“The diapers are very gross, horrible, but the shipping containers hold 100 percent of the smell,” assures Terracycle’s Albe Zakes. “We tested this by hiding them around the office and seeing if anyone noticed; they did not.” He may be joking, but the environmental dangers of dirty diapers are serious business, both in eco-impact and, Terracycle hopes, in profit potential. Disposable diapers take centuries to biodegrade. The average baby soils about 8,000 of them before toilet training kicks in, according to the EPA.