Yes, I've wondered about this.
I certainly remember a Harrier crash in Denmark, the first carbon winged one we lost, IIRC. An environmental hazard zone of some sort was placed around it; I remember reading an article about it in Air Clues by the chap in charge of the clean up.
It all went quiet after that and despite a few others being lost the same fuss never seemed to be made about the subsequent crash sites.