Chromium is a chemical element with symbol Cr and atomic number 24. It
is the first element in group 6. It is a steely-grey, lustrous, hard
and brittle metal which takes a high polish, resists tarnishing,
and has a high melting point. The name of the element is derived from
the Greek word χρῶμα, chrōma, meaning color, because many
chromium compounds are intensely colored.
Ferrochromium alloy is commercially produced from chromite by
silicothermic or aluminothermic reactions and chromium metal by
roasting and leaching processes followed by reduction with carbon and
Chromium metal is of high value for its high corrosion
resistance and hardness. A major development in steel production was
the discovery that steel could be made highly resistant to corrosion
and discoloration by adding metallic chromium to form stainless steel.
Stainless steel and chrome plating (electroplating with chromium)
together comprise 85% of the commercial use.
Trivalent chromium (Cr(III)) ion was considered an essential nutrient
in trace amounts in humans for insulin, sugar and lipid metabolism.
However in 2014, the
European Food Safety Authority
European Food Safety Authority concluded that
lacking evidence of benefits, setting any Adequate Intake is
While chromium metal and Cr(III) ions are not considered toxic,
hexavalent chromium (Cr(VI)) is toxic and carcinogenic. Abandoned
chromium production sites often require environmental cleanup.
2.3 Chromium(V) and chromium(IV)
Chromium as pigment
Dye and pigment
5.2.1 Synthetic ruby and the first laser
5.3 Wood preservative
5.7 Other use
6 Biological role
6.1 Dietary recommendations
7.2 Environmental issues
10 External links
Chromium is remarkable for its magnetic properties: it is the only
elemental solid which shows antiferromagnetic ordering at room
temperature (and below). Above 38 °C, it changes to
Chromium metal left standing in air is passivated by oxidation,
forming a thin, protective, surface layer. This layer is a spinel
structure only a few molecules thick. It is very dense, and prevents
the diffusion of oxygen into the underlying metal. This is different
from the oxide that forms on iron and carbon steel, through which
elemental oxygen continues to migrate, reaching the underlying
material to cause incessant rusting. Passivation can be enhanced by
short contact with oxidizing acids like nitric acid. Passivated
chromium is stable against acids. Passivation can be removed with a
strong reducing agent that destroys the protective oxide layer on the
Chromium metal treated in this way readily dissolves in weak
Chromium, unlike such metals as iron and nickel, does not suffer from
hydrogen embrittlement. However, it does suffer from nitrogen
embrittlement, reacting with nitrogen from air and forming brittle
nitrides at the high temperatures necessary to work the metal
See also: Category:
Chromium is the 22nd most abundant element in Earth's crust with an
average concentration of 100 ppm.
Chromium compounds are found in
the environment from the erosion of chromium-containing rocks, and can
be redistributed by volcanic eruptions. Typical background
concentrations of chromium in environmental media are: atmosphere
<10 ng m−3; soil <500 mg kg−1; vegetation
<0.5 mg kg−1; freshwater <10 ug L−1; seawater
<1 ug L−1; sediment <80 mg kg−1.
Chromium is mined as chromite (FeCr2O4) ore. About two-fifths of
the chromite ores and concentrates in the world are produced in South
Africa, about a third in Kazakhstan, while India, Russia, and
Turkey are also substantial producers. Untapped chromite deposits are
plentiful, but geographically concentrated in Kazakhstan and southern
Although rare, deposits of native chromium exist. The
Udachnaya Pipe in Russia produces samples of the native metal. This
mine is a kimberlite pipe, rich in diamonds, and the reducing
environment helped produce both elemental chromium and diamond.
The relation between Cr(III) and Cr(VI) strongly depends on pH and
oxidative properties of the location. In most cases, Cr(III) is the
dominating species, but in some areas, the ground water can
contain up to 39 µg/liter of total chromium of which
30 µg/liter is Cr(VI).
Main article: Isotopes of chromium
Naturally occurring chromium is composed of three stable isotopes;
52Cr, 53Cr and 54Cr, with 52Cr being the most abundant (83.789%
natural abundance). 19 radioisotopes have been characterized, with the
most stable being 50Cr with a half-life of (more than) 1.8×1017
years, and 51Cr with a half-life of 27.7 days. All of the remaining
radioactive isotopes have half-lives that are less than 24 hours and
the majority less than 1 minute. This element also has 2 meta
53Cr is the radiogenic decay product of 53Mn (half-life = 3.74 million
years), and chromium isotopes are typically collocated (and
compounded) with manganese isotopes. This circumstance is useful in
isotope geology. Mangenese-chromium isotope ratios reinforce the
evidence from 26Al and 107Pd concerning the early history of the solar
system. Variations in 53Cr/52Cr and Mn/Cr ratios from several
meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr
isotopic composition must result from in-situ decay of 53Mn in
differentiated planetary bodies. Hence 53Cr provides additional
evidence for nucleosynthetic processes immediately before coalescence
of the solar system.
The isotopes of chromium range in atomic mass from 43 u (43Cr) to
67 u (67Cr). The primary decay mode before the most abundant
stable isotope, 52Cr, is electron capture and the primary mode after
is beta decay. 53Cr has been posited as a proxy for atmospheric
See also: Category:
Chromium is a member of group 6, of the transition metals. Chromium(0)
has an electronic configuration of [Ar]3d54s1, owing to the lower
energy of the high spin configuration.
Chromium exhibits a wide range
of oxidation states, with +3 the most stable; the +3 and +6 states are
the most common in chromium compounds, while +1, +4 and +5 are
The following is the
Pourbaix diagram for chromium in pure water,
perchloric acid or sodium hydroxide:
Chromium(III) chloride hexahydrate ([CrCl2(H2O)4]Cl·2H2O)
Anhydrous chromium(III) chloride (CrCl3)
A large number of chromium(III) compounds are known. Chromium(III) can
be obtained by dissolving elemental chromium in acids like
hydrochloric acid or sulfuric acid. The Cr3+ ion has a similar radius
(63 pm) to Al3+ (radius 50 pm), and they can replace each
other in some compounds, such as in chrome alum and alum. When a trace
amount of Cr3+ replaces Al3+ in corundum (aluminium oxide, Al2O3),
pink sapphire or red-colored ruby is formed, depending on the amount
Chromium(III) ions tend to form octahedral complexes. The color of
these complexes is determined by the ligands attached to the Cr
center. Commercially available chromium(III) chloride hydrate is the
dark green complex [CrCl2(H2O)4]Cl. Closely related compounds have
different colors: pale green [CrCl(H2O)5]Cl2 and violet [Cr(H2O)6]Cl3.
If water-free green chromium(III) chloride is dissolved in water, the
green solution turns violet after some time as the chloride in the
inner coordination sphere is replaced by water. This kind of reaction
is also observed with solutions of chrome alum and other water-soluble
Chromium(III) hydroxide (Cr(OH)3) is amphoteric, dissolving in acidic
solutions to form [Cr(H2O)6]3+, and in basic solutions to form [Cr(OH)
6]3−. It is dehydrated by heating to form the green chromium(III)
oxide (Cr2O3), a stable oxide with a crystal structure identical to
that of corundum.
Chromium(VI) compounds are powerful oxidants at low or neutral pH.
Most important are chromate anion (CrO2−
4) and dichromate (Cr2O72−) anions, which exist in equilibrium:
2 [CrO4]2− + 2 H+ ⇌ [Cr2O7]2− + H2O
Chromium(VI) halides are known also and include the hexafluoride CrF6
and chromyl chloride (CrO
Sodium chromate is produced industrially by the oxidative roasting of
chromite ore with calcium or sodium carbonate. The dominant species is
therefore, by the law of mass action, determined by the pH of the
solution. The change in equilibrium is visible by a change from yellow
(chromate) to orange (dichromate), such as when an acid is added to a
neutral solution of potassium chromate. At yet lower pH values,
further condensation to more complex oxyanions of chromium is
Both the chromate and dichromate anions are strong oxidizing reagents
at low pH:
Sodium chromate (Na2CrO4)
7 + 14 H
3O+ + 6 e− → 2 Cr3+ + 21 H
2O (ε0 = 1.33 V)
They are, however, only moderately oxidizing at high pH:
4 + 4 H
2O + 3 e− → Cr(OH)
3 + 5 OH− (ε0 = −0.13 V)
Chromium(VI) compounds in solution can be detected by adding an acidic
hydrogen peroxide solution. The unstable dark blue chromium(VI)
peroxide (CrO5) is formed, which can be stabilized as an ether adduct
Chromic acid has the hypothetical formula H
4. It is a vaguely described chemical, despite many well-defined
chromates and dichromates being known. The dark red chromium(VI) oxide
3, the acid anhydride of chromic acid, is sold industrially as
"chromic acid". It can be produced by mixing sulfuric acid with
dichromate, and is a strong oxidizing agent.
Chromium(V) and chromium(IV)
The oxidation state +5 is only realized in few compounds but are
intermediates in many reactions involving oxidations by chromate. The
only binary compound is the volatile chromium(V) fluoride (CrF5). This
red solid has a melting point of 30 °C and a boiling point of
117 °C. It can be prepared by treating chromium metal with
fluorine at 400 °C and 200 bar pressure. The peroxochromate(V)
is another example of the +5 oxidation state.
(K3[Cr(O2)4]) is made by reacting potassium chromate with hydrogen
peroxide at low temperatures. This red brown compound is stable at
room temperature but decomposes spontaneously at
Compounds of chromium(IV) (in the +4 oxidation state) are slightly
more common than those of chromium(V). The tetrahalides, CrF4, CrCl4,
and CrBr4, can be produced by treating the trihalides (CrX
3) with the corresponding halogen at elevated temperatures. Such
compounds are susceptible to disproportionation reactions and are not
stable in water.
Many chromium(II) compounds are known, including the water-stable
chromium(II) chloride, CrCl
2, which can be made by reducing chromium(III) chloride with zinc. The
resulting bright blue solution is only stable at neutral pH. Many
chromous carboxylates are known, most famously the red chromous
acetate (Cr2(O2CCH3)4) that features a quadruple bond.
Most Cr(I) compounds are obtained by oxidation of electron-rich,
octahedral Cr(0) complexes. Other Cr(I) complexes contain
cyclopentadienyl ligands. As verified by X-ray diffraction, a Cr-Cr
quintuple bond (length 183.51(4) pm) has also been
described. Extremely bulky monodentate ligands stabilize this
compound by shielding the quintuple bond from further reactions.
Chromium compound determined experimentally to contain a Cr-Cr
Main article: Organochromium chemistry
Many chromium(0) compounds are known. Most are derivatives of chromium
hexacarbonyl or bis(benzene)chromium.
Chromium was discovered as an element after it came to the attention
of the Western world in the red crystalline mineral crocoite (lead(II)
chromate), discovered in 1761 and initially used as a pigment. Nearly
all chromium is commercially extracted from the single commercially
viable ore chromite, which is iron chromium oxide (FeCr2O4). Chromite
is now the principal source of chromium for pigments.
Weapons found in burial pits dating from the late 3rd century B.C. Qin
Dynasty of the
Terracotta Army near Xi'an,
China have been analyzed by
archaeologists. Although buried more than 2,000 years ago, the ancient
bronze tips of crossbow bolts and swords found at the site showed
unexpectedly little corrosion, possibly because the bronze was
deliberately coated with a thin layer of chromium oxide.[dubious
– discuss] However, this oxide layer was not chromium metal or
chrome plating as we know it.
Chromium as pigment
Chromium minerals as pigments came to the attention of the west in the
18th century. On 26 July 1761, Johann Gottlob Lehmann found an
orange-red mineral in the Beryozovskoye mines in the Ural Mountains
which he named Siberian red lead. Though misidentified as a lead
compound with selenium and iron components, the mineral was in fact
crocoite (lead chromate) with a formula of PbCrO4.
Peter Simon Pallas
Peter Simon Pallas visited the same site as Lehmann and found
a red lead mineral that had useful properties as a pigment in paints.
The use of Siberian red lead as a paint pigment then developed
rapidly. A bright yellow pigment made from crocoite also became
The red color of rubies is from a trace amount of chromium.
Louis Nicolas Vauquelin
Louis Nicolas Vauquelin received samples of crocoite ore. He
produced chromium trioxide (CrO3) by mixing crocoite with hydrochloric
acid. In 1798, Vauquelin discovered that he could isolate metallic
chromium by heating the oxide in a charcoal oven, for which he is
credited as the discoverer of the element. Vauquelin was also able
to detect traces of chromium in precious gemstones, such as ruby or
During the 1800s, chromium was primarily used as a component of paints
and in tanning salts. At first, crocoite from Russia was the main
source, but in 1827, a larger chromite deposit was discovered near
Baltimore, United States. This made the United States the largest
producer of chromium products till 1848 when large deposits of
chromite were found near Bursa, Turkey.
Chromium is also known for its luster when polished. It is used as a
protective and decorative coating on car parts, plumbing fixtures,
furniture parts and many other items, usually applied by
Chromium was used for electroplating as early as 1848,
but this use only became widespread with the development of an
improved process in 1924.
Piece of chromium produced with aluminothermic reaction
World production trend of chromium
Chromium, remelted in a horizontal arc zone-refiner, showing large
visible crystal grains
Approximately 28.8 million metric tons (Mt) of marketable chromite ore
was produced in 2013, and converted into 7.5 Mt of ferrochromium.
According to John F. Papp, writing for the USGS, "
Ferrochromium is the
leading end use of chromite ore, [and] stainless steel is the leading
end use of ferrochromium."
The largest producers of chromium ore in 2013 have been South Africa
(48%), Kazakhstan (13%), Turkey (11%), India (10%) with several other
countries producing the rest of about 18% of the world production.
The two main products of chromium ore refining are ferrochromium and
metallic chromium. For those products the ore smelter process differs
considerably. For the production of ferrochromium, the chromite ore
(FeCr2O4) is reduced in large scale in electric arc furnace or in
smaller smelters with either aluminium or silicon in an aluminothermic
Chromium ore output in 2002
For the production of pure chromium, the iron must be separated from
the chromium in a two step roasting and leaching process. The chromite
ore is heated with a mixture of calcium carbonate and sodium carbonate
in the presence of air. The chromium is oxidized to the hexavalent
form, while the iron forms the stable Fe2O3. The subsequent leaching
at higher elevated temperatures dissolves the chromates and leaves the
insoluble iron oxide. The chromate is converted by sulfuric acid into
4 FeCr2O4 + 8 Na2CO3 + 7 O2 → 8 Na2CrO4 + 2 Fe2O3 + 8 CO2
2 Na2CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4 + H2O
The dichromate is converted to the chromium(III) oxide by reduction
with carbon and then reduced in an aluminothermic reaction to
Na2Cr2O7 + 2 C → Cr2O3 + Na2CO3 + CO
Cr2O3 + 2 Al → Al2O3 + 2 Cr
Metal alloys account for 85% of the use of chromium. The remainder
is used in the chemical, refractory, and foundry industries.
Decorative chrome plating on a motorcycle.
Main article: Chrome plating
The strengthening effect of forming stable metal carbides at the grain
boundaries and the strong increase in corrosion resistance made
chromium an important alloying material for steel. The high-speed tool
steels contain between 3 and 5% chromium. Stainless steel, the main
corrosion-resistant metal alloy, is formed when chromium is added to
iron in sufficient concentrations, usually above 11%. For its
formation, ferrochromium is added to the molten iron. Also
nickel-based alloys increase in strength due to the formation of
discrete, stable metal carbide particles at the grain boundaries. For
Inconel 718 contains 18.6% chromium. Because of the excellent
high-temperature properties of these nickel superalloys, they are used
in jet engines and gas turbines in lieu of common structural
The relative high hardness and corrosion resistance of unalloyed
chromium makes it a good surface coating, being still the most
"popular" metal coating with unparalleled combined durability. A thin
layer of chromium is deposited on pretreated metallic surfaces by
electroplating techniques. There are two deposition methods: Thin,
below 1 µm thickness, layers are deposited by chrome plating,
and are used for decorative surfaces. If wear-resistant surfaces are
needed then thicker chromium layers are deposited. Both methods
normally use acidic chromate or dichromate solutions. To prevent the
energy-consuming change in oxidation state, the use of chromium(III)
sulfate is under development, but for most applications, the
established process is used.
In the chromate conversion coating process, the strong oxidative
properties of chromates are used to deposit a protective oxide layer
on metals like aluminium, zinc and cadmium. This passivation and the
self-healing properties by the chromate stored in the chromate
conversion coating, which is able to migrate to local defects, are the
benefits of this coating method. Because of environmental and
health regulations on chromates, alternative coating methods are under
Chromic acid anodizing (or Type I anodizing) of aluminium is another
electrochemical process, which does not lead to the deposition of
chromium, but uses chromic acid as electrolyte in the solution. During
anodization, an oxide layer is formed on the aluminium. The use of
chromic acid, instead of the normally used sulfuric acid, leads to a
slight difference of these oxide layers. The high toxicity of
Cr(VI) compounds, used in the established chromium electroplating
process, and the strengthening of safety and environmental regulations
demand a search for substitutes for chromium or at least a change to
less toxic chromium(III) compounds.
Dye and pigment
School bus painted in chrome yellow
The mineral crocoite (lead chromate PbCrO4) was used as a yellow
pigment shortly after its discovery. After a synthesis method became
available starting from the more abundant chromite, chrome yellow was,
together with cadmium yellow, one of the most used yellow pigments.
The pigment does not photodegrade, but it tends to darken due to the
formation of chromium(III) oxide. It has a strong color, and was used
for school buses in the US and for Postal Service (for example
Deutsche Post) in Europe. The use of chrome yellow declined due to
environmental and safety concerns and was replaced by organic pigments
or alternatives free from lead and chromium. Other pigments based on
chromium are, for example, the bright red pigment chrome red, which is
a basic lead chromate (PbCrO4·Pb(OH)2). A very important chromate
pigment, which was used widely in metal primer formulations, was zinc
chromate, now replaced by zinc phosphate. A wash primer was formulated
to replace the dangerous practice of pretreating aluminium aircraft
bodies with a phosphoric acid solution. This used zinc tetroxychromate
dispersed in a solution of polyvinyl butyral. An 8% solution of
phosphoric acid in solvent was added just before application. It was
found that an easily oxidized alcohol was an essential ingredient. A
thin layer of about 10–15 µm was applied, which turned from
yellow to dark green when it was cured. There is still a question as
to the correct mechanism. Chrome green is a mixture of Prussian blue
and chrome yellow, while the chrome oxide green is chromium(III)
Chromium oxides are also used as a green color in glassmaking and as a
glaze in ceramics. Green chromium oxide is extremely light-fast
and as such is used in cladding coatings. It is also the main
ingredient in infrared reflecting paints, used by the armed forces, to
paint vehicles, to give them the same IR reflectance as green
Synthetic ruby and the first laser
Natural rubies are corundum (aluminum oxide) crystals that are colored
red (the rarest type) due to chromium (III) ions (other colors of
corundum gems are termed sapphires). A red-colored artificial ruby may
also be achieved by doping chromium(III) into artificial corundum
crystals, thus making chromium a requirement for making synthetic
rubies. Such a synthetic ruby crystal was the basis for the first
laser, produced in 1960, which relied on stimulated emission of light
from the chromium atoms in such a crystal.
Because of their toxicity, chromium(VI) salts are used for the
preservation of wood. For example, chromated copper arsenate (CCA) is
used in timber treatment to protect wood from decay fungi,
wood-attacking insects, including termites, and marine borers. The
formulations contain chromium based on the oxide CrO3 between 35.3%
and 65.5%. In the United States, 65,300 metric tons of CCA solution
were used in 1996.
Main article: Tanning (leather)
Chromium(III) salts, especially chrome alum and chromium(III) sulfate,
are used in the tanning of leather. The chromium(III) stabilizes the
leather by cross linking the collagen fibers.
leather can contain between 4 and 5% of chromium, which is tightly
bound to the proteins. Although the form of chromium used for
tanning is not the toxic hexavalent variety, there remains interest in
management of chromium in the tanning industry such as recovery and
reuse, direct/indirect recycling, use of less chromium or
"chrome-less" tanning are practiced to better manage chromium in
The high heat resistivity and high melting point makes chromite and
chromium(III) oxide a material for high temperature refractory
applications, like blast furnaces, cement kilns, molds for the firing
of bricks and as foundry sands for the casting of metals. In these
applications, the refractory materials are made from mixtures of
chromite and magnesite. The use is declining because of the
environmental regulations due to the possibility of the formation of
Several chromium compounds are used as catalysts for processing
hydrocarbons. For example, the Phillips catalyst, prepared from
chromium oxides, is used for the production of about half the world's
polyethylene. Fe-Cr mixed oxides are employed as high-temperature
catalysts for the water gas shift reaction.
Copper chromite is
a useful hydrogenation catalyst.
Chromium(IV) oxide (CrO2) is a magnetic compound. Its ideal shape
anisotropy, which imparts high coercivity and remnant magnetization,
made it a compound superior to the γ-Fe2O3.
Chromium(IV) oxide is
used to manufacture magnetic tape used in high-performance audio tape
and standard audio cassettes. Chromates can prevent corrosion of
steel under wet conditions, and therefore chromates are added to
Chromium(III) oxide (Cr2O3) is a metal polish known as green rouge.
Chromic acid is a powerful oxidizing agent and is a useful compound
for cleaning laboratory glassware of any trace of organic compounds.
It is prepared by dissolving potassium dichromate in concentrated
sulfuric acid, which is then used to wash the apparatus. Sodium
dichromate is sometimes used because of its higher solubility (50 g/L
versus 200 g/L respectively). The use of dichromate cleaning solutions
is now phased out due to the high toxicity and environmental concerns.
Modern cleaning solutions are highly effective and chromium free.
Potassium dichromate is a chemical reagent, used as a titrating agent.
Chrome alum is
Chromium(III) potassium sulfate
Chromium(III) potassium sulfate and is used as a
mordant (i.e., a fixing agent) for dyes in fabric and in tanning.
In the form trivalent chromium, Cr(III), or Cr3+, chromium was
identified as an essential nutrient in the late 1950s and later
accepted as a trace element for its roles in the action of insulin, a
hormone critical to the metabolism and storage of carbohydrate, fat
and protein. The precise mechanism of its actions in the body,
however, have not been fully defined, leaving in question whether
chromium is essential for healthy people.
Trivalent chromium occurs in trace amounts in foods, wine and
water. In contrast, hexavalent chromium (Cr(VI) or Cr6+) is
highly toxic and mutagenic when inhaled. Ingestion of chromium(VI)
in water has been linked to stomach tumors, and it may also cause
allergic contact dermatitis (ACD).
Chromium deficiency, involving a lack of Cr(III) in the body, or
perhaps some complex of it, such as glucose tolerance factor is
controversial. Some studies suggest that the biologically active
form of chromium (III) in an oligopeptide called low-molecular-weight
chromium-binding substance (LMWCr), which might play a role in the
insulin signaling pathway.
Although the mechanism in biological roles for chromium is unclear,
dietary supplements for chromium include chromium(III) picolinate,
chromium(III) polynicotinate, and related materials. The benefit of
supplements has not been proven.
In the United States, the dietary guidelines for daily chromium intake
were lowered in 2001 from 50–200 µg for an adult to 35 µg
(adult male) and to 25 µg (adult female). In 2014, the
European Food Safety Authority
European Food Safety Authority published a report stating that the
intake of chromium(III) has no beneficial effect on healthy people,
thus the Panel removed chromium from the list of nutrients and
Chromium content of common foods is generally low (1-13 micrograms per
Chromium content of food varies widely due to
differences in soil mineral content, growing season, plant cultivar,
and contamination during processing. In addition, large amounts of
chromium (and nickel) leach into food cooked in stainless
The U.S. Institute of Medicine (IOM) updated Estimated Average
Requirements (EARs) and Recommended Dietary Allowances (RDAs) for
chromium in 2001. For chromium there was not sufficient information to
set EARs and RDAs, so needs are described as estimates for Adequate
Intakes (AIs). The current AIs for chromium for women ages 14 and up
is 25 μg/day up to age 50 and 20 μg/day for older. AI for pregnancy
is 30 μg/day. AI for lactation is 45 μg/day. For men ages 14 and up
35 μg/day up to age 50 and 30 μg/day for older. For infants to
children ages 1–13 years the AI increases with age from 0.2 to 25
μg/day. As for safety, the IOM sets tolerable upper intake levels
(ULs) for vitamins and minerals when evidence is sufficient. In the
case of chromium there is not yet enough information and hence no UL.
Collectively the EARs, RDAs, AIs and ULs are referred to as Dietary
Reference Intakes (DRIs).
European Food Safety Authority
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. The EFSA does not
consider chromium to be an essential nutrient, and so has not set
PRIs, AIs or ULs.
Chromium is the only mineral for which the United
States and the European Union disagree on essentiality.
For U.S. food and dietary supplement labeling purposes the amount in a
serving is expressed as a percent of Daily Value (%DV). For chromium
labeling purposes 100% of the Daily Value was 120 μg, but as of May
27, 2016 it was revised to 35 μg to bring it into agreement with the
RDA. A table of the old and new adult Daily Values is provided at
Reference Daily Intake. The original deadline to be in compliance was
July 28, 2018, but on September 29, 2017 the FDA released a proposed
rule that extended the deadline to January 1, 2020 for large companies
and January 1, 2021 for small companies.
Water-insoluble chromium(III) compounds and chromium metal are not
considered a health hazard, while the toxicity and carcinogenic
properties of chromium(VI) have been known for a long time.
Because of the specific transport mechanisms, only limited amounts of
chromium(III) enter the cells. Several in vitro studies indicated that
high concentrations of chromium(III) in the cell can lead to DNA
damage. Acute oral toxicity ranges between 1.5 and
3.3 mg/kg. A 2008 review suggested that moderate uptake of
chromium(III) through dietary supplements poses no genetic-toxic
risk. In the US, the Occupational Safety and Health Administration
(OSHA) has designated a permissible exposure limit (PEL) in the
workplace as a time-weighted average (TWA) of 1 mg/m3. The
National Institute for Occupational Safety and Health
National Institute for Occupational Safety and Health (NIOSH) has set
a recommended exposure limit (REL) of 0.5 mg/m3, time-weighted
IDLH (immediately dangerous to life and health) value is
The acute oral toxicity for chromium(VI) ranges between 50 and
150 mg/kg. In the body, chromium(VI) is reduced by several
mechanisms to chromium(III) already in the blood before it enters the
cells. The chromium(III) is excreted from the body, whereas the
chromate ion is transferred into the cell by a transport mechanism, by
which also sulfate and phosphate ions enter the cell. The acute
toxicity of chromium(VI) is due to its strong oxidational properties.
After it reaches the blood stream, it damages the kidneys, the liver
and blood cells through oxidation reactions. Hemolysis, renal, and
liver failure result. Aggressive dialysis can be therapeutic.
The carcinogenity of chromate dust has been known for a long time, and
in 1890 the first publication described the elevated cancer risk of
workers in a chromate dye company. Three mechanisms have been
proposed to describe the genotoxicity of chromium(VI). The first
mechanism includes highly reactive hydroxyl radicals and other
reactive radicals which are by products of the reduction of
chromium(VI) to chromium(III). The second process includes the direct
binding of chromium(V), produced by reduction in the cell, and
chromium(IV) compounds to the DNA. The last mechanism attributed the
genotoxicity to the binding to the
DNA of the end product of the
Chromium salts (chromates) are also the cause of allergic reactions in
some people. Chromates are often used to manufacture, amongst other
things, leather products, paints, cement, mortar and anti-corrosives.
Contact with products containing chromates can lead to allergic
contact dermatitis and irritant dermatitis, resulting in ulceration of
the skin, sometimes referred to as "chrome ulcers". This condition is
often found in workers that have been exposed to strong chromate
solutions in electroplating, tanning and chrome-producing
Because chromium compounds were used in dyes, paints, and leather
tanning compounds, these compounds are often found in soil and
groundwater at abandoned industrial sites, now needing environmental
cleanup and remediation. Primer paint containing hexavalent chromium
is still widely used for aerospace and automobile refinishing
In 2010, the
Environmental Working Group
Environmental Working Group studied the drinking water in
35 American cities in the first nationwide study. The study found
measurable hexavalent chromium in the tap water of 31 of the cities
sampled, with Norman, Oklahoma, at the top of list; 25 cities had
levels that exceeded California's proposed limit.
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BNF: cb12104829h (data)