The mercury cycle is a

biogeochemical cycle A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cyc ...

influenced by natural and

anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Anthropogenic may also refer to things that have been generated by humans, as follows: * Human impact on the enviro ...

processes that transform mercury through multiple chemical forms and environments. Mercury is present in the

Earth's crust Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper ...

and in various forms on the Earth's surface. It can be elemental, inorganic, or organic. Mercury exists in three

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

s: 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 A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

, 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

Primary sources

Primary sources of mercury emissions can be natural or

. Most natural mercury occurs as the mercury sulfide mineral,

cinnabar Cinnabar (; ), or cinnabarite (), also known as ''mercurblende'' is the bright scarlet to brick-red form of Mercury sulfide, mercury(II) sulfide (HgS). It is the most common source ore for refining mercury (element), elemental mercury and is t ...

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

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

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, sunlight, and biological organisms. It occurs '' in situ'' (on-site, with little or no move ...

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; it has symbol Cu (from Latin ) 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 pinkish-orang ...

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

Secondary sources

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

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

burning, including

forest fires A forest fire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire ( in Au ...

. 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 Atmosphere of Earth, 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 fro ...

, 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 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 ''w ...

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

and

archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

into

methylmercury Methylmercury is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a bioaccumulative environment ...

( 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