Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy uses, particularly in . 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.
Manganese was first isolated in 1774. It is familiar in the laboratory in the form of the deep violet salt potassium permanganate. It occurs at the in some enzymes.[ Electronic-book .] Of particular interest is the use of a Mn-O atom cluster, the oxygen-evolving complex, in the production of oxygen by plants.
Characteristics
Physical properties
Manganese is a silvery-gray
metal that resembles iron. It is hard and very brittle, difficult to fuse, but easy to oxidize.
Manganese metal 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
have been isolated and described, ranging in
atomic weight from 44 u (
44Mn) to 69 u (
69Mn). 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
.
Manganese is part of the iron group of elements, which are thought to be synthesized in large shortly before the supernova explosion.
Oxidation states
The most common
of manganese are +2, +3, +4, +6, and +7, though all oxidation states from −3 to +7 have been observed. Mn
2+ often competes with Mg
2+ in biological systems, with the ion also being very similar in its properties to Ca
2+ and Zn
2+. Manganese compounds where manganese is in oxidation state +7, which are mostly restricted to the unstable oxide Mn
2O
7, compounds of the intensely purple permanganate anion MnO
4−, and a few oxyhalides (MnO
3F and MnO
3Cl), are powerful
oxidation.
Compounds with oxidation states +5 (blue) and +6 (green) are strong oxidizing agents and are vulnerable to disproportionation.
The most stable oxidation state for manganese is +2, which has a pale pink color, and many manganese(II) compounds are known, such as manganese(II) sulfate (MnSO4) and manganese(II) chloride (MnCl2). This oxidation state is also seen in the mineral rhodochrosite (manganese(II) carbonate). Manganese(II) most commonly exists with a high spin, S = 5/2 ground state because of the high pairing energy for manganese(II). However, there are a few examples of low-spin, S =1/2 manganese(II).[Rayner-Canham, Geoffrey and Overton, Tina (2003) Descriptive Inorganic Chemistry, Macmillan, p. 491, .]
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| Common oxidation states are in bold. |
The +3 oxidation state is known in compounds like manganese(III) acetate, but these are quite powerful
Redox and also prone to disproportionation in solution, forming manganese(II) and manganese(IV). Solid compounds of manganese(III) are characterized by its strong purple-red color and a preference for distorted octahedral coordination resulting from the Jahn-Teller effect.
The oxidation state +5 can be produced by dissolving manganese dioxide in molten sodium nitrite.
Permanganate (+7 oxidation state) compounds are purple, and can give glass a violet color. Potassium permanganate, sodium permanganate, and barium permanganate are all potent oxidizers. Potassium permanganate, also called Condy's crystals, 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.
The rare oxidation state +1 exists in some organomanganese compounds such as the MnC5H4CH3(CO)3 compound cited in the table above.
History
The origin of the name manganese is complex. In ancient times, two black minerals were identified from the regions of the
Magnetes (either
Ancient 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).
Michele Mercati called magnesia nigra
manganesa, and finally the metal isolated from it became known as
manganese (German:
Mangan). The name
magnesia eventually was then 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.
Several colorful oxides of manganese, for example manganese dioxide, are abundant in nature and have been used as pigments since the Stone Age. The cave paintings in Gargas that are 30,000 to 24,000 years old contain manganese pigments.
Manganese compounds were used by Egyptian and Roman glassmakers, either to add to, or remove, color from glass.
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, Carl Wilhelm Scheele used pyrolusite to produce chlorine. Scheele and others were aware that pyrolusite (now known to be manganese dioxide) contained a new element. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, which he did by reducing the dioxide with carbon.
The manganese content of some iron ores used in Greece led to speculations that steel produced from that ore contains additional manganese, making the steel exceptionally hard.
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 cathodic for commercial disposable dry batteries of both the standard (zinc–carbon) and alkaline types.
Occurrence
Manganese comprises about 1000 ppm (0.1%) of the Earth's crust, the 12th most abundant of the crust's elements.
Soil contains 7–9000 ppm of manganese with an average of 440 ppm.
The atmosphere contains 0.01 μg/m
3.
Manganese occurs principally as
pyrolusite (MnO
2),
braunite (Mn
2+Mn
3+6)(SiO
12),
, and to a lesser extent as
rhodochrosite (MnCO
3).
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| 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.
In South Africa, most identified deposits are located near Hotazel in the Northern Cape Province, with a 2011 estimate of 15 billion tons. In 2011 South Africa produced 3.4 million tons, topping all other nations.
Manganese is mainly mined in South Africa, Australia, China, Gabon, Brazil, India, Kazakhstan, Ghana, Ukraine and Malaysia.
Production
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 to 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 in a heap leach. This is done by Percolation 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 approximately 92% recovery of the manganese. For further purification, the manganese can then be sent to an electrowinning facility.
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.
An abundant resource of manganese in the form of Manganese nodule found on the ocean floor.
Oceanic environment
Many trace elements in the ocean come from metal-rich hydrothermal particles from hydrothermal vents.
Dissolved manganese (dMn) 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, Mn
2+ and as brownish-black oxides and hydroxides containing Mn (III,IV), such as MnOOH and MnO
2. 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 Mn
2+ 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).
Applications
Manganese has no satisfactory substitute in its major applications in metallurgy.
In minor applications (e.g., manganese phosphating),
zinc and sometimes
vanadium are viable substitutes.
Steel
Manganese is essential to iron and
steelmaking by virtue of its sulfur-fixing,
deoxidized steel, and
alloying properties, as first recognized by the British metallurgist Robert Forester Mushet (1811–1891) who, in 1856, introduced the element, in the form of
Spiegeleisen, into steel for the specific purpose of removing excess dissolved oxygen, sulfur, and phosphorus in order to improve its malleability.
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.
[Manganese USGS 2006] 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.
Aluminium alloys
The second largest application for manganese is in aluminium alloys. 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
3004 and 3104 (0.8 to 1.5% manganese) are used for most
.
Before 2000, more than 1.6 million
of those alloys were used; at 1% manganese, this consumed 16,000 tonnes of manganese.
Other uses
Methylcyclopentadienyl manganese tricarbonyl is used as an additive in unleaded gasoline to boost
octane rating and reduce
engine knocking. The manganese in this unusual organometallic compound is in the +1 oxidation state.
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.
Tetravalence manganese is used as an activator in red-emitting . While many compounds are known which show luminescence,
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 battery (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
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.
Minting
The metal is occasionally used in coins; until 2000, the only United States coin to use manganese was the 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.
In both cases of nickel and dollar, the use of manganese in the coin was to duplicate the electromagnetic properties of a previous identically sized and valued coin in the mechanisms of vending machines. In the case of the later U.S. dollar coins, the manganese alloy was intended to duplicate the properties of the copper/nickel alloy used in the previous Susan B. Anthony dollar.
Ceramic coloring
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, Professor
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.
Biological role
Biochemistry
The classes of
that have manganese cofactors include
,
,
,
,
and
. Other enzymes containing manganese are
arginase and Mn-containing superoxide dismutase (
Mn-SOD). Also the enzyme class of reverse transcriptases of many
(though not
such as
HIV) contains manganese. Manganese-containing
polypeptides are the
diphtheria toxin,
and
.
Biological role in humans
Manganese is an essential human dietary element. It is present as a
coenzyme in several biological processes, which include macronutrient metabolism, bone formation, and
free radical defense systems. It 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
, most notably glutamine synthetase in
.
Nutrition
Dietary recommendations
+Current AIs of Mn by age group and sex | Males
!colspan="2" | Females |
|
| 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 |
| 19+ | 2.3 | 19+ | 1.8 |
| pregnant: 2 |
| lactating: 2.6 |
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
(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.
[ See ]
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 defined the same as in United States. For people ages 15 and older the AI is set at 3.0 mg/day. AIs for pregnancy and lactation is 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.
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.
Toxicity
Excessive exposure or intake may lead to a condition known as
manganism, a neurodegenerative disorder that causes
neuronal death and symptoms similar to Parkinson's disease.
Deficiency
Manganese deficiency in humans results in a number of medical problems. Many common vitamin and mineral supplement products fail to include manganese in their compositions. Relatively high dietary intake of other minerals such as iron, magnesium, and calcium may inhibit the proper intake of manganese. A deficiency of manganese causes skeletal deformation in animals and inhibits the production of collagen in wound healing.
Toxicity in marine life
Many enzymatic systems need Mn to function, but in high levels, Mn can become toxic. One environmental reason Mn levels can increase in seawater is 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.
Biological role in bacteria
Mn-SOD is the type of SOD present in
eukaryote mitochondria, and also in most bacteria (this fact is in keeping with the bacterial-origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for nearly all organisms living in the presence of oxygen use it to deal with the toxic effects of
superoxide (), formed from the 1-electron reduction of dioxygen. The exceptions, which are all bacteria, include
Lactobacillus plantarum and related
lactobacillus, which use a different nonenzymatic mechanism with manganese (Mn
2+) ions complexed with polyphosphate, suggesting a path of evolution for this function in aerobic life.
Biological role in plants
Manganese is also important in photosynthetic
oxygen evolution in
in plants. The oxygen-evolving complex (OEC) is a part of photosystem II contained in the thylakoid membranes of chloroplasts; it is responsible for the terminal
Oxygen evolution during the
light reactions of
photosynthesis, and has a metalloenzyme core containing four atoms of manganese.
To fulfill this requirement, most broad-spectrum plant fertilizers contain manganese.
Precautions
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/m
3 even for short periods because of its toxicity level.
Manganese poisoning has been linked to impaired motor skills and cognitive disorders.
Permanganate exhibits a higher toxicity than manganese(II) compounds. The fatal dose is about 10 g, and several fatal intoxications have occurred. The strong oxidative effect leads to necrosis of the mucous membrane. For example, the esophagus is affected if the permanganate is swallowed. Only a limited amount is absorbed by the intestines, but this small amount shows severe effects on the kidneys and on the liver.
Manganese exposure in United States is regulated by the Occupational Safety and Health Administration (OSHA).
Generally, exposure to ambient Mn air concentrations in excess of 5 μg Mn/m3 can lead to Mn-induced symptoms. Increased ferroportin protein expression in human embryonic kidney (HEK293) cells is associated with decreased intracellular Mn concentration and attenuated cytotoxicity, characterized by the reversal of Mn-reduced glutamate uptake and diminished lactate dehydrogenase leakage.
Environmental health concerns
In drinking 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.
In gasoline
Methylcyclopentadienyl manganese tricarbonyl (MMT) is a
gasoline additive used to replace lead compounds for unleaded gasolines to improve the
octane rating of low octane petroleum distillates. It reduces
Engine knocking agent through the action of the
Carbonyl. Fuels containing manganese tend to form manganese carbides, which damage
. Compared to 1953, levels of manganese in air have dropped.
[Agency for Toxic Substances and Disease Registry (2012) 6. Potential for human exposure, in Toxicological Profile for Manganese, Atlanta, GA: U.S. Department of Health and Human Services.]
In tobacco smoke
The
tobacco plant readily absorbs and accumulates
heavy metals such as manganese from the surrounding soil into its leaves. These are subsequently inhaled during
tobacco smoking.
While manganese is a constituent of
tobacco smoke,
studies have largely concluded that concentrations are not hazardous for human health.
Role in neurological disorders
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
[Baselt, R. (2008) Disposition of Toxic Drugs and Chemicals in Man, 8th edition, Biomedical Publications, Foster City, CA, pp. 883–886, .] have been at risk for developing manganism; however, current 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 m.
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.
Chronic manganese exposure has been shown to produce a parkinsonism-like illness characterized by movement abnormalities.
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.
Childhood developmental disorders
Several recent studies attempt to examine the effects of chronic low-dose manganese overexposure on child development. The earliest study was conducted in the Chinese province of Shanxi. Drinking water there had been contaminated through improper sewage irrigation and contained 240–350 μg Mn/L. Although Mn concentrations at or below 300 μg Mn/L were considered safe at the time of the study by the US EPA and 400 μg Mn/L by the World Health Organization, the 92 children sampled (between 11 and 13 years of age) from this province displayed lower performance on tests of manual dexterity and rapidity, short-term memory, and visual identification, compared to children from an uncontaminated area. More recently, a study of 10-year-old children in Bangladesh showed a relationship between Mn concentration in well water and diminished IQ scores. A third study conducted in Quebec examined school children between the ages of 6 and 15 living in homes that received water from a well containing 610 μg Mn/L; controls lived in homes that received water from a 160 μg Mn/L well. Children in the experimental group showed increased hyperactive and oppositional behavior.
The current maximum safe concentration under EPA rules is 50 μg Mn/L.
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
