It doesn’t take much silver to kill household germs. That is why microscopically tiny particles of silver are showing up in all manner of products, from sneakers to air freshnerers. But just because they’re small doesn’t mean they’re not dangerous to the environment. A growing number of scientists and environmentalists are concerned about the impacts those nanoparticles have on bacteria, aquatic habitats and humans once the particles are flushed down the drain or end up in landfills. So the US Environmental Protection Agency has decided to regulate nanosilver.