EPA Tightens Mercury and Air Toxics Standards for Coal Plants
The Environmental Protection Agency (EPA) announced a proposal on April 5, 2023, that will tighten existing rules to further limit the emissions of mercury produced by coal-fired power plants. Coal plants are the largest source of mercury pollution in the United States. In 2017 alone 8,800 pounds of mercury emissions were released.
The Mercury and Air Toxics Standards (MATS), enacted in 2012, have already reduced mercury emissions by 90%. The new proposal, which is expected to be finalized in 2024, proposes a 70% reduction in the emissions limit for mercury from lignite-fired sources. Lignite is a type of coal that is considered low grade and high polluting. While lignite plants only account for 8% of the total coal production in the US, the five highest polluting coal plants on the map below burn lignite coal.
The revisions will require all coal plants to achieve the same level of emission performance. Currently MATS requires lignite plants to meet a mercury emission standard of 4lbs per trillion British thermal units, while other coal plants are required to limit their emissions to 1.2lbs. The EPA believes this revision is necessary to protect the health of all Americans.
How is Mercury Released into the Environment?
Burning coal produces coal ash, also known as coal combustion residuals. Coal contains a high mercury concentration, and the metal is released in the combustion process.
One power plant can generate 100-300+ pounds of ash for every ton of coal burned. For plants with large generators that burn around 3 million tons of coal each year, 150,000-450,000 tons of coal ash are released.
Mercury is the only metal that is liquid at room temperature, when heated the liquid will evaporate into mercury vapor. This vapor is released through smokestacks at plants and most mercury will fall within 9 miles of the smokestack contaminating the surrounding soil and water.
Mercury also contaminates settling ponds used by power plants to discharge wastewater. Plants use water to cool and sluice bottom ash away from the boiler for final disposal. A typical sluice system collects ash from the furnace in an ash hopper, transports this ash through a sluice pipeline, and then dumps the mixture into a pond. These ash ponds pose a significant risk to the environment as mercury and other contaminates can leach into the ground water polluting private wells and waterways.
How does Mercury Impact Humans?
Once mercury reaches waterways it poses a risk to those who drink, bathe, and swim in contaminated water. Individuals residing near coal-fired power plants face a disproportionate level of mercury pollution.
Mercury travels up the food chain to humans as bacteria in water can change it to methylmercury which is absorbed by aquatic organisms. When fish consume these organisms, mercury builds up in fish tissue as it binds to the protein in muscles. Mercury cannot be removed through cooking or cleaning, which is why nearly all fish in the US contain traces of methylmercury and there are consumption advisories in all 50 states.
Mercury exposure damages the brain, heart, kidneys, lungs, and immune system. It has the potential to increase cancer risk and cause developmental delays in children. Fetuses are especially vulnerable to neurocognitive deficits and other birth defects while in their mother’s womb, making it imperative for pregnant women to remove fish and shellfish from their diet.
The revised standards would reduce mercury pollution thereby protecting public health and advancing environmental justice. The EPA believes that under the Clean Air Act they have an obligation to revise the existing standards to further regulate toxic emissions.
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