It depends on where in the world you are, really. Here in the States it usually gets tossed in a dump because we have the space. But sometimes, crowded, coastal cities (coughNewYorkcough) have been caught dumping into waterways. Here in Denver it's unlikely to reach the ocean - the dumps aren't near tributaries to the Colorado that I'm aware, which is really the only route, I think. Other parts of the world incinerate the trash in waste-to-energy plants. Etc. So ...yeah. Either way, it's better than blowing all over creation, killing wildlife.