I always figured if we had to be afraid of an Islamic sourced nuclear weapon in the eastern US, the delivery mechanism would be something low tech like this. The vast numbers make it difficult, if not totally impossible, to check thoroughly. None of this is to say that this is what's actually happened here, but it's easy to imagine.
Fortunately for me, I now live upwind and far enough away so that I don't have to fear any immediate problems. It may seem a little nuts to worry about that sort of thing, but I think of it like insurance. If it costs you close to nothing to give yourself that extra protection, then why not?