It depends on the coal, the scrubbing technology, and Mercury spread over larger areas, would be even more insignificant than without those considerations.  With a concentration of such materials in landfills however... ya know?

Buuuuut... Probably doesn't matter much anymore anyway. Edison invented the light bulb.. Upton UN-invented it, and the remaining builds are done in Mexico until a complete ban takes effect soon.  Then all the mercury in China will be headed our way..