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[Later: insert summary paragraph]

Forms of Mercury

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Hg(0), MeHg, DMHg, and Hg(II) can only be introduced in the environment through volcanism, geothermic processes, and anthropological sources, and unlike nutrient cycling, mercury does not follow cyclical distribution patterns[1]. It can also be found in mineral form, as both cinnabar and metacinnabar[2].

Because they're almost all found everywhere (albeit in varying concentrations) and directly below I list each reservoir and the forms we might expect to find there, maybe we could avoid listing where each one is found up here. To avoid being too repetitive, up here we could state some of the many forms of mercury (Hg(0), MeHg, DMHg, and Hg(II), HgS, among other forms), write which forms are organic vs. inorganic, and describe that they undergo exchanges between different reservoirs as well as both organic vs inorganic reactions to convert between different forms. Would that make sense?

Something like:

Mercury is introduced to the Earth's surface environment through volcanism, geothermic processes, and anthropological anthropogenic emissions. Mercury can be found in its elemental form (Hg(0)) as well as in compounds in two oxidized states (Hg(I), Hg(II)). (Then go into important organic) MeHg, DMHg (and inorganic) Hg(II), HgS compounds. (Reword) unlike nutrient cycling, mercury does not follow cyclical distribution patterns[1]. Use the rest of the paragraph and the existing content you have below to briefly describe the different organic vs. inorganic processes that move mercury between its various organic vs. inorganic forms.

Hg(II) undergoes methylation and demethylation reactions (is this converting to and from MeHg?). It can also be found in mineral form HgS, as both cinnabar and metacinnabar[2]. Methylmercury is one of these three forms that stem from elemental mercury (is there a specific chemical reaction we could mention here since "stem" is a bit vague? I also thought methylmercury was formed from Hg(II) during methylation?) and is more common than its other methylated form, dimethylmercury[1]. It is the most toxic form, acting as a neurotoxin in organisms due to its ability to combine with lipids and fats. Dimethylmercury, the lesser product of methylation, is created through the reduction of Hg(II) (great! this is specific which is helpful. Could we add a couple words at the end like "by marine organisms" or "in photochemical reactions" whichever is true. It's still a bit unclear to me how these different forms are created, if this is supposed to be organic methylation, which it sounds like it should be since the next sentence is about inorganic, then we should explicitly state that). Inorganic methylation has been documented as a result of anaerobic and aerobic microbes, as well as reduction reactions[1]. It is this form (which form?) that unicellular organisms ingest and is slowly eliminated relative to its uptake rate[3].


Elemental mercury is found in the atmosphere and surface waters[1]. With a solubility similar to oxygen, it is capable of dissolution and can be found in supersaturated concentrations under ice in surface water, but near saturation in open water[4]. This is the main form of mercury input into the ocean[5].

Terrestrial reservoir

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Most mercury resides in the lithosphere and occurs in the form of the mercury sulfide, cinnabar (HgS), which is one of the only significant ores of mercury.[6] Mercury accumulates in deep sediments, the largest mercury reservoir, from burial of deep-ocean mercury.[7] The burial of deep-ocean mercury in ocean sediments is the largest sink of mercury from surface reservoirs.[7] The residence time of mercury in the deep mineral reservoir is around a billion years.[8] Mercury is also accumulated in surface soils due to sequestration by vegetation or deposition of atmospheric mercury. Surface soils are a relatively small mercury reservoir (∼10–15 Gg) with a residence time of around 100 years, while slower-decaying soils and organic matter like peat act as a larger mercury reservoir (∼300 Gg) with a residence time of ~400 years.[9][10] Organic-rich sedimentary rocks can also be enriched in mercury.[11]

Oceanic reservoir

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In the ocean, mercury exists primarily in elemental (Hg(0)), reactive (Hg(II)), and particulate forms. In its various forms, mercury is scavenged by fish and primary producers, which is supported by its vertical distribution (what is supported? the consumption? and what is the vertical distribution? A couple extra words could make this more clear... am I interpreting correctly if it's reworded as "The vertical distribution of mercury throughout the water column allows for mercury to be scavenged in its various forms by fish and primary producers"). in the water column.[3] Marine organisms can also produce organic species of mercury such as Methylmercury (MeHg). It is estimated that ~200 Gg mercury exists in the deep ocean and ~70 Gg mercury exists in the surface (< 500 m) ocean.[12] Despite the smaller pool of mercury in the ocean's surface waters relative to the deep ocean, the effects of anthropogenic mercury emissions is most notable at the ocean's surface, where mercury concentrations are estimated to have increased by 200% over the past century.[13] Changes in deep ocean mercury concentrations are less significant and are primarily limited to regions of deep water formation in the North Atlantic and Southern Oceans where sinking surface waters have more recently been in contact with the atmosphere.[13] The residence time of mercury in the ocean's surface waters is ~0.6 years, and the residence time for mercury on continental shelves in the ocean is ~0.3 years.[14][15]

Atmospheric reservoir

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Approximately 95% of atmospheric mercury is in the form of gaseous elemental mercury (Hg(0)).[16] The residence time of Hg(0) in the atmosphere is around half a year, allowing Hg(0) to be transported long distances from its emission source and widely distributed across the planet.[17] Over time, Hg(0) is oxidized to form reactive gaseous mercury (Hg(II)), which is more readily deposited to the Earth's surface.[16][18] The Hg(II) form of mercury has a residence time in the atmosphere of only a few weeks, and can therefore not be transported far from its formation or emission source.[18][19] Some deposited Hg(II) is rapidly converted to Hg(0) and re-emitted to the atmosphere. Considering this recycling between the surface and atmosphere, the overall residence time of mercury in the atmosphere increases to 1.6 years.[17] Mercury concentrations in the atmosphere vary due to local sources and depositional processes. In the northern hemisphere troposphere, an average background concentration of 2 nanograms per cubic meter has been estimated. [19]

 
Major processes in the mercury cycle. Thick arrows represent fluxes of mercury between ocean, land, and atmosphere. Thin arrows represent transport within a reservoir or transformation between different forms of mercury, including elemental (Hg(0)), reactive (Hg(II)), organic methylated (MeHg), and mineral (HgS) mercury.



Emission of terrestrial mercury

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Terrestrial mercury is released to the atmosphere and hydrosphere by both geologic and anthropogenic processes. Primary sources of mercury emissions include natural processes such as volcanic activity, mineral weathering, and release from mercury-rich surface soils, as well as anthropogenic processes such as gold mining, burning coal, and production of non-iron metals such as copper or lead.[20][21][22] [23][24] Secondary natural sources, which re-emit previously deposited mercury, include vegetation, evasion from oceans and lakes, and biomass burning, including forest fires.[25] From 1997-2006, around 8% of all mercury emissions to the atmosphere was from biomass burning.[26] Anthropogenic mercury emissions from primary sources are leading to increased concentrations of mercury in surface reservoirs.[27]

Atmospheric transport and deposition of mercury

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Mercury is primarily transported and distributed throughout the planet by atmospheric circulation, which moves mercury between its land and ocean reservoirs. Atmospheric mercury is transferred back to land and water surfaces by wet deposition and dry deposition.[28] Elemental mercury (Hg(0)), which makes up around 95% of atmospheric mercury, is the most stable form of mercury found in the atmosphere.[29][30] [31] Despite localized emission sources, Hg(0) remains in the atmosphere for six months to a year and is therefore well-distributed throughout the globe.[29][28] Hg(0) does not readily dissolve in water and leaves the atmosphere primarily through dry deposition.[32] The other primary form of atmospheric mercury, reactive gaseous mercury (Hg(II)), is returned to the Earth's surface within a few weeks of formation by both dry and wet deposition.[32][30][33] Wet deposition of Hg(II) is the primary pathway for return of atmospheric mercury to the Earth's surface.[32] Due to this short residence time of Hg(II), Hg(II) is either deposited near its emission source or can be deposited in regions where local atmospheric reactions oxidize Hg(0) to form Hg(II). Mercury can be oxidized into more reactive forms, such as reactive gaseous Hg and particulate elemental Hg[29].This is most noted in the spring when favorable conditions occur in the Arctic (e.g. Cold temperatures, adequate sunlight) and the presence of reactive, catalyzing halogens in sea ice (i.e. Bromine, Chlorine, Bromine Oxide, Chlorine Oxide). However, there are uncertainties revolving around which major atmospheric oxidants play more specific roles. Previous data indicates elemental mercury in the atmosphere is a result of Hg (II) reduction in snow and becomes its gaseous form[29].Because photooxidation is very slow, Hg(0) can circulate over the entire globe before being oxidized and deposited.[32] Around 60% of atmospheric mercury is deposited to land while 40% is deposited to water.[32] A fraction of deposited mercury instantaneously re-volatilizes back to the atmosphere.[34]

Deposition and evasion of oceanic mercury

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The most predominant route of mercury input into the Arctic Ocean is long-range transport, as opposed to point source introduction which can be acute.[29] Wet and dry deposition of atmospheric mercury are responsible for 90% of the mercury found in surface waters, including in the open ocean.[35][36] Once in the ocean, Hg(II) is rapidly converted into Hg(0). Hg(II) is therefore not commonly found in undersurface waters, but reappears (This is a little vague, could reword to say: it is produced due to... or found in large quantities... whichever is true) in ocean sediment. Oceanic Hg(II) also undergoes methylation and demethylation reactions (converting to and from MeHg?). The ocean is generally supersaturated in Hg(0) with respect to the atmosphere, resulting in evasion of Hg(0) from the ocean and a net flux of Hg(0) to the atmosphere from the ocean on short time scales.[37] Over decadal time scales, mercury concentrations in the surface waters of the ocean respond to atmospheric changes.[38] Over long time scales, the ocean is the primary sink for atmospheric mercury from anthropogenic sources.[39] Deep-ocean mercury is buried in ocean sediments and returned to the terrestrial mercury reservoir, closing the mercury cycle. Anthropogenic influence

Due to anthropogenic emissions, release of mercury from land into the global atmosphere-ocean-land cycle is estimated to have increased by a factor of three to five from natural mercury mobilization rates.[40] The increased rate of mercury cycling is primarily due to mining, fossil fuel combustion, and production of metals and other industrial materials by humans.[40] Fossil fuel combustion, primary that of coal, is the largest anthropogenic mercury source, contributing around 60% of all human-released mercury.[40] From measurements beginning in the late 1970s, atmospheric mercury levels were observed to peak in the late 1980s, decrease in the late 1990s, and remain relatively constant into the 21st century. [41] It is estimated that human activities have released more than 1540 Gg of mercury since 1850.[42]

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  9. ^ Driscoll, Charles T.; Mason, Robert P.; Chan, Hing Man; Jacob, Daniel J.; Pirrone, Nicola (2013-05-21). "Mercury as a Global Pollutant: Sources, Pathways, and Effects". Environmental Science & Technology. 47 (10): 4967–4983. doi:10.1021/es305071v. ISSN 0013-936X. PMC 3701261. PMID 23590191. {{cite journal}}: line feed character in |first4= at position 7 (help); line feed character in |title= at position 50 (help)
  10. ^ Grigal, D. F. (2003). "Mercury Sequestration in Forests and Peatlands". Journal of Environmental Quality. 32 (2): 393–405. doi:10.2134/jeq2003.3930. ISSN 1537-2537.
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  13. ^ a b Driscoll, Charles T.; Mason, Robert P.; Chan, Hing Man; Jacob, Daniel J.; Pirrone, Nicola (2013-05-21). "Mercury as a Global Pollutant: Sources, Pathways, and Effects". Environmental Science & Technology. 47 (10): 4967–4983. doi:10.1021/es305071v. ISSN 0013-936X. PMC 3701261. PMID 23590191. {{cite journal}}: line feed character in |first4= at position 7 (help); line feed character in |title= at position 50 (help)
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  15. ^ Cossa, D.; Coquery, M.; Gobeil, C.; Martin, J.-M. (1996), Baeyens, Willy; Ebinghaus, Ralf; Vasiliev, Oleg (eds.), "Mercury Fluxes at the Ocean Margins", Global and Regional Mercury Cycles: Sources, Fluxes and Mass Balances, NATO ASI Series, Dordrecht: Springer Netherlands, pp. 229–247, doi:10.1007/978-94-009-1780-4_11, ISBN 978-94-009-1780-4, retrieved 2020-11-08
  16. ^ a b Morel, F.; Kraepiel, A.; Amyot, M. (1998). "THE CHEMICAL CYCLE AND BIOACCUMULATION OF MERCURY". doi:10.1146/ANNUREV.ECOLSYS.29.1.543. {{cite journal}}: Cite journal requires |journal= (help)
  17. ^ a b Selin, Noelle; Jacob, Daniel; Yantosca, Robert; Strode, Sarah; Jaegle, Lyatt; Sunderland, Elsie (2008). "Global 3‐D land‐ocean‐atmosphere model for mercury: Present‐day versus preindustrial cycles and anthropogenic enrichment factors for deposition". Global Biogeochem. Cycles. 22 (GB2011). doi:10.1029/2007GB003040 – via Wiley.
  18. ^ a b Steffen, A.; Douglas, T.; Amyot, M.; Ariya, P.; Aspmo, K.; Berg, T.; Bottenheim, J.; Brooks, S.; Cobbett, F.; Dastoor, A.; Dommergue, A. (2008-03-12). "A synthesis of atmospheric mercury depletion event chemistry in the atmosphere and snow". Atmospheric Chemistry and Physics. 8 (6): 1445–1482. doi:10.5194/acp-8-1445-2008. ISSN 1680-7324.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  19. ^ a b "WHO air quality guidelines for Europe, 2nd edition, 2000 (CD ROM version)". www.euro.who.int. Retrieved 2020-11-08.
  20. ^ Bagnato, E.; Aiuppa, A.; Parello, F.; Allard, P.; Shinohara, H.; Liuzzo, M.; Giudice, G. (2011-07-01). "New clues on the contribution of Earth's volcanism to the global mercury cycle". Bulletin of Volcanology. 73 (5): 497–510. doi:10.1007/s00445-010-0419-y. ISSN 1432-0819.
  21. ^ Xu, Jingying; Bravo, Andrea Garcia; Lagerkvist, Anders; Bertilsson, Stefan; Sjöblom, Rolf; Kumpiene, Jurate (2015-01-01). "Sources and remediation techniques for mercury contaminated soil". Environment International. 74: 42–53. doi:10.1016/j.envint.2014.09.007. ISSN 0160-4120.
  22. ^ US EPA, OITA (2014-02-27). "Mercury Emissions: The Global Context". US EPA. Retrieved 2020-11-08.
  23. ^ Xu, Jingying; Bravo, Andrea Garcia; Lagerkvist, Anders; Bertilsson, Stefan; Sjöblom, Rolf; Kumpiene, Jurate (2015-01-01). "Sources and remediation techniques for mercury contaminated soil". Environment International. 74: 42–53. doi:10.1016/j.envint.2014.09.007. ISSN 0160-4120.
  24. ^ Horowitz, Hannah Marie; Jacob, Daniel James; Amos, Helen Marie; Streets, David G.; Sunderland, Elynor M. (2014). "Historical Mercury Releases from Commercial Products: Global Environmental Implications". Environmental Science & Technology. doi:10.1021/es501337j. ISSN 0013-936X.
  25. ^ Pirrone, N.; Cinnirella, S.; Feng, X.; Finkelman, R. B.; Friedli, H. R.; Leaner, J.; Mason, R.; Mukherjee, A. B.; Stracher, G. B.; Streets, D. G.; Telmer, K. (2010-07-02). "Global mercury emissions to the atmosphere from anthropogenic and natural sources". Atmospheric Chemistry and Physics. 10 (13): 5951–5964. doi:10.5194/acp-10-5951-2010. ISSN 1680-7316.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  26. ^ Friedli, H.; Arellano, A.; Cinnirella, S.; Pirrone, N. (2009). "Initial Estimates of Mercury Emissions to the Atmosphere from Global Biomass Burning". Environ. Sci. Technol. 43 (10): 3507–3513. doi:10.1021/es802703g – via ACS publications.
  27. ^ Programme, United Nations Environment (2013). "Global Mercury Assessment 2013: Sources, emissions, releases, and environmental transport". {{cite journal}}: Cite journal requires |journal= (help)
  28. ^ a b Selin, Noelle; Jacob, Daniel; Yantosca, Robert; Strode, Sarah; Jaegle, Lyatt; Sunderland, Elsie (2008). "Global 3‐D land‐ocean‐atmosphere model for mercury: Present‐day versus preindustrial cycles and anthropogenic enrichment factors for deposition". Global Biogeochem. Cycles. 22 (GB2011). doi:10.1029/2007GB003040 – via Wiley.
  29. ^ a b c d e Kirk, Jane L (2012). "Mercury in Arctic marine ecosystems: sources, pathways and exposure". Environmental research. 119: 64-87. doi:10.1016/j.envres.2012.08.012.
  30. ^ a b Steffen, A.; Douglas, T.; Amyot, M.; Ariya, P.; Aspmo, K.; Berg, T.; Bottenheim, J.; Brooks, S.; Cobbett, F.; Dastoor, A.; Dommergue, A. (2008-03-12). "A synthesis of atmospheric mercury depletion event chemistry in the atmosphere and snow". Atmospheric Chemistry and Physics. 8 (6): 1445–1482. doi:10.5194/acp-8-1445-2008. ISSN 1680-7324.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  31. ^ Driscoll, Charles T.; Mason, Robert P.; Chan, Hing Man; Jacob, Daniel J.; Pirrone, Nicola (2013-05-21). "Mercury as a Global Pollutant: Sources, Pathways, and Effects". Environmental Science & Technology. 47 (10): 4967–4983. doi:10.1021/es305071v. ISSN 0013-936X. PMC 3701261. PMID 23590191. {{cite journal}}: line feed character in |first4= at position 7 (help); line feed character in |title= at position 50 (help)
  32. ^ a b c d e Morel, F.; Kraepiel, A.; Amyot, M. (1998). "THE CHEMICAL CYCLE AND BIOACCUMULATION OF MERCURY". doi:10.1146/ANNUREV.ECOLSYS.29.1.543. {{cite journal}}: Cite journal requires |journal= (help)
  33. ^ "WHO air quality guidelines for Europe, 2nd edition, 2000 (CD ROM version)". www.euro.who.int. Retrieved 2020-11-08.
  34. ^ Selin, Noelle E. (2009-10-15). "Global Biogeochemical Cycling of Mercury: A Review". Annual Review of Environment and Resources. 34 (1): 43–63. doi:10.1146/annurev.environ.051308.084314. ISSN 1543-5938.
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  37. ^ Lamborg, Carl H.; Hammerschmidt, Chad R.; Bowman, Katlin L.; Swarr, Gretchen J.; Munson, Kathleen M.; Ohnemus, Daniel C.; Lam, Phoebe J.; Heimbürger, Lars-Eric; Rijkenberg, Micha J. A.; Saito, Mak A. (2014-08). "A global ocean inventory of anthropogenic mercury based on water column measurements". Nature. 512 (7512): 65–68. doi:10.1038/nature13563. ISSN 0028-0836. {{cite journal}}: Check date values in: |date= (help)
  38. ^ Driscoll, Charles T.; Mason, Robert P.; Chan, Hing Man; Jacob, Daniel J.; Pirrone, Nicola (2013-05-21). "Mercury as a Global Pollutant: Sources, Pathways, and Effects". Environmental Science & Technology. 47 (10): 4967–4983. doi:10.1021/es305071v. ISSN 0013-936X. PMC 3701261. PMID 23590191. {{cite journal}}: line feed character in |first4= at position 7 (help); line feed character in |title= at position 50 (help)
  39. ^ Amos, Helen; Jacob, Daniel; Streets, David; Sunderland, Elsie (2013). "Legacy impacts of all‐time anthropogenic emissions on the global mercury cycle". Global Biogeochem. Cycles. 27 (2): 410–421. doi:10.1002/gbc.20040 – via Wiley.
  40. ^ a b c Selin, Noelle (2009). "Global Biogeochemical Cycling of Mercury: A Review". Annu. Rev. Environ. Resour. 34: 43–63. doi:10.1146/annurev.environ.051308.084314.
  41. ^ Slemr, F.; Brunke, E.G.; Ebinghaus, R.; Temme, C.; Munthe, J.; Wangberg, I.; Schroeder, W.; Steffen, A.; Berg, T. (2003). "Worldwide trend of atmospheric mercury since 1977". Geophys. Res. Lett. 30 (10): 1516. doi:10.1029/2003GL016954 – via American Geophysical Union.
  42. ^ Streets, David G.; Horowitz, Hannah M.; Jacob, Daniel J.; Lu, Zifeng; Levin, Leonard; ter Schure, Arnout F. H.; Sunderland, Elsie M. (2017-06-06). "Total Mercury Released to the Environment by Human Activities". Environmental Science & Technology. 51 (11): 5969–5977. doi:10.1021/acs.est.7b00451. ISSN 0013-936X.
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