Greta Jimenez
Mercury pollution in the ocean is a pressing issue that poses a serious threat to both human and animal health. Mercury is a heavy metal that cycles through the atmosphere, water, and soil, and its presence in the ocean has been on the rise since the Industrial Revolution. While mercury occurs naturally in the earth's crust, human activities such as coal-fired power plants, mining operations, and fossil fuel combustion have significantly contributed to its increasing levels in the ocean. The North Atlantic waters, for instance, exhibit the most evident signs of mercury pollution. The effects of mercury pollution on human health include neurological damage, cardiovascular risks, loss of peripheral vision, weakened muscles, impaired hearing and speech, and deteriorated movement coordination. Animal health is also severely impacted, as seen in the Minamata Bay incident, where animals exhibited strange behaviors and high mortality rates. Addressing mercury pollution is crucial to mitigating its harmful effects on both human and animal populations.
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What You'll Learn
Mercury's impact on human health
Mercury pollution in the oceans is a global concern, with two-thirds of all mercury emissions ending up in waters shallower than 1000m, where most consumable fish live. The ocean acts as a "storage closet" for mercury, and the natural mercury cycle means that irrespective of where mercury is released, it could impact another part of the world.
Mercury is toxic to human health, and even in small doses, it can cause numerous disorders in the body, including the nervous, respiratory, and cardiovascular systems. It can cause various cancers, endothelial dysfunction, gastric and vascular disorders, liver, kidney, and brain damage, hormonal imbalances, miscarriages, reproductive disorders, skin lesions, vision damage, and even death. The effects of mercury exposure can be severe, subtle, or may not occur at all.
Developing fetuses and young children are most at risk of the toxic effects of mercury. Mercury exposure inhibits the proper brain and nervous system development of children, damaging memory, cognitive thinking, language abilities, attention, and fine motor skills. The National Academy of Sciences estimated that more than 60,000 children born in the U.S. each year are at risk of nervous system damage from methylmercury exposure in the womb. A 2003 study found that 8% of American women of childbearing age had blood mercury levels exceeding safe levels.
Humans are primarily exposed to mercury through the consumption of contaminated fish and shellfish. Fish absorb mercury from their environment, and larger predatory fish tend to have higher levels of mercury due to eating smaller fish. The U.S. EPA has issued warnings against eating shark, swordfish, king mackerel, or tilefish and advises limiting the intake of other ocean fish. Almost all people worldwide have at least trace amounts of methylmercury in their tissues.
Mercury is released into the environment by human activities such as electricity production, waste incineration, mining, and fossil fuel combustion. It is estimated that two-thirds of the mercury in the world is released into the environment by human activities. Mercury can remain in the atmosphere for up to a year before being deposited on land or in water, where it can be washed into streams, lakes, and estuaries.
To reduce mercury emissions, the international community has adopted the Minamata Convention on Mercury, which aims to address mercury emissions and phase out certain mercury-containing products. The U.S. EPA advises a mercury dose limit of 0.1 μg/kg/day to avoid toxic effects.
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Sources of mercury pollution
Mercury is a naturally occurring metal found primarily in a mineral called cinnabar, which can contain up to 86% mercury. It is released through the natural weathering of rock and volcanic activity. However, the primary source of mercury in the environment is human activity, specifically coal-combustion electrical power generation and industrial waste disposal. Mercury is a leading contaminant threatening bodies of water as it is a potent neurological poison in fish, wildlife, and humans.
Natural Sources
Mercury occurs naturally in the earth's crust, and natural sources of mercury include volcanic eruptions and emissions from the ocean. It is released through the natural weathering of rock and volcanic activity.
Anthropogenic Sources
Anthropogenic or human-caused emissions include mercury released from fuels or raw materials, or from uses in products or industrial processes. The largest source of anthropogenic mercury emissions is small-scale artisanal gold mining, followed by coal-fired power plants, non-ferrous metals production, and cement production. Mercury is emitted into the air and eventually settles into water or onto land, where it is washed into water.
Bioaccumulation
Once deposited into water, certain microorganisms can convert inorganic mercury into methylmercury, a highly toxic form that builds up in fish, shellfish, and animals that eat fish. This process is called bioaccumulation, where tiny organisms absorb mercury, and are then eaten by small fish, which are then eaten by larger fish, causing the mercury to accumulate up the food chain. This results in high levels of mercury in top predator fish, which are consumed by humans.
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How mercury enters the ocean
Mercury is a toxic pollutant that poses serious health and environmental risks. Two-thirds of the mercury in the world is released into the environment by human activities, such as electricity production, waste incineration, mining, and fossil fuel combustion. Mercury emitted into the air eventually settles into water or onto land, where it can be washed into water. Once deposited, certain microorganisms can convert it into methylmercury, a highly toxic form that builds up in fish, shellfish, and animals that eat fish.
There are several ways mercury enters the ocean. Atmospheric deposition is the largest source, introducing three types of mercury to the ocean: gaseous elemental mercury (Hg0), inorganic mercury (Hg2+/HgII), and particle-bound mercury (Hg(P)). Gaseous elemental mercury enters the ocean through air-water exchange, while inorganic mercury and particle-bound mercury enter through wet and dry deposition. In addition, mercury enters the ocean via rivers, estuaries, sediments, hydrothermal vents, and other pathways. These sources also release organic mercury compounds, such as methylmercury, which is of particular concern due to its ability to bioaccumulate and bioconcentrate, leading to increased toxicity.
Methylmercury is formed through chemical reactions involving mercury and microorganisms in the ocean. Positively charged mercury ions (Hg+2), the most common form of mercury in the ocean, bond with negatively charged sulfide, creating a compound that can pass into microbial cells. Once inside, the mercury undergoes methylation, and the bacteria release methylmercury. Some of this methylmercury diffuses into the open water, where it is consumed by phytoplankton and begins its journey up the food chain.
The role of particles in transporting mercury to the ocean is also significant. Particles, such as sinking particles and aerosols, can act as a shuttle service, carrying mercury from the atmosphere, groundwater, or rivers into the ocean. These particles facilitate the movement of mercury to the low-oxygen zones where methylation occurs, contributing to the production of methylmercury.
Natural sources of mercury, such as volcanic eruptions and emissions from the ocean, also contribute to mercury levels in the ocean. However, human activities remain the primary drivers of mercury emissions. Globally, artisanal and small-scale gold mining (ASGM) is the largest source of anthropogenic mercury emissions, followed by stationary coal combustion. Reducing these emissions and transitioning to cleaner energy sources are crucial for mitigating mercury pollution in the ocean.
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How mercury affects marine life
Mercury pollution is a global issue that affects all oceans and presents a serious threat to human and animal health. The ocean acts as a "storage closet" for mercury, with two-thirds of anthropogenic mercury releases estimated to be found in waters shallower than 1000m, where most consumable fish live.
Mercury is a toxic pollutant that accumulates in fish and affects humans and animals that eat them. It can interfere with the development of nerve cells in unborn children and young children, resulting in abnormal brain development and cognitive deficits. In adults, higher doses can cause tingling or numbness in the lips, tongue, fingers, or toes, as well as fatigue and blurred vision.
In the environment, mercury is released into the air through human activities such as electricity production, waste incineration, and fossil fuel combustion. Once released, mercury can circulate in the air for up to a year before being deposited on land or in water. It then cycles through soils and surface waters, entering streams, lakes, and estuaries. Bacteria in the water can convert mercury into methylmercury, a highly toxic form that builds up in fish, shellfish, and animals that eat fish.
The effects of mercury on marine life have been observed in various studies. For example, high levels of mercury in ospreys near Montana's Clark Fork River resulted in about half of their eggs not hatching. In another study, white ibises from the Everglades showed reduced nesting behaviour and increased nest abandonment when exposed to mercury levels similar to those found in their wild fish prey. Additionally, mercury contamination has been linked to a decrease in loon populations in New Hampshire and Maine, with a 41% drop in the number of young fledged when mercury levels reached 3 ppm.
To reduce mercury emissions and protect marine life, international treaties and regulations have been implemented. The 2002 Global Mercury Assessment emphasized the urgency of addressing the global mercury problem. The Minamata Convention on Mercury, a global treaty, aims to reduce mercury emissions and protect human and environmental health. Additionally, the United States Environmental Protection Agency (EPA) has set a mercury dose limit of 0.1 μg/kg/day and issued warnings against consuming certain types of fish with higher mercury levels.
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Reducing mercury emissions
Mercury pollution is a global concern, threatening both human and animal health. The ocean acts as a "storage closet" for mercury, and irrespective of the part of the world where mercury is released, it can impact another part of the world. The United States Environmental Protection Agency (EPA) has warned that mercury consumption can result in loss of peripheral vision, weakened muscles, impaired hearing and speech, and deteriorated movement coordination. The effects of mercury are more severe on infants, children, and developing fetuses, as it inhibits proper brain and nervous system development.
To reduce mercury emissions, the EPA has taken several regulatory and policy measures. Some of these include:
- In 2011, the EPA issued the Mercury and Air Toxics Standards (MATS) regulation to reduce toxic air pollutants from coal- and oil-fired power plants. Power plants have since installed controls and updated operations to meet these standards.
- The EPA published a rule in 2011 limiting specific pollutant emissions, including mercury, from public incinerators that burn sewage.
- The EPA issued final standards for mercury from chlor-alkali production, a technology used to produce chlorine. Mercury emissions from chlor-alkali plants have been significantly reduced since then.
- The EPA partnered with the Argonne National Laboratory (ANL) to design a low-cost, easily constructible technology called the Gold Shop Mercury Capture System (MCS) to reduce airborne mercury emissions from small-scale gold buying and refining facilities worldwide.
- The EPA collaborated with international organizations on a project to demonstrate the effectiveness of injecting activated carbon sorbents to control mercury air emissions at a coal-fired power plant in Russia.
- The United States joined the Minamata Convention on Mercury in 2013, a multilateral environmental agreement that addresses specific human activities contributing to widespread mercury pollution.
In addition to these regulatory efforts, individuals can also play a role in reducing mercury emissions:
- People can choose to buy and use products that are mercury-free or have zero or minimum mercury emissions.
- Properly dispose of any mercury-containing items, such as medicinal packaging and thermometers, through recommended management and disposal options.
- Limit the consumption of fish that typically have higher levels of mercury, especially for children and women of childbearing age.
- Learn about the sources of electricity and opt for cleaner energy sources such as natural gas, nuclear power, wind, or solar energy instead of coal-burning power plants.
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Frequently asked questions
Mercury pollution is a global concern, and it is impossible to pinpoint one ocean that is most affected. Mercury is a heavy metal that cycles through the atmosphere, water, and soil, and can reach even the deepest ocean trenches. However, the North Atlantic waters show the most obvious signs of mercury pollution due to the circulation of surface waters forming deep and intermediate water flows.
Mercury pollution in the ocean has both natural and anthropogenic (human-caused) sources. Natural sources include volcanic eruptions, emissions from the ocean, and the breakdown of rocks on land. Human activities, such as mining, fossil fuel combustion, industrial processes, and wastewater dumps, are major contributors to mercury pollution in the ocean.
Mercury pollution has detrimental effects on both the environment and human health. In the ocean, mercury accumulates in fish, shellfish, and animals that eat fish, leading to high levels of toxic mercury in their tissues. This can result in strange behaviors, high mortality rates, and neurological issues. For humans, consuming contaminated seafood can lead to loss of peripheral vision, weakened muscles, impaired hearing and speech, and deteriorated movement coordination. Infants and developing children are especially vulnerable, as mercury exposure can inhibit brain and nervous system development.
