Mercury Pollution: Understanding The Root Causes

Mercury is a toxic pollutant that poses a significant threat to both human health and the environment. While mercury does occur naturally in the Earth's crust, human activities such as coal combustion, mining, and industrial processes have led to widespread global mercury pollution. This pollution has severe impacts on aquatic ecosystems, especially those with large wetland areas, and it accumulates in the bodies of fish and other wildlife, making them unsafe for human consumption. As a result, mercury is the leading cause of impairment in estuaries and lakes, with fish consumption advisories in place across the United States and worldwide.

Human activities like mining and fossil fuel combustion

Mercury pollution is a pressing issue that poses significant risks to both human health and wildlife. While mercury does occur naturally in the Earth's crust, human activities, such as mining and fossil fuel combustion, have exacerbated its presence in the environment, leading to widespread global mercury pollution.

Mining, particularly artisanal and small-scale gold mining (ASGM), is the largest source of anthropogenic mercury emissions. Mercury is often used in mining processes, and the burning of fossil fuels like coal, oil, and wood can release mercury into the atmosphere. This is because mercury occurs naturally in coal and other fossil fuels, and when these fuels are burned, the mercury becomes airborne. Mercury emitted into the air can then settle into water or land, where it is washed into water bodies. This process results in mercury pollution in lakes, rivers, and oceans, affecting aquatic life and contaminating drinking water sources.

The combustion of coal is a significant contributor to mercury pollution. Coal-fired power plants are a major source of mercury emissions, with the United States' power plants alone accounting for about 44% of all man-made mercury emissions. The burning of coal releases mercury into the atmosphere, which can then be deposited back onto land or water through air deposition. This deposition can occur in the form of raindrops, dust, or gravity.

Additionally, the mining and combustion of fossil fuels can release mercury into the environment through waste burning. When waste materials containing mercury are burned, the mercury is released into the air, contributing to air pollution. This includes the burning of municipal, medical, and industrial waste, which can contain high levels of mercury.

The release of mercury through mining and fossil fuel combustion has severe ecological and human health consequences. Once deposited in water, certain microorganisms can convert mercury into methylmercury, a highly toxic form. This methylmercury accumulates in fish, shellfish, and animals that consume contaminated fish, leading to bioaccumulation. As a result, the consumption of contaminated fish and shellfish is the primary source of human exposure to mercury, causing serious health issues, especially in developing fetuses and young children.

Industrial processes and commercial products

Mercury is a naturally occurring element found in the earth's crust. However, human activities, such as industrial processes and the combustion of fossil fuels, have led to its increased presence in the environment, causing widespread global mercury pollution.

Industrial processes that involve the burning of coal, such as coal-fired power plants, industrial boilers, and household stoves, release mercury into the atmosphere. Coal contains mercury and other hazardous air pollutants that are emitted when burned. Mercury can also be released during the industrial production of non-ferrous metals and cement, contributing significantly to global mercury emissions.

The use of mercury in various commercial products has also contributed to pollution. For many years, mercury was used in medical devices such as thermometers and blood pressure measurement tools. These devices can pose a hazard if they break or are not properly disposed of. Additionally, mercury has been used in dental amalgam, a common filling material for treating dental caries. The phase-down or phase-out of dental amalgam use is a global target in the WHO Global Oral Health Action Plan 2023–2030.

The release of mercury into the environment from industrial processes and commercial products can have significant health and environmental impacts. Mercury emitted into the air eventually settles into water bodies or onto land, where it can be washed into water. Certain bacteria can then convert it into methylmercury, a highly toxic form that bioaccumulates in fish, shellfish, and animals that consume these contaminated sources. This bioaccumulation results in higher concentrations of mercury in larger organisms, such as predatory fish. Consequently, human exposure to mercury occurs primarily through the consumption of contaminated fish and shellfish, as well as the inhalation of elemental mercury vapors during industrial processes.

Natural sources like volcanic eruptions and emissions from the ocean

Natural sources of mercury include volcanic eruptions and emissions from the ocean. While mercury occurs naturally in the earth's crust, human activities have led to widespread global mercury pollution.

Volcanic eruptions are a significant natural source of mercury pollution. Volcanoes release mercury from underground reservoirs when they erupt. Measurements of just one part of the Masaya volcano in Nicaragua showed that about 7 tons of natural volcanic mercury escape into the atmosphere from this vent each year. This is considerably more than the UK's total industrial emissions of mercury, recorded at about 5.5 tons in 2000. Scientists have also found high levels of mercury vapour in the gases of Mount Etna in Sicily and Masaya in Nicaragua.

Volcanic activities contribute to the global mercury cycle, and this mercury eventually settles into water or onto land, where it can be washed into water. Mercury released from volcanoes can end up in polar ice cores, even in regions without nearby volcanic activity. This has been observed in measurements of polar ice, which contain faint traces of mercury with a volcanic signature.

The ocean is another natural source of mercury emissions. The ocean acts as a "storage closet" for mercury, and it is estimated that two-thirds of anthropogenic mercury released into the ocean is found in waters shallower than the 1000m level, where much consumable fish live. In addition, natural processes in the ocean, such as abiotic reactions, can lead to the production of methylmercury, a highly toxic form of mercury that builds up in marine food chains, including fish and shellfish consumed by humans.

To address mercury pollution from natural sources, it is important to focus on reducing emissions and cleaning up existing pollution. While natural sources like volcanic eruptions and ocean emissions contribute to the problem, human activities have significantly added to the global pool of mercury. Public awareness and proper disposal of mercury-containing items are critical in reducing mercury pollution and minimizing its impact on human health and the environment.

Burning coal for power and heat

Coal-fired power plants are the largest source of mercury emissions in the United States, accounting for about 44% of all man-made mercury emissions. The combustion of coal releases mercury into the air, where it can stay airborne for over a year and travel long distances, affecting both local and global environments. Lignite, or "low-rank," coal is especially high in mercury and is subject to less stringent standards, making it a significant concern.

Once emitted, mercury can contaminate land, water, and air. It eventually settles into waterways and oceans, where it is converted into methylmercury, a highly toxic form of mercury. Methylmercury accumulates in fish, shellfish, and animals that eat fish, leading to serious health risks for humans and wildlife. People living near coal-fired power plants are particularly vulnerable to the harmful effects of mercury pollution.

The widespread distribution of mercury means that all fish from U.S. waters have detectable levels of mercury, resulting in consumption advisories in all fifty states. The impact of mercury pollution from coal-fired power plants is not limited to the United States, as mercury can also travel to remote ecosystems, especially those in the Arctic Circle.

While the EPA has implemented standards to reduce mercury emissions from coal-fired power plants, such as the Mercury and Air Toxics Standards (MATS), many power plants continue to emit large quantities of mercury. Stronger safeguards and improved technologies are needed to protect the health of communities affected by mercury pollution, especially those living near power plants.

Landfills and waste incineration

Mercury is a well-known environmental pollutant that poses significant risks to human health and wildlife. Landfills and waste incineration are major contributors to mercury pollution, as they release mercury into the air, soil, and water.

Landfills

Discarded products containing mercury, such as batteries and fluorescent lamps, are often disposed of in municipal solid waste (MSW) landfills. Even when properly collected and disposed of in MSW management facilities, these products can release mercury into the environment over time. This has been a particular issue in China, where mercury in MSW has not received adequate attention.

Landfills can also receive mercury-contaminated waste from other sources, such as dental amalgam waste and sewage incineration residues. Mercury from these sources can leach into the soil and groundwater, leading to environmental and health risks.

Waste Incineration

Waste incineration is another significant source of mercury pollution. When waste containing mercury is burned, the mercury is released into the air through flue gases. This can occur during municipal solid waste incineration, as well as during the combustion of coal and other fossil fuels. The released mercury can then settle onto land or water, where it can be washed into water bodies. Microorganisms can convert this mercury into methylmercury, a highly toxic form that accumulates in fish, shellfish, and other wildlife, posing risks to human health through the food chain.

To mitigate the impact of waste incineration on mercury pollution, various control measures have been implemented. These include the installation of amalgam separators in dental offices and the use of end-of-pipe technologies and substance flow analysis to monitor and reduce mercury emissions from incineration processes.

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