Nanosilver is used to kill harmful bacteria in food storage containers, shoe liners, washing machines and even bandages. Particles of nanosilver and other nanomaterials can be as small as one-millionth the size of a pinhead. However, the EPA, citing pressure from silver industry workers and environmental groups such as Natural Resources Defense Council, is investigating whether silver ions could pose an environmental threat by killing beneficial bacteria in the environment, or even harming humans. The agency also received a letter from Chuck Weir, chairman of a California wastewater treatment plant advisory group known as Tri-TAC, which claimed "silver is highly toxic to aquatic life at low concentrations and also bioaccumulates in some aquatic organisms, such as clams."

Silver was brought under close EPA scrutiny when washing machine manufacturers began making models that were lined with silver ions or sprayed them onto the clothes as an antibacterial agent. Last year, the EPA decided that the machines should not be regulated under the Federal Insecticide, Fungicide and Rodenticide Act, since they were considered devices rather than pesticides. Recently, however, the agency re-examined its decision and reversed it.

"We took a second look at the release of silver ions, and it was very clear that this is a pesticide and not a device," Jim Jones, director of the EPA's Office of Pesticide Programs, told the Washington Post. "Our original determination proved not to be a correct one."

Under the regulations, any silver product that claims it has antibacterial properties must prove the product is safe to be released into the environment. Mike Adams, a consumer health advocate and proponent of colloidal silver, suggested the regulations might work better were they aimed at antibiotics and pharmaceuticals.