Buildings are made of things like lead and asbestos, blowing small bits of a building over a huge radius seems like a likely hazard. Plus, whatever the hell the bomb is made of.
Ah, I see. Well, that's kind of true, but it's like saying that earthquakes cause cancer, because when the building collapses in an earthquake, it also spreads things like asbestos into the air. I mean, it's still true, but it's so much a smaller effect than the other problems, it's pretty much ignored.