April 27, 2012

EPA’S Toxic Science

Filed under: Climate Politics

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.

The total contribution from all human activity in the United States to the global mercury flux is approximately 120 tons, or about 1.6% of the total. The amount coming from U.S. coal-fired electricity plants is around 48 tons, 0.6% of the global load. But mercury can reside a long time in the atmosphere—up to two years, so, unless it quickly rains out as “wet deposition”, it’s likely to disperse far, far away. In fact, only about 25% of the mercury emitted by our power plants, or 0.2% of global emissions, falls on our soil.

For that we are going to close 68 power plants supplying electricity to about 22 million homes?

Oh, we know, it’s about the children. So just to show how much we care, we present here the relative magnitudes of the sources of atmospheric mercury in the form of babies:

Figure 1. Comparative size of mercury sources given as the area of each of these babies. The biggest baby—the total global annual flux—is about 153 times bigger than the baby representing U.S. power plants. The fact that mercury can reside as long as two years in the atmosphere is why at least well over half of the mercury deposited here is of foreign origin. The almost invisible dot on the extreme right is the amount coming from power plants that winds up on our soil.

Both the EPA and the Electric Power Research Institute (EPRI) used different models to estimate how much of the mercury deposited in the U.S. comes from power plants, and how much comes from foreign sources. They arrived at even lower numbers than we show here. According to EPRI’s 2006 Issue Briefing on mercury:

Analysis of mercury emissions from U.S. sources, including coal-fired power plants, shows that about 2/3 of this emitted mercury leaves the United States. Most of it is assumed to join the global atmospheric pool. Only about 1/15th of the mercury depositing in the U.S. originates from U.S. power plants, even though they account for nearly 40% of U.S. mercury emissions. Mercury deposition occurring over 70% or more of the U.S. surface area originates in other countries, and is often transported thousands of miles before arriving in the U.S. Thus, reducing domestic power plant sources of mercury will not result in proportional reductions in deposition occurring across the U.S.

The fact that the relative numbers are inconstant across the various sources shows how impossible detecting any effects of mercury emissions reductions will be. Further, there is simply no evidence linking mercury from power plants in the U.S. to any single specific case of illness or death.

The fact of the matter is that, in the near term, natural gas is likely to continue to displace coal for electrical generation as it has now become less costly due to the exploitation of the huge amounts of gas and oil lying beneath the nation’s surface in shale rock deposits. There is little doubt that, if this continues, power companies would gradually switch away from coal as plants aged. Unfortunately, the EPA’s activity accelerates this process, inducing unwanted costs and permanently displacing thousands of Appalachian coal workers, for no detectable mercury-related health effect.


Pirrone, N., et al., 2010. Global mercury emissions to the atmosphere from anthropogenic and natural sources. Atmospheric Chemistry and Physics Discussions, 10, 4719-4752.

Electric Power Research Institute, 2006. Sources of Mercury Depositing in the United States. Issue Brief. 3pp, http://dnr.wi.gov/air/pdf/am3205epriattachment7.pdf

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