Mercury Air Pollution: Is It A Concern?

Mercury (Hg) is a well-known global pollutant that poses a threat to human and ecosystem health. It is released into the atmosphere through the burning of fossil fuels, such as coal and oil, and can remain airborne for extended periods, travelling through the planet's atmosphere, waterways, and wildlife before eventually entering our bodies. Mercury pollution has severe socio-economic impacts, and its toxic effects on the brain, especially in children, are of particular concern. As a result, various policies and regulations have been implemented to limit mercury emissions and mitigate their regional and local dimensions.

Mercury is a global pollutant that affects human and ecosystem health

Mercury is a toxic pollutant that poses a serious threat to human health and ecosystems. It is a naturally occurring metal that, in its pure form, is not particularly toxic. However, human activities have led to widespread global mercury pollution. The largest sources of human mercury emissions are coal-fired power plants, industrial boilers, and household stoves that burn coal for power and heat. Mercury is also released into the environment through mining, waste incineration, and the combustion of fossil fuels.

Once emitted into the air, mercury can travel thousands of miles in the atmosphere before being deposited back to Earth in rainfall or dry gaseous form. It then cycles through soils and surface waters, entering streams, lakes, and estuaries. Mercury can undergo chemical transformations once it is deposited in the landscape. Of particular concern is its conversion to methylmercury, which is facilitated by bacteria in wetlands that are periodically flooded. Methylmercury is a highly toxic form of mercury that bioaccumulates in fish, shellfish, and animals that eat fish.

Most human exposure to mercury occurs through the consumption of contaminated fish and shellfish. It can cause severe health issues, including kidney and nervous system damage, skin problems, and respiratory failure. Developing fetuses and young children are especially vulnerable to the toxic effects of mercury, with potential adverse effects on the unborn child's growing brain and nervous system. Mercury poisoning can also have neurological and behavioural consequences, including tremors, insomnia, memory loss, and cognitive and motor dysfunction.

The effects of mercury pollution extend beyond human health, impacting wildlife and ecosystems. High levels of mercury have been detected in various species, such as birds, cats, and octopuses, leading to erratic behaviour, convulsions, and even death. In 2003, 44 states and American Samoa issued fish consumption advisories due to mercury contamination, highlighting the widespread presence of mercury in the environment.

To address the global challenge of mercury pollution, international cooperation and interventions are necessary. The Minamata Convention on Mercury, adopted in 2013, is one such effort, obliging participating governments to address mercury emissions and phase out certain mercury-containing products. Additionally, promoting non-mercury gold-extraction techniques and implementing safer work practices in industries that utilize mercury can help reduce human exposure and environmental releases.

Mercury emissions are a global problem that knows no national or continental boundaries

Mercury is a highly toxic trace element that poses significant risks to both human and environmental health. Exposure to mercury can have many often irreversible toxic effects, with developing fetuses and young children being particularly vulnerable. Mercury pollution also harms wildlife and ecosystems. For instance, once deposited, certain microorganisms can transform it into methylmercury, a highly toxic compound that accumulates in fish, shellfish, and animals that eat fish. As a result, most human exposure to mercury comes from the consumption of contaminated fish and shellfish, with some communities facing greater risks due to higher fish consumption.

Mercury emissions come from both natural and anthropogenic sources. Natural sources include volcanic eruptions and emissions from the ocean. However, human activities, such as mining and fossil fuel combustion, have significantly contributed to widespread global mercury pollution. Artisanal and small-scale gold mining (ASGM) is the largest source of anthropogenic mercury emissions, followed by stationary coal combustion, non-ferrous metals production, and cement production. These human-caused emissions continue to add to the global mercury pool, leading to increased environmental and health risks.

The global nature of mercury emissions has been recognized by international organizations, with the United Nations Environment Programme (UNEP) and the Minamata Convention on Mercury seeking to reduce mercury emissions through various policies and strategies. The inclusion of mercury in the Aarhus Protocol on Heavy Metals and the Convention on Long-range Transboundary Air Pollution further highlights the understanding that mercury pollution transcends geographical boundaries and requires international cooperation to address effectively.

Mercury's toxicity and its ability to bioaccumulate and bioconcentrate

Mercury is a toxic pollutant that poses serious health and environmental risks. It is released into the environment through both natural processes and human activities, such as industrial pollution and electricity production. Once emitted, mercury can remain in the atmosphere for up to a year, travelling thousands of miles before being deposited back to Earth. This long atmospheric lifespan contributes to its status as a "global pollutant".

Mercury's toxicity is well-documented, with human health effects including ataxia, constriction of vision, impaired hearing, and even death. It is particularly dangerous to developing fetuses and young children, who are at risk of learning disabilities and neurological damage from exposure. Mercury's toxic effects on wildlife and ecosystems are also significant, with fish and other aquatic organisms being especially vulnerable.

Bioaccumulation is a process where organisms, including humans, accumulate contaminants faster than their bodies can eliminate them. In the case of mercury, this accumulation occurs over time, and the body burden of the toxin can reach toxic levels if exposure is continuous. Fish, for example, accumulate mercury in their muscle tissue, and this cannot be removed through filleting or cooking. As a result, humans who consume contaminated fish are at risk of ingesting harmful levels of mercury.

Mercury's ability to bioaccumulate is compounded by its tendency to bioconcentrate at the top of the food chain. This means that larger, predatory game fish will likely have the highest mercury levels. This biomagnification occurs because the food sources for organisms higher on the food chain are progressively more concentrated in mercury, magnifying the bioaccumulation rates. As humans consume fish and other seafood, they are exposed to these accumulated toxins, which can lead to severe health issues.

Sources of mercury emissions: natural and anthropogenic

Mercury emissions are a global problem that does not respect national or continental boundaries. Once emitted into the air, mercury can travel thousands of miles before being deposited back onto the earth, threatening human and ecosystem health. Mercury occurs naturally in the earth's crust, but human activities have led to widespread global mercury pollution.

Natural Sources of Mercury Emissions

Natural sources of mercury emissions include volcanic eruptions and emissions from the ocean. The largest part of emissions originates in the oceans. Other natural geogenic sources include volcanism and erosion, estimated at 500 Mg a–1.

Anthropogenic Sources of Mercury Emissions

Anthropogenic (human-caused) emissions include mercury released from fuels or raw materials, or from the use of products or industrial processes. Primary anthropogenic sources of mercury emissions include fuel combustion, waste incineration, and mining, estimated at 2100 Mg a–1. The highest emissions can be found in South and Southeast Asia, accounting for 45% of global emissions. East Asia currently accounts for almost 40% of total primary global anthropogenic emissions of mercury. The main driver for increased Hg emissions is the expansion of coal-fired electricity generation in the developing world, particularly in Asia.

Globally, artisanal and small-scale gold mining (ASGM) is the largest source of anthropogenic mercury emissions (37.7%), followed by stationary combustion of coal (21%). Other large sources of emissions are non-ferrous metals production (15%) and cement production (11%).

Mercury removal from the air

Mercury is an atmospheric pollutant that poses a severe threat to air quality and human health. It has toxic effects on the environment and humans, with vulnerable populations such as developing fetuses and young children being most at risk. Mercury emissions are a global issue, travelling thousands of miles in the atmosphere before settling into water or land. Natural sources of mercury include volcanic eruptions and ocean emissions, while human activities, such as mining, fossil fuel combustion, and industrial processes, contribute significantly to mercury pollution.

To address this issue, several methods have been proposed for the removal of mercury from the air:

Oxidation Processes

Oxidation of gaseous species GEM (Hg0) with ozone (O3) is considered one of the most important processes for mercury removal from the air. This process involves the conversion of GEM into a less harmful form through chemical reactions. Additionally, the oxidation of GEM by hydroxyl radicals (•OH) helps remove substantial amounts of mercury from the atmosphere.

Flue Gas Treatment

Mercury removal from flue gases during coal combustion has been extensively studied. The use of coke dust (CD) has proven effective, with the fine fraction of CD removing up to 92% of mercury during coal combustion. This technology, known as FLUEPAC, combines high adsorption capacity for pollutants with excellent mercury removal rates and low carbon usage.

Bromine and Chlorine Enhancement

Studies have shown that increasing the concentration of bromine and chlorine in combusted coal promotes the conversion of Hg2+ into an intermediate form, Hg(p), resulting in higher mercury removal rates from conventional cleanup systems.

Ultraviolet (UV) Radiation

UV radiation is an effective method for the oxidation of mercury. While it does not directly affect mercury in flue gas, it causes oxygen molecules to break down into radicals, which then react with metallic mercury, oxidising it to Hg2+. This process contributes to the reduction of mercury in the atmosphere.

Regulatory Standards and Pollution Control Technology

The implementation of standards and regulations, such as the Mercury and Air Toxics Standards in the US, plays a crucial role in reducing mercury emissions. These standards mandate the use of pollution control technology in power plants, helping to cut emissions and protect public health.

By employing these methods and strategies, significant progress can be made in removing mercury from the air and mitigating its harmful effects on the environment and human well-being.

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