I get the feeling that Moscow is about to get -more- than leveled if Vlad’s comments about needing a hazmat suit is any indication.
Well, given that if Arkady drops it then it'll mean his death and the deaths of many others, and that he needs a MOPP suit, I don't think that it would be a nuclear weapon; for one thing, nuclear weapons don't need such full protection to be handled as they aren't too radioactive, and the Stalingrad government wouldn't bother with giving him hazmat gear just because otherwise he'd get cancer in twenty years. Plus, a nuclear weapon would be fine even if it was dropped, most likely; they have to be built to handle accidents such as this, as there'd obviously be rushed handling resulting in drops in a total thermonuclear war.
No, rather than nuclear weapons, I think this is either chemical weapons or biologicals.