I always wonder about small acrylic hairs and such that float about the house. In a bright room just flex your jumper, there's thousands of these weird impurities, and I can't imagine they can be filtered out easily before or after getting into the lungs.
The biggest shocker is when you disturb loft insulation. They claim it's not terrible (specifically if undisturbed), but floating glass strands can't be all that nice.