Coal Pollution: Mercury's Toxic Legacy

Mercury pollution from coal-fired power plants is a significant environmental concern, with serious health implications for humans, particularly pregnant women and children. While coal contains only low concentrations of mercury, it is burned in large volumes, releasing the toxic substance into the atmosphere. Mercury can stay airborne for extended periods, travelling to remote ecosystems, including the Arctic Circle. Once released, mercury contaminates land, water, and wildlife, eventually entering the human food chain. The combustion process of coal is a primary source of mercury emissions, and the pollutant's ability to disperse globally means that communities across the globe are affected. As a result, regulatory bodies like the EPA in the US have implemented standards to reduce mercury emissions from coal-fired power plants, recognising the urgent need to safeguard public health and protect vulnerable populations from the toxic effects of mercury pollution.

Mercury in coal is released when burned

Mercury is an element found in the earth’s crust. While it exists underground, it does not cause harm. However, when mercury is brought above ground, it can be released into the atmosphere and cause issues due to its neurotoxicity. Mercury is typically released into the atmosphere through the burning of fossil fuels, such as coal and oil.

Although coal contains only low concentrations of mercury, it is burnt in very large volumes. As a result, coal-fired power plants are the biggest source of mercury pollution in the United States, with EPA officials estimating that about 50 tons of elemental mercury are emitted each year from US coal-burning power plants. This accounts for 13 to 26% of the total airborne emissions of mercury in the US.

Once coal is burned, the mercury released can stay airborne for over a year and travel to remote ecosystems, especially in the Arctic Circle. Mercury can also enter waterways, such as rivers, and be transported far beyond its original emission point. This is particularly dangerous as mercury can enter the food chain, especially in aquatic organisms, and bioaccumulate. Bioaccumulation is the enrichment of a substance in an organism, which can include bioconcentration from environmental concentrations and additional uptake via the food chain.

Methylmercury, a type of mercury that forms when mercury passes through the environment, is the most concerning as it can more easily pass through the body’s blood-brain barrier and the placental barrier in the wombs of pregnant women. Exposure to methylmercury has been associated with neurocognitive deficits that can persist into adulthood. Exposure to mercury during adulthood is also linked to issues with fine motor function, verbal memory, and cardiovascular disease.

To reduce mercury emissions, the EPA has issued regulations tightening mercury emissions from coal-burning power plants. Additionally, up to 95% of mercury releases from power plants can be reduced by improving coal and plant performance and optimizing control systems for other pollutants. Other methods to reduce mercury emissions include selective mining of coal (avoiding parts of a coal bed that are higher in mercury content), coal washing, switching from coal to natural gas, and post-combustion removal of mercury from power plant stack emissions.

Mercury's impact on human health

Mercury is a toxic pollutant that is released into the environment by human activities, such as electricity production and waste incineration. Coal-burning power plants are the largest single source of mercury emissions, accounting for approximately 34% of the total in the United States. While coal contains only low concentrations of mercury, it is burned in very large volumes, releasing significant amounts of mercury into the atmosphere.

Once released, mercury can stay airborne for more than a year and travel long distances, eventually depositing on land or in water. It undergoes chemical transformations in the environment, converting into highly toxic forms such as methylmercury, which bioaccumulates in aquatic organisms, especially fish. This means that mercury accumulates in the tissues of these organisms over time, resulting in high levels of mercury in fish.

The consumption of contaminated fish is a primary source of human exposure to mercury. Cases of mercury poisoning have been documented in people who consume contaminated fish regularly, and certain populations are particularly vulnerable, including pregnant women, subsistence fishermen, and children. Methylmercury exposure is associated with neurocognitive deficits, and can impact fine motor function, verbal memory, and contribute to cardiovascular disease in adults. It can also pose dangers to the developing fetus, with potential neurocognitive effects persisting into adulthood.

Inorganic mercury, another form of mercury, can cause kidney damage if ingested in substantial amounts over the maximum contaminant level (MCL) set by the EPA. It can also be corrosive to the skin, eyes, and gastrointestinal tract. Exposure to elemental mercury in the air at concentrations of 20 μg/m3 or more for several years can result in mild central nervous system toxicity, with symptoms including tremors, insomnia, memory loss, and headaches.

To protect human health, the EPA has implemented regulations to tighten mercury emissions from coal-burning power plants, aiming to reduce mercury exposure, particularly for vulnerable communities living near these power plants. The Minamata Convention on Mercury, adopted in 2013, also addresses mercury emissions and the phase-out of certain mercury-containing products. These efforts are crucial in mitigating the toxic effects of mercury on human health.

Sources of mercury pollution

Mercury is a highly toxic pollutant that poses risks to human and wildlife health on a global scale. It is a neurotoxin that can accumulate in fish, birds, minks, and otters, which, when consumed by humans, can lead to severe health issues. Mercury pollution is caused by both natural and anthropogenic (human-caused) sources.

Natural sources of mercury pollution include volcanic eruptions, emissions from the ocean, and undersea vents. However, it is important to note that anthropogenic emissions have significantly added to the global pool of mercury.

The combustion of coal is a significant contributor to mercury pollution. Coal-fired power plants are major emitters, releasing mercury directly into the air and through coal waste. This emitted mercury can travel long distances in the atmosphere before settling into bodies of water, such as lakes and streams, or onto land. Once deposited, certain microorganisms can convert it into methylmercury, a highly toxic form that accumulates in fish, shellfish, and animals that consume fish.

Artisanal and small-scale gold mining (ASGM) is another significant source of anthropogenic mercury emissions. Mercury is used in the process of extracting gold, and improper handling can lead to significant mercury exposure for miners and surrounding ecosystems.

Other industrial processes, such as electricity production and waste incineration, also contribute to mercury emissions. Additionally, mercury can be released from products or devices that contain it, such as containers or thermometers, if they are damaged or broken and the mercury is not properly contained.

Reducing mercury emissions

Mercury is a neurotoxin that can cause neurocognitive deficits in children and issues with fine motor function, verbal memory, and cardiovascular disease in adults. It is typically trapped underground for hundreds of millions of years. However, burning coal and oil releases mercury into the atmosphere, where it can stay airborne for over a year and travel to remote ecosystems.

Coal contains only low concentrations of mercury, but it is burnt in very large volumes. Up to 95% of mercury releases from power plants can be reduced by improving coal and plant performance and optimizing control systems for pollutants.

The Clean Air Act requires the EPA to periodically review whether available technologies have improved to warrant strengthening standards for reducing mercury emissions. The EPA has also proposed regulations to tighten mercury emissions from coal-burning power plants, the biggest source of the pollutant in the United States.

• Use high-rank coals: High-rank coals contribute less mercury to the environment compared to coals with similar mercury concentrations.
• Selective mining: Avoid parts of a coal bed that are higher in mercury content.
• Coal washing: Reduce the amount of mercury in coal delivered to power plants.
• Fuel switching: Transition from coal to natural gas.
• Post-combustion removal: Remove mercury from power plant stack emissions after combustion.
• Bromine-based products: Bromide additives convert elemental mercury to its oxidized form, which can be more easily retrieved by emission control equipment. Brominated activated carbon can also be injected into the flue gas stream to absorb and capture mercury.
• Carbon capture: Separate and recover CO2 from emissions, then inject it underground for permanent storage.

Mercury as a global pollutant

Mercury is a dangerous neurotoxin that can cause brain damage in babies and is linked to heart disease and other serious health issues. It is released into the atmosphere when coal is burned, and it can stay airborne for over a year, travelling to remote ecosystems, particularly in the Arctic Circle. Mercury is not only a global pollutant but also has significant regional and local impacts.

Coal-fired power plants are a major source of mercury pollution, with up to 95% of mercury releases coming from these plants. The combustion of coal releases mercury that has been trapped underground for hundreds of millions of years. While coal contains only low concentrations of mercury, it is burned in very large volumes, and the mercury released contributes significantly to global mercury emissions. The largest sources of mercury pollution from coal-fired power plants are in North Dakota and Texas, with other large polluters in Appalachia and the Midwest.

Once released into the atmosphere, mercury can contaminate lands, oceans, and streams, where it is converted into methylmercury, a harmful toxic substance that can accumulate in our food, particularly in fish. This is a significant concern as people can ingest methylmercury by eating contaminated fish, leading to mercury poisoning. Exposure to methylmercury during pregnancy can cause brain damage in babies, and exposure during adulthood is linked to issues with fine motor function, verbal memory, and cardiovascular disease.

To address this issue, the U.S. Environmental Protection Agency (EPA) has implemented regulations to tighten mercury emissions from coal-burning power plants. The Biden administration is also working to revive mercury limits for these plants. Additionally, the UNEP Global Mercury Partnership aims to support the minimization and elimination of mercury releases from coal combustion, providing information on cost-effective approaches for mercury reduction.

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