Arsenic is the
chemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
that has the symbol
As,
atomic numberIn chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
33 and atomic mass 74.92. Arsenic was first documented by
Albertus MagnusSaint Albertus Magnus, O.P. , also known as Saint Albert the Great and Albert of Cologne, was a Dominican friar and bishop who achieved fame for his comprehensive knowledge of and advocacy for the peaceful coexistence of science and religion. He is considered to be the greatest German philosopher...
in 1250. Arsenic is a notoriously poisonous
metalloidMetalloid, or semi metal is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, nearly every element in the periodic table can be termed either a metal or a nonmetal...
with many
allotropicAllotropy or allotropism is a behavior exhibited by certain chemical elements: these elements can exist in two or more different forms, known as allotropes of that element. In each allotrope, the element's atoms are bonded together in a different manner...
forms, including a yellow (molecular non-metallic) and several black and grey forms (metalloids). Three metalloidal forms of arsenic, each with a different crystal structure, are found free in nature (the minerals arsenic
sensu stricto and the much rarer arsenolamprite and pararsenolamprite). However, it is more commonly found as arsenide and in arsenate compounds, several hundred of which are known. Arsenic and its compounds are used as pesticides,
herbicideA herbicide is a substance used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant hormones...
s,
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
s and in various
alloyAn alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history...
s.
History
The word
arsenic was borrowed from the
PersianPersian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is widely spoken in Iran, Afghanistan, Tajikistan, Uzbekistan and to some extent in Iraq and Bahrain, and has a status of official language in the first three countries under different names...
word
Zarnikh, meaning "yellow
orpimentOrpiment, As2S3, is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46. It melts at 300 °C to 325 °C...
", into
GreekGreek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
as
arsenikon. It is also related to the similar Greek word "arsenikos", meaning "masculine" or "potent". Arsenic compounds (orpiment,
realgarRealgar, α-As
4S
4, is an arsenic sulfide mineral. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment . It is orange-red in colour, melts at 320 °C, and burns with a...
) have been known and used since ancient times. As the symptoms of
arsenic poisoningArsenic poisoning kills by allosteric inhibition of essential metabolic enzymes, leading to death from multi-system organ failure. It primarily inhibits enzymes that require lipoic acid as a cofactor, such as pyruvate and alpha-ketoglutarate dehydrogenase. Because of this, substrates before the...
were somewhat ill-defined, it was frequently used for
murderMurder, as defined in common law countries, is the unlawful killing of another human being with intent , and generally this state of mind distinguishes murder from other forms of unlawful homicide...
until the advent of the
Marsh testThe Marsh test is a highly sensitive method in the detection of arsenic, especially useful in the field of forensic toxicology when arsenic was used as a poison...
, a sensitive chemical test for its presence. (Another less sensitive but more general test is the
Reinsch testThe Reinsch test is an initial indicator to detect the presence of one or more of the following heavy metals in a biological sample, and is often used by toxicologists where poisoning by such metals is suspected.* Antimony* Arsenic* Bismuth* Selenium...
.) Owing to its use by the ruling class to murder one another and its potency and discreetness, arsenic has been called the
Poison of Kings and the
King of Poisons.
During the
Bronze AgeThe Bronze Age of a culture is the period when the most advanced metalworking in that culture utilised bronze. This could either have been based on the local smelting of copper and tin from ores, or trading for bronze from production areas elsewhere...
, arsenic was often included in
bronzeBronze is a metal alloy consisting primarily of copper, usually with tin as the main additive, but sometimes with other elements such as phosphorus, manganese, aluminium, or silicon. It was particularly significant in antiquity, giving its name to the Bronze Age...
, which made the alloy harder (so-called "
arsenical bronzeArsenical bronze is an alloy in which arsenic is added to copper as opposed to, or in addition to other constituent metals. The use of arsenic in bronze, either as the secondary constituent or with another component such as tin, results in a stronger final product.Since copper ore is often...
").
Albertus MagnusSaint Albertus Magnus, O.P. , also known as Saint Albert the Great and Albert of Cologne, was a Dominican friar and bishop who achieved fame for his comprehensive knowledge of and advocacy for the peaceful coexistence of science and religion. He is considered to be the greatest German philosopher...
(Albert the Great, 1193–1280) is believed to have been the first European to isolate the element in 1250 by heating soap together with
arsenic trisulfideArsenic trisulfide is the chemical compound with the formula As2S3. This bright yellow solid is well known because it occurs as the mineral orpiment , has been used as a pigment, and has played a role in the analysis of arsenic compounds...
. In 1649,
Johann SchröderJohann Schröder was a German physician and pharmacologist who was the first person to recognise that arsenic was an element. In 1649, he produced the elemental form of arsenic by heating its oxide, and published two methods for its preparation....
published two ways of preparing arsenic.
Cadet's fuming liquidIn 1760, the French chemist Louis Claude Cadet de Gassicourt synthesized a red liquid by the reaction of potassium acetate with arsenic trioxide....
(impure
cacodylCacodyl, dicacodyl, tetramethyldiarsine, alkarsine or minor part of the "Cadet's fuming liquid" 2As—As2 is a poisonous oily liquid with a garlicky odor...
), the first
organometallic compoundOrganometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
, was synthesized in 1760 by
Louis Claude Cadet de Gassicourt Louis Claude Cadet de Gassicourt was a French chemist who synthesised the first organometalic compound.He obtained a red liquid by the reaction of potassium acetate with arsenic trioxide...
by the reaction of
potassium acetatePotassium acetate is a chemical compound.It can be prepared by reacting a potassium-containing base such as potassium hydroxide or potassium carbonate with acetic acid:...
with
arsenic trioxideArsenic trioxide is the inorganic compound with the formula As2O3. This commercially important oxide of arsenic is the main precursor to other arsenic compounds, including organoarsenic compounds. Approximately 50,000 tons are produced annually...
.
In the
Victorian eraThe Victorian era of the United Kingdom was the period of Queen Victoria's reign from June 1837 until her death on the 22nd of January 1901. The reign was a long period of prosperity for the British people, as profits gained from the overseas British Empire, as well as from industrial improvements...
, "arsenic" (colourless, crystalline, soluble "white arsenic" trioxide) was mixed with
vinegarVinegar is an acidic liquid processed from the fermentation of ethanol in a process that yields its key ingredient, acetic acid. It also may come in a diluted form. The acetic acid concentration typically ranges from 4 to 8 percent by volume for table vinegar and higher concentrations for pickling...
and
chalkChalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. It forms under relatively deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores. It is common to find flint and chert...
and eaten by women to improve the
complexionComplexion refers to the natural color, texture, and appearance of the skin, especially that of the face. The word is derived from the Late Latin complexi, which initially referred in general terms to a combination of things, and later in physiological terms, to the balance of humors.The four...
of their faces, making their skin paler to show they did not work in the fields. Arsenic was also rubbed into the faces and arms of women to "improve their complexion". The accidental use of arsenic in the adulteration of foodstuffs led to the Bradford sweet poisoning in 1858, which resulted in approximately 20 deaths and 200 people taken ill with arsenic poisoning.
Isotopes
Naturally occurring arsenic is composed of one stable
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
,
75As. As of 2003, at least 33 radioisotopes have also been synthesized, ranging in
atomic massThe atomic mass is the mass of an atom, most often expressed in unified atomic mass units. The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom...
from 60 to 92. The most stable of these is
73As with a
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
of 80.3 days. Isotopes that are lighter than the stable
75As tend to decay by
β+ decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
, and those that are heavier tend to decay by
β- decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
, with some exceptions.
At least 10
nuclear isomerA nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons. A nuclear isomer occupies a higher energy state than the corresponding non-excited nucleus, called the ground state. Most nuclear excited states decay by gamma ray emission or...
s have been described, ranging in atomic mass from 66 to 84. The most stable of arsenic's isomers is
68mAs with a half-life of 111 seconds.
Allotropes
Like phosphorus, arsenic is an excellent example of an element that exhibits
allotropyAllotropy or allotropism is a behavior exhibited by certain chemical elements: these elements can exist in two or more different forms, known as allotropes of that element. In each allotrope, the element's atoms are bonded together in a different manner...
, as its various allotropes have strikingly different properties. The three most common allotropes are
metallic grey,
yellow and
black arsenic.
The most common allotrope of arsenic is
grey arsenic. It has a similar structure to black phosphorus (β-metallic phosphorus) and has a layered crystal structure somewhat resembling that of
graphiteThe mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek γραφειν : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead...
. It consists of many six-membered rings which are interlinked. Each atom is bound to three other atoms in the layer and is coordinated by each 3 arsenic atoms in the upper and lower layer. This relatively close packing leads to a high density of 5.73 g/cm
3.
Yellow arsenic is soft and waxy, not unlike . Both have four atoms arranged in a tetrahedral structure in which each atom is bound to the other three atoms by a single bond, resulting in very high
ring strainRing strain is an organic chemistry term that describes the destabilization of a cyclic molecule—such as a cycloalkane—due to the non-favorable high energy spatial orientations of its atoms...
and instability. This form of arsenic is the least stable, most reactive, more volatile, less
denseThe density of a material is defined as its mass per unit volume. The symbol of density is ρ .- Formula :Mathematically:where: is the density, is the mass, is the volume....
, and more toxic than the other allotropes. Yellow arsenic is produced by rapid cooling of arsenic vapour with liquid nitrogen. It is rapidly transformed into the grey arsenic by light. The yellow form has a density of 1.97 g/cm
3.
Black arsenic is similar in structure to red phosphorus.
Chemical
The most common
oxidation stateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
s for arsenic are −3 (
arsenideAn arsenide ion is an arsenic atom with three extra electrons and charge −3.An arsenide is a compound with arsenic in oxidation state −3.-Examples:* sodium arsenide * gallium arsenide...
s: usually alloy-like intermetallic compounds), +3 (arsenates(III) or
arseniteIn chemistry an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Examples of arsenites include sodium arsenite which contains a polymeric linear anion, [AsO2−]n, silver arsenite, Ag3AsO3,...
s, and most organoarsenic compounds), and +5 (
arsenateThe arsenate ion is AsO
43−.An arsenate is any compound that contains this ion.The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As[V]....
s: the most stable inorganic arsenic oxycompounds). Arsenic also bonds readily to itself, forming square As ions in the arsenide
skutteruditeSkutterudite is a naturally occurring cobalt arsenide mineral. The crystal structure of this mineral has been found to have important technological uses for several compounds isostructural with the mineral.-The skutterudite mineral:...
. In the +3 oxidation state, the stereochemistry of arsenic is affected by possession of a
lone pairA lone pair is a electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...
of electrons.
Arsenic is very similar chemically to its predecessor in the Periodic Table,
phosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
. Like phosphorus, it forms colourless, odourless, crystalline oxides As
2O
3 and
As2O5Arsenic pentoxide, As2O5, is an important commercial compound of arsenic. Its usage with respect to arsenic chemistry, as well as its toxicology are similar to arsenic trioxide, As2O3...
which are hygroscopic and readily soluble in water to form acidic solutions.
Arsenic(V) acidArsenic acid is the chemical compound with the formula H3AsO4. More descriptively written as AsO3, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but...
is a weak acid. Like phosphorus, arsenic forms an unstable, gaseous hydride:
arsineArsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
(AsH
3). The similarity is so great that arsenic will partly substitute for phosphorus in biochemical reactions and is thus
poisonArsenic poisoning kills by allosteric inhibition of essential metabolic enzymes, leading to death from multi-system organ failure. It primarily inhibits enzymes that require lipoic acid as a cofactor, such as pyruvate and alpha-ketoglutarate dehydrogenase. Because of this, substrates before the...
ous. However, in subtoxic doses, soluble arsenic compounds act as
stimulantStimulants, also sometimes called psychostimulants, are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others...
s, and were once popular in small doses as medicine by people in the mid 18th century.
When heated in air, arsenic oxidizes to arsenic trioxide; the fumes from this reaction have an odour resembling
garlicAllium sativum, commonly known as garlic, is a species in the onion family Alliaceae. Its close relatives include the onion, shallot, leek, and chive. Garlic has been used throughout recorded history for both culinary and medicinal purposes. It has a characteristic pungent, spicy flavor that...
. This odour can be detected on striking arsenide minerals such as
arsenopyriteArsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
with a hammer. Arsenic (and some arsenic compounds) sublimes upon heating at atmospheric pressure, converting directly to a gaseous form without an intervening liquid state. The liquid state appears at 20 atmospheres and above, which explains why the melting point is higher than the boiling point.
Compounds
Arsenic compounds resemble in many respects those of
phosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
as both arsenic and phosphorus occur in the same group (column) of the
periodic tableThe periodiс table of the chemical elements is a tabular display of the chemical elements...
.
The most important compounds of arsenic are arsenic(III) oxide, As
2O
3, ("white arsenic"), the yellow sulfide
orpimentOrpiment, As2S3, is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46. It melts at 300 °C to 325 °C...
(As
2S
3) and red
realgarRealgar, α-As
4S
4, is an arsenic sulfide mineral. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment . It is orange-red in colour, melts at 320 °C, and burns with a...
(As
4S
4),
Paris GreenParis Green is a common name for copper acetoarsenite, or C.I. Pigment Green 21, an extremely toxic blue green chemical with four main uses: pigment, animal poison , insecticide, and blue colorant for fireworks...
,
calcium arsenateCalcium arsenate is an extremely poisonous chemical compound. It was originally used as a pesticide and as a germicide. It is highly soluble in water, as compared with lead arsenate, which makes it more toxic....
, and
lead hydrogen arsenateLead hydrogen arsenate, also called lead arsenate, acid lead arsenate or LA, chemical formula PbHAsO4, is an inorganic insecticide used primarily against the potato beetle.-Chemistry:...
. The latter three have been used as
agriculturalAgriculture is the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of human civilization, with the husbandry of domesticated animals and plants creating food surpluses that enabled the development of more densely populated and...
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
s and
poisonIn the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism...
s.
Whilst arsenic trioxide forms during oxidation of arsenic,
arsenic pentoxideArsenic pentoxide, As2O5, is an important commercial compound of arsenic. Its usage with respect to arsenic chemistry, as well as its toxicology are similar to arsenic trioxide, As2O3...
is formed by the dehydration of
arsenic acidArsenic acid is the chemical compound with the formula H3AsO4. More descriptively written as AsO3, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but...
. Both oxides dissolve in strong alkaline solution, with the formation of
arseniteIn chemistry an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Examples of arsenites include sodium arsenite which contains a polymeric linear anion, [AsO2−]n, silver arsenite, Ag3AsO3,...
AsO and
arsenateThe arsenate ion is AsO
43−.An arsenate is any compound that contains this ion.The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As[V]....
AsO respectively. The protonation steps between the arsenate and arsenic acid are similar to those between
phosphateA phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
and
phosphoric acidPhosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more...
. However, arsenite and
arsenous acidArsenous acid, also known as arsenious acid, is the hydrolyzed form of arsenic trioxide and has the formula As3. As3 occurs in aqueous solutions and has not been isolated as a pure material, although this fact does not detract from the significance of...
contain arsenic bonded to three oxygens and not hydrogen, in contrast to
phosphiteThe phosphite ion is a polyatomic ion with a phosphorus central atom where phosphorus has an oxidation state of +3...
and
phosphorous acidPhosphorous acid is the compound described by the formula H3PO3. It can be formulated as HP2 and therefore contains phosphorus in oxidation state +3. It is one of the oxoacids of phosphorus, other important members being phosphoric acid and hypophosphorous acid...
(more accurately termed 'phosphonic acid'), which contain non-acidic P-H bonds. Arsenous acid is genuinely tribasic, whereas phosphonic acid is not.
A broad variety of sulfur compounds of arsenic are known, As
4S
3, As
4S
4,
As2S3Arsenic trisulfide is the chemical compound with the formula As2S3. This bright yellow solid is well known because it occurs as the mineral orpiment , has been used as a pigment, and has played a role in the analysis of arsenic compounds...
and As
4S
10. All arsenic(III) halogen compounds (except with astatine) are known and stable. For the arsenic(V) compounds the situation is different: only the
arsenic pentafluorideArsenic pentafluoride is a chemical compound of arsenic and fluorine. The oxidation state of arsenic is +5.-Synthesis:Arsenic pentafluoride can be prepared by direct combination of arsenic and fluorine:...
is stable at room temperature.
Arsenic pentachlorideArsenic pentachloride is a chemical compound of arsenic and chlorine . This compound was first prepared in 1976 through the UV irradiation of arsenic trichloride, AsCl3, in liquid chlorine at −105°C. AsCl5 decomposes at around −50°C. The structure of the solid was finally...
is only stable at temperatures below -50 °C and the pentabromide and pentaiodide are unknown.
Arsenic is used as group 5 element as part of the III-V semiconducting compounds. Gallium arsenide, indium arsenide and
aluminium arsenideAluminium arsenide , AlAs, is a chemical compound of aluminium and arsenic. It is semiconductor material with almost the same lattice constant as GaAs and AlGaAs and wider band gap than GaAs.-Physical properties:...
are used as semiconductor material when the properties of silicon are not suitable for the application and the higher price of the compounds is acceptable. Other arsenic compounds include:
- Arsenic acid
Arsenic acid is the chemical compound with the formula H3AsO4. More descriptively written as AsO3, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but...
(H3AsO4)
- Arsenous acid
Arsenous acid, also known as arsenious acid, is the hydrolyzed form of arsenic trioxide and has the formula As3. As3 occurs in aqueous solutions and has not been isolated as a pure material, although this fact does not detract from the significance of...
(H3AsO3)
- Arsenic trioxide
Arsenic trioxide is the inorganic compound with the formula As2O3. This commercially important oxide of arsenic is the main precursor to other arsenic compounds, including organoarsenic compounds. Approximately 50,000 tons are produced annually...
(As2O3)
- Arsine
Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
(arsenic trihydride AsH3)
- Cadmium arsenide
Cadmium arsenide is a crystalline semiconductor with a tetragonal structure in the II-V family. It is a narrow gap semiconductor with an energy gap of 0.14 eV. The electron mobility is very large at ambient temperature...
(Cd3As2)
- Gallium arsenide (GaAs)
- Lead hydrogen arsenate
Lead hydrogen arsenate, also called lead arsenate, acid lead arsenate or LA, chemical formula PbHAsO4, is an inorganic insecticide used primarily against the potato beetle.-Chemistry:...
(PbHAsO4)
Arsenic also has a formal oxidation state of +2 in As
4S
4,
realgarRealgar, α-As
4S
4, is an arsenic sulfide mineral. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment . It is orange-red in colour, melts at 320 °C, and burns with a...
. This is achieved by pairing As atoms to produce dimeric cations [As-As]
2+, so the total covalency of As is still in fact three.
Occurrence
ArsenopyriteArsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
, also unofficially called mispickel, (
FeIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
As
SSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
) is the most common arsenic-bearing
mineralA mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific...
.
In the lithosphere, the minerals of the formula M(II)AsS, with M(II) being mostly Fe, Ni and Co, are the dominant arsenic minerals.
Orpiment and realgar were formerly used as painting pigments, though they have fallen out of use owing to their toxicity and reactivity. Although arsenic is sometimes found native in nature, its main economic source is the mineral
arsenopyriteArsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
mentioned above; it is also found in arsenides of metals such as
silverSilver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
,
cobaltCobalt is a hard, lustrous, gray metal, a chemical element with symbol Co and atomic number 27. Although cobalt-based colors and pigments have been used since ancient times for making jewelry and paints, and miners have long used the name kobold ore for some minerals, the free metallic cobalt was...
(cobaltite: CoAsS and skutterudite: CoAs
3) and
nickelNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
, as
sulfideA sulfide is a chemical compound containing sulfur in its lowest oxidation number of −2.- Properties :...
s, and when oxidised as arsenate minerals such as
mimetiteMimetite, whose name derives from the Greek mimethes, meaning "imitator", is an arsenate mineral which forms as a secondary mineral in lead deposits, usually by the oxidation of galena and arsenopyrite. The name is a reference to mimetite's resemblance to the mineral pyromorphite...
, Pb
5(AsO
4)
3Cl and
erythriteErythrite or red cobalt is a secondary hydrated arsenate of cobalt minerals with the formula...
, Co
3(AsO
4)
2·8H
2O, and more rarely arsenites ('arsenite' = arsenate(III), AsO
33- as opposed to arsenate (V), AsO
43-).
In addition to the inorganic forms mentioned above, arsenic also occurs in various organic forms in the environment.
Other naturally occurring pathways of exposure include volcanic ash, weathering of the arsenic-containing mineral and ores as well as groundwater. It is also found in food, water, soil and air.
Production
In 2005, China was the top producer of white arsenic with almost 50% world share, followed by Chile, Peru and Morocco, reports the
British Geological SurveyThe British Geological Survey is a partly publicly-funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS headquarters are in Keyworth, Nottinghamshire, but other centres...
and the
United States Geological SurveyThe United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning...
. The arsenic was recovered mostly during mining operations, for example the production from Peru comes mostly from copper mining and the production in China is owing to gold mining. Arsenic is part of the smelter dust from copper, gold, and lead smelters.
On roasting in air of arsenopyrite, arsenic sublimes as arsenic (III) oxide leaving iron oxides, while roasting without air results in the production of metallic arsenic. For further purification of the arsenic from sulfur and other chalcogenes is sublimed in vacuum or in a hydrogen atmosphere or by distilling it from molten lead-arsenic mixture.
Wood preservation
The toxicity of arsenic to
insectInsects are arthropods, having a hard exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae. They are the most diverse group of animals on the planet and include more than a million species that are already described. Insects represent more than half of all...
s,
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, and fungi led to its use as a wood preservative. In the 1950s a process of treating wood with
chromated copper arsenateChromated copper arsenate is a wood preservative used for timber treatment since the mid-1930s. It is a mix of copper, chromium, and arsenic formulated as oxides or salts. It preserves the wood from decay fungi, wood attacking insects, including termites, and marine borers...
(also known as CCA or Tanalith) was invented, and for decades this treatment was the most extensive industrial use of arsenic. Due to improved understanding of arsenic's high level of toxicity, most countries banned the use of CCA in consumer products. The
European UnionThe European Union is an economic and political union of 27 Member States, located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht on 1 November 1993 upon the foundations of the pre-existing European Economic Community...
and United States led this ban, beginning in 2004.
As of 2002, US-based industries consumed 19,600 metric tons of arsenic. 90% of this was used for treatment of wood with CCA. In 2007, 50% of the 5,280 metric tons of consumption was still used for this purpose. In the United States, the use of arsenic in consumer products was discontinued for residential and general consumer construction on December 31, 2003 and alternative chemicals are now used, such as ACQ,
borateBorates in chemistry are chemical compounds containing boron oxoanions, with boron in oxidation state +3. The simplest borate ion is the trigonal planar, BO33−, although many others are known. BO33− forms salts with metallic elements. Boron found in...
s, copper azole, cyproconazole, and
propiconazolePropiconazole is a triazole fungicide used agriculturally on grasses grown for seed, mushrooms, corn, wild rice, peanuts, almonds, sorghum, oats, pecans, apricots, peaches, nectarines, plums and prunes. Propiconazole was first developed in 1979 by Janssen Pharmaceutica.-External links:*...
.
Although discontinued, this application is also one of the most concern to the general public. The vast majority of older pressure-treated wood was treated with CCA. CCA lumber is still in widespread use in many countries, and was heavily used during the latter half of the 20th century as a structural and outdoor
building materialBuilding material is any material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more...
. Although the use of CCA lumber was banned in many areas after studies showed that arsenic could leach out of the wood into the surrounding
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
(from playground equipment, for instance), a risk is also presented by the burning of older CCA timber. The direct or indirect ingestion of wood ash from burnt CCA lumber has caused fatalities in animals and serious poisonings in humans; the lethal human dose is approximately 20 grams of ash. Scrap CCA lumber from construction and demolition sites may be inadvertently used in commercial and domestic fires. Protocols for safe disposal of CCA lumber do not exist evenly throughout the world; there is also concern in some quarters about the widespread
landfillA landfill, also known as a dump , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...
disposal of such timber.
Medical
During the 18th, 19th, and 20th centuries, a number of arsenic compounds have been used as medicines, including
arsphenamineArsphenamine, also known as Salvarsan and 606, is a drug that was used to treat syphilis and trypanosomiasis. It was the first modern chemotherapeutic agent.-History:...
(by
Paul EhrlichPaul Ehrlich was a German scientist in the fields of hematology, immunology, and chemotherapy, and Nobel laureate. He is noted for curing syphilis and for his research in autoimmunity, calling it "horror autotoxicus"...
) and
arsenic trioxideArsenic trioxide is the inorganic compound with the formula As2O3. This commercially important oxide of arsenic is the main precursor to other arsenic compounds, including organoarsenic compounds. Approximately 50,000 tons are produced annually...
(by Thomas Fowler).
Arsphenamine as well as
NeosalvarsanNeosalvarsan is a synthetic chemotherapeutic that is an organoarsenic compound. It became available in 1912 and superseded the more toxic and less water-soluble salvarsan as an effective treatment for syphilis...
was indicated for
syphilisSyphilis is a sexually transmitted disease caused by the spirochetal bacterium Treponema pallidum subspecies pallidum. The route of transmission of syphilis is almost always through sexual contact, although there are examples of congenital syphilis via transmission from mother to child in utero.The...
and
trypanosomiasisTrypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus Trypanosoma. More than 66 million women, men, and children in 36 countries of sub-Saharan Africa suffer from human African trypanosomiasis which is caused by...
, but has been superseded by modern antibiotics.
Arsenic trioxide has been used in a variety of ways over the past 500 years, but most commonly in the treatment of
cancerCancer is a class of diseases in which a group of cells display uncontrolled growth , invasion , and sometimes metastasis...
. The US
Food and Drug AdministrationThe Food and Drug Administration is a Government agency of the United States Department of Health and Human Services and is responsible for regulating and supervising the safety of foods, tobacco products, dietary supplements, Medication drugs, vaccines, Biopharmaceutical, blood transfusion,...
in 2000 approved this compound for the treatment of patients with
acute promyelocytic leukemiaAcute promyelocytic leukemia is a subtype of acute myelogenous leukemia , a cancer of the blood and bone marrow. It is also known as acute progranulocytic leukemia; APL; AML with t, PML-RARA and variants; FAB subtype M3 and M3 variant.In APL, there is an abnormal accumulation of immature...
that is resistant to ATRA. It was also used as Fowler's solution in
psoriasisPsoriasis is a chronic, non-contagious autoimmune disease that affects the skin and joints. It commonly causes red, scaly patches to appear on the skin. The scaly patches caused by psoriasis, called psoriatic plaques, are areas of inflammation and excessive skin production. Skin rapidly...
. Recently new research has been done in locating tumours using arsenic-74 (a positron emitter). The advantages of using this isotope instead of the previously used
iodineIodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
-124 is that the signal in the
PET scanPositron emission tomography is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
is clearer as the iodine tends to transport iodine to the thyroid gland producing a lot of noise.
Pigments
Copper acetoarsenite was used as a green
pigmentA pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
known under many different names, including '
Paris GreenParis Green is a common name for copper acetoarsenite, or C.I. Pigment Green 21, an extremely toxic blue green chemical with four main uses: pigment, animal poison , insecticide, and blue colorant for fireworks...
' and 'Emerald Green'. It caused numerous
arsenic poisoningArsenic poisoning kills by allosteric inhibition of essential metabolic enzymes, leading to death from multi-system organ failure. It primarily inhibits enzymes that require lipoic acid as a cofactor, such as pyruvate and alpha-ketoglutarate dehydrogenase. Because of this, substrates before the...
s.
Scheele's GreenScheele's Green, also called Schloss Green, is chemically a cupric hydrogen arsenite , CuHAsO
3. It is a compound similar to Paris Green...
, a copper arsenate, was used in the 19th century as a colouring agent in
sweetsis a Japanese idol group. Put together through auditions, the group debuted in 2003 on the avex trax label. Although the group met minor success, they disbanded after three years with the release of a final single in June 2006.- History :...
.
Military
After
World War IWorld War I , also known as the First World War, the Great War, and the War to End All Wars, was a global military conflict which involved most of the world's great powers, assembled in two opposing alliances: the Triple Entente and the Triple Alliance...
the United States built up a stockpile of 20,000 tons of
lewisiteLewisite is an organoarsenic compound, specifically an arsine. It was once manufactured in the U.S. and Japan as a chemical weapon, acting as a vesicant and lung irritant...
; a
chemical weaponChemical warfare involves using the toxic properties of chemical substances as weapons to kill, injure, or incapacitate an enemy....
, acting as a vesicant (blister agent) and
lungThe lung or pulmonary system is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart...
irritant. The stockpile was neutralized with bleach and dumped into the
Gulf of MexicoThe Gulf of Mexico is the ninth largest body of water in the world. Considered a smaller part of the Atlantic Ocean, it is an ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United...
after the 1950s. During the
Vietnam WarThe Vietnam War or the Second Indochina War was a Cold War military conflict that occurred in Vietnam, Laos, and Cambodia from 1959 to 30 April 1975...
the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
used
Agent BlueAgent Blue is one of the "rainbow herbicides" that is known for its use by the United States during the Vietnam War. It was sprayed on rice paddies and other crops in an attempt to deprive the Vietnamese of valuable crops. Agent Blue is a mixture of two arsenic-containing compounds, sodium...
(a mixture of sodium cacodylate) and dimethyl arsinic acid (
cacodylic acidCacodylic acid is the chemical compound with the formula 2AsO2H. Derivatives of cacodylic acid, cacodylates, were frequently used as herbicides. For example, "Agent Blue," one of the chemicals used during the Vietnam War, is a mixture of cacodylic acid and sodium cacodylate...
) as one of the
rainbow herbicidesThe Rainbow Herbicides are a group of chemicals used by the United States military in Southeast Asia during the Vietnam War. Success with Project AGILE field tests with herbicides in South Vietnam in 1961 led to the formal herbicidal program Trail Dust...
to deprive the Vietnamese of valuable crops.
Other uses
- Various agricultural
Agriculture is the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of human civilization, with the husbandry of domesticated animals and plants creating food surpluses that enabled the development of more densely populated and...
insecticides, termination and poisons. For example Lead hydrogen arsenateLead hydrogen arsenate, also called lead arsenate, acid lead arsenate or LA, chemical formula PbHAsO4, is an inorganic insecticide used primarily against the potato beetle.-Chemistry:...
was used well into the 20th century as an insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
on fruit treeA fruit tree is a tree bearing fruit that is consumed or used by people — all trees that are flowering plants produce fruit, which are the ripened ovary of a flower containing one or more seeds. In horticultural usage, the term 'fruit tree' is limited to those that provide fruit for human food...
s. Its use sometimes resulted in brain damageBrain damage, or acquired brain injury, is the destruction or degeneration of brain cells.-Causes:Brain damage may occur due to a wide range of conditions, illnesses, injuries, and as a result of iatrogenesis...
to those working the sprayers. In the last half century, monosodium methyl arsenateMonosodium methyl arsenate is an arsenic-based herbicide and fungicide. It is an organic arsenate; but it is a less toxic organic form of arsenic, which has replaced the role of lead hydrogen arsenate in agriculture. It is one of the most common herbicides used on golf courses. It is typically...
(MSMA) and disodium methyl arsenateDisodium methyl arsonate is an arsenic-based herbicide.Trade names include Metharsinat, Arrhenal, Disomear, Metharsan, Stenosine, Tonarsan, Tonarsin, Arsinyl, Arsynal, and Diarsen....
(DSMA), a less toxic organic form of arsenic, has replaced lead arsenate's role in agriculture.
- Used in animal feed, particularly in the US as a method of disease prevention and growth stimulation. One example is roxarsone which was used by 69.8 and 73.9% of the broiler
A broiler is a type of chicken raised specifically for meat production. Modern commercial broilers, typically known as Cornish crosses or Cornish-Rocks are specially bred for large scale, efficient meat production and grow much faster than egg or traditional dual purpose breeds...
starter and growers between 1995 to 2000.
- Gallium arsenide is an important semiconductor
A semiconductor is a material that has an electrical resistivity between that of a conductor and an insulator, that is, generally in the range 10
3 Siemens/cm to 10
−8 S/cm. Devices made from semiconductor materials are the foundation of modern electronics, including radio,...
material, used in integrated circuitIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
s. Circuits made using the compound are much faster (but also much more expensive) than those made in siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
. Unlike silicon it is direct bandgap, and so can be used in laser diodeA laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common and practical type of laser diode is formed from a p-n junction and powered by injected electric current...
s and LEDLEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
s to directly convert electricityElectricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge...
into lightLight is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye ....
.
- Also used in bronzing
Bronzing is a process by which a bronze-like surface is applied to other materials . Some bronzing processes are merely simulated finishes applied to existing metal surfaces, or coatings of powdered metal that give the appearance of a solid metal surface...
and pyrotechnicsPyrotechnics is the science of materials capable of undergoing self-contained and self-sustained exothermic chemical reactions for the production of heat, light, gas, smoke and/or sound...
.
- Up to 2% of arsenic is used in lead alloys for lead shot
Lead shot is a collective term for small balls of lead. It is used primarily as projectiles in shotguns, but is also used for a variety of other purposes...
s and bulletA bullet is a projectile propelled by a firearm, sling, or air gun. A bullet does not contain explosives, but damages the intended target by its impact or penetration...
s.
- Arsenic is added in small quantities to brass to make it dezincification
Dezincification refer to:* DZR, dezincification resistant* Selective leaching...
resistant. This grade of brass is used to make plumbing fittings.
- Arsenic is also used for taxonomic sample preservation.
Biological role
Inorganic arsenic and its compounds, upon entering the
food chainFood chains describe the eating relationships between species within an ecosystem or a particular living place. Many types of food chains or webs are applicable depending on habitat or environmental factors...
, are progressively metabolised to less toxic forms of arsenic through a process of
methylationMethylation in the chemical sciences denotes the attachment or substitution of a methyl group on various substrates. Methylation is a form of alkylation with specifically a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...
. For example, the mold Scopulariopsis brevicaulis produce significant amounts of
trimethylarsineTrimethylarsine is the chemical compound with the formula 3As, commonly abbreviated AsMe3. This organic derivative of arsine has been used as a source of arsenic in microelectronics industry, a building block to other organoarsenic compounds, and serves as a ligand in...
if inorganic arsenic is present. The organic compound
arsenobetaineArsenobetaine is an organoarsenic compound that is the main source of arsenic found in fish. It is the arsenic analogue of trimethylglycine, commonly known as betaine. The biochemistry and its biosynthesis are similar to the biosynthesis of choline and betaine...
is found in some marine foods such as fish and algae, and also in mushrooms in larger concentrations. The average person's intake is about 10–50 µg/day. Values about 1000 µg are not unusual following consumption of fish or mushrooms. But there is little danger in eating fish because this arsenic compound is nearly non-toxic.
Some species of
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
obtain their energy by
oxidizingRedox describes all chemical reactions in which atoms have their oxidation number changed....
various fuels while
reducingRedox describes all chemical reactions in which atoms have their oxidation number changed....
arsenate to arsenite. The
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at...
s involved are known as arsenate reductases (Arr).
In 2008, bacteria were discovered that employ a version of
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
in the absence of oxygen with arsenites as
electron donorAn electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process....
s, producing arsenates (just like ordinary photosynthesis uses water as electron donor, producing molecular oxygen). Researchers conjecture that historically these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive. One
strainIn biology, strain is a low-level taxonomic rank used in three related ways.-Microbiology and virology:A strain is a genetic variant or subtype of a microorganism . For example, a "flu strain" is a certain biological form of the influenza or "flu" virus...
PHS-1 has been isolated and is related to the γ-Proteobacterium
Ectothiorhodospira shaposhnikovii. The mechanism is unknown, but an encoded Arr enzyme may function in reverse to its known
homologuesIn evolutionary biology, homology refers to any similarity between characteristics of organisms that is due to their shared ancestry. The word homologous derives from the ancient Greek ομολογειν, 'to agree'. There are examples in different branches of biology...
.
Arsenic has been linked to epigenetic changes which are heritable changes in gene expression that occur without changes in DNA sequence and include DNA methylation, histone modification and RNA interference. Toxic levels of arsenic cause significant DNA hypermethylation of tumour suppressor genes p16 and p53 thus increasing risk of carcinogenesis. These epigenetic events have been observed in
in vitro studies with human kidney cells and
in vivo tests with rat liver cells and peripheral blood leukocytes in humans. Inductive coupled plasma mass spectrometry (ICP-MS) is used to detect precise levels of intracellular of arsenic and its other bases involved in epigenetic modification of DNA. Studies investigating arsenic as an epigenetic factor will help in developing precise biomarkers of exposure and susceptibility.
Safety
Arsenic and many of its compounds are especially potent poisons. Arsenic disrupts
ATPAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
production through several mechanisms. At the level of the
citric acid cycleThe citric acid cycle — also known as the tricarboxylic acid cycle , the Krebs cycle, or more rarely, the Szent-Györgyi-Krebs cycle — is a series of enzyme-catalysed chemical reactions, which is of central importance in all living cells that use oxygen as part of cellular respiration...
, arsenic inhibits
lipoic acidLipoic acid is an organosulfur compound, one enantiomer of which is an essential cofactor for many enzyme complexes. This yellow solid is a carboxylic acid and features a cyclic disulfide, or ditholane ring, functional group. The R-enantiomer is biosynthesized and used as a cofactor. It is...
which is a
cofactorA cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes and cofactors can be considered "helper molecules/ions" that assist in biochemical transformations...
for
pyruvate dehydrogenasePyruvate dehydrogenase complex is a complex of three enzymes that transform pyruvate into acetyl-CoA by a process called pyruvate decarboxylation. Acetyl-CoA may then be used in the citric acid cycle to carry out cellular respiration, and this complex links the glycolysis metabolic pathway to the...
; and by competing with phosphate it uncouples
oxidative phosphorylationOxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all carry out oxidative phosphorylation to produce ATP, the molecule that...
, thus inhibiting energy-linked reduction of
NAD+Nicotinamide adenine dinucleotide, abbreviated NAD
+, is a coenzyme found in all living cells. The compound is a dinucleotide, since it consists of two nucleotides joined through their phosphate groups, with one nucleotide containing an adenine base and the other containing...
, mitochondrial respiration, and ATP synthesis. Hydrogen peroxide production is also increased, which might form reactive oxygen species and oxidative stress. These metabolic interferences lead to death from multi-system
organ failureOrgan failure is a condition where an organ does not perform its expected function.It is not a diagnosis. It can be classified by the cause, but when the cause is not known, it can also be classified by whether the onset is chronic or acute....
, probably from necrotic cell death, not
apoptosisApoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed cell death involves a series of biochemical events leading to a characteristic cell morphology and death; in more specific terms, a series of biochemical events that lead to a variety of...
. A post mortem reveals brick red coloured mucosa, owing to severe haemorrhage. Although arsenic causes toxicity, it can also play a protective role.
Elemental arsenic and arsenic compounds are classified as "
toxicToxicity is the degree to which a substance is able to damage an exposed organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
" and "dangerous for the environment" in the
European UnionThe European Union is an economic and political union of 27 Member States, located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht on 1 November 1993 upon the foundations of the pre-existing European Economic Community...
under
directive 67/548/EECThe Dangerous Substances Directive is one of the main European Union laws concerning chemical safety. It was made under Article 100 of the Treaty of Rome...
.
The
International Agency for Research on CancerThe International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
(IARC) recognizes arsenic and arsenic compounds as
group 1 carcinogens, and the EU lists arsenic trioxide,
arsenic pentoxideArsenic pentoxide, As2O5, is an important commercial compound of arsenic. Its usage with respect to arsenic chemistry, as well as its toxicology are similar to arsenic trioxide, As2O3...
and
arsenateThe arsenate ion is AsO
43−.An arsenate is any compound that contains this ion.The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As[V]....
salts as category 1
carcinogenA carcinogen is any substance, radionuclide or radiation that is an agent directly involved in the promotion of cancer or in the increase of its propagation. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
s.
Arsenic is known to cause arsenicosis owing to its manifestation in drinking water, “the most common species being arsenate [HAsO
42- ; As(V)] and arsenite [H
3AsO
3 ; As(III)]”. The ability of arsenic to undergo redox conversion between As(III) and As(V) makes its availability in the environment more abundant. According to Croal, Gralnick, Malasarn, and Newman, “[the] understanding [of] what stimulates As(III) oxidation and/or limits As(V) reduction is relevant for bioremediation of contaminated sites (Croal). The study of chemolithoautotrophic As(III) oxidizers and the heterotrophic As(V) reducers can help the understanding of the oxidation and/or reduction of arsenic.
Treatment of chronic arsenic poisoning is easily accomplished. British anti-lewisite (
dimercaprolDimercaprol or British anti-Lewisite , is a compound developed by British biochemists at Oxford University during World War II. It was developed secretly as an antidote for Lewisite, the now-obsolete arsenic-based chemical warfare agent. Today, it is used medically in treatment of arsenic, mercury...
) is prescribed in dosages of 5 mg/kg up to 300 mg each 4 hours for the first day. Then administer the same dosage each 6 hours for the second day. Then prescribe this dosage each 8 hours for eight additional days.
Arsenic in drinking water
Arsenic contamination of groundwaterArsenic contamination of groundwater is a natural occurring high concentration of arsenic in deeper levels of groundwater, which became a high-profile problem in recent years due to the use of deep tubewells for water supply in the Ganges Delta, causing serious arsenic poisoning to large numbers of...
has led to a massive epidemic of arsenic poisoning in
BangladeshWater supply and sanitation in Bangladesh is characterized by a number of achievements and challenges. The share of the population with access to an improved water source was estimated at 98% in 2004, a very high level for a low-income country. This has been achieved to a large extent through the...
and neighbouring countries. Presently 42 major incidents around the world have been reported on groundwater arsenic contamination. It is estimated that approximately 57 million people are drinking
groundwaterGroundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in...
with arsenic concentrations elevated above the
World Health OrganizationThe World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health...
's standard of 10 parts per billion. However,
a study of cancer rates in Taiwan suggested that significant increases in cancer mortality appear only at levels above 150 parts per billion. The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater owing to the anoxic conditions of the subsurface. This groundwater began to be used after local and western
NGOsNon-governmental organization is a term that has become widely accepted as referring to a legally constituted, non-governmental organization created by natural or legal persons with no participation or representation of any government...
and the Bangladeshi government undertook a massive shallow tube
wellA water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a vertical turbine pump, a handpump or a mechanical pump...
drinking-water program in the late twentieth century. This program was designed to prevent drinking of bacterially contaminated surface waters, but failed to test for arsenic in the groundwater. Many other countries and districts in
South East AsiaManila
Bangkok
Ho Chi Minh City
Kuala Lumpur
Singapore
Yangon
Bandung
Hanoi
Surabaya
Taichung
Kaohsiung
Medan|-|}...
, such as
VietnamVietnam , officially the Socialist Republic of Vietnam , is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea to the east...
,
CambodiaThe Kingdom of Cambodia , formerly known as Kampuchea , is a country in South East Asia with a population of over 14 million people. The kingdom's capital and largest city is Phnom Penh...
, and
ChinaChina is a cultural region, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
have geological environments conducive to generation of high-arsenic groundwaters. Arsenicosis was reported in
Nakhon Si ThammaratNakhon Si Thammarat is a town in southern Thailand, capital of the Nakhon Si Thammarat Province and the Nakhon Si Thammarat district. It is about 610 km south of Bangkok, on the east coast of the Malay Peninsula...
,
ThailandThe Kingdom of Thailand is an independent country that lies in the heart of Southeast Asia.It is bordered to the north by Laos and Burma, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the west by the Andaman Sea and Burma...
in 1987, and the dissolved arsenic in the
Chao Phraya RiverThe Chao Phraya is a major river in Thailand, with its low alluvial river plain marking the mainland of the country. It runs through Bangkok, the capital of Thailand.-Etymology:...
is suspected of containing high levels of naturally occurring arsenic, but has not been a public health problem owing to the use of bottled water.
The northern United States, including parts of
MichiganMichigan is a Midwestern state of the United States of America. It was named after Lake Michigan, whose name is a French adaptation of the Ojibwe term mishigama, meaning "large water" or "large lake"....
,
WisconsinWisconsin is one of the fifty U.S. states. Located in the north-central United States, Wisconsin is considered part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the...
,
MinnesotaMinnesota is a state in the Midwestern region of the United States. The twelfth largest state by area in the U.S., it is the twenty-first most populous, with 5.2 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the...
and the Dakotas are known to have significant concentrations of arsenic in ground water. Increased levels of skin cancer have been associated with arsenic exposure in Wisconsin, even at levels below the 10 part per billion drinking water standard.
Low-level exposure to arsenic at concentrations found commonly in US drinking water compromises the initial immune response to H1N1 or swine flu infection according to NIEHS-supported scientists. The study, conducted in laboratory mice, suggests that people exposed to arsenic in their drinking water may be at increased risk for more serious illness or death in response to infection from the virus.
Epidemiological evidence from
ChileChile, officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
shows a dose dependent connection between chronic arsenic exposure and various forms of cancer, particularly when other risk factors, such as cigarette smoking, are present. These effects have been demonstrated to persist below 50 parts per billion.
Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable risk increase for bladder cancer at 10 parts per billion. According to Peter Ravenscroft of the Department of Geography at the University of Cambridge, roughly 80 million people worldwide consume between 10 and 50 parts per billion arsenic in their drinking water. If they all consumed exactly 10 parts per billion arsenic in their drinking water, the previously cited multiple epidemiological study analysis would predict an additional 2,000 cases of bladder cancer alone. This represents a clear underestimate of the overall impact, since it does not include lung or skin cancer, and explicitly underestimates the exposure. Those exposed to levels of arsenic above the current WHO standard should weigh the costs and benefits of arsenic remediation.
Arsenic can be removed from drinking water through
coprecipitationIn chemistry, coprecipitation or co-precipitation is the carrying down by a precipitate of substances normally soluble under the conditions employed...
of iron minerals by oxidation and filtering. When this treatment fails to produce acceptable results, adsorptive arsenic removal media may be utilized. Several adsorptive media systems have been approved for point-of-service use in a study funded by the
United States Environmental Protection AgencyThe U.S. Environmental Protection Agency is an agency of the federal government of the United States charged to regulate chemicals and protect human health by safeguarding the natural environment: air, water, and land...
(U.S.EPA) and the
National Science FoundationThe National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
(NSF). A team of European and Indian engineers have set up six arsenic treatment plants in
West BengalWest Bengal is a state in eastern India. With Bangladesh, which lies on its eastern border, the state forms the ethno-linguistic region of Bengal. To its northeast lie the states of Assam and Sikkim and the country Bhutan, and to its southwest, the state of Orissa...
based on in-situ remediation method. This technology does not use any chemicals and arsenic is turned into an insoluble form in the subterranean zone by recharging aerated water into the aquifer. This process does not produce any waste stream or sludge and it costs about 1 US$ to produce 10 cubic meters of water.
Magnetic separations of arsenic at very low magnetic field
gradientIn vector calculus, the gradient of a scalar field is a vector field which points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
s have been demonstrated in point-of-use water purification with high-surface-area and
monodisperseA collection of objects are called monodisperse, or monosized, if they have the same size, and shape when discussing particles, and the same mass, when discussing polymers...
magnetiteMagnetite is a ferrimagnetic mineral with chemical formula Fe
3O
4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name ferrous-ferric oxide...
(Fe
3O
4)
nanocrystalFahlman, B. D. has described a nanocrystal as any nanomaterial with at least one dimension ≤ 100nm and that is singlecrystalline. More properly, any material with a dimension of less than 1 micrometre, i.e., 1000 nanometers, should be referred to as a nanoparticle, not a nanocrystal...
s. Using the high specific surface area of Fe
3O
4 nanocrystals the mass of waste associated with arsenic removal from water has been dramatically reduced.
Epidemiological studies have suggested a correlation between chronic consumption of drinking water contaminated with arsenic and the incidence of
type 2 diabetesDiabetes mellitus type 2 or type 2 diabetes is a disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency...
. However, the literature provides insufficient scientific evidence to show cause and effect between arsenic and the onset of diabetes mellitus type 2.
Occupational exposures
Industries that use inorganic arsenic and its compounds include wood preservation, glass production, nonferrous metal alloys, and electronic semiconductor manufacturing. Inorganic arsenic is also found in coke oven emissions associated with the smelter industry. Occupational exposure and poisoning may occur in persons working in these industries.
See also
- Aqua Tofana
Aqua Tofana was a strong poison that was reputedly widely used in Naples and Rome, Italy...
- Arsenic poisoning
Arsenic poisoning kills by allosteric inhibition of essential metabolic enzymes, leading to death from multi-system organ failure. It primarily inhibits enzymes that require lipoic acid as a cofactor, such as pyruvate and alpha-ketoglutarate dehydrogenase. Because of this, substrates before the...
- Fowler's solution
Fowler's solution is a solution containing potassium arsenite that once was prescribed as a remedy or a tonic. A Dr. Fowler of Stafford, England proposed its use in 1786 as a substitute for a patented medicine, "tasteless ague drop." It was prescribed in the United States until the late 1950's...
- Grainger challenge
The Grainger challenge is a scientific competition to find an economical way to remove arsenic from arsenic-contaminated groundwater. This competition is being funded by the United States National Academy of Engineering and the Grainger Foundation and is meant to help provide safe drinking water to...
- White arsenic
- Arsenic trioxide
Arsenic trioxide is the inorganic compound with the formula As2O3. This commercially important oxide of arsenic is the main precursor to other arsenic compounds, including organoarsenic compounds. Approximately 50,000 tons are produced annually...
External links