Arsenic - arsenic history, occurrence, use, Prices

 

Arsenic is a chemical element with the element symbol As and the atomic number 33. In the periodic table of elements it is in the 4. Period and the 5. Main group, or 15. IUPAC group or nitrogen group. Arsenic is seldom dainty, mostly in the form of sulphides. It belongs to the semi-metals, as it shows depending on the modification metallic or non-metallic properties.

Colloquially, the arsenic known as murder venom is usually called simply "arsenic". Arsenic compounds have been known since ancient times. As a mutagenic clastogen arsenic compounds can act as a poison, causing chromosome aberrations and thus may have a carcinogenic effect.

Arsenic is used for doping semiconductors and as a constituent of III-V semiconductors such as gallium arsenide. The organic arsenic compound arsphenamine (salvarsan) was considered to be the beginning of 20 despite severe and severe side effects. Century as a breakthrough in the treatment of syphilis. Today, arsenic trioxide is used as the last treatment option in the treatment of promyelocytic leukemia.

History

The name Arsen goes back directly to ancient Greek ἀρσενικόν arsenikón, the ancient name of the arsenic mineral Auripigment. It can already be found at Dioscorides in 1. Century. The Greek name, in turn, seems to have its origin in Old Persian (al-) zarnik (gold, auripigment, "arsenic") and probably reached the Greek through Semitic mediation. Folk etymologically, the name was falsely derived from the identical (old and new) Greek word αρσενικός arsenikós, which can be translated as male / strong. Only since the 19. Century is the name arsenic in use. The element symbol was proposed by Jöns Jakob Berzelius to 1814.

The first contact of people with arsenic leaves the 3. Millennium BC In the hair of the mummy of the alpine dwellers mentioned in the glacier ice of the alpine dweller known as Ötzi, large quantities of arsenic were detected, which is archaeologically interpreted as an indication that the affected man was involved in copper processing - copper ores are often contaminated with arsenic. In classical antiquity, arsenic was known in the form of the arsenic sulphides Auripigment (As2S3) and Realgar (As4S4), which were described by Greek Theophrastos, Aristotle's successor. Even the Greek philosopher Democritus had in the 5. Century BC Chr. Demonstrable knowledge of arsenic compounds. The Leiden Papyrus X from the 3. Century AD suggests that they were used to color silver gold-like and copper white. The Roman emperor Caligula had allegedly already in the 1. Century after Chr. A project for the production of gold from the (golden yellow) Auripigment in order. The alchemists, who knew that arsenic compounds were known to be mentioned in the ancient standard work Physica et Mystica, suspected a relationship with sulfur and mercury. Arsenic (III) sulfide was used as a painter's paint and depilatory and for the external and internal treatment of lung diseases.

In the Middle Ages, arsenic (arsenic (III) oxide) was found in smelter (dust-laden exhaust gas from metallurgical furnaces). Albertus Magnus first described the production of arsenic by reducing arsenic with coal around 1250. He is therefore considered to be the discoverer of the element, even if there are indications that the elementary metal was produced earlier. Paracelsus introduced it to medicine in the 16th century. Around the same time, arsenic preparations were described in the Chinese encyclopedia Pen-ts'ao Kang-mu by the pharmacist Li Shi-zhen. This author particularly highlights its use as a pesticide in rice fields.

In the 17. In the 16th century, the yellow auripigment became popular among Dutch painters as the royal yellow. As the pigment transforms into arsenic (III) oxide over long periods of time and crumbles off the canvas, difficulties arise in the restoration. From 1740, arsenic preparations have been used successfully in Europe as a seed dressing in crop protection. However, this use was banned by 1808 because of its high toxicity. The use of arsenic additives for lead casting is based on the greater hardness of such lead alloys, typical application are shot pellets. Although the toxicity and use was known as murder venom, arsenic is in the beginning 19. Century one of the most important asthma remedies. It is based on reports that the Chinese were said to smoke arsenic in combination with tobacco in order to develop lungs that are as strong as bellows. Also into the 19. Arsenic compounds found external and internal applications in malignant tumors, skin diseases and (in the form of Fowler drops) fever.

Arsenic was used in the form of copper arsenates in colorants such as the Parisian green to print on wallpaper. In high humidity, these pigments were transformed by mold into toxic volatile arsenic compounds, which often led to chronic arsenic poisoning.

Arsenic was also used in wars. Arsenic compounds were used in chemical warfare agents (blue cross) or Lewisite in the First World War. In the victims, they caused cruel pain and severe bodily injury by attacking the skin and lungs.

occurrence

Arsenic occurs in low concentrations of up to 10 ppm practically everywhere in the soil. It is about as abundant in the earth's crust as uranium or germanium. In the continental crust arsenic occurs at an average of 1,7 ppm, being enriched in the upper crust by its lithophilic character (= silicate loving) (2 ppm vs 1,3 ppm in the lower crust); This places Arsen in the table of most common elements in 53. Location.

Arsenic (Scherbenkobalt) is naturally, ie in elemental form, found in nature and is therefore recognized as an independent mineral by the International Mineralogical Association (IMA). According to the classification of minerals according to Strunz (9 edition) Arsen is under the system no. 1.CA.05 (elements - semi-metals (metalloids) and nonmetals - arsenic elements). The classification of minerals according to Dana, which is also common in English-speaking countries, leads the element mineral under the system no. 01.03.01.01.

2011 sites for solid arsenic are currently known around the world (as of 330). In Germany it was found at several sites in the Black Forest (Baden-Württemberg), in the Bavarian Spessart and Oberpfälzer Wald, in the Hessian Odenwald, in the silver deposits of the Westerzgebirge (Saxony), Hunsrück (Rhineland-Palatinate) and in the Thuringian Forest. In Austria arsenic appeared at several sites in Carinthia, Salzburg and Styria. In Switzerland, arsenic was found in the cantons of Aargau and Valais.

Other localities are in Australia, Belgium, Bolivia, Bulgaria, Chile, China, Finland, France, Greece, Ireland, Italy, Japan, Canada, Kazakhstan, Kyrgyzstan, Madagascar, Malaysia, Morocco, Mexico, Mongolia, New Zealand, Norway, Austria, Peru, Poland, Romania, Russia, Sweden, Slovakia, Spain, the Czech Republic, Ukraine, Hungary, the United Kingdom (United Kingdom) and the United States (USA).

More widely, however, the element occurs in various intermetallic compounds with antimony (allemontite) and copper (whitneyite) as well as in various minerals, which belong mainly to the class of sulfides and sulfosalts. Altogether so far (state: 2011) 565 Arsenminerale are well-known. The highest concentrations of arsenic include, among others, the minerals Duranusit (about 90%), skutterudite and arsenite (each about 76%), which are rarely found. Arsenopyrite (Arsenkies), Löllingite, Realgar (Rauschrot) and Auripigment (Orpiment, Rauschgelb) are widely used. Other well-known minerals are Cobaltite (cobalt shine), Domeykit (arsenic copper), Enargit, Gersdorffit (Nickelarsenkies), Proustite (light red ore, Rubinblende), Rammelsbergit and Safflorit and Sperrylith.

Arsenates are often found in phosphate-bearing rocks because they have comparable solubility, and the most abundant sulfide mineral pyrite can incorporate up to a few mass percent arsenic.

Arsenic is nowadays obtained as a by-product of the smelting of gold, silver, tin, copper, cobalt and other non-ferrous metals and in the processing of phosphate raw materials. The largest producers in 2009 were China, Chile, Morocco and Peru. Arsenic is difficult to dissolve in water and is therefore found only in minor traces, such as 1,6 ppb (billionths by mass) in oceans and oceans.

Arsenic is found in the air in the form of particulate arsenic (III) oxide. The natural cause of this has been identified as volcanic eruptions, which collect a total of 3000 tonnes estimated annually into the Earth's atmosphere. Bacteria release more 20.000 tonnes in the form of organic arsenic compounds such as trimethylarsine. A large part of the released arsenic comes from the burning of fossil fuels such as coal or oil. The estimated emissions caused by road traffic and stationary sources amounted to 1990 in the Federal Republic of Germany 120 tons (20 tons in the old, 100 tons in the new federal states). The outdoor air concentration of arsenic is between 0,5 and 15 nanograms per cubic meter.

Extraction and presentation

Arsenic is a major by-product of copper, lead, cobalt and gold mining. This is the main source of commercial use of the item.

It can be obtained by thermal reduction of arsenic (III) oxide with coke or iron and by heating arsenic (FeAsS) or arsenic (FeAs2) calculi in the absence of air in horizontal sound tubes. Elemental arsenic sublimates, returning to its solid state on cold surfaces.

Arsenkies decomposes into iron sulfide and elemental arsenic.

Arsenic kiesite decomposes into iron arsenide and elemental arsenic.

For semiconductor technology, arsenic, whose purity must be greater than 99,99999 percent, prepared by reduction of multi-distilled arsenic (III) chloride in a hydrogen stream:

Arsenic trichloride reacts with hydrogen to form hydrogen chloride and elemental arsenic.

Previously, it was also produced by sublimation from solutions in liquid lead. The sulfur of the arsenic ores is bound by the lead in the form of lead (II) sulfide. The resulting purities of over 99,999 percent were insufficient for semiconductor applications. Another possibility is crystallization at elevated temperatures from molten arsenic or conversion to monoarsan followed by purification and decomposition at 600 ° C into arsenic and hydrogen.

Features

Arsenic forms the 5 with nitrogen, phosphorus, antimony and bismuth. Main group of the periodic table and occupies because of its physical and chemical properties the middle place in this element group. Arsenic has a relative atomic mass of 74,92159. The radius of the arsenic atom is 124,5 Pikometer. When covalently bound, it is slightly smaller (121 picometer). Due to the emission of the outer electrons (valence electrons) during ionization, the radius is considerably reduced to 34 picometers (As5 +, the outermost p- and the outermost s-orbital remain unoccupied) or 58 picometer (As3 +, only the p-orbital is unoccupied) , In chemical complexes, the As5 + cation is surrounded by four binding partners (ligands), As3 + of six. However, arsenic rarely occurs in clearly ionic form.

According to Pauling, the value for electronegativity lies on the 0 scale, which ranges from 4 (metals) to 2,18 (nonmetal), and is therefore comparable to the value of the group neighbor Phosphorus. The semi-metal character of the arsenic is also shown by the fact that the required dissociation energy of 302,7 kJ / mol, ie the energy that must be applied to dissolve a single arsenic atom from an arsenic solid, between the non-metal nitrogen (473,02 kJ / mol; covalent bond) and the metal bismuth (207,2 kJ / mol, metallic bond). Under normal pressure, arsenic sublimates at a temperature of 613 ° C, ie it goes from the solid state directly into the gas phase. Arsenic vapor is lemon yellow and is composed of As800 molecules to approximately 4 ° C. Above 1700 ° C, As2 molecules are present.

Arsenic shows oxidation states between -3 and + 5, depending on the compound partner. With electropositive elements such as hydrogen or metals, it forms compounds in which it occupies an oxidation state of -3. Examples are monoarsan (AsH3) and arsenic copper (Cu3As). In compounds with electronegative elements such as the nonmetals oxygen, sulfur and chlorine, it has the oxidation state + 3 or + 5; The former tends to prefer nitrogen and phosphorus over the elements in the same main group.

modifications

Arsenic, like other elements of the nitrogen group, occurs in various allotropic modifications. Unlike nitrogen, which occurs in the form of diatomic molecules with covalent triple bonds, the corresponding As2 molecules are unstable and arsenic instead forms covalent networks.

Gray or metallic arsenic is the most stable form. It has a density of 5,73 g / cm3. Its crystals are steel gray, metallic shiny and conduct electricity.

Looking at the structural composition of gray arsenic, layers of corrugated arsenic six-membered rings occupy the chair's conformation. Here, the arsenic atoms form a double layer, if one looks at the structure of the layer in cross section. The superimposition of these bilayers is very compact. Certain atoms of the next overlying or underlying layer are almost as far removed from a reference atom as within the considered bilayer. This structure makes the gray arsenic modification, like the homologous elements antimony and bismuth, very brittle. Therefore, these three elements are often referred to as brittle metals.

Yellow arsenic

When arsenic steam, in which arsenic is usually present as an As4 tetrahedron, is rapidly cooled, the metastable yellow arsenic forms with a density of 1,97 g / cm3. It also consists of tetrahedral As4 molecules. Yellow arsenic is a nonmetal and consequently does not conduct electricity. It crystallizes from carbon disulfide and forms cubic, highly refractive crystals that smell of garlic. At room temperature and especially rapidly under the action of light, yellow arsenic transforms into gray arsenic.

Black arsenic

Black arsenic itself can occur in two different forms. Amorphous black arsenic is formed by cooling arsenic vapor on 100 to 200 ° C hot surfaces. It has no ordered structure, but is in an amorphous, glassy form, analogous to the red phosphorus. The density is 4,7 to 5,1 g / cm3. Above 270 ° C, the black arsenic changes to the gray modification. When glassy, ​​amorphous black arsenic is heated to 100 to 175 ° C in the presence of metallic mercury, the result is metastable orthorhombic black arsenic, which is comparable to black phosphorus.

Naturally formed orthorhombic black arsenic is known in nature as the rare mineral arsenolamprit.

Brown arsenic

In the reduction of arsenic compounds in aqueous solution, similar to the phosphorus, copolymers are formed. In these, some of the free valencies of the arsenic bind hydroxy groups (-OH). This form of arsenic is called brown arsenic.

isotope

Arsenic is known to contain artificially produced radioactive isotopes with mass numbers between 65 and 87. The half lives are between 96 milliseconds (66As) and 80,3 days (73As). Naturally occurring arsenic consists of 100 percent of the isotope 75As, it is therefore an anisotropic element. The corresponding arsenic core therefore consists of exactly 33 protons and 42 neutrons. Physically, it is therefore counted to the ug-kernels (u stands for odd, g for straight). Its core spin is 3 / 2.

Usage

Arsenic is added to lead alloys to improve their strength and to make the lead pourable. Especially the finely structured plates of accumulators could not be poured without arsenic. Historically, arsenic was an important ingredient in copper alloys, making them more processable. Metallic arsenic has previously been used on occasion to create dull gray surfaces on metal parts to simulate aging.

In electronics, it plays as at least 99,9999 percent pure element for gallium arsenide semiconductors, so-called III-V semiconductors (due to the combination of elements of the 3 and 5 main group of the periodic table), and for epitaxial layers on wafers in the form of Indium arsenide phosphide and gallium arsenide phosphide play an essential role in the manufacture of high frequency devices such as integrated circuits (ICs), light emitting diodes (LEDs) and laser diodes (LDs). At the beginning of 2004, there were only three manufacturers of high purity arsenic worldwide, two in Germany and one in Japan.

Arsenic, in the form of its compounds, is used in some countries as pesticides in viticulture, as a fungicide (antifungal) in the wood industry, as a wood preservative, as a rat poison and as a decolorant in glassmaking. The use is controversial, since the arsenic compounds used (mainly arsenic (III) oxide) are toxic.

Arsenic in medicines

The use of arsenic-containing minerals as a remedy is already attested in antiquity by Hippocrates and Pliny. They have been used as a fever, as a tonic and for the treatment of migraine, rheumatism, malaria, tuberculosis and diabetes. In the 18. Century was a mixture of potassium arsenite and lavender water known as Fowler 's solution, which was long considered a medical wonder drug and was used as antipyretics, medicinal water and even as an aphrodisiac. Potassium arsenite was used as part of the Fowler solution until the 1960 years in Germany as a treatment for psoriasis.

Constantinus Africanus (1017-1087) recommended an arsenic application to combat toothache. As early as 2700 BC, the use of arsenic to treat a sore tooth in Chinese medicine has been described. In the middle of the 10. The Arabic physician Haly Abbas ('Ali ibn al-'Abbās, † 944) also recommended the use of arsenic for devitalization of the pulp. Arsenic (III) oxide was used for the devitalization of dental pulp into the modern age and disappeared in the 1970er years because of the carcinogenic effect, inflammation of the periodontium, the loss of one or more teeth including necrosis of the surrounding alveolar bone, allergies and intoxication from the spectrum of therapy.

An upswing experienced arsenic or arsenic containing drugs at the beginning of 20. Century. Harold Wolferstan Thomas and Anton Breinl were able to observe 1905 that the arsenic-containing drug Atoxyl kills trypanosomes, which are the causative agents of sleeping sickness. 1920 was an advancement, the Tryparsamid, used in the period from 1922 to 1970 in tropical Africa for the treatment of sleeping sickness. It was important in limiting this epidemic in the first half of the last century, but it could lead to blindness. Developed in the 1950 years, melarsoprol has been the drug of choice for treating sleeping sickness for several decades and is still used today as there are no effective follow-up supplements available.

Also stimulated by the trypanosome-toxic effects of atoxyl, Paul Ehrlich developed the arsenic-containing arsphenamine (salvarsan). The 1910 drug introduced in the treatment of syphilis was the first based on theoretical considerations, systematically developed, specific-acting chemotherapeutic agent and was a model for the development of the sulfa drugs used to date. It has long been used in the treatment of dysentery.

In 2000, an arsenic-containing drug called Trisenox was approved in the US for the treatment of acute promyelocytic leukemia (APL). Since 2002, Trisenox has been approved in Europe for treatment of APL (distribution in the EU and US: Cephalon). Its effectiveness in cancer therapy is also attributed to the antiangiogenic effect.

The various arsenic sulphides are part of medicines of Chinese medicine.

Arsenic as an insecticide in taxidermy

Due to the toxic properties of arsenic compounds, arsenic was previously widely used as an insecticide for the preservation of vertebrates (taxidermy). Many other substances, such as lindane, have been used for the same purpose as described in the specialized literature of taxidermists from 1868 to 1996. However, such substances are also toxic to humans and present today on taxidermy special requirements, as they come into contact with such contaminated preparations.

Biological significance

The biological significance of arsenic for humans is not fully understood. It is considered a trace element in humans, but deficiency symptoms have so far only been detected in animals. The necessary need, if it exists, is between 5 and 50 μg per day. A daily intake of arsenic of - depending on the choice of food - up to one milligram is considered harmless. In a new study, increased arsenic exposure to high levels of arsenic in groundwater from rice-growing areas has been linked to the development of cancer. The promotion of cancer development is, however, dose-dependent and only given when consuming contaminated rice as a daily staple food. There is a habit with regular consumption of arsenic compounds, especially arsenic trioxide, which are accompanied by the withdrawal of the dose even from withdrawal symptoms. People who have acquired such habituation are called arsenic eater.

Sea creatures like mussels or shrimps contain a lot of arsenic, the latter up to 175 ppm. Presumably, it acts as an inhibitor by binding to free thiol groups in enzymes, thus preventing their action.

Arsenic is an essential trace element for many animals. Thus, chickens or rats show marked growth disorders in arsenic-free diets; this is probably related to the influence of the element on the metabolism of the amino acid arginine. Numerous algae and crustaceans contain organic arsenic compounds such as the already mentioned arsenobetaine. Arsenic leads to increased formation of oxygen-carrying red blood cells. For this reason, it was previously added to the feed of poultry and swine to allow faster fattening. Trainers of racehorses used it to illegally doping their animals - today, however, the addition of arsenic to food can easily be detected in the urine.

Soluble arsenic compounds are readily absorbed through the gastrointestinal tract and rapidly distributed throughout the body within 24 hours. Most of the ingested arsenic is found in the muscles, bones, kidneys and lungs. In humans, it has been detected along with thallium in almost every organ. Blood contains up to 8 ppb arsenic, in the other organs of the body such as the bone it has a share of between 0,1 and 1,5 ppm, in hairs the proportion is about 1 ppm. The total content of arsenic in an adult's body is about 7 milligrams on average.

Organic arsenic compounds such as the derived from fish and seafood dimethylarsinic acid, trimethylarsenoxide, trimethylarsine and arsenobetaine leave the human body almost unchanged within two to three days through the kidneys. Inorganic arsenic compounds are converted in the liver to monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) and then excreted as well via the kidneys.

In plants, the element increases carbohydrate turnover. The banded hemisphere (Pteris vittata) prefers to pick up the semi-metal from the ground and can absorb up to five percent of its dry weight of arsenic. For this reason, the fast-growing plant is used for the biological cleaning of arsenic-contaminated soils.

The stimulating effect of arsenic is probably also the cause of the arsenic food that was once widespread in some alpine areas. In the 17. At the turn of the 19th century, some of its residents consumed bi-weekly 250 milligrams of arsenic twice a week - for men, because it helped them work at high altitudes, and women, as it allegedly contributed to a strong complexion. Long dismissed as a fairy tale in science, a farmer from the Styrian Alps 1875 in front of the German experts gathered in Graz a dose of 400 milligrams of arsenic trioxide, which was later detected in his urine. The dose was well over twice the amount of arsenic lethal to normal humans, but did not show any negative effects on the farmer. Something similar is reported by residents of a settlement in the high Chilean Atacama Desert, whose drinking water is highly contaminated with arsenic, but which show no symptoms of intoxication. Today it is assumed that a slow habituation to the poison with successively increasing doses is physiologically possible.

About the bacterial strain GFAJ-1, 2010 has been reported to be able to incorporate arsenate into biomolecules such as DNA, rather than dying off what was previously considered impossible, under certain conditions in arsenic-rich media. The finding, however, seems to be based on dirty methods, the findings could not be replicated.

safety instructions

Arsenic dusts are highly flammable. Arsenic trivalent soluble compounds are highly toxic because they interfere with biochemical processes such as DNA repair, cellular energy metabolism, receptor-mediated transport, and signal transduction. It is presumed that there is no direct effect on the DNA, but rather a displacement of the zinc ion from its binding to metallothioneins and thus inactivation of tumor repressor proteins (see also zinc finger protein). Arsenic (III) and zinc (II) ions have comparable ionic radii and thus similar affinity to these zinc finger proteins, but arsenic does not then activate the tumor repressor proteins.

Acute arsenic poisoning leads to convulsions, nausea, vomiting, internal bleeding, diarrhea and colic, to renal and circulatory failure. In severe poisoning, the skin feels damp and cold and the person can fall into a coma. Taking 60 to 170 milligrams of arsenic is considered a lethal dose to humans (LD50 = 1,4 mg / kg body weight); usually, death occurs within several hours to a few days due to renal and cardiovascular failure. Chronic arsenic exposure can cause skin diseases and damage to the blood vessels leading to the death of affected areas (black foot disease) and to malignant tumors of the skin, lungs, liver and bladder. These symptoms were also referred to as Reichensteiner disease, after a place in Silesia, whose drinking water contained up to 0,6 mg of arsenic per liter by the arsenic degradation.

Chronic arsenic intoxication, via binding to sulfhydryl groups of hematopoietic enzymes (eg, delta-amino-levulin acid synthetase), results in an initial decrease in hemoglobin in the blood, resulting in a reactive polyglobulin. Furthermore, in the case of chronic intake of arsenic, substitution of the phosphorus atoms in the adenosine triphosphate (ATP) leads to a decoupling of the respiratory chain, which leads to a further reactive polyglobulin. Clinically, after years of As exposure, drumstick fingers, watch glass nails, Mees nail bands and acrocyanosis (Raynaud's syndrome) are the result of Black Foot Disease.

Metallic arsenic, on the other hand, shows only low toxicity because of its insolubility, since it is hardly absorbed by the body (LD50 = 763 mg / kg rat, oral). However, it should always be handled with the utmost caution, as it is easily coated with very toxic oxides such as arsenic in the air. The situation is different with arsenic, which was used in former times as a stimulant of arsenic eaters, to prevent arsenic poisoning. The mechanism of this immunization against arsenic is unknown.

Limits

Anionic arsenic occurs as arsenite ([AsO3] 3-) and arsenate ([AsO4] 3-) in groundwater in many countries in high concentrations. As a result of leaching of arsenic ores in the form of trivalent and pentavalent ions, millions of people worldwide drink contaminated water via 100. Especially in India, Bangladesh and Thailand, where in 20. In the 19th century, with international support, numerous wells were dug to dodge surface water contaminated with pathogens on groundwater, causing this unrecognized contamination of drinking water to cause chronic arsenic poisoning in large parts of the affected population. The problem can, where it becomes known, be remedied chemically by oxidation of the arsenic compounds and subsequent precipitation with iron ions. Rice University has developed a cost-effective filter option with nano-magnetite.

Since 1992, the World Health Organization (WHO) has recommended a limit for arsenic in drinking water of 10 micrograms per liter. The value is still exceeded in many European countries and in the USA. In Germany, however, he is respected since 1996. A European Union (EU) directive by 1999 requires a maximum level of 10 micrograms per liter of drinking water across the EU. The US committed to 2001 in the year to comply with this limit from 2006.

Arsenic, which accumulates in groundwater, accumulates ten times as much in rice as in other cereals. On the world market offered varieties contain between 20 and 900 microgram arsenic per kilogram. In 2005, the Chinese government lowered the permitted content of 700 inorganic arsenic compounds to 150 micrograms per kilogram of food, and in July 2014, the Codex Alimentarius Commission set a new high for 200 micrograms for polished rice. The EU Commission responsible for food safety is discussing a threshold that is 15 percent higher for products made from puffed rice and only half as high for special products for small children (ie 100 micrograms per kg).

For other contaminated foods such as beer or fruit juices, there are still no limits, although they may contain more arsenic than is permitted for drinking water. Consumer organizations are demanding a limit on 3 for apple juice, but no more than 4,4 ppb (equivalent to micrograms per kg).

Although fish and seafood have high levels of arsenic, but almost exclusively in the considered harmless organic bound form. Limit values ​​such as for mercury or cadmium do not exist.

The new EU chemicals law transposed by 2005 into the German Hazardous Substance Ordinance prohibits the "commercial" (non-private) processing of arsenic compounds and preparations containing more than 4 by weight of arsenic in Annex 0,3. Such limit controls are in place because arsenic is added to the galvanizing industry of the galvanizing industry worldwide to improve the adhesion properties of the zinc to the iron surface of the metal piece to be galvanized. Due to the temperature in the zinc molten bath of 460 ° C to 480 ° C, the evaporation of arsenic, cadmium and other volatile metals and their accumulation in the air of the workplace. For example, permissible limit values ​​can be exceeded by a factor of a thousand in the short term, with the result of aerogen alveolar uptake into the body. Measurements showed that arsenic (and cadmium) was in the high purity zinc (99,995 grade, DIN 1179 grade) at less than 0,0004% by weight, and after adding 450 grams of this high purity zinc to the zinc melt, the cd / As concentration from 3 to 7 μg / m3 air led to over 3000 μg / m3 air. For arsenic, this fact was surprisingly found in a galvanizing plant by measuring the arsenic concentration in molten zinc, blood and urine (unpublished). In the case of electroplating workers, the urine-arsenic concentration is measured with 25 to 68 μg / L urine, compared to unencumbered population with 0,1 μg arsenic / L urine.

depletion

For the removal of ionic arsenic from drinking water, there are processes based on adsorption on activated carbon, activated alumina or iron hydroxide granules. In addition, ion exchangers are used. It is possible to remove arsenic from the soil using genetically modified plants that store it in leaves. For the phytoremediation of drinking water, the thick-stemmed water hyacinth, which stores arsenic in particular in their root tissue and thus causes a depletion of the contaminated water offers. Organic arsenic compounds in contaminated soils can be degraded enzymatically with the help of fungi.

In Bangladesh, an attempt is made by the Swiss research institution EAWAG to deplete arsenic using transparent PET bottles and lemon juice. In this method called SORAS (Solar Oxidation and Removal of Arsenic), sunlight oxidizes the arsenic; The ingredients of lemon juice help with precipitation. With this low-cost method, the arsenic content can be reduced by 75 to 90 percent.

In the waters of Yellowstone National Park, which feed on geysers and other thermal springs of volcanic origin, eukaryotic algae of the genus Cyanidioschyzon have been found that can tolerate the high arsenic concentrations of the waters and oxidize them to less biologically available organic compounds. A use for depletion in drinking water is being worked on.

Antidote

As antidotes in acute arsenic poisoning, the sulfur-containing complexing agents dimercaptopropanesulfonic acid (= DMPS), dimercaptosuccinic acid and the older, less compatible dimercaprol are available. They are still effective in heavy arsenic doses if the poisoning is diagnosed on time. Their role in the treatment of chronic arsenic poisoning, however, is controversial. Activated carbon one to several hours after ingestion may also bind and excrete the metal.

 

prophylaxis

Indian researchers have found in animal studies that taking garlic can lower blood levels of arsenic and increase levels of urinary arsenic. This is explained by a precipitation of the arsenic in reaction with sulfur-containing substances such as allicin, which is part of garlic. For prophylaxis, two to three cloves of garlic are recommended daily.

Instrumental determination of arsenic
Atomic absorption spectrometry (AAS)

In flame AAS, the arsenic compounds are ionized in a reducing air-acetylene flame. Subsequently, an atomic absorption measurement is carried out at 189,0 nm or 193,8 nm. Detection limits up to 1 μg / ml have been described. Frequently, the arsenic is also converted into the gaseous arsine (AsH4) with the aid of NaBH3 (hydride technology). In quartz tube technology, AsH3 is first thermally decomposed into its atomic constituents at around 1000 ° C in an electrically heated quartz tube in order to subsequently determine the absorption at the aforementioned wavelengths. The detection limit for this technique is 0,01 μg / l. Another method is the so-called graphite furnace technique, in which the arsenic of a solid sample is volatilized at 1700 ° C and higher and then the extinction at 193,8 nm is measured.

Atomic Emission Spectrometry

The coupling of hydride technology with the inductively coupled plasma / laser-induced fluorescence measurement is a very strong detection method for the determination of arsenic. AsH3 released by hydride generation is atomized in the plasma and excited by a laser to emit. Detection limits of 0,04 ng / mL were achieved with this method.

Mass spectrometry (MS)

In mass spectrometry, the arsenic species is first thermally ionized by an inductively coupled argon plasma (ICP-MS). Subsequently, the plasma is passed into the mass spectrometer. A detection limit of 0,2 μg / L has been reported for arsenite.
photometry

Widely used is the photometric detection of As as arsenomolybdenum blue. As (V) reacts first with (NH4) 2MoO4. This is followed by reduction with SnCl2 or hydrazine to a blue complex. The photometry takes place at 730 nm and is thus almost trouble-free. The detection limits can be improved by using basic dyes as complexing agents.

Neutron Activation Analysis

A very sensitive determination of arsenic in the ppt range is possible by means of neutron activation analysis. It is used in particular when the sample has a complex composition or is difficult to digest. However, this method gives no indication of the chemical compound in which the arsenic is present. The interaction of neutrons with the sample containing the natural isotope arsenic 75 results in formation of the heavier isotope arsenic 76, which is unstable and undergoes a β decay to convert to selenium 76. In this case, the β-rays, by means of which a conclusion on the amount of arsenic is possible, are measured.

biosensors

In biosensors, the bioluminescence is detected upon contact of arsenic dissolved in water with genetically modified bacteria (eg Escherichia coli K12) and a light meter (luminometer). The existing arsenic concentration correlates directly with the amount of light emitted.

 

Connections
Arsenic hydrogens

Arsenic and hydrogen (Arsane) chemical compounds are not very abundant and very unstable compared to the corresponding compounds of the major group neighbors, nitrogen and phosphorus. There are currently three known Arsane.

• Arsenic hydrogen (also called monoarsan or arsine) with the molecular formula AsH3 is an important starting material for the production of gallium arsenide in the semiconductor industry.
• Diarsan (As2H4)
• Triarsan (As3H5)

halogen compounds

Arsenic forms with halogens binary compounds of the type AsX3, AsX5 and As2X4 (X denotes the corresponding halogen).

• Arsenic (III) fluoride (AsF3)
• Arsenic (V) fluoride (AsF5)
• Arsenic (III) chloride (AsCl3)
• Arsenic pentachloride (AsCl5)
• Arsenic tribromide (AsBr3)
• Arsenic triiodide (AsI3)
• Diarsetetraiodide (As2I4)

oxygen compounds

Important oxygen acids are:

• Arsenic acid (2 H3AsO4 · H2O), the salts of which are called arsenates or arsenates (V) and which are similar to phosphates. Examples are calcium arsenate (Ca3 (AsO4) 2 3H2O) and lead hydrogen arsenate (PbHAsO4) used as crop protection agents
• Arsenious acid (H3AsO3), the salts of which are called arsenites or arsenates (III).

The most important arsenic oxide is arsenic (III) oxide (arsenic trioxide also arsenic or white arsenic, As2O3, the arsenic acid anhydride), which is present in the gas phase in the form of double molecules with the formula As4O6. It is amphoteric, indicating the semi-metal character of the arsenic. In addition to As2O3, we know As2O5 (arsenic pentaoxide, the anhydride of arsenic acid) and the mixed anhydride of arsenious acid and arsenic acid As2O4 (arsenic tetraoxide).

A historically important dyeing and pesticide is a copper arsenic oxide with the trivial name Schweinfurter Green (Cu (AsO2) 2 · Cu (CH3COO) 2).

 

Schwefelverbindungen

There are two important arsenic sulphides, both of which are found as minerals in nature.

• Arsenic monosulfide (Realgar, As4S4)
• Arsenic (III) sulfide (Auripigment, As2S3)

 

Arsenic-metal compounds

Important compounds of arsenic with metals are

• Gallium arsenide (GaAs), an important semiconductor
• Indium arsenide (InAs), an important semiconductor
• Nickel arsenide (NiAs)
• Aluminum gallium arsenide (AlGaAs)

 

Organic compounds

By analogy with the amines and phosphines, corresponding compounds are found with arsenic instead of nitrogen or phosphorus. They are called Arsine.

• Dimethylarsine (AsH (CH3) 2)
• Trimethylarsin (As (CH3) 3), a malodorous liquid used to treat bacterial infections and as a fungicide.

The arsoranes, compounds of the R5As type, where R5 represents five, possibly different, organic groups, include, for example, pentaphenylarsene or pentamethylarsene. If one of the five groups is missing, a simply positively charged ion is left behind (R again stands for - possibly different - organic groups), which is called the arsonium ion (AsR4) +.

Analogous to the carboxylic acids, two classes of arsenic-organic acids can be formed:

• Arsinic acids (RR'AsOOH)
• Arsonic acids (RAsO (OH) 2)

In addition, heteroaromatics with arsenic are known as heteroatom, such as arsabenzene, which consists of a benzene ring in which a carbon atom is replaced by arsenic and which is thus constructed analogously to pyridine.

Homocyclic arsenic compounds also exist. examples are

• Pentamethylcyclopentaarsen (AsCH3) 5
• Hexamethylcyclohexaarsen (AsCH3) 6

whose molecules have a five- or six-membered ring of arsenic atoms as the backbone, to which one methyl group per arsenic atom is bound to the outside. A polycyclic variant forms the adjacent molecule, whose backbone is composed of a six- and two-attached five-membered rings (R stands for a tert-butyl group).

Finally, arsenic polymers can be represented, long chain molecules called polyarsines. They consist of a central "rope ladder" of the arsenic atoms, to each side of each "rung" is attached a methyl group on the outside, so that the chemical formula (AsCH3) 2n results, where the natural number n can be much higher than 100. Polyarsines show clear semiconducting properties.

Bioorganic compounds

In bioorganic arsenolipids, arsenosaccharides and arsenic glycolipids play an important role. Important representatives of these classes are, for example, arsenobetaine, arsenocholine and differently substituted arseno riboses. Above all, they occur cumulatively in maritime organisms and can thus enter the human food chain. Arsenic-containing biomolecules could be detected in algae, marine sponges and fish tissues after extraction by HPLC-ICP-MS. The analysis of organo-arsenic compounds (including their speciation) is very expensive.

Arsenic in crime history, literature and film

The element Arsen reached dubious fame as a murder venom, evidenced by historical records as well as the instrumentalization in literature and film. However, the murder venom was never elemental arsenic but its compounds.

In Italy and France, dukes, kings and popes died of deliberately induced arsenic poisoning. In France, 17. The Marquise de Brinvilliers, who poisoned her father and two brothers with an arsenic mixture, is at the center of a poison scandal. In Germany, the serial killer Gesche Gottfried from Bremen brought 15 people to death. The case of serial killer Anna Margaretha Zwanziger at the beginning of the 19 also caused quite a stir. Century. The authors of the murders, however, mostly remained unrecognized, since arsenic to 1836 could not be detected in small quantities. It was not until the Marsh sample developed and named after him by James Marsh that it was possible to identify traces of the element and thus prove an unnatural cause of death. In the 19. and 20. In the 19th century, deliberate poisoning with arsenic-containing compounds took place - on the one hand because they were readily available as herbicides, on the other hand, a chronic death of small doses could be faked a disease-related death. In September 1840 filed its first verdict in the trial of Marie Lafarge, based solely on the results of the Marsh trial. In the case of Marie Besnard, who allegedly was responsible for several deaths in her environment in Loudun between 1927 and 1949, clear evidence could not be provided because the findings of the investigation were contradictory, and she eventually had to be acquitted of 1954.

For years, the experts believed that the death of former French Emperor Napoleon Bonaparte with 51 years on the island of St. Helena must be attributed to a poison attack with arsenic. At least you had discovered in his hair highly concentrated traces of the poison. Today, there are several other theses to explain the factual findings. One possibility is that the arsenic was added to the hair after his death to preserve it, a method quite common at that time. It is possible to overuse the use of the arsenic-containing Fowler solution, which in his day was regarded by many of his contemporaries as a medical miracle cure. The third and most probable possibility today is that Napoleon was poisoned by organic arsenic compounds that consistently released mold from his wallpaper made with green arsenic pigments. Their high arsenic content is conclusively proven by a material sample found in a notebook by 1980.

The famous philosopher René Descartes died 1650 few months after his arrival at the court of the Swedish queen Christine. The suspicion that he had been poisoned by arsenic for religious reasons by one of the Jesuits who were at the court of the Protestant queen, intensified when Christine later actually converted to Catholicism, but could not be substantiated, so that the official cause of death, Pneumonia, established in the biographies. More recently, evidence has been reaffirmed on the basis of newly discovered and reinterpreted documents, claiming that the "Descartes poisoning is highly likely, if not to say, almost certain".

In the year 1900 there was a mass poisoning in the British Manchester, which affected several thousand humans. As it turned out, all the beer from the same brewery had been drunk. In preliminary stages of beer production, sulfuric acid was apparently used, which in turn was made from sulfur derived from arsenopyrite-contaminated sulfide minerals. Around 70 people succumbed to their poisonings.

In the years 2010 and 2011 two men died in Austria from an arsenic poisoning. On the 11. April 2013 was found guilty of murdering 52-year-old Polin at the Krems district court and sentenced to life imprisonment by the jury. Even in the 1950 years at the height of the Cold War, the American ambassador, Clare Booth Luce, fell ill in Rome by poisoning with arsenic released from wallpaper. The fact that the disease was caused by the mold-infested wallpaper and not by enemy intelligence agents contributed not only to the recovery of the ambassador, but also to the maintenance of peace.

In Friedrich Schiller's bourgeois play "Kabale und Liebe", the young Major Ferdinand von Walter first poisoned his lover Luise Millerin and then himself. However, in "Kabale und Liebe", death unrealistically occurs within minutes.

The protagonist of the famous novel Madame Bovary by Gustave Flaubert, the unlucky married country doctor's wife Emma Bovary, dies at the end of the novel by suicide with arsenic in the form of a white powder. The offspring of a physician family Flaubert describes the symptoms of poisoning and the extremely painful death of Bovary in great detail.

In the novel "Strong Poison" by Dorothy L. Sayers, the victim was poisoned with arsenic. The suspect, crime novelist Harriet Vane, was at the time in question intensively concerned with arsenic murders and even consulted by the pharmacist.

The famous detective "Kalle Blomquist" from the eponymous children's book by Astrid Lindgren used the Marsh sample to check an arsenic-poisoned piece of chocolate.

In the play by Joseph Kesselring Arsenic and Old Lace (English: Arsenic and Old Lace) two old ladies poison with good intentions older lonely men with an arsenic, strychnine and cyanide mixture. The piece became known through the eponymous film adaptation of Frank Capra with Cary Grant, Peter Lorre and Priscilla Lane in the lead roles.

 

Arsenic - Arsenic price under Strategic Metals