Warning: Toxic nanoparticles in your socks

Scientists are raising concerns on toxic nanoparticles being woven into fabrics as "odor neutralizers" in socks and as antibacterial agents in bandages.

Silver nanoparticles used in fabrics were found by researchers to leach out after just a few washings, releasing harmful toxins shown to harm aquatic life. While the effects of silver nanoparticles on humans have yet to be established, the researchers recommended that the Environmental Protection Agency (EPA) require manufacturers to bind silver nanoparticles to fabrics to prevent leaching during washing. They also recommended labeling products as containing potentially harmful nanoparticles.

"Nanosilver is used in products because it produces ionic silver when exposed to moisture—it is this ionic silver that is well known to have antimicrobial effects as well as detrimental effects to aquatic organisms," said Troy Benn, an environmental engineer and doctoral candidate at Arizona State University (ASU). He performed the tests with Paul Westerhoff, an environmental engineering professor at ASU.

Benn and Westerhoff purchased socks and bandages from six different manufacturers to test whether the silver nanoparticles leached out during washing. Testing consisted of soaking socks in distilled water, shaking the contents for one hour, then testing the water for the presence of toxic ionic silver as well as for silver nanoparticles. The toxicity of silver nanoparticles has yet to be established by EPA.

The results showed a wide spectrum of toxicity, with some socks releasing both toxic ionic silver and silver nanoparticles, and some retaining silver. The worst brands released all their silver after just a few washings; others gradually released it while some brands retained silver nanoparticles through repeated washings.

The scientists concluded that it should be possible to require fabric makers to use processes that retain silver nanoparticles. They added that is it up to the EPA to specify a requirement.

"If we know that some of these particles are leaching nanomaterials into the environment, we may put some kind of policy in place to encourage manufacturers to redesign their products to release fewer nanoparticles," said Benn.

Effect on humans
Ionic silver reduces odor in fabrics by suppressing bacteria. In bandages, ionic silver suppresses the growth of bacteria that can cause skin infections. However, the abrasions being protected by bandages can also serve as a conduit to the bloodstream, where ionic silver could have toxic effects on human microorganisms.

"It is unknown if the nanosilver can penetrate through the skin. Studies have shown that healthy skin is an efficient barrier to nanomaterials, but openings in the skin may allow nanoparticles to enter the body," Benn said. "Research also indicates that microorganisms may develop an immunity to silver. Therefore, we may be making some microbial communities more difficult to control."

Silver nanoparticles may also inhibit the growth of beneficial microbes in the environment, Benn added.

Westerhoff and Benn presented their findings this week at the national meeting of the American Chemical Society in New Orleans.

- R. Colin Johnson
EE Times