Mercury is a natural chemical element and a metal, also known as quicksilver or hydrargyrum (watery or liquid silver in Latinized Greek), as is heavy, shiny, silvery-white and the only liquid metallic element at ordinary temperatures.
It is identified with the symbol «Hg» on the periodic table and its atomic number is 80. It exists in several chemical forms.
Compared to other metals, it is a poor conductor of heat but a good conductor of electricity.

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Elemental (metallic) mercury

Elemental or metallic mercury is an extremely rare element in the environment.
Elemental mercury is used in gold and silver mining, older thermometers, barometers, dental amalgams, fluorescent and mercury-vapor lamps, some electrical switches and other industrial processes.

Mercury can react with inorganic and organic molecules and a large variety of mercury chemical forms occurs naturally.

All the mercury compounds are toxic, especially the most soluble forms.

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Inorganic mercury compounds

Mercury forms chemical compounds in two oxidation states (+1 and +2) when reacts with inorganic compounds. Most of mercury (I) or Hg22+ compounds are water insoluble and easily transformed to mercury (II) or Hg2+ and elemental mercury (Hg0). Whereas mercury (II) compounds are mostly soluble.

Mercury minerals are then, highly concentrated in deposits (i.e. cinnabar and metacinnabar), generally found in areas of recent orogenesis, where high-density rocks are forced to emerge into the Earth’s crust, driven by hot springs or by the activity of certain volcanic regions.

Mercury mining deposits are easily accessible and cost-effective places for mineral extraction. The Almadén (Spain), Monte Amiata (Italy) and Idrija (Slovenia) mines dominated mercury production from the opening of the Almadén mine, until new deposits appeared in China.

Although the natural sources of mercury are scarce, its presence can be traced on a multitude of objects and products until recently in everyday and, since then, the spread of mercury in the environment has been increased exponentially.

Inorganic mercury is transported in water or soil from the weathering of rocks that contain inorganic mercury salts, and from factories or water treatment facilities that release water contaminated with mercury.

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Methylmercury and other organic compounds

When inorganic mercury salts can become attached to airborne particles. Rain and snow deposit these particles on land. Even after mercury gets deposited on land, it often returns to the atmosphere, as a gas or associated with particles, and then redeposits elsewhere. As it cycles between the atmosphere, land, and water, mercury undergoes a series of complex chemical and physical transformations, many of which are not completely understood.

Microscopic organisms can combine mercury with carbon, thus converting it from an inorganic to organic form. Methylmercury is the most common organic mercury compound found in the environment, and is highly toxic.

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Mercury becomes a problem for the environment when it is released from rock and ends up in the atmosphere and in water. These releases can happen naturally. Both volcanoes and forest fires send mercury into the atmosphere.

Human activities, however, are responsible for much of the mercury that is released into the environment. The burning of coal, oil and wood as fuel can cause mercury to become airborne, as can burning wastes that contain mercury.

This airborne mercury can fall to the ground in raindrops, in dust, or simply due to gravity (known as “air deposition”). The amount of mercury deposited in a given area depends on how much mercury is released from local, regional, national, and international sources.

Effects on health and enviroment

The main way that people are exposed to mercury is by eating fish and shellfish that have high levels of methylmercury, a highly toxic form of mercury, in their tissues. A less common way people are exposed to mercury is breathing mercury vapor. This can happen when mercury is released from a container, or from a product or device that breaks. If the mercury is not immediately contained or cleaned up, it can evaporate, becoming an invisible, odorless, toxic vapor.

  • Mercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages.
  • High levels of methylmercury in the bloodstream of babies developing in the womb and young children may harm their developing nervous systems, affecting their ability to think and learn.

Birds and mammals that eat fish are have more exposures to methylmercury than other animals in water ecosystems. Predators that eat these birds and mammals are also at risk. Methylmercury has been found in eagles, otters, and endangered Florida panthers. At high levels of exposure, methylmercury’s harmful effects on these animals include:

  • Death and reduced reproduction
  • Slower growth and development
  • Abnormal behavior

Minamata Convention

The Minamata Convention on Mercury is a global treaty to protect human health and the environment from the adverse effects of mercury. It was agreed at the fifth session of the Intergovernmental Negotiating Committee on mercury in Geneva, Switzerland at 7 a.m. on the morning of Saturday, 19 January 2013 and adopted later that year on 10 October 2013 at a Diplomatic Conference (Conference of Plenipotentiaries), held in Kumamoto, Japan.

The Minamata Convention entered into force on 16 August 2017, on the 90th day after the date of deposit of the 50th instrument of ratification, acceptance, approval or accession.

The Convention draws attention to a global and ubiquitous metal that, while naturally occurring, has broad uses in everyday objects and is released to the atmosphere, soil and water from a variety of sources. Controlling the anthropogenic releases of mercury throughout its lifecycle has been a key factor in shaping the obligations under the Convention.
Major highlights of the Minamata Convention include a ban on new mercury mines, the phase-out of existing ones, the phase out and phase down of mercury use in a number of products and processes, control measures on emissions to air and on releases to land and water, and the regulation of the informal sector of artisanal and small-scale gold mining.

The Convention also addresses interim storage of mercury and its disposal once it becomes waste, sites contaminated by mercury as well as health issues.

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