I’m surprised we have not seen it yet. But the terrorist do not need radioactivity. 10 lb of mercury (about a pint) would contaminate 1800 acre feet or drinking water or about 2.3 billion liters. Drones are a serious safety problem because a 10lb payload flying 1000 feet above security fences and guards adds a new dimension to domestic terrorism.
“10 lb of mercury (about a pint) would contaminate 1800 acre feet or drinking water or about 2.3 billion liters. “
Your math is decent but the rest not so.
Ingesting elemental mercury is relatively harmless.