|Mercury Fact sheet|
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Mercury is highly toxic, causing damage to the nervous system at even relatively low levels of exposure. It is particularly harmful to the development of unborn children. It collects in human and animal bodies and can be concentrated through the food chain, especially in certain types of fish. The Commission’s Directorate-General for Health and Consumer Protection has recommended that women who are breastfeeding or who are or might become pregnant should limit their consumption of large predatory fish, such as swordfish, shark, marlin, pike and tuna.
It is well known that mercury has no respect for national or regional boundaries, travelling long distances through the atmosphere, and has contaminated both the European and global food supplies at levels posing a significant risk to human health, according to the World Health Organisation, food safety authorities, medical and public health professionals around the world. Even the arctic, which has no sources of mercury pollution, is experiencing dangerous levels of contamination in its marine mammals and other species which are part of the food supply.
Mercury occurs naturally in the environment and exists in different forms. In pure form it is known as “elemental” or “metallic” mercury (Hg(0) or Hg0). Mercury is rarely found in nature as the pure, liquid metal, but rather within compounds and inorganic salts. Mercury can be bound to other compounds as monovalent or divalent mercury (also expressed as Hg(I) and Hg(II) or Hg2+, respectively). Many inorganic and organic compounds of mercury can be formed from Hg(II).
Mercury is mined as mercuric sulphide (cinnabar ore). Through history, deposits of cinnabar have been the source ores for commercial mining of metallic mercury. The metallic form is most simply refined from mercuric sulphide ore by heating the ore to temperatures above 540º C. This vaporises the mercury in the ore, and the vapours are then captured and cooled to form the liquid metal mercury.
Inorganic mercuric compounds include mercuric sulphide (HgS), mercuric oxide (HgO) and mercuric chloride (HgCl2). These mercury compounds are also called mercury salts. Most inorganic mercury compounds are white powders or crystals, except for mercuric sulphide, which is red and turns black after exposure to light. Some mercury salts (such as HgCl2) are sufficiently volatile to exist as an atmospheric gas. However, the water solubility and chemical reactivity of these inorganic (or divalent) mercury gases lead to much more rapid deposition from the atmosphere than for elemental mercury. This results in significantly shorter atmospheric lifetimes for these divalent mercury gases than for the elemental mercury gas.
When mercury combines with carbon, the compounds formed are called "organic" mercury compounds or organomercurials. There is a potentially large number of organic mercury compounds (such as methylmercury, dimethylmercury, phenylmercury, and ethylmercury); however, by far the most common organic mercury compound in the environment is methylmercury. Like the inorganic mercuric compounds, both methylmercury and phenylmercury exist as "salts" (for example, methylmercuric chloride or phenylmercuric acetate). When pure, most forms of methylmercury and phenylmercury are white crystalline solids. Dimethylmercury, however, is a colourless liquid.
The most common organic mercury compound that micro-organisms and natural processes generate from other forms is methylmercury. Methylmercury is of particular concern because it can build up (bioaccumulate and biomagnify) in many edible freshwater and saltwater fish and marine mammals to levels that are many thousands of times greater than levels in the surrounding water.
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.
|Last Updated on Friday, 30 July 2010 16:40|