Perchlorate

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Perchlorate
Identifiers
CAS number14797-73-0 YesY
PubChem123351
ChemSpider109953 YesY
DrugBankDB03138
MeSH180053
ChEBICHEBI:49706 YesY
ChEMBLCHEMBL180053 N
Gmelin Reference2136
Jmol-3D imagesImage 1
Properties
Molecular formulaClO4
Molar mass99.451 g mol−1
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references
 
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Perchlorate
Identifiers
CAS number14797-73-0 YesY
PubChem123351
ChemSpider109953 YesY
DrugBankDB03138
MeSH180053
ChEBICHEBI:49706 YesY
ChEMBLCHEMBL180053 N
Gmelin Reference2136
Jmol-3D imagesImage 1
Properties
Molecular formulaClO4
Molar mass99.451 g mol−1
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Perchlorates are the salts derived from perchloric acid—in particular when referencing the polyatomic anions found in solution, perchlorate is often written with the formula ClO4. Perchlorates are often produced by natural processes but can also be produced artificially. They have been used for more than fifty years to treat thyroid disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a component of solid rocket fuel. Lithium perchlorate, which decomposes exothermically to produce oxygen, is used in oxygen "candles" on spacecraft, submarines, and in other situations where a reliable backup oxygen supply is needed. Most perchlorates are soluble in water,[2] except for potassium perchlorate which has the lowest solubility of any alkali metal perchlorate (1.5 g in 100 mL of water at 25 °C).

Production and use[edit]

Perchlorate salts are produced industrially by the oxidation of solutions of sodium chlorate by electrolysis. This method is used to prepare sodium perchlorate. Four perchlorates are of primary commercial interest: ammonium perchlorate (NH4ClO4), perchloric acid (HClO4), potassium perchlorate (KClO4), and sodium perchlorate (NaClO4). The main application is for rocket fuel.[3]

Reactivity as an oxidant[edit]

The perchlorate ion is the least reactive oxidizer of the generalized chlorates. This appears to be a paradox, since higher oxidation numbers are expected to be progressively stronger oxidizers, and less stable. A table of reduction potentials of the four chlorates shows that, contrary to expectation, perchlorate is the weakest oxidant among the four in water.[4]

Half-reactionE° (V)
H+ + HOCl + e → ½Cl2(g) + H2O1.63
3H+ + HOClO + 3e → ½Cl2(g) + 2H2O1.64
6H+ + ClO3 + 5e → ½Cl2(g) + 3H2O1.47
8H+ + ClO4 + 7e → ½Cl2(g) + 4H2O1.42
½Cl2(g) + e → Cl1.36
ClO + H2O + 2e → Cl + 2OH0.89
ClO2 + 2H2O + 4e → Cl + 4OH0.78
ClO3 + 3H2O + 6e → Cl + 6OH0.63
ClO4 + 4H2O + 8e → Cl + 8OH0.56

These data show that the perchlorate and chlorate are stronger oxidizers in acidic conditions than in basic conditions.

Gas phase measurements of heats of reaction (which allow computation of ΔHf°) of various chlorine oxides do follow the expected trend wherein Cl2O7 exhibits the largest endothermic value of ΔHf° (238.1 kJ/mol) while Cl2O exhibits the lowest endothermic value of ΔHf° (80.3 kJ/mol).[5]

The central chlorine in the perchlorate anion is a closed shell atom and is well protected by the four oxygens. Hence, perchlorate reacts sluggishly. Most perchlorate compounds, especially salts of electropositive metals such as sodium perchlorate or potassium perchlorate, are slow to react unless heated. This property is useful in many applications, such as flares, where the device should not explode, or even catch fire spontaneously.

Mixtures of perchlorates with organic compounds are more reactive. Although they do not usually catch fire or explode unless heated, there are a number of exceptions. Large amounts of improperly stored ammonium perchlorate led to the PEPCON disaster, in which an explosion destroyed one of the two large-scale production plants for ammonium perchlorate in the US.

Occurrence[edit]

Low levels of perchlorate have been detected in both drinking water and groundwater in 26 states in the U.S., according to the Environmental Protection Agency. In 2004, the chemical was also found in cow's milk in California with an average level of 1.3 parts per billion ("ppb" or µg/L), which may have entered the cows through feeding on crops that had exposure to water containing perchlorates.[6] According to the Impact Area Groundwater Study Program, the chemical has been detected as high as 5 µg/L in Massachusetts, well over the state regulation of 2 µg/L.[7]

In some places, perchlorate is detected because of contamination from industrial sites that use or manufacture it. In other places, there is no clear source of perchlorate. In those areas it may be naturally occurring, or could be present because of the use of Chilean fertilizers, which were imported to the U.S. by the hundreds of tons in the early 19th century. One recent area of research has even suggested that perchlorate can be created when lightning strikes a body of water, and perchlorates are created as a byproduct of chlorine generators used in swimming pool chlorination systems.[8] In 2010, perchlorate was found at the 1000ppb levels in a vast section of Antarctica, with implications that it is formed naturally and globally on Earth and, it is presumed, on Mars[9] most likely by photochemical reactions in the atmosphere.[10]

Fireworks are also a source of perchlorate in lakes.[11]

Perchlorate on surface of Mars[edit]

In May 2008, the Wet Chemistry Laboratory (WCL) on board the 2007 Phoenix Mars Lander performed the first wet chemical analysis of martian soil. The analyses on three samples, two from the surface and one from 5 cm depth, revealed a slightly alkaline soil and low levels of salts typically found on Earth. Unexpected though was the presence of ~ 0.6 wt % perchlorate (ClO4), most likely as a Mg(ClO4)2 phase.[12] The salts formed from perchlorates discovered at the Phoenix landing site act as "anti-freeze" and will substantially lower the freezing point of water. Based on the temperature and pressure conditions on present-day Mars at the Phoenix lander site, conditions would allow a perchlorate salt solution to be present in liquid form for a few hours each day during the summer.[13]

The possibility that the perchlorate was a contaminant brought from Earth has been eliminated by several lines of evidence. The Phoenix retro-rockets used ultra pure hydrazine and launch propellants consisted of ammonium perchlorate. Sensors on board Phoenix found no traces of ammonium, and thus the perchlorate in the quantities present in all three soil samples is indigenous to the martian soil.

In 2006, a mechanism was proposed for the formation of perchlorates that is particularly relevant to the discovery of perchlorate at the Mars Phoenix lander site. It was shown that soils with high concentrations of chloride converted to perchlorate in the presence of sunlight and/or ultraviolet light. The conversion was reproduced in the lab using chloride-rich soils from Death Valley.[14] Other experiments have demonstrated the formation of perchlorate is associated with wide band gap semiconducting oxides.[15]

Perchlorate in Antarctica[edit]

In 2010, perchlorate was found at the 1000 ppb levels in a vast section of Antarctica, with implications that it is formed naturally and globally on Earth and probably on Mars.[9] Recent isotopic studies have shown that perchlorate is produced on Earth by the oxidation of chloride species through pathways involving tropospheric ozone or its photochemical products.[10]

Regulatory issues in the U.S.[edit]

On February 11, 2011, the U.S. Environmental Protection Agency (EPA) issued a "regulatory determination" that perchlorate meets the Safe Drinking Water Act criteria for regulation as a contaminant. The agency found that perchlorate may have an adverse effect on the health of persons and is known to occur in public water systems with a frequency and at levels that it presents a public health concern. As a result of EPA's regulatory determination, it begins a process to determine what level of contamination is the appropriate level for regulation. The EPA prepared, as part of its regulatory determination, extensive responses to submitted public comments. The "docket ID" for EPA's regulatory action is EPA-HQ-OW-2009-0297 and can be found on regulations.gov.

Prior to issuance of its regulatory determination, the U.S. EPA issued a recommended Drinking Water Equivalent Level (DWEL) for perchlorate of 24.5 µg/L. In early 2006, EPA issued a "Cleanup Guidance" for this same amount. Both the DWEL and the Cleanup Guidance were based on a thorough review of the existing research by the National Academy of Science (NAS).[16] This followed numerous other studies, including one that suggested human breast milk had an average of 10.5 µg/L of perchlorate.[17] Both the Pentagon and some environmental groups have voiced questions about the NAS report, but no credible science has emerged to challenge the NAS findings. In February 2008, U.S. Food and Drug Administration said that U.S. toddlers on average are being exposed to more than half of the U.S. EPA's safe dose from food alone.[18] In March 2009, a Centers for Disease Control study found 15 brands of infant formula contaminated with perchlorate. Combined with existing perchlorate drinking water contamination, infants could be at risk for exposure to perchlorate above the levels considered safe by E.P.A.[19]

The US Environmental Protection Agency has issued substantial guidance and analysis concerning the impacts of perchlorate on the environment as well as drinking water.[1] California has also issued guidance regarding perchlorate use.[2]

Several states in the U.S. have enacted drinking water standard for perchlorate including Massachusetts in 2006. California's legislature enacted AB 826, the Perchlorate Contamination Prevention Act of 2003, requiring California's Department of Toxic Substance Control (DTSC) to adopt regulations specifying best management practices for perchlorate and perchlorate-containing substances. The Perchlorate Best Management Practices were adopted on December 31, 2005, and became operative on July 1, 2006. [3] California issued drinking water standards in 2007. Several other states, including Arizona, Maryland, Nevada, New Mexico, New York, and Texas have established non-enforceable, advisory levels for perchlorate.

In 2003, a federal district court in California found that the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) applied because perchlorate is ignitable and therefore a "characteristic" hazardous waste. (see Castaic Lake Water Agency v. Whittaker, 272 F. Supp. 2d 1053, 1059–61 (C.D. Cal. 2003)).

One example of perchlorate related problems was found at the Olin Flare Facility, Morgan Hill, California—Perchlorate contamination beneath a former flare manufacturing plant in California was first discovered in 2000, several years after the plant had closed. The plant had used potassium perchlorate as one of the ingredients during its 40 years of operation. By late 2003, the state of California and the Santa Clara Valley Water District had confirmed a groundwater plume currently extending over nine miles through residential and agricultural communities.

The Regional Water Quality Control Board and the Santa Clara Valley Water District have engaged in a major outreach effort that has received extensive press and community response. A well testing program is underway for approximately 1,200 residential, municipal, and agricultural wells in the area. Large ion exchange treatment units are operating in three public water supply systems that include seven municipal wells where perchlorate has been detected. The potentially responsible parties, Olin Corporation and Standard Fuse Incorporated, are supplying bottled water to nearly 800 households with private wells. The Regional Water Quality Control Board is overseeing potentially responsible party (PRP) cleanup efforts.[4]

Biological functions[edit]

Over 40 phylogenetically and metabolically diverse microorganisms capable of perchlorate reduction have been isolated since 1996, including members of the Proteobacteria as well as two recently identified Firmicutes, Moorella perchloratireducens and Sporomusa sp.[20]

Health effects[edit]

Thyroidal problems[edit]

Perchlorate is a potent competitive inhibitor of the thyroid sodium-iodide symporter.[21] Thus, it has been used to treat hyperthyroidism since the 1950s.[22] At very high doses (70,000–300,000 ppb) the administration of potassium perchlorate was considered the standard of care in the United States, and remains the approved pharmacologic intervention for many countries.

Perchlorate, in large amounts, interferes with iodine uptake into the thyroid gland. In adults, the thyroid gland helps regulate the metabolism by releasing hormones, while in children, the thyroid helps in proper development. The NAS, in its 2005 report, Health Implications of Perchlorate Ingestion, emphasized that this effect, also known as IUI is not an adverse health effect. In January 2008, California's Department of Toxic Substances Control stated that perchlorate is becoming a serious threat to human health and water resources.[23] However, in 2010, the Environmental Protectional Agency's (EPA) Office of the Inspector General determined that the EPA's own perchlorate reference dose of 24.5 parts per billion protects against all human biological effects from exposure. This finding was due to a significant shift in policy at the EPA in basing its risk assessment on non-adverse effects such as IUI instead of adverse effects. The Office of the Inspector General also found that because the EPA's perchlorate reference dose is conservative and protective of human health further reducing perchlorate exposure below the reference dose does not effectively lower risk.[24]

The NAS found that perchlorate affects only the thyroid gland. It is not stored in the body, it is not metabolized, and any effects of perchlorate on the thyroid gland are fully reversible once exposure stops.[25] There has been some concern on perchlorate's effects on fetuses, newborns and children, but several peer-reviewed studies on children and newborns also provide reason to believe that low levels of perchlorate do not pose a threat to these populations. On October 1, 2004, the American Thyroid Association (ATA) reported that perchlorate may not be as harmful to newborns, pregnant women and other adults as previously thought. This finding was later supported in 2010 and 2011 by research on thousands of pregnant women in Italy, Wales, Argentina, and the United States.[26][27]

A study involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate can temporarily inhibit the thyroid gland's ability to absorb iodine from the bloodstream ("iodide uptake inhibition", thus perchlorate is a known goitrogen).[28] The EPA converted this dose into a reference dose of 0.0007 mg/(kg·d) by dividing this level by the standard intraspecies uncertainty factor of 10. The agency then calculated a "drinking water equivalent level" of 24.5 ppb by assuming a person weighs 70 kilograms (154 pounds) and consumes 2 liters (68 ounces) of drinking water per day over a lifetime.[29]

In 2006, a study by Blount, et al. reported a statistical association between environmental levels of perchlorate and changes in thyroid hormones of women with low iodine. The study authors were careful to point out that hormone levels in all the study subjects remained within normal ranges. Importantly, the authors also indicated that they did not normalize their findings for creatinine, which essentially accounts for fluctuations in the concentrations of one-time urine samples like those used in this study.[30] When the Blount research was re-analyzed with the creatinine adjustment made, the study population limited to women of reproductive age, and results not shown in the original analysis, the association with perchlorate disappeared.[31] Soon after the Blount Study was released, NAS panelist Dr. Robert Utiger, a physician with the Harvard Institutes of Medicine, testified before Congress and stated: "I continue to believe that that reference dose, 0.007 milligrams per kilo (24.5 ppb,) which includes a factor of 10 to protect those who might be more vulnerable, is quite adequate."[32]

Treatment of aplastic anemia[edit]

In the early 1960s, potassium perchlorate was implicated in the development of aplastic anemia—a condition where the bone marrow fails to produce new blood cells in sufficient quantity—in thirteen patients, seven of whom died.[33] Subsequent investigations have indicated the connection between administration of potassium perchlorate and development of aplastic anemia to be "equivocable at best", which means that the benefit of treatment, if it is the only known treatment, outweighs the risk, and it appeared a contaminant poisoned the 13.[34]

Appendix: oxyanions of chlorine[edit]

Using Stock nomenclature, if a Roman numeral in brackets follows the word "chlorate", this indicates the oxyanion contains chlorine in the indicated oxidation state, namely

Common nameStock nameOxidation stateFormula
HypochloriteChlorate(I)+1ClO
ChloriteChlorate(III)+3ClO2
ChlorateChlorate(V)+5ClO3
PerchlorateChlorate(VII)+7ClO4

Commonly, "chlorate" refers only to the oxyanion where chlorine is in the +5 oxidation state.

References[edit]

  1. ^ "Perchlorate - PubChem Public Chemical Database". The PubChem Project. USA: National Center for Biotechnology Information. 
  2. ^ Draft Toxicological Profile for Perchlorates, Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services, September, 2005.
  3. ^ Helmut Vogt, Jan Balej, John E. Bennett, Peter Wintzer, Saeed Akbar Sheikh, Patrizio Gallone "Chlorine Oxides and Chlorine Oxygen Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH. doi:10.1002/14356007.a06_483
  4. ^ Cotton, F. A. and Wilkinson, G. Advanced Inorganic Chemistry 5th ed. page 564 ©1988, by John Wiley and Sons
  5. ^ Wagman, D. D.; Evans, W. H.; Parker, V. P.; Schumm, R. H.; Halow, I.; Bailey, S. M.; Churney, K. L.; Nuttall, R. L. J. Phys. Chem. Ref. Data Vol. 11(2); &169;1982 by the American Chemical Society and the American Institute of Physics.
  6. ^ Associated Press. "Toxic chemical found in California milk". MSNBC. June 22, 2004.
  7. ^ http://www.mass.gov/dep/water/dwstand.pdf
  8. ^ William E. Motzer (2001). "Perchlorate: Problems, Detection, and Solutions". Environmental Forensics 2 (4): 301–311. doi:10.1006/enfo.2001.0059. 
  9. ^ a b S. P. Kounaves et al. (2010). "Natural Perchlorate in the Antarctic Dry Valleys and Implications for its Global Distribution and History". Environmental Science & Technology 44 (7): 2360–2364. doi:10.1021/es9033606. PMID 20155929. 
  10. ^ a b D. C. Catling et al. (2010). "Atmospheric origins of perchlorate on Mars and in the Atacama". Journal of Geophysical Research 115: E00E11. Bibcode:2010JGRE..11500E11C. doi:10.1029/2009JE003425. 
  11. ^ Fireworks Displays Linked To Perchlorate Contamination In Lakes
  12. ^ Hecht, M. H., S. P. Kounaves, R. Quinn, et al. (2009). "Detection of Perchlorate & the Soluble Chemistry of Martian Soil at the Phoenix Mars Lander Site". Science 325 (5936): 64–67. Bibcode:2009Sci...325...64H. doi:10.1126/science.1172466. PMID 19574385. 
  13. ^ Chevrier, V. C., Hanley, J., and Altheide, T.S. (2009). "Stability of perchlorate hydrates and their liquid solutions at the Phoenix landing site, Mars". Geophysical Research Letters 36 (10): L10202. Bibcode:2009GeoRL..3610202C. doi:10.1029/2009GL037497. 
  14. ^ Miller, Glen. "Photooxidation of chloride to perchlorate in the presence of desert soils and titanium dioxide". American Chemical Society. March 29, 2006
  15. ^ Jennifer D. Schuttlefield, Justin B. Sambur, Melissa Gelwicks, Carrick M. Eggleston, and B. A. Parkinson "Photooxidation of Chloride by Oxide Minerals: Implications for Perchlorate on Mars" J. Am. Chem. Soc. 2011, vol. 133, pp. 17521–17523. doi:10.1021/ja2064878
  16. ^ Health Implications of Perchlorate Ingestion. Washington, DC: The National Academies Press. 2005. ISBN 10: 0-309-09568-9 Check |isbn= value (help). 
  17. ^ McKee, Maggie. "Perchlorate found in breast milk across US". New Scientist. February 23, 2005
  18. ^ Perchlorate In Food
  19. ^ "CDC Scientists Find Rocket Fuel Chemical In Infant Formula". Anila Jacob, M.D., M.P.H.. Environmental Working Group. 2 April 2009.
  20. ^ John D. Coates, Laurie A. Achenbach (2004). "Microbial perchlorate reduction: rocket-fuelled metabolism". Nature Reviews Microbiology 2 (7): 569–580. doi:10.1038/nrmicro926. PMID 15197392. 
  21. ^ Braverman, L. E.; He X.; Pino S.; et. al (2005). "The effect of perchlorate, thiocyanate, and nitrate on thyroid function in workers exposed to perchlorate long-term". J Clin Endocrinol Metab. 90 (2): 700–706. PMID 15572417. 
  22. ^ Godley, A. F.; Stanbury, J. B. (1954). "Preliminary experience in the treatment of hyperthyroidism with potassium perchlorate". J Clin Endocrinol Metab 14 (1): 70–78. doi:10.1210/jcem-14-1-70. PMID 13130654. 
  23. ^ California Department of Toxic Substances Control Jan 26, 2008
  24. ^ Scientific Analysis of Perchlorate (Report). United States Environmental Protection Agency, Office of the Inspector General. 19 April 2010. ""What We Found""
  25. ^ J. Wolff (1998). "Perchlorate and the Thyroid Gland". Pharmacological Reviews 50 (1): 89–105. PMID 9549759. 
  26. ^ "Various Levels of Perchlorate Exposure Found Not to Be Harmful to Newborns, Pregnant Women, and Other Adults" (Press release). American Thyroid Association. 1 October 2004. 
  27. ^ Pearce, et al. (2010). "Perchlorate and Thiocyanate Exposure and Thyroid Function in First Trimester Pregnant Women". The Journal of Clinical Endocrinology and Metabolism. 
  28. ^ Greer, M. A., Goodman, G., Pleuss, R. C., Greer, S. E. (2002). "Health effect assessment for environmental perchlorate contamination: The dose response for inhibition of thyroidal radioiodide uptake in humans" (free online). Environmental Health Perspectives 110 (9): 927–937. doi:10.1289/ehp.02110927. PMC 1240994. PMID 12204829. 
  29. ^ US EPA Memorandum Jan 26, 2006
  30. ^ Benjamin C. Blount, James L. Pirkle, John D. Osterloh, Liza Valentin-Blasini, and Kathleen L. Caldwell (2006). "Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States". Environmental Health Perspectives 114 (12): 1865–71. doi:10.1289/ehp.9466. PMC 1764147. PMID 17185277. 
  31. ^ Tarone, et al. (2010). "The Epidemiology of Environmental Perchlorate Exposure and Thyroid Function: A Cmprehensive Review". Journal of Occupational and Environmental Medicine 52 (June): 653–60. doi:10.1097/JOM.0b013e3181e31955. PMID 20523234. 
  32. ^ "Perchlorate: Health and Environmental Impacts of Unregulated Exposure". United States Congress. Retrieved 15 April 2012. 
  33. ^ National Research Council (2005). "Perchlorate and the thyroid". Health implications of perchlorate ingestion. Washington, D.C: National Academies Press. p. 7. ISBN 0-309-09568-9.  Retrieved on April 3, 2009 through Google Book Search.
  34. ^ Clark, J. J. J. (2000). "Toxicology of perchlorate". In Urbansky ET (ed.). Perchlorate in the environment. New York: Kluwer Academic/Plenum Publishers. pp. 19–20. ISBN 978-0-306-46389-1.  Retrieved on April 3, 2009 through Google Book Search.

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