A report released by the UK Royal Commission on Environmental Pollution indicates that we might not know enough about nano-engineered materials for them to be widely used. In fact, the commission chair will not wear clothing that has nano silver in it until more study is completed.
Nano silver is an antibacterial particle that's used in a lot of clothing like socks. And while it is not thought that an individual wearing anything with this substance in it, would be harmed by it, it is the idea that the silver could potentially leave the clothing during washings.
This could make it so the silver leaks into the water supply, which would kill good bacteria and cause unprecedented problems. This commission wants to see more information about nanomaterials and full disclosure on new products. Even with these invigorated efforts, however, we still probably won't know the real effect of nano materials for twenty years.