Mercury regulation in the United States limit the maximum concentrations of mercury (Hg) that is permitted in air, water, soil, food and drugs. The regulations are promulgated by agencies such as the Environmental Protection Agency (EPA) and Food and Drug Administration (FDA), as well as a variety of state and local authorities. EPA published the Mercury and Air Toxics Standards (MATS) regulation in 2012; the first federal standards requiring power plants to limit emissions of mercury and other toxic gases.United States Environmental Protection Agency (EPA), Washington, D.C. (2012-02-16). "National Emission Standards for Hazardous Air Pollutants From Coal- and Oil-Fired Electric Utility Steam Generating Units and Standards of Performance for Fossil-Fuel-Fired Electric Utility, Industrial-Commercial-Institutional, and Small Industrial-Commercial-Institutional Steam Generating Units." Final rule. Federal Register,
Background Forms of mercury Mercury occurs naturally in the environment and exists in many forms. In pure form, it is known as "elemental" or "metallic" mercury. Elemental mercury is a shiny, silver-white metal that is liquid at room temperature. If not sealed off, mercury slowly evaporates into the air, forming a vapor. The quantity of vapor formed increases as temperatures rise. Elemental mercury is traditionally used in thermometers and some electrical switches.
Inorganic mercury compounds or mercury salts, more commonly found in nature, include mercuric sulphide (HgS), mercuric oxide (HgO) and mercuric chloride (HgCl2). Most of these are white powders or crystals, except for mercuric sulphide which is red and turns black after exposure to light.
Organic mercury is formed when mercury combines with carbon and other elements. Examples of organic mercury compounds are dimethylmercury, phenylmercuric acetate, and methylmercuric chloride. The form most commonly found in the environment is methylmercury.
How mercury exists in the environment Elemental mercury in the atmosphere can undergo transformation into inorganic mercury forms, providing a significant pathway for deposition of emitted elemental mercury.
Some micro-organisms can produce organic mercury, particularly methylmercury, from other mercury forms. Methylmercury can accumulate in living organisms and reach high levels in fish and marine mammals via a process called biomagnification (i.e. concentrations increase in the food chain).
Being an element, mercury cannot be broken down or degraded into harmless substances. Mercury may change between different states and species in its cycle, but its simplest form is elemental mercury, which itself is harmful to humans and the environment. Once mercury has been liberated from either ores or from fossil fuel and mineral deposits hidden in the Earth's crust and released into the biosphere, it can be highly mobile, cycling between the Earth's surface and the atmosphere. The Earth's surface soils, water bodies and bottom sediments are thought to be the primary biospheric sinks for mercury.
Mercury speciation The different forms mercury exists in (such as elemental mercury vapour, methylmercury, or mercuric chloride) are commonly designated "species". As mentioned above, the main groups of mercury species are elemental mercury, inorganic and organic mercury forms. Speciation is the term commonly used to represent the distribution of a quantity of mercury among various species.
Speciation influences the transport of mercury within and between environmental compartments including the atmosphere and oceans, among others. For example, the speciation is a determining factor for how far from the source mercury emitted to air is transported. Mercury adsorbed on particles and ionic (e.g., divalent) mercury compounds will fall on land and water mainly in the vicinity of the sources (local to regional distances), while elemental mercury vapour is transported on a hemispherical/global scale making mercury emissions a global concern. Another example is the so-called "polar sunrise mercury depletion incidence", where the transformation of elemental mercury to divalent mercury is influenced by increased solar activity and the presence of ice crystals, resulting in a substantial increase in mercury deposition during a three-month period (approximately March to June).
Moreover, speciation determines how to control mercury emissions to air. For example, emissions of inorganic mercuric compounds (such as mercuric chloride) are captured reasonably well by some control devices (such as wet-scrubbers), while capture of elemental mercury tends to be low for most emission control devices.
Sources of mercury The releases of mercury to the biosphere can be grouped in four categories: Natural sources - releases due to natural mobilization of naturally occurring mercury from the Earth's crust, such as volcanic activity and weathering of rocks Current anthropogenic (associated with human activity) releases from the mobilization of mercury impurities in raw materials such as fossil fuels – particularly coal, and to a lesser extent gas and oil and other extracted, treated and recycled minerals Current anthropogenic releases resulting from mercury used intentionally in products and processes, due to releases during manufacturing, leaks, disposal or incineration of spent products or other releases Re-mobilization of historic anthropogenic mercury releases previously deposited in soils, sediments, water bodies, landfills and waste/tailings piles.
The majority of atmospheric anthropogenic emissions are released as gaseous elemental mercury. The atmospheric residence time of elemental mercury is in the range of months to roughly one year. This makes transport on a hemispherical scale possible and emissions in any continent can thus contribute to the deposition in other continents. Estimates developed in the early 2000s are that less than half of all mercury deposition within the U.S. comes from U.S. sources.
Anthropogenic sources The largest emissions of mercury to the global atmosphere occur from combustion of fossil fuels; mainly coal in utility, industrial, and residential boilers. As much as two thirds of the total emission of ca. 2269 tonnes of mercury emitted from all anthropogenic sources worldwide in 2000 came from combustion of fossil fuels. Other anthropogenic sources of mercury include: cement production (mercury in lime), mining (iron/steel, zinc, gold), use of fluorescent lamps, various instruments and dental amalgam fillings, manufacturing of products containing mercury (thermometers, manometers and other instruments, electrical and electronic switches) and waste disposal.
Exposure to mercury
Mercury in the air eventually settles into water or onto land where it can be washed into water. Once deposited, certain microorganisms can change it into methylmercury, a highly toxic form that builds up in fish, shellfish and animals that eat fish. The general population is primarily exposed to methylmercury through the diet (especially fish) and to elemental mercury vapors due to dental amalgams. Depending on local mercury pollution load, substantial additional contributions to the intake of total mercury can occur through air and water.
Health effects Exposure to mercury differs depending on the type of food as well as dietetic practices. In fact, the biggest contribution of mercury comes from different fish sources and seafood. This contribution is estimated to be around 20 to 85% of the mercury intake of the general population. Other sources are significant such as water consumption, some of the cereals choices, some specific vegetables as well as a variety of red and white meat. Dietetic practices are able to alter mercury toxicity such as chewing boiled eggs or even chewing gum. In fact, those two practices have been proved to be able to reduce mercury exposure by increasing the mercury release. Such practices, in addition to food intakes, might explain the differences observed between the populations regarding the mercury toxicity. Nutrients intake is another factor explaining the changes in the toxicity levels of mercury as well as their effects. Selenium for example works as a protective agent against mercury toxicity obtained through fish intake. Other nutrients such as thiamine deficiency at the general population demonstrates an aggravation of the mercury exposure symptoms. Similar to thiamine, iron aggravates mercury exposure effect while ascorbic acid will help reduce the mercury toxicity effect. Fat is another agent that participates in the reduction of the mercury toxicity. In fact, higher LDL levels has been proved to help reducing mercury effects.
In fact, those nutrients are able not only to affect the mercury bioavailability but they affect as well their immunological influences as well as their biochemical, cytological and metabolic responses to mercury. On the other hand, multiple nutrients are found to interact with several other nutrients and elements in such a manner that would affect the mercury exposure toxicity as well as their metabolism.
Moreover, a variety of fish, milk, meat and wheat accompagned of selenium, zinc, magnesium, and vitamins C, E and B allow an alteration of the mercury metabolism.
Those multifactorial correlations are extremely hard to establish. In fact, concluding that it is a protective or aggravating correlation is always complicated and dependent on metabolic conditions.
Mercury exposure might have a variety of health effects depending on the population. In fact, some populations are affected by a lack of appetite others have seen a reduction of their food or fluid intake as well as a significant weight loss. Those alterations as well as the chronic intake of mercury might worsen a certain nutrition deficiency. Some of the most common deficiency observed with chronic mercury intake is a selenium deficiency. Such deficiency might impact neuronal functions as well as behaviour disorders and learning disabilities for children. Other deficiencies that are observed with a persisting mercury intake are vitamin E, vitamin B12 and vitamin C. Long term deficiency in vitamin E might cause muscle weakness as well as loss of muscle mass, abnormal eye movements and even vision problems. As for vitamin B12 deficiency, it might cause anemia and confusion for the elderly population. Finally, for long term vitamin C deficiencies, high blood pressure as well as gallbladder disease and stroke are all possible outcomes of those deficiencies. In order to avoid such deficiencies, a higher intake of those nutrients and vitamins are necessary.
Methylmercury is a type of mercury that is liquid at room temperature. The methylmercury is used for the preservation of grains that are used for animal food. The methylmercury is obtained through the methylation of the mercury with the presence of anaerobic bacteria in the waters as well as sediments and soils. In fact, most microbes that live in lakes, rivers, oceans are able to create the methylmercury.
Methylmercury has different ways of transferring itself. In fact, methylmercury is transferred through maternal milk during breast feeding. This methylmercury in breast feeding milk is transferred through fatty cells that allows the methylmercury to be transported through the milk. Methylmercury can pass through the placental barrier, allowing the compound to accumulate within the fetus.
Almost all people have at least trace amounts of methylmercury in their tissues, reflecting methylmercury's widespread presence in the environment and people's exposure through the consumption of fish and shellfish. Although the presence of Mercury is quite common, most people remain below the levels that can lead to contamination or poisoning.