The Truth About Coal And Mercury

One of the most common justifications for seeking to restrict and ban the use of coal is that burning coal causes massive health dangers such as high mercury levels in our bodies.

But does it? Let’s separate myth from truth.

The myth in a sentence

Burning coal to generate electricity releases dangerous amounts of mercury that cause birth defects and other problems.

The truth in a sentence

Burning coal to generate electricity releases small amounts of mercury–far less than natural sources of mercury such as volcanoes, wildfires, dust and the oceans.

The myth in a paragraph

Coal naturally contains mercury, a neurotoxin that can damage the nervous system, the brain and other organs. When we burn coal, that mercury gets released into the atmosphere and ultimately rains down into bodies of water. This leads to higher mercury levels in fish, which leads to higher mercury levels in our bodies when we eat fish. Those levels are dangerous, particularly to the fetuses of pregnant women, whose children can experience developmental problems and learning disabilities. Therefore, coal is a massive threat to public health.

The truth in a paragraph

Mercury, a metal element, exists naturally throughout the world–most notably in the oceans, which are estimated to contain hundreds of thousands of tons of mercury, as well as in the air, soil and consequently in most forms of plant and animal life in various concentrations and chemical forms. Mercury is released in the air in substantial, though by no means toxic, quantities by volcanoes and wildfires. It is released in far smaller quantities by coal plants–an estimated 2,000 tons of manmade sources vs. tens of thousands of tons from natural sources. The most relevant form of human exposure is methylmercury from marine life, which is substantially influenced by biological processes but not by human emissions. Consuming above average amounts of fish is not detrimental to human health. Coal plants are not a dangerous source of mercury. They are, however, an essential source of electricity, which is an essential of every aspect of modern food production and health care.

The whole truth

Mercury, a metal element, exists naturally throughout the world–most notably in the oceans, which contain an estimated hundreds of thousands of tons of mercury, as well as in most forms of plant and animal life. Mercury is released in the air by volcanoes, wildfires, and in far lesser quantities, the burning of coal. That mercury eventually settles on land or water, and constitutes a portion of the small amounts of mercury that exists in most living things.

As the map below shows, the regions with the most airborne mercury concentrations (Rocky Mountain and desert areas) do not match the regions with most coal emissions (New England).

Source: National Atmospheric Deposition Program/Mercury Deposition Network

Mercury, like any substance, is toxic in certain forms and doses and harmless in others. The form of mercury that is of particular concern to human health is called methylmercury (or monomethylmercury), a combination of mercury, carbon and hydrogen. Discussions of “mercury poisoning” are misleading, because mercury only becomes methylmercury under certain conditions, and methylmercury can only be absorbed by human beings in relevant quantities under certain conditions (for example, the element Selenium seems to prevent the absorption of methylmercury).

While these are important scientific questions, they are essentially irrelevant to the issue of coal, which is a minor source of mercury–especially because it has little if any impact on the amount of methylmercury consumed by humans, as the accumulation of methylmercury in living organisms is dominated by natural, local, geological, chemical and biological processes, such as the microbiology of wetlands. The availability of mercury is not the key factor in the formation of methylmercury. Coal has been singled out for political, not scientific reasons.

Coal is one of the most important supplies of affordable and reliable energy and it is not significantly impacting human exposure to mercury in the environment. Given those two facts, it is very disingenuous to use mercury emission reductions as an argument to restrict the use of coal. Shutting down coal power will make electricity more expensive and threaten human health, while the impact on mercury exposure would be so small that it will have no observable effect.