======================================================================
= Manganese =
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Introduction
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Manganese is a chemical element; it has symbol Mn and atomic number
25. It is a hard, brittle, silvery metal, often found in minerals in
combination with iron. Manganese was first isolated in the 1770s. It
is a transition metal with a multifaceted array of industrial alloy
uses, particularly in stainless steels. It improves strength,
workability, and resistance to wear. Manganese oxide is used as an
oxidising agent, as a rubber additive, and in glass making,
fertilisers, and ceramics. Manganese sulfate can be used as a
fungicide.
Manganese is also an essential human dietary element, important in
macronutrient metabolism, bone formation, and free radical defense
systems. It is a critical component in dozens of proteins and enzymes.
It is found mostly in the bones, but also the liver, kidneys, and
brain. In the human brain, the manganese is bound to manganese
metalloproteins, most notably glutamine synthetase in astrocytes.
Manganese is commonly found in laboratories in the form of the deep
violet salt potassium permanganate where it is used as an oxidizer.
Potassium permanganate is also used as a biocide in water treatment.
It occurs at the active sites in some enzymes. Of particular interest
is the use of a Mn-O cluster, the oxygen-evolving complex, in the
production of oxygen by plants.
Physical properties
=====================
Manganese is a silvery-gray metal that resembles iron. It is hard and
very brittle, difficult to melt, but easy to oxidize. Manganese and
its common ions are paramagnetic. Manganese tarnishes slowly in air
and oxidizes ("rusts") like iron in water containing dissolved oxygen.
Isotopes
==========
Naturally occurring manganese is composed of one stable isotope, 55Mn.
Several radioisotopes have been isolated and described, ranging in
atomic weight from (46Mn) to (72Mn). The most stable are 53Mn with a
half-life of 3.7 million years, 54Mn with a half-life of 312.2 days,
and 52Mn with a half-life of 5.591 days. All of the remaining
radioactive isotopes have half-lives of less than three hours, and the
majority of less than one minute. The primary decay mode in isotopes
lighter than the most abundant stable isotope, 55Mn, is electron
capture, and the primary mode in heavier isotopes is beta decay.
Manganese also has three meta states.
Manganese is part of the iron group of elements, which are thought to
be synthesized in large stars shortly before the supernova explosion.
53Mn decays to 53Cr with a half-life of 3.7 million years. Because of
its short half-life, 53Mn is relatively rare; it is produced by the
impact of cosmic rays on iron. Manganese isotopic contents are
typically combined with chromium isotopic contents and have found
application in isotope geology and radiometric dating. Mn-Cr isotopic
ratios reinforce the evidence from 26Al and 107Pd for the early
history of the Solar System. Variations in 53Cr/52Cr and Mn/Cr ratios
from several meteorites suggest an initial 53Mn/55Mn ratio, which
indicate that Mn-Cr isotopic composition must result from 'in situ'
decay of 53Mn in differentiated planetary bodies. Hence, 53Mn provides
additional evidence for nucleosynthetic processes immediately before
the coalescence of the Solar System.
Allotropes
============
align=right Unit cell of an α-Mn crystal Unit cell of a β-Mn crystal
Four allotropes (structural forms) of solid manganese are known,
labeled α, β, γ and δ, and occur at successively higher temperatures.
All are metallic, stable at standard pressure, and have a cubic
crystal lattice, but they vary widely in their atomic structures.
Alpha manganese (α-Mn) is the equilibrium phase at room temperature.
It has a body-centered cubic lattice and is unusual among elemental
metals in that it has a very complex unit cell, with 58 atoms per cell
(29 atoms per primitive unit cell) with manganese atoms in four
different types of surroundings (sites). It is paramagnetic at room
temperature and antiferromagnetic at temperatures below 95 K.
Beta manganese (β-Mn) forms when heated above the transition
temperature of 973 K. It has a primitive cubic structure with 20
atoms per unit cell at two types of sites, which is as complex as that
of any other elemental metal. It is easily obtained as a metastable
phase at room temperature by rapid quenching of manganese at 850 C in
ice water. It does not show magnetic ordering, remaining paramagnetic
down to the lowest temperature measured (1.1 K).
Gamma manganese (γ-Mn) forms when heated above 1370 K. It has a simple
face-centered cubic structure (four atoms per unit cell). When
quenched to room temperature it converts to β-Mn, but it can be
stabilized at room temperature by alloying it with at least 5 percent
of other elements (such as C, Fe, Ni, Cu, Pd or Au). These
solute-stabilized alloys distort into a face-centered tetragonal
structure.
Delta manganese (δ-Mn) forms when heated above 1406 K and is stable up
to the manganese melting point of 1519 K. It has a body-centered cubic
structure (two atoms per cubic unit cell).
Chemical compounds
======================================================================
Common oxidation states of manganese are +2, +3, +4, +6, and +7,
although all oxidation states from −3 to +7 have been observed.
Manganese in oxidation state +7 is represented by salts of the
intensely purple permanganate anion . Potassium permanganate is a
commonly used laboratory reagent because of its oxidizing properties;
it is used as a topical medicine (for example, in the treatment of
fish diseases). Solutions of potassium permanganate were among the
first stains and fixatives to be used in the preparation of biological
cells and tissues for electron microscopy.
Aside from various permanganate salts, Mn(VII) is represented by the
unstable, volatile derivative Mn2O7. Oxyhalides (MnO3F and MnO3Cl) are
powerful oxidizing agents. The most prominent example of Mn in the +6
oxidation state is the green anion manganate, [MnO4]2−. Manganate
salts are intermediates in the extraction of manganese from its ores.
Compounds with oxidation states +5 are somewhat elusive, and often
found associated to an oxide (O2−) or nitride (N3−) ligand. One
example is the blue anion hypomanganate [MnO4]3−.
Mn(IV) is somewhat enigmatic because it is common in nature but far
rarer in synthetic chemistry. The most common Mn ore, pyrolusite, is
MnO2. It is the dark brown pigment of many cave drawings and is also a
common ingredient in dry cell batteries. Complexes of Mn(IV), such as
in K2[MnF6], are known but are rarer than those of manganese in the
lower oxidation states. Mn(IV)-OH complexes are an intermediate in
some enzymes, including the oxygen-evolving center (OEC) in plants.
Simple derivatives of Mn3+ are rarely encountered but can be
stabilized by suitably alkaline ligands. Manganese(III) acetate is an
oxidant useful in organic synthesis. Solid compounds of manganese(III)
are characterized by a strong purple-red color and a preference for
distorted octahedral coordination resulting from the Jahn-Teller
effect. Aqueous solution of KMnO4 illustrating the deep purple of
Mn(VII) as it occurs in permanganate
A particularly common oxidation state for manganese in aqueous
solution is +2, which has a pale pink color. Many manganese(II)
compounds are known, such as the aquo complexes derived from
manganese(II) sulfate (MnSO4) and manganese(II) chloride (MnCl2). This
oxidation state is also seen in the mineral rhodochrosite
(manganese(II) carbonate). Manganese(II) commonly exists with a
high-spin ground state, with 5 unpaired electrons, because of its high
pairing energy. There are no spin-allowed d-d transitions in
manganese(II), which explain its faint color.
colspan=2|Oxidation states of manganese
−3 {{chem|Mn(CO)(NO)|3}
|-
| −2 || [Mn(1,5-COD)2]2−
|-
| −1 || Pentacarbonylhydridomanganese
|-
| 0 || Dimanganese decacarbonyl
|-
| +1 || Methylcyclopentadienyl manganese tricarbonyl
|-
| +2 || Manganese(II) chloride, Manganese(II) carbonate, Manganese(II)
oxide
|-
| +3 || Manganese(III) fluoride, Manganese(III) acetate,
Manganese(III) oxide
|-
| +4 || Manganese dioxide
|-
| +5 || Potassium hypomanganate
|-
| +6 || Potassium manganate
|-
| +7 || Potassium permanganate, Manganese heptoxide
|-
|colspan=2 style="font-size: smaller; text-align: center"|Common
oxidation states are in bold.
|}
Organomanganese compounds
===========================
Manganese forms a large variety of organometallic derivatives, i.e.,
compounds with Mn-C bonds. The organometallic derivatives include
numerous examples of Mn in its lower oxidation states, i.e. Mn(−III)
up through Mn(I). This area of organometallic chemistry is attractive
because Mn is inexpensive and of relatively low toxicity.
Of greatest commercial interest is methylcyclopentadienyl manganese
tricarbonyl (MMT), which is used as an anti-knock compound added to
gasoline in some countries, featuring Mn(I). Consistent with other
aspects of Mn(II) chemistry, manganocene () is high-spin. In contrast,
its neighboring metal, iron, forms an air-stable, low-spin derivative
in the form of ferrocene (). When conducted under an atmosphere of
carbon monoxide, reduction of Mn(II) salts gives dimanganese
decacarbonyl , an orange and volatile solid. The air-stability of
this Mn(0) compound (and its many derivatives) reflects the powerful
electron-acceptor properties of carbon monoxide. Many alkene complexes
and alkyne complexes are derived from .
In Mn(CH3)2(dmpe)2, Mn(II) is low spin, which contrasts with the high
spin character of its precursor, MnBr2(dmpe)2 (dmpe =
(CH3)2PCH2CH2P(CH3)2). Polyalkyl and polyaryl derivatives of manganese
often exist in higher oxidation states, reflecting the
electron-releasing properties of alkyl and aryl ligands. One example
is [Mn(CH3)6]2−.
History
======================================================================
The origin of the name manganese is complex. In ancient times, two
black minerals were identified from the regions of the Magnetes
(either Magnesia, located within modern Greece, or Magnesia ad
Sipylum, located within modern Turkey). They were both called 'magnes'
from their place of origin, but were considered to differ in sex. The
male 'magnes' attracted iron, and was the iron ore now known as
lodestone or magnetite, and which probably gave us the term magnet.
The female 'magnes' ore did not attract iron, but was used to
decolorize glass. This female 'magnes' was later called 'magnesia',
known now in modern times as pyrolusite or manganese dioxide. Neither
this mineral nor elemental manganese is magnetic. In the 16th century,
manganese dioxide was called 'manganesum' (note the two Ns instead of
one) by glassmakers, possibly as a corruption and concatenation of two
words, since alchemists and glassmakers eventually had to
differentiate a 'magnesia nigra' (the black ore) from 'magnesia alba'
(a white ore, also from Magnesia, also useful in glassmaking). Italian
physician Michele Mercati called magnesia nigra 'manganesa', and
finally the metal isolated from it became known as 'manganese' (). The
name 'magnesia' was eventually used to refer only to the white
magnesia alba (magnesium oxide), which provided the name magnesium for
the free element when it was isolated much later.
Manganese dioxide, which is abundant in nature, has long been used as
a pigment. The cave paintings in Gargas that are 30,000 to 24,000
years old are made from the mineral form of MnO2 pigments.
Manganese compounds were used by Egyptian and Roman glassmakers,
either to add to, or remove, color from glass. Use as "glassmakers
soap" continued through the Middle Ages until modern times and is
evident in 14th-century glass from Venice.
Because it was used in glassmaking, manganese dioxide was available
for experiments by alchemists, the first chemists. Ignatius Gottfried
Kaim (1770) and Johann Glauber (17th century) discovered that
manganese dioxide could be converted to permanganate, a useful
laboratory reagent. By the mid-18th century, the Swedish chemist Carl
Wilhelm Scheele used manganese dioxide to produce chlorine. First,
hydrochloric acid, or a mixture of dilute sulfuric acid and sodium
chloride was made to react with manganese dioxide, and later
hydrochloric acid from the Leblanc process was used and the manganese
dioxide was recycled by the Weldon process.
Scheele and others were aware that pyrolusite (mineral form of
manganese dioxide) contained a new element. Johan Gottlieb Gahn
isolated an impure sample of manganese metal in 1774, which he did by
reducing the dioxide with carbon. Ignatius Gottfried Kaim also may
have reduced manganese dioxide to isolate the metal, but that is
uncertain.
The manganese content of some iron ores used in Greece led to
speculations that steel produced from that ore contains additional
manganese, making the Spartan steel exceptionally hard. Around the
beginning of the 19th century, manganese was used in steelmaking and
several patents were granted. In 1816, it was documented that iron
alloyed with manganese was harder but not more brittle. In 1837,
British academic James Couper noted an association between miners'
heavy exposure to manganese and a form of Parkinson's disease. In
1912, United States patents were granted for protecting firearms
against rust and corrosion with manganese phosphate electrochemical
conversion coatings, and the process has seen widespread use ever
since.
The invention of the Leclanché cell in 1866 and the subsequent
improvement of batteries containing manganese dioxide as cathodic
depolarizer increased the demand for manganese dioxide. Until the
development of batteries with nickel-cadmium and lithium, most
batteries contained manganese. The zinc-carbon battery and the
alkaline battery normally use industrially produced manganese dioxide
because naturally occurring manganese dioxide contains impurities. In
the 20th century, manganese dioxide was widely used as the cathode for
commercial disposable dry batteries of both the standard (zinc-carbon)
and alkaline types.
Manganese is essential to iron and steel production by virtue of its
sulfur-fixing, deoxidizing, and alloying properties. This application
was first recognized by the British metallurgist Robert Forester
Mushet (1811-1891), who introduced the element to the steel
manufacture process in 1856 in the form of spiegeleisen.
Occurrence
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Manganese comprises about 1000 ppm (0.1%) of the Earth's crust and is
the 12th most abundant element. Soil contains 7-9000 ppm of manganese
with an average of 440 ppm. The atmosphere contains 0.01 μg/m3.
Manganese occurs principally as pyrolusite (MnO2), braunite
(Mn2+Mn3+6)SiO12), psilomelane , and to a lesser extent as
rhodochrosite (MnCO3).
|120px |140px |150px |130px |140px
|Manganese ore |Psilomelane (manganese ore) |Spiegeleisen is an iron
alloy with a manganese content of approximately 15%. |Manganese oxide
dendrites on limestone from Solnhofen, Germany - a kind of
pseudofossil. Scale is in mm |Mineral rhodochrosite (manganese(II)
carbonate)
The most important manganese ore is pyrolusite (MnO2). Other
economically important manganese ores usually show a close spatial
relation to the iron ores, such as sphalerite. Land-based resources
are large but irregularly distributed. About 80% of the known world
manganese resources are in South Africa; other important manganese
deposits are in Ukraine, Australia, India, China, Gabon and Brazil.
Manganese is mainly mined in South Africa, Australia, China, Gabon,
Brazil, India, Kazakhstan, Ghana, Ukraine and Malaysia. In South
Africa, most identified deposits are located near Hotazel in the
Northern Cape Province, (Kalahari manganese fields), with a 2011
estimate of 15 billion tons. In 2011 South Africa produced 3.4 million
tons, topping all other nations.
Oceanic environment
=====================
An abundant resource of manganese in the form of manganese nodules
found on the ocean floor. These nodules, which are composed of 29%
manganese, are located along the ocean floor. The environmental
impacts of nodule collection are of interest. According to 1978
estimate, the ocean floor has 500 billion tons of manganese nodules. ,
attempts to find economically viable methods of harvesting manganese
nodules are still ongoing, however, none has been commercialized.
In 1972, the CIA's Project Azorian, through billionaire Howard Hughes,
commissioned the ship 'Hughes Glomar Explorer' with the cover story of
harvesting manganese nodules from the sea floor. This cover story
triggered a rush of activity to collect manganese nodules. The real
mission of 'Hughes Glomar Explorer' was to raise a sunken Soviet
submarine, the K-129, with the goal of retrieving Soviet code books.
Manganese also occurs in the oceanic environment, as dissolved
manganese (dMn), which is found throughout the world's oceans, 90% of
which originates from hydrothermal vents. Particulate Mn develops in
buoyant plumes over an active vent source, while the dMn behaves
conservatively. Mn concentrations vary between the water columns of
the ocean. At the surface, dMn is elevated due to input from external
sources such as rivers, dust, and shelf sediments. Coastal sediments
normally have lower Mn concentrations, but can increase due to
anthropogenic discharges from industries such as mining and steel
manufacturing, which enter the ocean from river inputs. Surface dMn
concentrations can also be elevated biologically through
photosynthesis and physically from coastal upwelling and wind-driven
surface currents. Internal cycling such as photo-reduction from UV
radiation can also elevate levels by speeding up the dissolution of
Mn-oxides and oxidative scavenging, preventing Mn from sinking to
deeper waters. Elevated levels at mid-depths can occur near mid-ocean
ridges and hydrothermal vents. The hydrothermal vents release dMn
enriched fluid into the water. The dMn can then travel up to 4,000 km
due to the microbial capsules present, preventing exchange with
particles, lowing the sinking rates. Dissolved Mn concentrations are
even higher when oxygen levels are low. Overall, dMn concentrations
are normally higher in coastal regions and decrease when moving
offshore.
Soils
=======
Manganese occurs in soils in three oxidation states: the divalent
cation, Mn2+ and as brownish-black oxides and hydroxides containing Mn
(III,IV), such as MnOOH and MnO2. Soil pH and oxidation-reduction
conditions affect which of these three forms of Mn is dominant in a
given soil. At pH values less than 6 or under anaerobic conditions,
Mn(II) dominates, while under more alkaline and aerobic conditions,
Mn(III,IV) oxides and hydroxides predominate. These effects of soil
acidity and aeration state on the form of Mn can be modified or
controlled by microbial activity. Microbial respiration can cause both
the oxidation of Mn2+ to the oxides, and it can cause reduction of the
oxides to the divalent cation.
The Mn(III,IV) oxides exist as brownish-black stains and small nodules
on sand, silt, and clay particles. These surface coatings on other
soil particles have high surface area and carry negative charge. The
charged sites can adsorb and retain various cations, especially heavy
metals (e.g., Cr3+, Cu2+, Zn2+, and Pb2+). In addition, the oxides can
adsorb organic acids and other compounds. The adsorption of the metals
and organic compounds can then cause them to be oxidized while the
Mn(III,IV) oxides are reduced to Mn2+ (e.g., Cr3+ to Cr(VI) and
colorless hydroquinone to tea-colored quinone polymers).
Production
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A significant proportion of the manganese ore mined, around 85% in the
United States, is used in iron and steel production, such as in the
production of ferromanganese. For the production of ferromanganese,
the manganese ore is mixed with iron ore and carbon, and then reduced
either in a blast furnace or in an electric arc furnace. The resulting
ferromanganese has a manganese content of 30-80%. Pure manganese used
for the production of iron-free alloys is produced by leaching
manganese ore with sulfuric acid and a subsequent electrowinning
process.
A more progressive extraction process involves directly reducing (a
low grade) manganese ore by heap leaching. This is done by percolating
natural gas through the bottom of the heap; the natural gas provides
the heat (needs to be at least 850 °C) and the reducing agent (carbon
monoxide). This reduces all of the manganese ore to manganese oxide
(MnO), which is a leachable form. The ore then travels through a
grinding circuit to reduce the particle size of the ore to between 150
and 250 μm, increasing the surface area to aid leaching. The ore is
then added to a leach tank of sulfuric acid and ferrous iron (Fe2+) in
a 1.6:1 ratio. The iron reacts with the manganese dioxide (MnO2) to
form iron hydroxide (FeO(OH)) and elemental manganese (Mn).
This process yields greater than 90% recovery of the manganese. For
further purification, the manganese can then be sent to an
electrowinning facility.
Steel
=======
Manganese is essential to iron and steel production by virtue of its
sulfur-fixing, deoxidizing, and alloying properties. Manganese has no
satisfactory substitute in these applications in metallurgy.
Steelmaking, including its ironmaking component, has accounted for
most manganese demand, presently in the range of 85% to 90% of the
total demand. Manganese is a key component of low-cost stainless
steel. Often ferromanganese (usually about 80% manganese) is the
intermediate in modern processes.
Small amounts of manganese improve the workability of steel at high
temperatures by forming a high-melting sulfide and preventing the
formation of a liquid iron sulfide at the grain boundaries. If the
manganese content reaches 4%, the embrittlement of the steel becomes a
dominant feature. The embrittlement decreases at higher manganese
concentrations and reaches an acceptable level at 8%. Steel containing
8 to 15% of manganese has a high tensile strength of up to 863 MPa.
Steel with 12% manganese was discovered in 1882 by Robert Hadfield and
is still known as Hadfield steel (mangalloy). It was used for British
military steel helmets and later by the U.S. military.
Aluminium alloys
==================
Manganese is used in production of alloys with aluminium. Aluminium
with roughly 1.5% manganese has increased resistance to corrosion
through grains that absorb impurities which would lead to galvanic
corrosion. The corrosion-resistant aluminium alloys 3004 and 3104 (0.8
to 1.5% manganese) are used for most beverage cans. Before 2000, more
than 1.6 million tonnes of those alloys were used; at 1% manganese,
this consumed 16,000 tonnes of manganese.
Batteries
===========
Manganese(IV) oxide was used in the original type of dry cell battery
as an electron acceptor from zinc, and is the blackish material in
carbon-zinc type flashlight cells. The manganese dioxide is reduced to
the manganese oxide-hydroxide MnO(OH) during discharging, preventing
the formation of hydrogen at the anode of the battery.
: MnO2 + H2O + e− → MnO(OH) +
The same material also functions in newer alkaline batteries (usually
battery cells), which use the same basic reaction, but a different
electrolyte mixture. In 2002, more than 230,000 tons of manganese
dioxide was used for this purpose.
Resistors
===========
Copper alloys of manganese, such as Manganin, are commonly found in
metal element shunt resistors used for measuring relatively large
amounts of current. These alloys have very low temperature coefficient
of resistance and are resistant to sulfur. This makes the alloys
particularly useful in harsh automotive and industrial environments.
Fertilizers and feed additive
===============================
Manganese oxide and sulfate are components of fertilizers. In the year
2000, an estimated 20,000 tons of these compounds were used in
fertilizers in the US alone. A comparable amount of Mn compounds was
also used in animal feeds.
Niche
=======
Methylcyclopentadienyl manganese tricarbonyl is an additive in some
unleaded gasoline to boost octane rating and reduce engine knocking.
Manganese(IV) oxide (manganese dioxide, MnO2) is used as a reagent in
organic chemistry for the oxidation of benzylic alcohols (where the
hydroxyl group is adjacent to an aromatic ring). Manganese dioxide has
been used since antiquity to oxidize and neutralize the greenish tinge
in glass from trace amounts of iron contamination. MnO2 is also used
in the manufacture of oxygen and chlorine and in drying black paints.
In some preparations, it is a brown pigment for paint and is a
constituent of natural umber.
Tetravalent manganese is used as an activator in red-emitting
phosphors. While many compounds are known which show luminescence, the
majority are not used in commercial application due to low efficiency
or deep red emission. However, several Mn4+ activated fluorides were
reported as potential red-emitting phosphors for warm-white LEDs. But
to this day, only K2SiF6:Mn4+ is commercially available for use in
warm-white LEDs.
The metal is occasionally used in coins; until 2000, the only United
States coin to use manganese was the "wartime" nickel from 1942 to
1945. An alloy of 75% copper and 25% nickel was traditionally used for
the production of nickel coins. However, because of shortage of nickel
metal during the war, it was substituted by more available silver and
manganese, thus resulting in an alloy of 56% copper, 35% silver and 9%
manganese. Since 2000, dollar coins, for example the Sacagawea dollar
and the Presidential $1 coins, are made from a brass containing 7% of
manganese with a pure copper core.
Manganese compounds have been used as pigments and for the coloring of
ceramics and glass. The brown color of ceramic is sometimes the result
of manganese compounds. In the glass industry, manganese compounds are
used for two effects. Manganese(III) reacts with iron(II) to reduce
strong green color in glass by forming less-colored iron(III) and
slightly pink manganese(II), compensating for the residual color of
the iron(III). Larger quantities of manganese are used to produce pink
colored glass. In 2009, Mas Subramanian and associates at Oregon State
University discovered that manganese can be combined with yttrium and
indium to form an intensely blue, non-toxic, inert, fade-resistant
pigment, YInMn Blue, the first new blue pigment discovered in 200
years.
Biochemistry
======================================================================
Many classes of enzymes contain manganese cofactors including
oxidoreductases, transferases, hydrolases, lyases, isomerases and
ligases. Other enzymes containing manganese are arginase and a
Mn-containing superoxide dismutase (Mn-SOD). Some reverse
transcriptases of many retroviruses (although not lentiviruses such as
HIV) contain manganese. Manganese-containing polypeptides are the
diphtheria toxin, lectins, and integrins.
The oxygen-evolving complex (OEC), containing four atoms of manganese,
is a part of photosystem II contained in the thylakoid membranes of
chloroplasts. The OEC is responsible for the terminal photooxidation
of water during the light reactions of photosynthesis, i.e., it is the
catalyst that makes the O2 produced by plants.
Human health and nutrition
======================================================================
Manganese is an essential human dietary element and is present as a
coenzyme in several biological processes, which include macronutrient
metabolism, bone formation, and free radical defense systems.
Manganese is a critical component in dozens of proteins and enzymes.
The human body contains about 12 mg of manganese, mostly in the bones.
The soft tissue remainder is concentrated in the liver and kidneys. In
the human brain, the manganese is bound to manganese metalloproteins,
most notably glutamine synthetase in astrocytes.
Current AIs of Mn by age group and sex
!colspan="2"|Males !colspan="2"|Females
!Age !AI (mg/day) !Age !AI (mg/day)
|1-3 |1.2 |1-3 |1.2
|4-8 |1.5 |4-8 |1.5
|9-13 |1.9 |9-13 |1.6
|14-18 |2.2 |14-18 |1.6
|rowspan=3|19+ |rowspan=3|2.3 |rowspan=3|19+ |1.8
|pregnant: 2
|lactating: 2.6
Regulation
============
The U.S. Institute of Medicine (IOM) updated Estimated Average
Requirements (EARs) and Recommended Dietary Allowances (RDAs) for
minerals in 2001. For manganese, there was not sufficient information
to set EARs and RDAs, so needs are described as estimates for Adequate
Intakes (AIs). As for safety, the IOM sets Tolerable upper intake
levels (ULs) for vitamins and minerals when evidence is sufficient. In
the case of manganese, the adult UL is set at 11 mg/day. Collectively
the EARs, RDAs, AIs and ULs are referred to as Dietary Reference
Intakes (DRIs). Manganese deficiency is rare.
The European Food Safety Authority (EFSA) refers to the collective set
of information as Dietary Reference Values, with Population Reference
Intake (PRI) instead of RDA, and Average Requirement instead of EAR.
AI and UL are defined the same as in the United States. For people
ages 15 and older, the AI is set at 3.0 mg/day. AIs for pregnancy and
lactation are 3.0 mg/day. For children ages 1-14 years, the AIs
increase with age from 0.5 to 2.0 mg/day. The adult AIs are higher
than the U.S. RDAs. The EFSA reviewed the same safety question and
decided that there was insufficient information to set a UL.
For U.S. food and dietary supplement labeling purposes, the amount in
a serving is expressed as a percent of Daily Value (%DV). For
manganese labeling purposes, 100% of the Daily Value was 2.0 mg, but
as of 27 May 2016 it was revised to 2.3 mg to bring it into agreement
with the RDA. A table of the old and new adult daily values is
provided at Reference Daily Intake.
Excessive exposure or intake may lead to a condition known as
manganism, a neurodegenerative disorder that causes dopaminergic
neuronal death and symptoms similar to Parkinson's disease.
Manganese exposure in United States is regulated by the Occupational
Safety and Health Administration (OSHA). People can be exposed to
manganese in the workplace by breathing it in or swallowing it. OSHA
has set the legal limit (permissible exposure limit) for manganese
exposure in the workplace as 5 mg/m3 over an 8-hour workday. The
National Institute for Occupational Safety and Health (NIOSH) has set
a recommended exposure limit (REL) of 1 mg/m3 over an 8-hour workday
and a short term limit of 3 mg/m3. At levels of 500 mg/m3, manganese
is immediately dangerous to life and health. In other countries, such
as Germany, a general ceiling value for airborne manganese has been
set to 0.5 mg/m3 () and the maximum level of manganese in the body has
been set to 20 mg/L.
Deficiency
============
Manganese deficiency in humans, which is rare, results in a number of
medical problems. A deficiency of manganese causes skeletal
deformation in animals and inhibits the production of collagen in
wound healing.
In water
==========
Waterborne manganese has a greater bioavailability than dietary
manganese. According to results from a 2010 study, higher levels of
exposure to manganese in drinking water are associated with increased
intellectual impairment and reduced intelligence quotients in
school-age children. It is hypothesized that long-term exposure due to
inhaling the naturally occurring manganese in shower water puts up to
8.7 million Americans at risk. However, data indicates that the human
body can recover from certain adverse effects of overexposure to
manganese if the exposure is stopped and the body can clear the
excess.
Mn levels can increase in seawater when hypoxic periods occur. Since
1990 there have been reports of Mn accumulation in marine organisms
including fish, crustaceans, mollusks, and echinoderms. Specific
tissues are targets in different species, including the gills, brain,
blood, kidney, and liver/hepatopancreas. Physiological effects have
been reported in these species. Mn can affect the renewal of
immunocytes and their functionality, such as phagocytosis and
activation of pro-phenoloxidase, suppressing the organisms' immune
systems. This causes the organisms to be more susceptible to
infections. As climate change occurs, pathogen distributions increase,
and in order for organisms to survive and defend themselves against
these pathogens, they need a healthy, strong immune system. If their
systems are compromised from high Mn levels, they will not be able to
fight off these pathogens and die.
Gasoline
==========
Methylcyclopentadienyl manganese tricarbonyl (MMT) is an additive
developed to replace lead compounds for gasolines to improve the
octane rating. MMT is used only in a few countries. When exposed to
the environment, fuels containing methylcyclopentadienyl manganese
tricarbonyl degrade, releasing manganese into water and soils.
Air
=====
Manganese levels in the air decreased between 1953 and 1982, with
higher levels in 1953. In general, breathing air with more than 5
micrograms of manganese per cubic meter can cause symptoms of
manganese exposure. In lab-grown human kidney cells, higher levels of
a protein called ferroportin are linked to lower manganese levels
inside the cells and reduced cell damage, shown by better glutamate
uptake and less leakage of a damage marker known as lactate
dehydrogenase.
Health and safety
======================================================================
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Manganese is essential for human health, albeit in milligram amounts.
The current maximum safe concentration under U.S. EPA rules is 50 μg
Mn/L.
Manganism
===========
Manganese overexposure is most frequently associated with manganism, a
rare neurological disorder associated with excessive manganese
ingestion or inhalation. Historically, persons employed in the
production or processing of manganese alloys have been at risk for
developing manganism; however, health and safety regulations protect
workers in developed nations. The disorder was first described in 1837
by British academic John Couper, who studied two patients who were
manganese grinders.
Manganism is a biphasic disorder. In its early stages, an intoxicated
person may experience depression, mood swings, compulsive behaviors,
and psychosis. Early neurological symptoms give way to late-stage
manganism, which resembles Parkinson's disease. Symptoms include
weakness, monotone and slowed speech, an expressionless face, tremor,
forward-leaning gait, inability to walk backwards without falling,
rigidity, and general problems with dexterity, gait and balance.
Unlike Parkinson's disease, manganism is not associated with loss of
the sense of smell and patients are typically unresponsive to
treatment with L-DOPA. Symptoms of late-stage manganism become more
severe over time even if the source of exposure is removed and brain
manganese levels return to normal.
Chronic manganese exposure has been shown to produce a
parkinsonism-like illness characterized by movement abnormalities.
This condition is not responsive to typical therapies used in the
treatment of PD, suggesting an alternative pathway to the typical
dopaminergic loss within the substantia nigra. Manganese may
accumulate in the basal ganglia, leading to the abnormal movements. A
mutation of the SLC30A10 gene, a manganese efflux transporter
necessary for decreasing intracellular Mn, has been linked with the
development of this Parkinsonism-like disease. The Lewy bodies typical
to PD are not seen in Mn-induced parkinsonism.
Animal experiments have given the opportunity to examine the
consequences of manganese overexposure under controlled conditions. In
(non-aggressive) rats, manganese induces mouse-killing behavior.
Toxicity
==========
Manganese compounds are less toxic than those of other widespread
metals, such as nickel and copper. However, exposure to manganese
dusts and fumes should not exceed the ceiling value of 5 mg/m3 even
for short periods because of its toxicity level. Manganese poisoning
has been linked to impaired motor skills and cognitive disorders.
Neurodegenerative diseases
============================
A protein called DMT1 is the major transporter in manganese absorption
from the intestine and may be the major transporter of manganese
across the blood-brain barrier. DMT1 also transports inhaled manganese
across the nasal epithelium. The proposed mechanism for manganese
toxicity is that dysregulation leads to oxidative stress,
mitochondrial dysfunction, glutamate-mediated excitotoxicity, and
aggregation of proteins.
See also
======================================================================
* Manganese exporter, membrane transport protein
* List of countries by manganese production
* Parkerizing
External links
======================================================================
* [
http://www.npi.gov.au/substances/manganese/index.html National
Pollutant Inventory - Manganese and compounds Fact Sheet]
* [
http://www.manganese.org International Manganese Institute]
* [
https://www.cdc.gov/niosh/topics/manganese/ NIOSH Manganese Topic
Page]
* [
http://www.periodicvideos.com/videos/025.htm Manganese] at 'The
Periodic Table of Videos' (University of Nottingham)
* [
https://www.manganese-dendrite.com All about Manganese Dendrites]
* [
https://www.epa.gov/smm/electric-arc-furnace-eaf-slag Electric Arc
Furnace (EAF) Slag]
License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Manganese
