A broad array of consumer and medical products employ billionths-of-a-meter scale silver particles as embedded disinfectants. A study now suggests that if those nanoparticles get loose and into the body, they might wreak havoc with the human immune system. Documented effects occurred at very low concentrations — levels as minute as parts per trillion or even, sometimes, one-thousandth that much (i.e. parts per quadrillion).
Perturbing immunity could, of course, be very bad.
(via Robot Wisdom)