Mercury cycle

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Physical mercury cycle PhysicalMercuryCycle.png
Physical mercury cycle

The mercury cycle is a biogeochemical cycle influenced by natural and anthropogenic processes that transform mercury through multiple chemical forms and environments.

Contents

Mercury is present in the Earth's crust and in various forms on the Earth's surface. It can be elemental, inorganic, or organic. [1] 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. [2] Annually, over 5000 metric tons of mercury is released to the atmosphere by primary emissions and secondary re-emissions. [3]

Sources of mercury

Sample of the mercury sulfide ore, cinnabar Cinnabar (New Almaden, California, USA) (18824306236).jpg
Sample of the mercury sulfide ore, cinnabar

Primary sources

Primary sources of mercury emissions can be natural or anthropogenic. [4] Most natural mercury occurs as the mercury sulfide mineral, cinnabar, which is one of the only significant ores of mercury. [5] [6] Organic-rich sedimentary rocks can also contain elevated mercury. Weathering of minerals and geothermal activity release mercury to the environment. [7] [8] Active volcanoes are another significant primary source of natural mercury. [9] Anthropogenic primary sources of mercury include gold mining, burning coal, and production of non-iron metals, such as copper or lead. [8] [10]

Secondary sources

Secondary natural sources, which re-emit previously deposited mercury, include vegetation, evasion from oceans and lakes, and biomass burning, including forest fires. [3] Primary anthropogenic emissions are leading to increased sizes of mercury in surface reservoirs. [11]

Processes

Mercury is transported and distributed by atmospheric circulation, which moves elemental mercury from the land to the ocean. [12] 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. [13] 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. [14] Because photooxidation is very slow, elemental mercury can circulate over the entire globe before being oxidized and deposited. [14] Wet and dry deposition is responsible for 90% of the mercury of surface waters, including open ocean. [15] [16]

A fraction of deposited mercury instantaneously re-volatilize back to the atmosphere. [17]

Inorganic mercury can be converted by bacteria and archaea into methylmercury ([CH3 Hg] +), [18] which bioaccumulates in marine species such as tuna and swordfish and biomagnifies further up the food chain. [19] [20]

Certain xenophyophores have been found to have abnormally high concentrations of mercury within their bodies. [21]

See also

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References

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  5. ↑ "Cinnabar: A toxic ore of mercury, once used as a pigment". geology.com. Retrieved April 12, 2019.
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  15. ↑ Mason RP, Fitzgerald WF, Morel FM (1994). "The biogeochemical cycling of elemental mercury: Anthropogenic influences". Geochimica et Cosmochimica Acta. 58 (15): 3191–3198. Bibcode:1994GeCoA..58.3191M. doi:10.1016/0016-7037(94)90046-9.
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  18. ↑ Gilmour CC, Podar M, Bullock AL, Graham AM, Brown SD, Somenahally AC, Johs A, Hurt RA, Bailey KL, Elias DA (October 2013). "Mercury methylation by novel microorganisms from new environments". Environmental Science & Technology. 47 (20): 11810–20. Bibcode:2013EnST...4711810G. doi:10.1021/es403075t. PMID   24024607.
  19. ↑ "Mercury: Overview". Oceana. Oceana: Protecting the World's Oceans. 2012. Archived from the original on January 4, 2015. Retrieved February 28, 2012.
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  21. ↑ Gooday AJ, Sykes D, Góral T, Zubkov MV, Glover AG (August 2018). "Micro-CT 3D imaging reveals the internal structure of three abyssal xenophyophore species (Protista, Foraminifera) from the eastern equatorial Pacific Ocean". Scientific Reports. 8 (1): 12103. Bibcode:2018NatSR...812103G. doi:10.1038/s41598-018-30186-2. PMC   6092355 . PMID   30108286.
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