Interesting thoughts. I agree that soot on the ice is exacerbating the melting, and I don't know how much mercury is in the soot, or what it takes to turn it to ethyl mercury which is the dangerous form. I do know that the fish near the poles are the least contaminated--that has been tested a lot--so it's not in the water and food chain as much up there yet. Your theory could be true. We'll know as soon as the polar ice caps melt.