Several manufacturers are incorporating nano-sized particles of silver into socks to kill bacteria that cause odor. But does the silver stay in the socks? And what happens to it if it washes out? Arizona State University's Troy Benn tested a variety of socks containing nanosilver. He wrote in the journal Environmental Science and Technology that some socks released nearly all of their nanosilver within the first four washings.

Surprisingly, says Benn, "Others that contained a lot of silver in the sock didn't release any silver that was detectable." He says there must be some differences in the manufacturing process. "We assume there is a way to contain the silver within sock because we did see a large difference between different manufacturers of the sock material."

For someone with diabetes or a soldier in the field, says Benn, a sock that kills microbes and prevents infection could be critical, but for other people, "The question is whether the benefits really outweigh the potential environmental cost."

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