Calcium arsenate: Difference between revisions

| verifiedrevid = 431587969

| Name = Calcium arsenate

| ImageFile = Calciumarsenaat.png

| ImageSize = 200px

| ImageName = Calcium arsenate

| OtherNames = Calcium orthoarsenate<br /> Cucumber dust

| Section1 = {{Chembox Identifiers

| CASNo = 7778-44-1

| CASNo_Ref =

| PubChem = 24501

| RTECS = CG0830000

| Section2 = {{Chembox Properties

| Formula = Ca₃As₂O₈

| MolarMass = 398.072 g/mol

| Appearance = white powder

| Density = 3.63 g/cm³, solid

| Solubility = 0.013 g/100 mL (25°C)

| Solvent1 = Organic solvents

| Solubility1 = insoluble

| Solvent2 = acids

| Solubility2 = soluble

| MeltingPt = 1455°C (decomposes)

| BoilingPt =

'''Calcium arsenate''' ([[Calcium|Ca₃]]([[Arsenic|As]][[Oxygen|O₄]])₂) is an extremely poisonous [[chemical compound]] that most commonly exists as a colorless to white amorphous solid. 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.

==Synthesis==

The synthesis of calcium arsenate is commonly prepared by adding disodium hydrogen arsenate in excess to [[calcium chloride]]. The resulting solution is then made alkaline by adding [[sodium hydroxide]]. This reaction occurs via [[ion exchange]] and the resulting precipitate is calcium arsenate.

2Na₂H[AsO₄] + 3CaCl₂ → 4NaCl + Ca₃[AsO₄]₂ +2HCl

The solubility of this compound was found by Tartar, et al. to be 0.014g in 100g of water at 25˚ C. This molecule is fairly reactive. When placed in an aqueous solution and heated, H₂AsO₄ gas is released.<ref name="ReferenceA">Tartar, H.V.; Wood, L; Hiner, E; A Basic Arsenate of Calcium. ''J. Am. Chem''; '''1924''', ''46'', 809-813</ref>

==Toxicity==

Calcium arsenate is considered highly toxic, having both [[carcinogen]]ic and systematic health effects.<ref name="ReferenceB">Tchounwou, P.B.; Patlolla, A.K.; Centeno, J.A.; Carcinogenic and Systematic Health Effects Associated with Arsenic – A Critical Review. ''Toxicologic Pathology''; '''2003''', ''31'', 575-588</ref> This compound, considered non-combustible, gives off irritating or toxic fumes when heated (H₂AsO₄ as outlined above). The compound also reacts with strong acids to form toxic [[Arsine|arsine gas]] (AsH₃).<ref name="ReferenceC">Smith, C.M.; Murray, C.W.; The Composition of Commercial Calcium Arsenate. ''Journal of Industrial and Engineering Chemistry''; '''1931''', 23</ref> The substance is normally absorbed into the body by inhalation of its aerosol form or by ingestion.

Hazardous Class/Division: 6.1 – meaning the material, when not in its gas form, is known to be so toxic to humans to afford a hazard to health during transportation.<ref name="inchem.org">International Program on Chemical Safety Database. http://www.inchem.org/documents/icsc/icsc/eics0765.htm (Accessed 16 April 2010)</ref>

Oral LD50: 298&nbsp;mg/kg in rats<ref name="ReferenceB"/>

In cases of exposure, symptoms include cough, sore throat, headache, labored breathing, weakness, redness of eyes, abdominal pain, diarrhea, vomiting, burning sensation in throat and chest, and shock or collapse.

=== Effects of short-term exposure ===

Calcium arsenate irritates skin, eyes, and the respiratory tract. It may affects the gastrointestinal tract, cardiovascular system, central nervous system and kidneys, resulting in severe gastroenteritis, loss of fluid and electrolytes, cardiac disorders, shock and kidney impairment. Exposure above OEL(**) may result in death, though effects may be delayed.

=== Effects of long-term exposure ===

Repeated or prolonged contact with skin may cause dermatitis. The substance may have effects on the skin, mucous membranes, peripheral nervous system, bone marrow and liver, resulting in pigmentation disorders, perforation of nasal septum, neuropathy, lesions of blood cells and liver impairment. This substance is carcinogenic to humans. Animal tests show that this substance possibly causes malformations in human babies<ref name="inchem.org"/>.

==Use as an Herbicide==

Once commonly used as an herbicide, Calcium Arsenate use is now banned in the UK, and its use is strictly regulated in the United States. It is currently the active ingredient in TURF-Cal manufactured by Mallinckrodt, it is one of the few herbicides – used mainly for the control of ''Poa annua'' and crabgrass- that hinders earthworm activity. Its label states that it will “reduce and inhibit earthworm activity and survival” and is only recommended against serious earthworm infestations in places such as golf course greens.<ref>Turf insect pest control guide: Urban Phytonarian Series. learningstore.uwex.edu/pdf/A2934.pdf (Accessed 04/16/10)</ref>

In the 1920s Calcium Arsenate was considered a “very important agricultural insecticide,” made in large manufacturing vats by mixing 4 moles of Calcium Oxide with 1 mole of Arsenic Oxide<ref>Smith, C.M.; Murray, C.W.; The Composition of Commercial Calcium Arsenate. '' Journal of Industrial and Engineering Chemistry''; '''1931''', 23</ref>. In the United States, 1360 metric tons were produced in 1919, 4540 in 1920, and 7270 in 1922<ref name="ReferenceA"/>. The total arsenic content was calculated from the total Ca₃(AsO₄)₂ in order to obtain the percentage of the active ingredient, but even then it was speculated that a considerable portion of the product was basic arsenate. In a study in 1931, 16 brands of pesticides were tested for basic arsenic content and it was found that “the presence of basic arsenate in undetermined compositions was definitely established."<ref name="ReferenceC"/>

==Mechanism of Toxicity==

Arsenic’s mechanisms as a successful herbicide and germicide and in its toxicity to humans are very similar. Arsenic forms very stable bonds with sulfur, and is therefore able to bind with many sulfhydryl groups on proteins – causing non-specific toxic effects<ref name="ReferenceB"/>. It is able to both weaken the structural integrity of proteins, and inactivate some enzymes. The lethal risk of arsenic exposure comes from its ability to interfere with cellular metabolism. Arsenic binds to sulfur groups present on pyruvate dehydrogenase complex, an enzyme responsible for converting pyruvate into acetyl-CoA, inactivating it. Without this conversion, the cell is unable to proceed into the Citric Acid cycle, which along with oxidative phosphorylation provide 90% of the cell’s biochemical energy<ref>Fenton, J.; Toxicology: A case-oriented approach. CRC Press: Boca Raton, '''2001'''; pp.</ref>. The loss of function of the Citric Acid cycle is detrimental to the cell. In plants, Arsenic is often mistaken for silicon because of its similar size and solubility. Arsenic enters via phosphate channels and is toxic because of its ability to form a stable bond with ADP (Adenine Di-Phosphate) and prevent the formation of ATP – a vital energy source within the plant’s cells.<ref>National Institute for Environmental Health Sciences Database: Dartmouth Toxic Metals Program. http://www.dartmouth.edu/~toxmetal/research/projects/plants.html (Accessed 04/28/10)</ref>

==Recent Findings==

Recent hypotheses have been made possibly linking exposure to Arsenic pesticides to Paget’s disease of bone – a condition affecting how bones break down and rebuild, which over time results in bones that are brittle and fragile. A cluster of six small towns in Lancashire County in North west England, which have a high prevalence of the disease have a noted links with the cotton industry – where calcium arsenate pesticide as used intensely to combat the boll weevil and imported to Lancashire in cotton bails from 1917 to 1945. This era of Calcium Arsenate use is consistent with the high prevalence of the disease until 1974 and its decline in numbers in 1993, given appropriate time for lags. Geochemical arsenate is widespread within the local environment and could possibly account for the geographical variations of the disease’s prevalence, although according this 2002

Article the data acquired was inadequate for correlation studies. Toxicity-level doses of arsenic affect all the steroid receptors and signal transduction pathways, which may lead to dysfunction of osteoclast signaling and differentiation. Human cells are. more susceptible than animal cells to arsenic, but this is based on studies of non-bone cells. It is speculative that arsenic may be a factor in the abnormal variation in prevalence rates of Paget’s disease in Lancashire. This hypothesis is not yet a general theory in Paget’s disease of the bone.<ref>Lever, J.H.; Paget's disease of bone in Lancashire and arsenic pesticide in cotton mill wastewater: a speculative hypothesis. ''Bone''; '''2002''', ''31'', 434-436</ref>

Calcium Arsenate has also been proven to have tumorigenic tendencies in male Syrian Golden Hamsters when given in 15 intratracheal instillations weekly in doses of 3&nbsp;mg/kg of body weight.<ref>Pershagin, G.; Bjorklund, N.E.; On the pulmonary tumorigenicity of arsenic trisulfide and calcium arsenate in hamsters. ''Cancer Letters''; '''1985''', ''1'', 99-104.</ref> It is also theorized to remain in tissue for longer periods of time when compared to arsenic trioxide.<ref>Inamasu, T; Hisanaga, A.; Ishinishi, N; Comparison of arsenic trioxide and calcium arsenate retention in rat lung after intratracheal instillation. ''Toxicology Letters''. '''1982''', ''1'', 1-5</ref>

Arsenic poisoning is given as the latest reason for the widespread prevalence of kidney disease in north central province of Sri Lanka.Thousands of lives have fallen victim to various kidney ailments in the province during the past two decades or so. At present, around 20,000 patients are seeking treatment at state hospitals.All the patients have symptoms of arsenic poisoning, and an analysis of their drinking water has found high arsenic and mercury contents.The two, and the high salinity of the water in the north central province, has make it more toxic. The researcher said further details would be released in the coming weeks.

(1) International Program on Chemical Safety Database. http://www.inchem.org/documents/icsc/icsc/eics0765.htm (Accessed 16 April 2010)

(2) Lever, J.H.; Paget's disease of bone in Lancashire and arsenic pesticide in cotton mill wastewater: a speculative hypothesis. Bone; '''2002''', 31, 434-436

(3) Tartar, H.V.; Wood, L; Hiner, E; A Basic Arsenate of Calcium. J. Am. Chem; '''1924''', 46, 809-813

(4) Pershagin, G.; Bjorklund, N.E.; On the pulmonary tumorigenicity of arsenic trisulfide and calcium arsenate in hamsters. Cancer Letters; '''1985''', 1, 99-104.

(5) Inamasu, T; Hisanaga, A.; Ishinishi, N; Comparison of arsenic trioxide and calcium arsenate retention in rat lung after intratracheal instillation. Toxicology Letters. '''1982''', 1, 1-5

(6) Smith, C.M.; Murray, C.W.; The Composition of Commercial Calcium Arsenate. Journal of Industrial and Engineering Chemistry; '''1931''', 23

(7) Tchounwou, P.B.; Patlolla, A.K.; Centeno, J.A.; Carcinogenic and Systematic Health Effects Associated with Arsenic – A Critical Review. Toxicologic Pathology; '''2003''', 31, 575-588

(8) Turf insect pest control guide: Urban Phytonarian Series. learningstore.uwex.edu/pdf/A2934.pdf (Accessed 04/16/10)

(9) Fenton, J.; Toxicology: A case-oriented approach. CRC Press: Boca Raton, 2001; pp.

(10) National Institute for Environmental Health Sciences Database: Dartmouth Toxic Metals Program. http://www.dartmouth.edu/~toxmetal/research/projects/plants.html (Accessed 04/28/10)

(11) http://www.srilankamirror.com/english/index.php?option=com_content&view=article&id=1450:arsenic-poisoning-causes-kidney-disease-in-ncp-researcher&catid=1:latest-news&Itemid=50

* Sunset Western Garden Book, First Edition, 1954

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