The mercury cycle is a biogeochemical cycle influenced by natural and anthropogenic processes that transform mercury through multiple chemical forms and environments. Mercury is present in the Earth's crust and in various forms on the Earth’s surface. It can be elemental, inorganic, or organic. Mercury exists in three oxidation states: 0 (elemental mercury), I (mercurous mercury), and II (mercuric mercury). Mercury emissions to the atmosphere can be primary sources, which release mercury from the lithosphere, or secondary sources, which exchange mercury between surface reservoirs. Annually, over 5000 metric tons of mercury is released to the atmosphere by primary emissions and secondary re-emissions.

Sources of mercury

Cinnabar (New Almaden, California, USA) (18824306236)

Primary sources

Primary sources of mercury emissions can be natural or anthropogenic. Most natural mercury occurs as the mercury sulfide mineral,

cinnabar Cinnabar (), or cinnabarite (), from the grc, κιννάβαρι (), is the bright scarlet to brick-red form of mercury(II) sulfide (HgS). It is the most common source ore for refining elemental mercury and is the historic source for the bri ...

, which is one of the only significant ores of mercury. Organic-rich

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s can also contain elevated mercury.

Weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement) ...

of minerals and geothermal activity release mercury to the environment. Active volcanoes are another significant primary source of natural mercury. Anthropogenic primary sources of mercury include gold mining, burning coal, and production of non-iron metals, such as

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

Secondary sources

Secondary natural sources, which re-emit previously deposited mercury, include vegetation, evasion from oceans and lakes, and biomass burning, including

forest fires A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identif ...

. Primary anthropogenic emissions are leading to increased sizes of mercury in surface reservoirs.

Processes

Mercury is transported and distributed by

atmospheric circulation Atmospheric circulation is the large-scale movement of air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth. The Earth's atmospheric circulation varies from year to year, bu ...

, which moves elemental mercury from the land to the ocean. Elemental mercury in the atmosphere is returned to the Earth's surface by several routes. A major sink of elemental mercury (Hg(0)) in the atmosphere is through dry deposition. Some of elemental mercury, on the other hand, is photooxidized to gaseous mercury(II), and is returned to the Earth's surface by both dry and

wet deposition In the physics of aerosols, deposition is the process by which aerosol particles collect or deposit themselves on solid surfaces, decreasing the concentration of the particles in the air. It can be divided into two sub-processes: ''dry'' and '' ...

. Because photooxidation is very slow, elemental mercury can circulate over the entire globe before being oxidized and deposited. Wet and dry deposition is responsible for 90% of the mercury of surface waters, including open ocean. A fraction of deposited mercury instantaneously re-volatilize back to the atmosphere. Inorganic mercury can be converted by

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

and archaea into methylmercury ( Hg/nowiki>.html" ;"title="Mercury_(element).html" ;"title="H₃ Hg/nowiki>">Mercury_(element).html"_;"title="H₃Mercury_(element)">Hg/nowiki>⁺),_which_bioaccumulate.html" ;"title="Mercury (element)">Hg/nowiki>">Mercury_(element).html" ;"title="H₃Mercury (element)">Hg/nowiki>⁺), which bioaccumulate">Mercury (element)">Hg/nowiki>">Mercury_(element).html" ;"title="H₃Mercury (element)">Hg/nowiki>⁺), which bioaccumulates in marine species such as tuna and swordfish and Biomagnification, biomagnifies further up the food chain. Certain Xenophyophorea, xenophyophores have been found to have abnormally high concentrations of mercury within their bodies.

References

{{Authority control Biogeochemical cycle Mercury (element) Use mdy dates from March 2012

Sources of mercury

Primary sources

Secondary sources

Processes

See also

References