Mercury has been attacked as a dangerous toxin emitted by coal-fired power plants.
But how much do coal-fired power plants contribute to the mercury found in our environment? And how dangerous is the mercury that’s been deposited around the country?
U.S. coal-fired power plants emit 41 tons of mercury into the atmosphere, but this is a fraction of the 9,100 tons of mercury emitted globally each year, mostly from natural sources.
Mercury emitted into the atmosphere travels around the globe, so mercury emitted by coal-fired power plants in China is probably being deposited in the U.S.
The EPA has undertaken a program to eliminate the use of coal in power plants, and its efforts will cost billions of dollars. Are these expenditures necessary? Will they really reduce the effect of mercury on our health? Are coal-fired power plants the villains portrayed by the EPA?
A recent study by the USGS can shed light on these questions.
This graph produced by the United States Geological Survey (USGS) shows mercury deposition as determined from ice cores taken in Wyoming.
The spikes are mostly from volcano eruptions, and show how mercury travels around the world.
While mercury deposition increased during the industrial revolution, the important question is: Did the increase create a danger to public health?
If the mercury levels found in the ice cores exceed the safety limits established by OSHA and others, then we could conclude that mercury deposition from coal-fired power plants may be affecting public health.
But, if the mercury found in the ice-cores were well below the safety limits, then we could conclude that coal-fired power plants are not affecting public health and the phasing out of coal-fired power plants, at great cost to the economy and in jobs lost, is unnecessary.
The highest level of mercury on the USGS graph was 23 ppt (parts per trillion).
This is an extremely small amount of mercury.
Professor James Rust (nuclear engineering, retired) converted the ng/L (nano grams per cubic liter) shown on the USGS graph, to parts per trillion (ppt) and then compared these concentrations with the safety limits established by OSHA and others.
- “The Occupational Safety and Health Administration (OSHA) occupational exposure limit (8 hr, 5-day week) is 100 micrograms per cubic meter.
- “The National Institute for Occupational Safety and Health (NIOSH) recommended safety limit is 50 micrograms per cubic meter.
- “The American Conference of Government and Industrial Hygienists (ACGIH) recommend 25 micrograms per cubic meter for the same conditions as OSHA.
- “The Agency for Toxic Substance and Disease Registry (ATSDR) recommends a maximum level of 0.2 micrograms per cubic meter for exposure of children on a continual basis.
“A cubic meter of air has a mass of 1280 grams. Thus 1 microgram per cubic meter is a concentration of 780 parts per trillion by mass.”
Here are the results of these calculations by Professor Rust, for the safe limits for mercury established by each of these organizations,.
- OSHA 78,000 ppt
- NIOSH 39,000 ppt
- ACGIH 19,000 ppt
- ATSDR 156 ppt
The highest level of 23 ppt from the USGS graph is infinitesimal when compared with the safety limits established by OSHA, NIOSH or AGOG, and is well below the level established for children.
The amount is so small that, if the USGS chart was posted horizontally at street level on the side of a building, with the highest peak on the graph being 2 inches high, the OSHA limit would be drawn at a height of over 500 feet above the peak amount of mercury, or at a height that was approximately forty stories above the USGS chart.
The USGS study demonstrates that the EPA is pursuing a strategy to eliminate coal-fired power plants for no legitimate scientific reason.
Concentrations in the USGS graph are given in nanograms per liter. Assuming 1000 grams of ice per liter, the USGS concentrations are also parts per trillion (ppt). Ice is about 900 rather than 1000 grams per liter, but the comparison is sufficiently close to permit a reasonable approximation of ppt.
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