I recall reading the story of the divers who discovered the U-boat off the coast of NJ. For a brief period of time, they thought they had discovered this mercury-carrying sub. At first they thought they'd be rich, till they realized how dangerous the material was.
Mercury is indeed poisonous, but it is not so bad as the alarmists and lawyers make of it. It generally pools together and lends itself mightily to being picked up. I've handled it a great deal, and I'm still very much intact. One does need to be cautious of the vapors. A mask takes care of that. In cold water, there would be very little danger from the stuff. Alarmists. We could do quite well without all of the fear mongering. I put this in the same category as the danger level schools assign to one inch long GI Joe weapons.