3 March 2010
New concerns over nanosilver
by Kate Melville 
Purdue University scientists have found that when nanosilver - a nanoparticle growing in popularity as a bactericidal agent - is suspended in solution, its toxicity increases tenfold, causing birth defects and death in aquatic species. When the nanosilver was allowed to settle, the solution became several times less toxic but still caused malformations. The study, appearing in the journal Ecotoxicology, studied the effects of the nanoparticles on fathead minnows, an organism often used for toxicity tests on aquatic life. "When nanosilver was sonicated, or suspended, its toxicity increased tenfold," said Maria Sepúlveda, an assistant professor of forestry and natural resources at Purdue. "There is reason to be concerned." Sepúlveda exposed the fathead minnows to nanosilver at several stages of their development, from embryo to the point where they swim up from the bottom of their habitats to eat for the first time. Even without sonication, nanosilver caused malformations that included head hemorrhages and edema, and ultimately proved lethal.
Using electron microscopy, Sepúlveda was able to detect nanosilver particles measuring 30 nanometers (about 3,000 times smaller than the diameter of a human hair) or less inside the minnow embryos. "These nanosilver particles are so small they are able to cross the egg membranes and move into the fish embryos in less than a day," Sepúlveda explained. "They had a potentially high dose of silver in them." Nanosilver is growing in popularity as a component of many products. It is used to kill bacteria in goods such as odor-control clothing, countertops, cutting boards and detergents. Currently, there are few regulations for nanosilver's use in products. There has also been very little work done to estimate the current level of nanosilver being released into the environment. "Silver has been used in the past as an antimicrobial agent. It's a known toxicant to microorganisms," said co-researcher Ron Turco. "Nanosilver is being considered by the EPA for environmental exposure profiling, much like a pesticide." The researchers now hope to develop tests to determine nanosilver concentrations in the environment. "How are we going to know the risk unless we know the concentration of these particles?" Sepúlveda asks. Related:
Size matters! Nanosilver risks unknown, say watchdog group
Nanoparticle Laced Wastewater Could Compromise Treatment Plants
Brain can "tidy-up" nanojunk, say Swedish boffins
From Little Things, Big Conundrums Grow
Source: Purdue University
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