Kobold

Kobolds are a race of creatures originating from Germanic folklore, where they were goblin-like malevolent spirits who were believed to haunt mines, occasionally leaving nasty surprises in the form of worthless, poisonous metal - the element we now know as "cobalt". The ore is naturally found as sharp shards, bonded with arsenic oxide. The shards are sharp enough to penetrate boots and feet, hurting miners and making them sick just as if they were poisoned caltrop traps left by kobolds. A "cobalt bomb" is a proposed nuclear weapon designed to poison a large territory with super-radioactive cobalt dust, making the target area uninhabitable for 105 years. The (relatively) short half-life makes it especially deadly, but possible for your great-grandchildren to recover the empty territory. So watch out for "kobold bombs" or "magic missiles".