulated—based upon size.”
“In addition, the generation of nanoparticles from objects that humans have contacted for millennia suggests that humans have been exposed to these nanoparticles throughout time.
“Rather than raise concern, I think this suggests that we would have already linked exposure to these materials to health hazards if there were any.”
The study, reported online the American Chemistry Society’s journal ACS Nano, concludes that any potential federal regulatory policies should allow for the presence of background levels of nanoparticles and their dynamic behavior in the environment.
Because copper behaved similarly, the researchers theorize that their findings represent a general phenomenon for metals readily oxidized and reduced under certain environmental conditions. “These findings,” they write, “challenge conventional thinking about nanoparticle reactivity and imply that the production of new nanoparticles is an intrinsic property of the material that is now strongly size dependent.”
While not addressed directly, Hutchison says the naturally occurring and spontaneous activity seen in the research suggests that exposure to toxic metal ions, for example, might not be reduced simply by using larger particles in the presence of living tissue or organisms.
The electron microscopes used in the study are located at the Center for Advanced Materials Characterization in Oregon in the underground Lorry I. Lokey Laboratories at the UO. The U.S. Air Force Research Laboratory and W.M. Keck Foundation supported the research. Glover’s participation also was funded by the National Science Foundation’s STEM (science, technology, engineering, mathematics) Fellows in K-12 Education Program.
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