EPA's recently announced regulations on mercury from power plants will, in fact, do nothing substantial about the amount of this element in the global atmosphere. If they were really serious, they would ban volcanoes and forest fires, which are much larger sources.
Total annual releases of mercury to the atmosphere from such natural sources are about 5,200 metric tons per year. The world's volcanoes tend to concentrate along the Pacific Rim, where the great tectonic plates that define the world's continents are in flux, and in the mid-Atlantic, where continental drift is expanding the Atlantic ocean, opening up huge rifts that extend far beneath the surface. Forest fires tend to take place where there are forests-especially dry ones like those in the western U.S.
Data published in the refereed scientific journal Atmospheric Chemistry and Physics Discussions indicate that the amount of mercury released into the atmosphere by human activities-mainly from smelting of metals and combustion of coal-is about 2,320 tons, for a total atmospheric increment (natural + anthropogenerated) of a bit over 7,500 tons per year. The human contribution makes up about 31% of the annual total.
Now it gets good, and we can see how absurd EPA's perseveration on mercury from U.S. power plants is.