They need to clean up the Sierra. Go to any river in gold country, pull up a clump of grass from the bank, wash out the dirt and mercury will probably be in the pan. I once washed out a pint of it from 5 five gallon buckets of fine dirt which had fallen through a long tom (the long tom was long gone but its path could be traced from the hydraulic diggings to where it ended at a cliff above the North Fork of the Yuba River).
Maybe that explains some of the brain damage in gold-mining country of Northern California.