View source for Perchlorate

{{Short description|Ion, and compounds containing the ion}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 464198728
| ImageFile1 = Perchlorate-2D-dimensions.png
| ImageFile1_Ref = {{chemboximage|correct|??}}
| ImageSize1 = 170
| ImageName1 = Skeletal model of perchlorate showing various dimensions
| ImageFileL1 = Perchlorate-3D-balls.png
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageSizeL1 = 130
| ImageNameL1 = Ball-and-stick model of the perchlorate ion
| ImageFileR1 = Perchlorate-3D-vdW.png
| ImageFileR1_Ref = {{chemboximage|correct|??}}
| ImageSizeR1 = 130
| ImageNameR1 = Spacefill model of perchlorate
| SystematicName = Perchlorate<ref>{{Cite web|title = Perchlorate – PubChem Public Chemical Database|url = https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=123351&loc=ec_rcs|work = The PubChem Project|location = USA|publisher = National Center for Biotechnology Information}}</ref>
|Section1={{Chembox Identifiers
| IUPHAR_ligand = 4524
| CASNo = 14797-73-0
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = VLA4NZX2P4
| PubChem = 123351
| ChemSpiderID = 109953
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB03138
| MeSHName = 180053
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 49706
| ChEMBL = 1161634
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| Gmelin = 2136
| SMILES = [O-][Cl+3]([O-])([O-])[O-]
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/ClHO4/c2-1(3,4)5/h(H,2,3,4,5)/p-1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = VLTRZXGMWDSKGL-UHFFFAOYSA-M
}}
|Section2={{Chembox Properties
| Formula = {{chem2|ClO4−}}
| Cl=1|O=4
| ConjugateAcid = [[Perchloric acid]]
}}
}}
A '''perchlorate''' is a [[chemical compound]] containing the perchlorate [[ion]], {{chem2|ClO4-}}, the [[conjugate base]] of [[perchloric acid]] ('''ionic perchlorate'''). As counterions, there can be [[metal]] [[cations]], [[quaternary ammonium cation]]s or other ions, for example, [[Nitronium ion|nitronium cation]] ({{chem2|NO2+}}).

The term ''perchlorate'' can also describe '''perchlorate esters''' or '''covalent perchlorates'''.<ref name=":0" /> These are organic compounds that are [[Alkyl group|alkyl]] or [[Aryl group|aryl]] [[ester]]s of [[perchloric acid]]. They are characterized by a [[covalent bond]] between an [[oxygen]] atom of the ClO<sub>4</sub> [[Moiety (chemistry)|moiety]] and an [[organyl group]].

In most ionic perchlorates, the cation is [[non-coordinating anion|non-coordinating]]. The majority of ionic perchlorates are commercially produced salts commonly used as oxidizers for pyrotechnic devices and for their ability to control [[static electricity]] in [[food packaging]].<ref>[http://www.atsdr.cdc.gov/toxprofiles/tp162.pdf Draft Toxicological Profile for Perchlorates], [[Agency for Toxic Substances and Disease Registry]], U.S. Department of Health and Human Services, September, 2005.</ref> Additionally, they have been used in [[rocket propellant]]s, [[fertilizer]]s, and as [[bleaching agent]]s in the [[Paper industry|paper]] and [[Textile industry|textile industries]].

Perchlorate contamination of food and [[water]] endangers human health, primarily affecting the [[thyroid gland]].

Ionic perchlorates are typically colorless solids that exhibit good [[solubility]] in water. The perchlorate ion forms when they dissolve in water, [[Dissociation (chemistry)|dissociating]] into ions.&nbsp; Many perchlorate salts also exhibit good solubility in non-aqueous [[solvent]]s.<ref name="Kucharzyk" />  Four perchlorates are of primary commercial interest: [[ammonium perchlorate]] {{chem2|(NH4)ClO4}}, [[perchloric acid]] {{chem2|HClO4}}, [[potassium perchlorate]] {{chem2|KClO4}} and [[sodium perchlorate]] {{chem2|NaClO4}}.

==Production==
Very few chemical oxidants are strong enough to convert chlorate to perchlorate.  [[Persulfate]], [[ozone]], or [[lead dioxide]] are all known to do so, but the reactions are too delicate and low-yielding for commercial viability.<ref name=ull/>  

Perchlorate salts are typically manufactured through the process of [[electrolysis]], which involves oxidizing aqueous solutions of corresponding [[chlorate]]s. This technique is commonly employed in the production of [[sodium perchlorate]], which finds widespread use as a key ingredient in [[rocket fuel]].<ref name=ull>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}}</ref>  Perchlorate salts are also commonly produced by reacting [[perchloric acid]] with bases, such as [[Ammonia solution|ammonium hydroxide]] or [[sodium hydroxide]]. [[Ammonium perchlorate]], which is highly valued,{{Why|date=May 2024}} can also be produced via an [[Electrochemistry|electrochemical]] process.<ref>{{cite journal | author = Dotson R.L. | year = 1993 | title = A novel electrochemical process for the production of ammonium perchlorate | journal = Journal of Applied Electrochemistry | volume = 23 | issue = 9| pages = 897–904 | doi = 10.1007/BF00251024 | s2cid = 96020879}}</ref>  

Perchlorate esters are formed in the presence of a nucleophilic [[catalyst]] via a perchlorate salt's [[nucleophilic substitution]] onto an [[alkylating agent]].<ref>{{cite journal |last1=Zefirov |first1=N.&nbsp;S. |last2=Zedankin |first2=V.&nbsp;V. |last3=Koz'min |first3=A.&nbsp;S. |year=1988 |title=The synthesis and properties of covalent organic perchlorates |journal=Russian Chemical Reviews |publisher=Turpion |volume=57 |issue=11 |page=1042 |bibcode=1988RuCRv..57.1041Z |doi=10.1070/RC1988v057n11ABEH003410 |s2cid=250838799}}  Translated from ''[[Uspekhi Khimii]]'' volume&nbsp;57 (1988), pp.&nbsp;1815-1839.</ref>

==Uses==
* The dominant use of perchlorates is as oxidizers in propellants for rockets, fireworks and highway flares. Of particular value is [[ammonium perchlorate composite propellant]] as a component of solid rocket fuel. In a related but smaller application, perchlorates are used extensively within the [[pyrotechnics]] industry and in certain munitions and for the manufacture of matches.<ref name=ull/> Martian perchlorates might also be used to produce fuel on that planet.<ref>{{Cite journal |last=Hoganson |first=Alexander C. C. |last2=Afriat |first2=Aaron |last3=Wernex |first3=Chase M. |last4=Ferguson |first4=Robert E. |last5=Rathore |first5=Hetal |last6=Patel |first6=Dhruval N. |last7=Tappan |first7=Bryce |last8=Son |first8=Steven F. |date=May 2024 |title=Novel Solid Propellants Enabled Through In Situ Martian Perchlorates |url=https://arc.aiaa.org/doi/10.2514/1.B39269 |journal=Journal of Propulsion and Power |volume=40 |issue=3 |pages=388–396 |doi=10.2514/1.B39269 |issn=0748-4658|url-access=subscription }}</ref>
* Perchlorate is used to control [[static electricity]] in food packaging. Sprayed onto containers it stops statically charged food from clinging to plastic or paper/cardboard surface.<ref>{{cite journal | doi = 10.1210/jc.2017-00046 | volume=102 | issue=7 | title=Identifying Subpopulations Vulnerable to the Thyroid-Blocking Effects of Perchlorate and Thiocyanate | year=2017 | journal=The Journal of Clinical Endocrinology & Metabolism | pages=2637–2645 | author=McMullen Jenica, Ghassabian Akhgar, Kohn Brenda, Trasande Leonardo| pmid=28430972 | doi-access=free }}</ref>
* Niche uses include [[lithium perchlorate]], which decomposes [[exothermic]]ally to produce oxygen, useful in [[chemical oxygen generator|oxygen "candles"]] on spacecraft, submarines, and in other situations where a reliable backup oxygen supply is needed.<ref name="candle">{{cite journal |doi=10.1021/i360012a016|title=Lithium Perchlorate Oxygen Candle. Pyrochemical Source of Pure Oxygen|journal=Industrial & Engineering Chemistry Product Research and Development|volume=3|issue=4|pages=321–330|year=1964|last1=Markowitz|first1=M. M.|last2=Boryta|first2=D. A.|last3=Stewart|first3=Harvey}}</ref> 
* Potassium perchlorate has, in the past, been used therapeutically to help manage [[Graves' disease]]. It impedes production of the thyroid hormones that contain iodine.<ref name="Sridhar Susarla 1999">{{cite journal |author1=Susarla Sridhar |author2=Collette C. W. |author3=Garrison A. W. |author4=Wolfe N. L. |author5=McCutcheon S. C. | year = 1999 | title = Perchlorate Identification in Fertilizers | journal = Environmental Science and Technology | volume = 33 | issue = 19| pages = 3469–3472 | doi = 10.1021/es990577k |bibcode=1999EnST...33.3469S }}</ref>
* As perchlorate is generally a non-[[Coordination complex|complexing]] [[anion]] and that its sodium salts is particularly [[Solubility|soluble]], it is commonly used as a [[supporting electrolyte|background]], or [[supporting electrolyte|supporting, electrolyte]] in [[Aqueous solution|solution chemistry]], [[electrophoresis]], and [[electrochemistry]]. Although used as a powerful [[Oxidizing agent|oxidizer]] in propulsive powders and explosives, quite surprisingly, the perchlorate anion is a weak [[Oxidizing agent|oxidant]] in [[aqueous solution]] because of [[Chemical kinetics|kinetics]] limitations severely hindering the [[electron transfer]].

==Chemical properties==
The perchlorate ion is the least [[redox]] reactive of the generalized [[:Category:chlorates|chlorates]]. Perchlorate contains [[chlorine]] in its highest [[oxidation state|oxidation number]] (+7). A table of [[reduction potential]]s of the four [[:Category:chlorates|chlorates]] shows that, contrary to expectation, perchlorate in [[aqueous solution]] is the weakest [[Oxidizing agent|oxidant]] among the four.<ref>{{Cotton&Wilkinson5th|page=564}}</ref>

{|class="wikitable"
|-
!Ion !!Acidic reaction !!''E''° (V) !!Neutral/basic reaction !!''E''° (V)
|-
|align="center" |[[Hypochlorite]] ||{{chem2|2 H+ + 2 HOCl + 2 e− → Cl2 (''g'') + 2 H2O}} ||align="center" |1.63||{{chem2|ClO− + H2O + 2 e− → Cl− + 2 OH−}} ||align="center" |0.89
|-
|align="center" |[[Chlorite]] ||{{chem2|6 H+ + 2 HOClO + 6 e− → Cl2 (''g'') + 4 H2O}} ||align="center" |1.64||{{chem2|ClO2− + 2 H2O + 4 e− → Cl− + 4 OH−}} ||align="center" |0.78
|-
|align="center" |[[Chlorate]] ||{{chem2|12 H+ + 2 ClO3− + 10 e− → Cl2 (''g'') + 6 H2O}} ||align="center" |1.47||{{chem2|ClO3− + 3 H2O + 6 e− → Cl− + 6 OH−}} ||align="center" |0.63
|-
|align="center" |Perchlorate ||{{chem2|16 H+ + 2 ClO4− + 14 e− → Cl2 (''g'') + 8 H2O}} ||align="center" |1.42||{{chem2|ClO4− + 4 H2O + 8 e− → Cl− + 8 OH−}} ||align="center" |0.56
|}

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 Δ<sub>f</sub>''H''°) of various chlorine oxides do follow the expected trend wherein [[Dichlorine heptoxide|{{chem2|Cl2O7}}]] exhibits the largest endothermic value of Δ<sub>f</sub>''H''° (238.1&nbsp;kJ/mol) while [[Dichlorine monoxide|{{chem2|Cl2O}}]] exhibits the lowest endothermic value of Δ<sub>f</sub>''H''° (80.3&nbsp;kJ/mol).<ref>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); 1982, American Chemical Society and the American Institute of Physics.</ref>

===Weak base and weak coordinating anion===
As [[perchloric acid]] is one of the strongest mineral acids, perchlorate is a very weak [[Base (chemistry)|base]] in the sense of [[Brønsted–Lowry acid–base theory]]. 
As it is also generally a [[weakly coordinating anion]], perchlorate is commonly used as a [[supporting electrolyte|background]], or [[supporting electrolyte|supporting, electrolyte]].

===Weak oxidant in aqueous solution due to kinetic limitations===
{{Main articles|Inner sphere electron transfer|Outer sphere electron transfer}}
Perchlorate compounds oxidize organic compounds, especially when the mixture is heated. The explosive decomposition of [[ammonium perchlorate]] is catalyzed by metals and heat.<ref name="Housecroft2018">{{cite book | last1=Housecroft | first1=C.E. | last2=Sharpe | first2=A.G. | year=2018 | title=Inorganic Chemistry. 5th edition | publisher=Pearson | isbn=978-1-292-13414-7 | url=https://books.google.com/books?id=8VyjtAEACAAJ | access-date=2024-09-02 | page=1298}}</ref>

As perchlorate is a weak [[Lewis base]] (''i.e.'', a weak electron pair donor) and a weak [[Nucleophile|nucleophilic]] anion, it is also a very weakly [[Coordination complex|coordinating]] [[anion]].<ref name="Housecroft2018" /> This is why it is often used as a [[supporting electrolyte]] to study the [[Coordination complex|complexation]] and the [[Chemical species|chemical speciation]] of many [[cation]]s in [[aqueous solution]] or in [[electroanalytical methods]] ([[voltammetry]], [[electrophoresis]]…).<ref name="Housecroft2018" /> Although the perchlorate reduction is [[thermodynamics|thermodynamically]] favorable {{Nowrap|(∆''G'' < 0; ''E''° > 0)}}, and that {{chem2|ClO4-}} is expected to be a strong [[oxidant]], most often in aqueous solution, it is practically an inert species behaving as an extremely slow [[oxidant]] because of severe [[Chemical kinetics|kinetics limitations]].<ref name="Taube1953">{{cite journal | last1=Taube | first1=Henry | last2=Myers | first2=Howard | last3=Rich | first3=Ronald L. | title=Observations on the mechanism of electron transfer in solution | journal=Journal of the American Chemical Society | volume=75 | issue=16 | date=1953 | issn=0002-7863 | doi=10.1021/ja01112a546 | pages=4118–4119}}</ref><ref name="Brown2006">{{cite book | last1=Brown | first1=Gilbert M. | last2=Gu | first2=Baohua | title=Perchlorate | chapter=The Chemistry of Perchlorate in the Environment | publisher=Kluwer Academic Publishers | publication-place=Boston, MA | date=2006 | isbn=978-0-387-31114-2 | doi=10.1007/0-387-31113-0_2 | pages=17–47}}</ref> The [[metastable]] character of perchlorate in the presence of [[reducing agent|reducing]] cations such as {{Chem2|Fe(2+)}} in solution is due to the difficulty to form an [[activated complex]] facilitating the [[electron transfer]] and the exchange of oxo groups in the opposite direction. These strongly hydrated cations cannot form a sufficiently stable coordination bridge with one of the four oxo groups of the perchlorate anion. Although thermodynamically a mild reductant, {{Chem2|Fe(2+)}} ion exhibits a stronger trend to remain coordinated by water molecules to form the corresponding hexa-aquo complex in solution. The high [[activation energy]] of the cation binding with perchlorate to form a transient [[inner sphere complex]] more favourable to [[electron transfer]] considerably hinders the [[redox]] reaction.<ref name="Marcus1992_NobelLecture">{{cite web | last1=Marcus | first1=Rudolph A. | title=Electron transfer reactions in chemistry: Theory and experiment | url=https://www.nobelprize.org/uploads/2018/06/marcus-lecture.pdf | access-date=2024-09-02}}</ref> The redox reaction rate is limited by the formation of a favorable [[activated complex]] involving an oxo-bridge between the perchlorate anion and the metallic cation.<ref name="Taube1954">{{cite journal | last1=Taube | first1=Henry | last2=Myers | first2=Howard | title=Evidence for a bridged activated complex for electron transfer reactions | journal=Journal of the American Chemical Society | volume=76 | issue=8 | date=1954 | issn=0002-7863 | doi=10.1021/ja01637a020 | pages=2103–2111}}</ref> It depends on the [[molecular orbital]] rearrangement ([[HOMO and LUMO]] [[Orbital hybridisation|orbitals]]) necessary for a fast [[Transition metal oxo complex#Oxygen-atom transfer|oxygen atom transfer]] (OAT)<ref name="OAT">{{cite web | last1=Bakhtchadjian | first1=Robert | last2=Rajeev | first2=Anjana | last3=Liao | first3=Guangjian | last4=Yin | first4=Guochuan | last5=Sankaralingam | first5=Muniyandi | year=2023 | title=Oxygen Atom Transfer Reactions | publisher=Bentham Science Publishers | url=https://benthambooks.com/book/9789815050929/ | isbn=9789815050929 | access-date=2024-09-17}}</ref> and the associated electron transfer as studied experimentally by [[Henry Taube]] (1983 Nobel Prize in Chemistry)<ref name="Taube1983">{{cite web|title=Press Release: The 1983 Nobel Prize in Chemistry| url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1983/press.html|publisher=NobelPrize.org The Official Website of the Nobel Prize|access-date=2024-09-02}}</ref><ref name="Taube1984">{{cite journal | last1=Taube | first1=Henry | title=Electron transfer between metal complexes: Retrospective | journal=Science | volume=226 | issue=4678 | date=1984-11-30 | issn=0036-8075 | doi=10.1126/science.6494920 | pages=1028–1036| pmid=6494920 | bibcode=1984Sci...226.1028T }}</ref> and theoretically by [[Rudolph A. Marcus]] (1992 Nobel Prize in Chemistry),<ref name="Marcus1992">{{cite web | title=The Nobel Prize in Chemistry 1992 | website=NobelPrize.org | date=1992 | url=https://www.nobelprize.org/prizes/chemistry/1992/marcus/facts/ | access-date=2024-09-02}}</ref> both awarded for their respective works on the mechanisms of electron-transfer reactions with metal complexes and in chemical systems. 

In contrast to the {{Chem2|Fe(2+)}} cations which remain unoxidized in deaerated perchlorate aqueous solutions free of dissolved oxygen, other cations such as Ru(II) and Ti(III) can form a more stable bridge between the metal centre and one of the oxo groups of {{chem2|ClO4-}}. In the [[inner sphere electron transfer]] mechanism to observe the perchlorate reduction, the {{chem2|ClO4-}} anion must quickly transfer an oxygen atom to the reducing cation.<ref name="Taube1982">{{cite book | last1=Taube | first1=Henry | editor1=Rorabacher, D. B. | editor2=Endicott, J. F. | title=Observations on Atom-Transfer Reactions. In: Mechanistic Aspects of Inorganic Reactions | publisher=American Chemical Society | publication-place=Washington, D. C. | volume=198 | date=1982-09-27 | isbn=978-0-8412-0734-9 | doi=10.1021/bk-1982-0198.ch007 | page=151}}</ref><ref name="Bakac2010">{{cite book | last1=Bakac | first1=Andreja | year=2010 | title=Physical Inorganic Chemistry: Reactions, Processes, and Applications | publisher=Wiley | pages=620 | isbn=978-0-470-60255-3 | url=https://books.google.com/books?id=dl7z0JscRTQC&pg=PR7 | access-date=2024-09-02}}</ref> When it is the case, metallic cations can readily reduce perchlorate in solution.<ref name="Taube1983" /> Ru(II) can reduce {{chem2|ClO4-}} to {{chem2|ClO3-}}, while V(II), V(III), Mo(III), Cr(II) and Ti(III) can reduce {{chem2|ClO4-}} to {{chem2|Cl-}}.<ref>Urbansky, Edward T. (1998). [https://clu-in.org/download/contaminantfocus/perchlorate/urbansky2.pdf Perchlorate Chemistry: Implications for Analysis and Remediation] {{Webarchive|url=https://web.archive.org/web/20220129071859/https://clu-in.org/download/contaminantfocus/perchlorate/urbansky2.pdf |date=29 January 2022}}</ref>
 
Some metal complexes, especially those of [[rhenium]], and some metalloenzymes can [[Catalyst|catalyze]] the reduction of perchlorate under mild conditions.<ref>{{cite journal|doi=10.1002/1521-3773(20001201)39:23<4310::AID-ANIE4310>3.0.CO;2-D |date=2000 |volume=39 |issue=23 |last1=Abu-Omar |first1=Mahdi M. |last2=McPherson |first2=Lee D. |last3=Arias |first3=Joachin |last4=Béreau |first4=Virginie M. |title=Clean and Efficient Catalytic Reduction of Perchlorate |journal=Angewandte Chemie |pages=4310–4313 |pmid=29711910 |bibcode=2000AngCh..39.4310A }}</ref> [[Perchlorate reductase]] (see below), a [[Molybdenum in biology|molybdoenzyme]], also catalyzes the reduction of perchlorate.<ref>{{cite journal |doi=10.1074/jbc.M116.714618|doi-access=free |date=2016 |volume=291 |issue=17 |last1=Youngblut |first1=Matthew D. |last2=Tsai |first2=Chi-Lin |last3=Clark |first3=Iain C. |last4=Carlson |first4=Hans K. |last5=Maglaqui |first5=Adrian P. |last6=Gau-Pan |first6=Phonchien S. |last7=Redford |first7=Steven A. |last8=Wong |first8=Alan |last9=Tainer |first9=John A. |last10=Coates |first10=John D. |title=Perchlorate Reductase is Distinguished by Active Site Aromatic Gate Residues |journal=Journal of Biological Chemistry |pages=9190–9302 |pmid=26940877 |pmc=4861485 }}</ref>  Both the Re- and Mo-based [[catalyst]]s operate via metal-oxo intermediates.

===Microbiology===
Over 40 phylogenetically and metabolically diverse microorganisms capable of growth using perchlorate as an electron acceptor<ref>{{cite journal | pmid = 19921177 | doi=10.1007/s00253-009-2336-6 | volume=86 | issue=1 | title=Description of the novel perchlorate-reducing bacteria ''Dechlorobacter hydrogenophilus'' gen. nov., sp. nov. and ''Propionivibrio militaris'', sp. nov | pmc=2822220 | year=2010 | journal=Appl Microbiol Biotechnol | pages=335–43 | author=Thrash JC, Pollock J, Torok T, Coates JD}}</ref> have been isolated since 1996. Most originate from the [[Pseudomonadota]], but others include the [[Bacillota]], ''[[Moorella perchloratireducens]]'' and ''Sporomusa'' sp., and the [[archaeon]] ''[[Archaeoglobus|Archaeoglobus fulgidus]]''.<ref name=Coates>{{cite journal | title = Microbial perchlorate reduction: rocket-fuelled metabolism |author1=John D. Coates |author2=Laurie A. Achenbach | journal = [[Nature Reviews Microbiology]] | volume = 2 | issue = 7 | pages = 569–580 | year = 2004 | pmid = 15197392| doi = 10.1038/nrmicro926|s2cid=21600794 }}</ref><ref>{{cite journal|journal=Science|date=5 April 2013|volume=340|issue=6128|pages=85–87| doi=10.1126/science.1233957|title=Archaeal (Per)Chlorate Reduction at High Temperature: An Interplay of Biotic and Abiotic Reactions|author=Martin G. Liebensteiner, Martijn W. H. Pinkse, Peter J. Schaap, Alfons J. M. Stams, Bart P. Lomans|pmid=23559251|bibcode=2013Sci...340...85L|s2cid=32634949}}</ref> With the exception of ''A. fulgidus'', microbes that grow via perchlorate reduction utilize the enzymes [[perchlorate reductase]] and [[chlorite dismutase]], which collectively take perchlorate to chloride.<ref name=Coates/> In the process, free [[oxygen]] ({{chem2|O2}}) is generated.<ref name=Coates/>

==Natural abundance==
===Terrestrial abundance===
Perchlorate is created by lightning discharges in the presence of chloride. Perchlorate has been detected in rain and snow samples from [[Florida]] and [[Lubbock, Texas]].<ref>Kathleen Sellers, Katherine Weeks, William R. Alsop, Stephen R. Clough, Marilyn Hoyt, Barbara Pugh, Joseph Robb. ''Perchlorate: Environmental Problems and Solutions'', 2007, p 9. Taylor & Francis Group, LLC.</ref> It is also present in [[Martian soil]].

Naturally occurring perchlorate at its most abundant can be found commingled with deposits of sodium nitrate in the [[Atacama Desert]] of northern Chile. These deposits have been heavily mined as sources for nitrate-based fertilizers. Chilean nitrate is in fact estimated to be the source of around {{convert|81000|tonne}} of perchlorate imported to the U.S. (1909–1997). Results from surveys of ground water, ice, and relatively unperturbed deserts have been used to estimate a {{convert|100000|to|3000000|tonne}} "global inventory" of natural perchlorate presently on Earth.<ref>
{{cite book
| first1=Jennifer L. 
| last1= DuBois 
| first2= Sunil
| last2= Ojha
| editor=Peter M.H. Kroneck and Martha E. Sosa Torres
| title=Sustaining Life on Planet Earth: Metalloenzymes Mastering Dioxygen and Other Chewy Gases
| series=Metal Ions in Life Sciences
| volume=15
| pages= 45–87 
| year=2015
| publisher=Springer
| chapter=Chapter 3, Section 2.2 ''Natural Abundance of Perchlorate on Earth''
| doi=10.1007/978-3-319-12415-5_3
| pmid= 25707466 
| pmc= 5012666 
| isbn= 978-3-319-12414-8 
}}
</ref>

===On Mars===
{{undue weight|date=April 2023}}
Perchlorate was detected in Martian soil at the level of ~0.6% by weight.<ref>{{cite journal | title = Detection of Perchlorate & the Soluble Chemistry of Martian Soil at the Phoenix Mars Lander Site | author = Hecht, M. H., S. P. Kounaves, R. Quinn| journal = [[Science (journal)|Science]] | volume = 325 |pages = 64–67 | year = 2009 | pmid=19574385 | doi=10.1126/science.1172466 | issue = 5936|bibcode = 2009Sci...325...64H | s2cid = 24299495|display-authors=etal}}</ref><ref>{{cite journal | author = Kounaves S. P. | year = 2010 | title = Wet Chemistry Experiments on the 2007 Phoenix Mars Scout Lander: Data Analysis and Results | journal = J. Geophys. Res. | volume = 115 | issue = E3| pages = E00E10 | doi = 10.1029/2008JE003084 | bibcode=2009JGRE..114.0A19K|display-authors=etal| doi-access = free }}</ref> It was shown that at the Phoenix landing site it was present as a mixture of 60% {{chem2|Ca(ClO4)2}} and 40% {{chem2|Mg(ClO4)2}}.<ref>{{cite journal | author = Kounaves S. P. | year = 2014 | title = Identification of the Perchlorate Parent Salts at the Phoenix Mars Landing Site and Possible Implications | journal = Icarus | volume = 232 | pages = 226–231 | doi = 10.1016/j.icarus.2014.01.016 |display-authors=etal | bibcode=2014Icar..232..226K}}</ref> These salts, formed from perchlorates, act as [[antifreeze]] and substantially lower the [[Melting point|freezing point]] of water. Based on the temperature and pressure conditions on present-day Mars at the ''[[Phoenix (spacecraft)|Phoenix]]'' lander site, conditions would allow a perchlorate salt solution to be stable in liquid form for a few hours each day during the summer.<ref>{{cite journal | title = Stability of perchlorate hydrates and their liquid solutions at the Phoenix landing site, Mars | author = Chevrier, V. C., Hanley, J., and Altheide, T.S. | journal = [[Geophysical Research Letters]] | volume = 36 | pages = L10202 | year = 2009 | doi = 10.1029/2009GL037497 | bibcode=2009GeoRL..3610202C | issue = 10| s2cid = 42150205 | doi-access = free }}</ref>

The possibility that the perchlorate was a contaminant brought from Earth was eliminated by several lines of evidence. The ''Phoenix'' retro-rockets used ultra pure [[hydrazine]] and launch propellants consisting of [[ammonium perchlorate]] or [[ammonium nitrate]]. Sensors on board ''Phoenix'' found no traces of [[ammonium nitrate]], and thus the nitrate in the quantities present in all three soil samples is indigenous to the Martian soil.  Perchlorate is widespread in Martian soils at concentrations between 0.5 and 1%. At such concentrations, perchlorate could be an important source of oxygen, but it could also become a critical chemical hazard to astronauts.<ref name="DavilaWillson2013">{{cite journal|last1=Davila|first1=Alfonso F.|last2=Willson|first2=David|last3=Coates|first3=John D.|last4=McKay|first4=Christopher P.|title=Perchlorate on Mars: a chemical hazard and a resource for humans|journal=International Journal of Astrobiology|volume=12|issue=4|year=2013|pages=321–325|issn=1473-5504|doi=10.1017/S1473550413000189|bibcode=2013IJAsB..12..321D|s2cid=123983003}}</ref>

In 2006, a mechanism was proposed for the formation of perchlorates that is particularly relevant to the discovery of perchlorate at the ''Phoenix'' lander site. It was shown that soils with high concentrations of [[chloride]] converted to perchlorate in the presence of titanium dioxide and sunlight/ultraviolet light. The conversion was reproduced in the lab using chloride-rich soils from [[Death Valley]].<ref>Miller, Glen. "[http://oasys2.confex.com/acs/231nm/techprogram/P945888.HTM Photooxidation of chloride to perchlorate in the presence of desert soils and titanium dioxide] {{Webarchive|url=https://web.archive.org/web/20160907085946/http://oasys2.confex.com/acs/231nm/techprogram/P945888.HTM |date=2016-09-07 }}". ''[[American Chemical Society]]''. March 29, 2006</ref> Other experiments have demonstrated that the formation of perchlorate is associated with wide band gap semiconducting oxides.<ref>{{cite journal |author1=Schuttlefield Jennifer D. |author2=Sambur Justin B. |author3=Gelwicks Melissa |author4=Eggleston Carrick M. |author5=Parkinson B. A. | year = 2011 | title = Photooxidation of Chloride by Oxide Minerals: Implications for Perchlorate on Mars | journal = J. Am. Chem. Soc. | volume = 133 | issue = 44| pages = 17521–17523 | doi = 10.1021/ja2064878 | pmid=21961793}}</ref> In 2014, it was shown that perchlorate and chlorate can be produced from chloride minerals under Martian conditions via UV using only NaCl and silicate.<ref>{{cite journal |author1=Carrier B. L. |author2=Kounaves S. P. | year = 2015 | title = The Origin of Perchlorates in the Martian Soil | journal = Geophys. Res. Lett. | volume = 42 | issue = 10| pages = 3746–3754 | doi = 10.1002/2015GL064290 | bibcode = 2015GeoRL..42.3739C |hdl=10044/1/53915 |s2cid=97694189 | hdl-access = free }}</ref>

Further findings of perchlorate and chlorate in the Martian meteorite EETA79001 <ref>{{cite journal |author1=Kounaves S. P. |author2=Carrier B. L. |author3=O'Neil G. D. |author4=Stroble S. T. |author5=Clair M. W. |name-list-style=amp | year = 2014 | title = Evidence of Martian Perchlorate, Chlorate, and Nitrate in Mars Meteorite EETA79001: Implications for Oxidants and Organics | journal = Icarus | volume = 229 | pages = 206–213 | doi = 10.1016/j.icarus.2013.11.012 | bibcode=2014Icar..229..206K}}</ref> and by the Mars [[Curiosity (rover)|''Curiosity'']] rover in 2012-2013 support the notion that perchlorates are globally distributed throughout the Martian surface.<ref>Adam Mann. "[https://www.wired.com/wiredscience/2013/09/curiosity-science-package/#slideid-263511 Look What We Found on Mars – Curiosity Rover Serves Up Awesome Science]". ''[[Slate (magazine)]].'' 26 September 2013.</ref><ref name="NYT-20131001">{{cite news |last=Chang |first=Kenneth |title=Hitting Pay Dirt on Mars |url=https://www.nytimes.com/2013/10/01/science/space/hitting-pay-dirt-on-mars.html |date=1 October 2013 |work=[[New York Times]] |access-date=2 October 2013 }}</ref><ref>{{cite journal | author = Kerr Richard A | year = 2013 | title = Pesky Perchlorates All Over Mars | journal = [[Science (journal)|Science]] | volume = 340 | issue = 6129| page = 138 | doi = 10.1126/science.340.6129.138-b | pmid=23580505| bibcode = 2013Sci...340R.138K }}</ref> With concentrations approaching 0.5% and exceeding toxic levels on Martian soil, Martian perchlorates would present a serious challenge to [[Colonization of Mars|human settlement]],<ref name="David">{{cite web|last1=David|first1=Leonard|title=Toxic Mars: Astronauts Must Deal with Perchlorate on the Red Planet|url=http://www.space.com/21554-mars-toxic-perchlorate-chemicals.html|website=Space.com|access-date=May 9, 2017|date=June 13, 2013}}</ref> as well as microorganisms.<ref>[https://www.theguardian.com/science/2017/jul/06/mars-covered-in-toxic-chemicals-that-can-wipe-out-living-organisms-tests-reveal Mars covered in toxic chemicals that can wipe out living organisms, tests reveal]. Ian Sample, ''The Guardian''. 6 July 2017.</ref> On the other hand, the perchlorate would provide a convenient source of [[oxygen]] for the settlements.

On September 28, 2015, NASA announced that analyses of spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars instrument (CRISM) on board the Mars Reconnaissance Orbiter from four different locations where [[recurring slope lineae]] (RSL) are present found evidence for hydrated salts. The hydrated salts most consistent with the spectral absorption features are magnesium perchlorate, magnesium chlorate and sodium perchlorate. The findings strongly support the hypothesis that RSL form as a result of contemporary water activity on Mars.<ref name="NASA-20150928">{{cite web |last1=Webster |first1=Guy |last2=Agle |first2=DC |last3=Brown |first3=Dwayne |last4=Cantillo |first4=Laurie |title=NASA Confirms Evidence That Liquid Water Flows on Today's Mars |website=[[Jet Propulsion Laboratory]] |url=http://www.jpl.nasa.gov/news/news.php?feature=4722 |date=28 September 2015 |access-date=28 September 2015 }}</ref><ref name="NYT-20150928">{{cite news |last=Chang |first=Kenneth |title=NASA Says Signs of Liquid Water Flowing on Mars |url=https://www.nytimes.com/2015/09/29/science/space/mars-life-liquid-water.html |date=28 September 2015 |work=[[New York Times]] |access-date=28 September 2015 }}</ref><ref name="NG-20150928">{{cite journal |last1=Ojha |first1=Lujendra |last2=Wilhelm |first2=Mary Beth |last3=Murchie |first3=scortt L. |last4=McEwen |first4=Alfred S. |last5=Wray |first5=James J. |last6=Hanley |first6=Jennifer |last7=Massé |first7=Marion |last8=Chojnacki |first8=Matt |title=Spectral evidence for hydrated salts in recurring slope lineae on Mars |date=28 September 2015 |journal=[[Nature Geoscience]] |doi=10.1038/ngeo2546 |volume=8 |issue=11 |pages=829–832 |bibcode=2015NatGe...8..829O}}</ref><ref name="NASA-20150928b">{{cite web |author=Staff |title=Video Highlight (02:58) - NASA News Conference - Evidence of Liquid Water on Today's Mars |url=https://www.youtube.com/watch?v=bDv4FRHI3J8 |archive-url=https://ghostarchive.org/varchive/youtube/20211221/bDv4FRHI3J8 |archive-date=2021-12-21 |url-status=live|date=28 September 2015 |work=[[NASA]] |access-date=30 September 2015 }}{{cbignore}}</ref><ref name="NASA-20150928a">{{cite web |author=Staff |title=Video Complete (58:18) – NASA News Conference – Water Flowing on Present-Day Mars m|url=https://www.youtube.com/watch?v=MRQ5B_ik2dU |archive-url=https://ghostarchive.org/varchive/youtube/20211221/MRQ5B_ik2dU |archive-date=2021-12-21 |url-status=live|date=28 September 2015 |work=[[NASA]] |access-date=30 September 2015 }}{{cbignore}}</ref>

==Contamination in environment==
Perchlorates are of concern because of uncertainties about toxicity and health effects at low levels in drinking water, impact on ecosystems, and indirect exposure pathways for humans due to accumulation in vegetables.<ref name="Sridhar Susarla 1999"/> They are water-soluble, exceedingly mobile in aqueous systems, and can persist for many decades under typical groundwater and surface water conditions.<ref name="ReferenceA"/>

===Industrial origin===
Perchlorates are used mostly in [[rocket propellant]]s but also in disinfectants, bleaching agents, and herbicides. Perchlorate contamination is caused during both the manufacture and ignition of rockets and fireworks.<ref name="Kucharzyk">{{cite journal|last=Kucharzyk|first=Katarzyna|title=Development of drinking water standards for perchlorate in the United States |date=2009 |doi=10.1016/j.jenvman.2009.09.023|volume=91|issue=2|journal=Journal of Environmental Management |pages=303–310|pmid=19850401|bibcode=2009JEnvM..91..303K }}</ref> Fireworks are also a source of perchlorate in lakes.<ref>{{cite news |author=<!--Staff writer(s); no by-line.--> |title=Fireworks Displays Linked To Perchlorate Contamination In Lakes |url=https://www.sciencedaily.com/releases/2007/05/070528095714.htm |work=Science Daily |location=Rockville, MD |date=2007-05-28}}</ref> Removal and recovery methods of these compounds from explosives and rocket propellants include high-pressure water washout, which generates aqueous ammonium perchlorate.

===In U.S. drinking water===
In 2000, perchlorate contamination beneath the former flare manufacturing plant [[Olin Corporation]] Flare Facility, [[Morgan Hill, California]] was first discovered 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.{{citation needed|date=November 2017}}
The California Regional Water Quality Control Board and the [[Santa Clara Valley Water District]] have engaged{{when|date=November 2017}} in a major outreach effort, a [[water well test]]ing program has been underway for about 1,200 residential, municipal, and agricultural wells. Large ion exchange treatment units are operating in three public water supply systems which include seven municipal wells with perchlorate detection. The [[potentially responsible parties]], Olin Corporation and Standard Fuse Incorporated, have been supplying bottled water to nearly 800 households with private wells,{{when|date=November 2017}} and the Regional Water Quality Control Board has been overseeing cleanup efforts.<ref>{{cite web |url=http://archive.epa.gov/region9/toxic/web/html/per_ca.html#olin |title=Perchlorate in the Pacific Southwest: California |website=EPA – Region 9 |publisher=EPA |location=San Francisco, CA}}</ref>

The source of perchlorate in California was mainly attributed to two manufacturers in the southeast portion of the Las Vegas Valley in Nevada, where perchlorate has been produced for industrial use.<ref>{{cite web |url=https://www.lvvwd.com/wq/facts_perchlorate.html |title=Perchlorate |website=Las Vegas Valley Water District |location=Las Vegas, NV |access-date=2017-07-06 |archive-date=2016-11-04 |archive-url=https://web.archive.org/web/20161104210252/https://www.lvvwd.com/wq/facts_perchlorate.html |url-status=dead }}</ref> This led to perchlorate release into [[Lake Mead]] in Nevada and the [[Colorado River]] which affected regions of Nevada, California and [[Arizona]], where water from this reservoir is used for consumption, irrigation and recreation for approximately half the population of these states.<ref name="Kucharzyk"/> Lake Mead has been attributed{{when|date=November 2017}} as the source of 90% of the perchlorate in Southern Nevada's drinking water. Based on sampling, perchlorate has been affecting 20&nbsp;million people, with highest detection in [[Texas]], southern California, [[New Jersey]], and Massachusetts, but intensive sampling of the [[Great Plains]] and other middle state regions may lead to revised estimates with additional affected regions.<ref name="Kucharzyk"/> An action level of 18&nbsp;μg/L has been adopted{{when|date=November 2017}} by several affected states.<ref name="ReferenceA"/>

In 2001, the chemical was detected at levels as high as 5&nbsp;μg/L at [[Joint Base Cape Cod]] (formerly [[Massachusetts Military Reservation]]), over the [[Massachusetts]] then state regulation of 2&nbsp;μg/L.<ref>{{cite web |url=http://jbcc-iagwsp.org/groundwater/papers/EPATSP2001Perchlorat%20pres.pdf |last=Clausen |first=Jay |title=Perchlorate, Source and Distribution in Groundwater at Massachusetts Military Reservation |date=November 2001 |id=Presentation at U.S. EPA Technical Support Project Semi-Annual Meeting, Cambridge, MA}}</ref><ref>{{cite web |url=http://www.mass.gov/eea/docs/dep/water/laws/i-thru-z/perchlorate-310cmr22-07282006.pdf |title=Inorganic Chemical Maximum Contaminant Levels, Monitoring Requirements and Analytical Methods |access-date=2017-07-05 |publisher=Massachusetts Office of Energy and Environmental Affairs |id=''Code of Massachusetts Regulations'' (CMR), 310 CMR 22.06 |archive-date=2017-02-28 |archive-url=https://web.archive.org/web/20170228075214/http://www.mass.gov/eea/docs/dep/water/laws/i-thru-z/perchlorate-310cmr22-07282006.pdf |url-status=dead }}</ref>

As of 2009, low levels of perchlorate had been detected in both drinking water and [[groundwater]] in 26 states in the U.S., according to the [[United States Environmental Protection Agency|Environmental Protection Agency]] (EPA).<ref>{{cite journal |last1=Brandhuber |first1=Philip |last2=Clark |first2=Sarah |last3=Morley |first3=Kevin |date=November 2009 |title=A review of perchlorate occurrence in public drinking water systems |url=https://www.epa.gov/sites/production/files/2015-09/documents/12004-exhibita.pdf |journal=Journal of the American Water Works Association |volume=101 |issue=11 |pages=63–73 |doi=10.1002/j.1551-8833.2009.tb09991.x|bibcode=2009JAWWA.101k..63B |s2cid=17523940 }}</ref>

===In food===
In 2004, the chemical was found in cow's milk in California at an average level of 1.3 [[parts per billion]] (ppb, or μg/L), which may have entered the cows through feeding on crops exposed to water containing perchlorates.<ref name=AP2004>[[Associated Press]]. "[https://www.nbcnews.com/id/wbna5268705 Toxic chemical found in California milk]". ''[[NBC News]]''. June 22, 2004.</ref>
A 2005 study suggested [[human breast milk]] had an average of 10.5&nbsp;μg/L of perchlorate.<ref>McKee, Maggie. "[https://www.newscientist.com/article.ns?id=dn7057 Perchlorate found in breast milk across US] {{Webarchive|url=https://web.archive.org/web/20080927031838/http://www.newscientist.com/article.ns?id=dn7057 |date=2008-09-27 }}". ''[[New Scientist]]''. February 23, 2005</ref>

===From minerals and other natural occurrences===
In some places, there is no clear source of perchlorate, and it may be naturally occurring. Natural perchlorate on Earth was first identified in terrestrial nitrate deposits /fertilizers of the [[Atacama Desert]] in Chile as early as the 1880s<ref>Ericksen, G. E. "Geology and origin of the Chilean nitrate deposits"; U.S. Geological Survey Prof. Paper 1188; USGS: Reston, VA, 1981, 37 pp.</ref> and for a long time considered a unique perchlorate source. The perchlorate released from historic use of Chilean nitrate based fertilizer which the U.S.imported by the hundreds of tons in the early 19th century can still be found in some groundwater sources of the United States, for example Long Island, New York.<ref>{{cite journal |author1=Böhlke J. K. |author2=Hatzinger P. B. |author3=Sturchio N. C. |author4=Gu B. |author5=Abbene I. |author6=Mroczkowski S. J. |year = 2009 | title = Atacama perchlorate as an agricultural contaminant in groundwater: Isotopic and chronologic evidence from Long Island, New York |journal = Environmental Science & Technology |volume = 43 |issue = 15| pages = 5619–5625 |doi=10.1021/es9006433|pmid=19731653 |bibcode=2009EnST...43.5619B }}</ref> Recent improvements in analytical sensitivity using ion chromatography based techniques have revealed a more widespread presence of natural perchlorate, particularly in subsoils of Southwest USA,<ref>{{cite journal |author1=Rao B. |author2=Anderson T. A. |author3=Orris G. J. |author4=Rainwater K. A. |author5=Rajagopalan S. |author6=Sandvig R. M. |author7=Scanlon B. R.|author7-link= Bridget Scanlon |author8=Stonestrom S. A. |author9=Walvoord M. A. |author10=Jackson W. A. |year = 2007 |title = Widespread NaturalPerchlorate in Unsaturated zones of the Southwest United States |journal = Environ. Sci. Technol. |volume = 41 |issue = 13|pages = 4522–4528 |doi=10.1021/es062853i|pmid=17695891 |bibcode=2007EnST...41.4522R }}</ref> salt evaporites in California and Nevada,<ref>Orris, G. J.; Harvey, G. J.; Tsui, D. T.; Eldridge, J. E. Preliminaryanalyses for perchlorate in selected natural materials and theirderivative products; USGS Open File Report 03-314; USGS, U.S.Government Printing Office: Washington, DC, 2003.</ref> Pleistocene groundwater in New Mexico,<ref>{{cite journal |author1=Plummer L. N. |author2=Bohlke J. K. |author3=Doughten M. W. | year = 2005 | title = Perchlorate in Pleistocene and Holocene groundwater in North-Central New Mexico | doi = 10.1021/es051739h |pmid=16570594 | journal = Environ. Sci. Technol. | volume = 40 | issue = 6| pages = 1757–1763| bibcode = 2006EnST...40.1757P }}</ref> and even present in extremely remote places such as [[Antarctica]].<ref name="S. P. Kounaves et al. 2010 2360–2364">{{cite journal | doi = 10.1021/es9033606 | title = Natural Perchlorate in the Antarctic Dry Valleys and Implications for its Global Distribution and History | author = S. P. Kounaves| journal = [[Environmental Science & Technology]] | volume = 44 | issue = 7 |pages = 2360–2364 | year = 2010 | pmid = 20155929|bibcode = 2010EnST...44.2360K |display-authors=etal}}</ref> The data from these studies and others indicate that natural perchlorate is globally deposited on Earth with the subsequent accumulation and transport governed by the local hydrologic conditions.

Despite its importance to environmental contamination, the specific source and processes involved in natural perchlorate production remain poorly understood. Laboratory experiments in conjunction with isotopic studies<ref>{{cite journal | author = Böhlke, Karl John, Sturchio Neil C., Gu Baohua, Horita Juske, Brown Gilbert M., Jackson W. Andrew, Batista Jacimaria, Hatzinger Paul B. | year = 2005 | title = Perchlorate isotope forensics | journal = Analytical Chemistry | volume = 77 | issue = 23| pages = 7838–7842 | doi=10.1021/ac051360d| pmid = 16316196 | bibcode = 2005AnaCh..77.7838B }}</ref> have implied that perchlorate may be produced on earth by oxidation of chlorine species through pathways involving ozone or its photochemical products.<ref>{{cite journal | author = Rao B., Anderson T. A., Redder A., Jackson W. A. | year = 2010 | title = Perchlorate Formation by Ozone Oxidation of AqueousChlorine/Oxy-Chlorine Species: Role of ClxOy Radicals | journal = Environ. Sci. Technol. | volume = 44 | issue = 8| pages = 2961–2967 | doi=10.1021/es903065f| pmid = 20345093 | bibcode = 2010EnST...44.2961R }}</ref><ref>{{cite journal | author = Catling, D. C., M. W. Claire, K. J. Zahnle, R. C. Quinn, B. C. Clark, M. H. Hecht, and S. Kounaves | year = 2010 | title = Atmospheric origins of perchlorate on Mars and in the Atacama | journal = J. Geophys. Res. | volume = 115 | issue = E1| pages = E00E11 | doi= 10.1029/2009JE003425| pmid = 32487988 | pmc = 7265485 | bibcode = 2010JGRE..115.0E11C }}</ref> Other studies have suggested that perchlorate can also be formed by lightning activated oxidation of chloride aerosols (e.g., chloride in sea salt sprays),<ref>{{cite journal |author1=Dasgupta P. K. |author2=Martinelango P. K. |author3=Jackson W. A. |author4=Anderson T. A. |author5=Tian K. |author6=Tock R.W. |author7=Rajagopalan S. |year = 2005 |title = The origin of naturally occurring perchlorate: the role ofatmospheric processes |journal = Environmental Science & Technology |volume = 39 | issue = 6|pages = 1569–1575 |doi=10.1021/es048612x|pmid=15819211 |bibcode=2005EnST...39.1569D }}</ref> and ultraviolet or thermal oxidation of chlorine (e.g., bleach solutions used in swimming pools) in water.<ref>{{cite journal |author1=Rao B. |author2=Estrada N |author3=Mangold J. |author4=Shelly M. |author5=Gu B. |author6=Jackson W. A. | year = 2012 | title = Perchlorate production byphotodecomposition of aqueous chlorine |journal = Environ. Sci. Technol. |volume = 46 |issue = 21|pages =11635–11643| doi = 10.1021/es3015277|pmid=22962844 |bibcode=2012EnST...4611635R}}</ref><ref>{{cite journal |author1=Stanford B. D. |author2=Pisarenko A. N. |author3=Snyder S. A. |author4=Gordon G. |year = 2011 |title = Perchlorate, bromate, and chlorate in hypochlorite solutions: Guidelines for utilities | journal = Journal of the American Water Works Association | volume = 103 |issue = 6|page = 71|doi=10.1002/j.1551-8833.2011.tb11474.x |bibcode=2011JAWWA.103f..71S |s2cid=21620375 }}</ref><ref>{{cite journal |author = William E. Motzer |title = Perchlorate: Problems, Detection, and Solutions |pages = 301–311 |doi = 10.1006/enfo.2001.0059 |journal = Environmental Forensics |volume = 2 |issue = 4 |year = 2001|bibcode = 2001EnvFo...2..301M |s2cid = 95709844 }}</ref>

===From nitrate fertilizers===
Although perchlorate as an environmental contaminant is usually associated with the manufacture, storage, and testing of [[solid rocket motor]]s,<ref name="Matthew L. Magnuson 2000">{{cite journal |author1=Magnuson Matthew L. |author2=Urbansky Edward T. |author3=Kelty Catherine A. | year = 2000 | title = Determination of Perchlorate at Trace Levels in Drinking Water by Ion-Pair Extraction with Electrospray Ionization Mass Spectrometry | journal = Analytical Chemistry | volume = 72 |issue=1 | pages = 25–29| doi=10.1021/ac9909204|pmid=10655630 }}</ref> contamination of perchlorate has been focused as a side effect of the use of natural nitrate [[fertilizer]] and its release into ground water. The use of naturally contaminated nitrate fertilizer contributes to the infiltration of perchlorate anions into the ground water and threaten the water supplies of many regions in the US.<ref name="Matthew L. Magnuson 2000"/>

One of the main sources of perchlorate contamination from natural nitrate fertilizer use was found to come from the fertilizer derived from Chilean [[caliche]] ([[calcium carbonate]]), because Chile has rich source of naturally occurring perchlorate anion.<ref name="S.K. Brown, M.L. Magnuson 2001">{{cite journal |author1=Urbansky T. |author2=Brown S.K. |author3=Magnuson M.L. |author4=Kelty C.A. | year = 2001 | title = Perchlorate levels in samples of sodium nitrate fertilizer derived from Chilean caliche | url = https://zenodo.org/record/1259965| journal = Environmental Pollution | volume = 112 | issue = 3| pages = 299–302| doi=10.1016/s0269-7491(00)00132-9|pmid=11291435 }}</ref> Perchlorate concentration was the highest in Chilean nitrate, ranging from 3.3 to 3.98%.<ref name="ReferenceA"/> Perchlorate in the solid fertilizer ranged from 0.7 to 2.0&nbsp;mg g<sup>−1</sup>, variation of less than a factor of 3 and it is estimated that sodium nitrate fertilizers derived from Chilean caliche contain approximately 0.5–2&nbsp;mg g<sup>−1</sup> of perchlorate anion.<ref name="S.K. Brown, M.L. Magnuson 2001"/> The direct ecological effect of perchlorate is not well known; its impact can be influenced by factors including rainfall and irrigation, dilution, natural attenuation, soil adsorption, and bioavailability.<ref name="S.K. Brown, M.L. Magnuson 2001"/> Quantification of perchlorate concentrations in nitrate fertilizer components via [[ion chromatography]] revealed that in horticultural fertilizer components contained perchlorate ranging between 0.1 and 0.46%.<ref name="ReferenceA">{{cite journal |author1=Susarla Sridhar |author2=Collette T. W. |author3=Garrison A. W. |author4=Wolfe N. L. |author5=McCutcheon S. C. | year = 1999 | title = Perchlorate Identification in Fertilizers | journal = Environmental Science and Technology | volume = 33 | issue = 19| pages = 3469–3472| doi=10.1021/es990577k|bibcode=1999EnST...33.3469S}}</ref>

==Environmental cleanup==
There have been many attempts to eliminate perchlorate contamination. Current [[Environmental remediation|remediation]] technologies for perchlorate have downsides of high costs and difficulty in operation.<ref name="Eliminating Water Contamination by Inorganic Disinfection Byproducts.">{{cite web|title=Eliminating Water Contamination by Inorganic Disinfection Byproducts.|url=http://www.hazenandsawyer.com/news/eliminating-water-contamination-by-inorganic-disinfection-byproducts/|work=Hazen and Sawyer|date=19 July 2012|access-date=28 March 2014|archive-date=29 April 2021|archive-url=https://web.archive.org/web/20210429022151/https://www.hazenandsawyer.com/news/eliminating-water-contamination-by-inorganic-disinfection-byproducts/|url-status=dead}}</ref> Thus, there have been interests in developing systems that would offer economic and green alternatives.<ref name="Eliminating Water Contamination by Inorganic Disinfection Byproducts."/>

===Treatment ex situ and in situ===
Several technologies can remove perchlorate, via treatments [[ex situ]] (away from the location) and [[in situ]] (at the location).

Ex situ treatments include ion exchange using perchlorate-selective or nitrite-specific resins, [[bioremediation]] using packed-bed or fluidized-bed [[bioreactor]]s, and membrane technologies via [[electrodialysis]] and [[reverse osmosis]].<ref name="Technical Fact Sheet – Perchlorate.">{{cite web|title=Technical Fact Sheet – Perchlorate.|url=http://www.epa.gov/fedfac/pdf/technical_fact_sheet_perchlorate.pdf|work=US EPA|date=2013-04-23|archive-url=https://web.archive.org/web/20130607125351/http://www.epa.gov/fedfac/pdf/technical_fact_sheet_perchlorate.pdf|archive-date=7 June 2013}}</ref> In ex situ treatment via ion exchange, contaminants are attracted and adhere to the ion exchange resin because such resins and ions of contaminants have opposite charge.<ref name="ara.com">{{cite web|title=ARA Perchlorate Contamination Solutions|publisher=[[Applied Research Associates|Applied Research Associates, Inc.]]|url=http://www.ara.com/perchlorate/Ion-Exchange-Perchlorate.html|archive-url=https://web.archive.org/web/20140429203505/http://www.ara.com/perchlorate/Ion-Exchange-Perchlorate.html|archive-date=29 April 2014}}</ref> As the ion of the contaminant adheres to the resin, another charged ion is expelled into the water being treated, in which then ion is exchanged for the contaminant.<ref name="ara.com"/> Ion exchange technology has advantages of being well-suitable for perchlorate treatment and high volume throughput but has a downside that it does not treat [[organochloride|chlorinated solvents]]. In addition, ex situ technology of liquid phase carbon adsorption is employed, where granular activated carbon (GAC) is used to eliminate low levels of perchlorate and pretreatment may be required in arranging GAC for perchlorate elimination.<ref name="Technical Fact Sheet – Perchlorate."/>

In situ treatments, such as bioremediation via perchlorate-selective microbes and permeable reactive barrier, are also being used to treat perchlorate.<ref name="Technical Fact Sheet – Perchlorate."/> In situ bioremediation has advantages of minimal above-ground [[infrastructure]] and its ability to treat chlorinated solvents, perchlorate, [[nitrate]], and [[RDX]] simultaneously. However, it has a downside that it may negatively affect secondary water quality. In situ technology of [[phytoremediation]] could also be utilized, even though perchlorate phytoremediation mechanism is not fully founded yet.<ref name="Technical Fact Sheet – Perchlorate."/>

Bioremediation using perchlorate-reducing bacteria, which reduce perchlorate ions to harmless chloride, has also been proposed.<ref>{{cite journal|doi=10.1016/j.micres.2010.11.005|title=Dissimilatory perchlorate reduction: A review|journal=Microbiological Research|volume=166|issue=4|pages=237–254|year=2011|last1=Bardiya|first1=Nirmala|last2=Bae|first2=Jae-Ho|pmid=21242067|doi-access=free}}</ref>

== Health effects ==

===Thyroid inhibition===
Perchlorate is a potent competitive inhibitor of the thyroid [[sodium-iodide symporter]].<ref name="pmid15572417">{{cite journal | author1 = Braverman, L. E. | author2 = He X. | author3 = Pino S. | display-authors = etal | title = The effect of perchlorate, thiocyanate, and nitrate on thyroid function in workers exposed to perchlorate long-term | journal = J Clin Endocrinol Metab | year = 2005 | volume = 90 | issue = 2 | pages = 700–706 | pmid = 15572417 | doi = 10.1210/jc.2004-1821 | doi-access = free }}</ref> Thus, it has been used to treat [[hyperthyroidism]] since the 1950s.<ref>{{cite journal |last=Godley |first=A. F. |author2=Stanbury, J. B. |year=1954 |title=Preliminary experience in the treatment of hyperthyroidism with potassium perchlorate |journal=J Clin Endocrinol Metab |volume=14 |issue= 1|pages=70–78 |pmid=13130654 |doi=10.1210/jcem-14-1-70 }}</ref> At very high doses (70,000–300,000&nbsp;[[Parts per billion|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.

<!--removed from elsewhere, needs integration Further, there are studies that show correlations between the concentrations of byproduct perchlorate with other chemicals such as [[nitrate]] and [[chlorate]].<ref>{{cite journal |author1=Wu Q. |author2=Zhang T. |author3=Sun H. |author4=Kannan K. | date = Apr 2010 | title = Perchlorate in tap water, groundwater, surface waters, and bottled water from China and its association with other inorganic anions and with disinfection byproducts | journal = Archives of Environmental Contamination and Toxicology | volume = 58 | issue = 3| pages = 543–50 | doi = 10.1007/s00244-010-9485-6 | pmid = 20162260 }}</ref>-->
In large amounts perchlorate 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 [[National Academy of Sciences|NAS]], in its 2005 report, ''Health Implications of Perchlorate Ingestion'', emphasized that this effect, also known as Iodide Uptake Inhibition (IUI) is not an adverse health effect. However, in January 2008, California's Department of Toxic Substances Control stated that perchlorate is becoming a serious threat to human health and water resources.<ref>{{cite web|url=http://www.dtsc.ca.gov/hazardouswaste/perchlorate/|title=Perchlorate|publisher=California Department of Toxic Substances Control|date=Jan 26, 2008|access-date=January 27, 2008|archive-url=https://web.archive.org/web/20090823021109/http://www.dtsc.ca.gov/HazardousWaste/Perchlorate/|archive-date=August 23, 2009|url-status=dead}}</ref> In 2010, the EPA's Office of the Inspector General determined that the agency's own perchlorate [[reference dose]] (RfD) of 24.5 parts per billion protects against all human biological effects from exposure, as the federal government is responsible for all US military base groundwater contamination. 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.<ref name="EPA1">{{Cite report |date=19 April 2010 |title=Scientific Analysis of Perchlorate: What We Found |publisher=Office of the Inspector General, Environmental Protection Agency}}</ref>

Because of ammonium perchlorate's adverse effects upon children, Massachusetts set its maximum allowed limit of [[ammonium perchlorate]] in drinking water at 2 parts per billion (2 ppb = 2 micrograms per liter).<ref>{{Cite web | title=Perchlorate Frequently Asked Questions {{!}} Mass.gov | url=https://www.mass.gov/guides/perchlorate-frequently-asked-questions | access-date=2025-03-22 | website=www.mass.gov}}</ref>

Perchlorate affects only thyroid hormone. Because it is neither stored nor [[metabolism|metabolized]], effects of perchlorate on the thyroid gland are reversible, though effects on brain development from lack of thyroid hormone in [[fetus]]es, [[newborn]]s, and children are not.<ref>{{cite journal |author = J. Wolff |year = 1998 |title = Perchlorate and the Thyroid Gland |journal = Pharmacological Reviews |volume = 50 |issue = 1 |pages = 89–105 |pmid = 9549759}}</ref>

Toxic effects of perchlorate have been studied in a survey of industrial plant workers who had been exposed to perchlorate, compared to a control group of other industrial plant workers who had no known exposure to perchlorate. After undergoing multiple tests, workers exposed to perchlorate were found to have a significant systolic blood pressure rise compared to the workers who were not exposed to perchlorate, as well as a significant decreased thyroid function compared to the control workers.<ref>{{cite journal |vauthors=Chen HX, Shao YP, Wu FH, Li YP, Peng KL | date = Jan 2013 | title = [original title not given] |trans-title=Health survey of plant workers for an occupational exposure to ammonium perchlorate | journal = Zhonghua Lao Dong Wei Sheng Zhi Ye Bing Za Zhi. | volume = 31 | issue = 1| pages = 45–7 | pmid = 23433158 }}</ref>

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 [[blood]]stream ("iodide uptake inhibition", thus perchlorate is a known [[goitrogen]]).<ref>{{cite journal |doi=10.1289/ehp.02110927 |author1=Greer, M. A. |author2=Goodman, G. |author3=Pleuss, R. C. |author4=Greer, S. E. |year=2002 |title=Health effect assessment for environmental perchlorate contamination: The dose response for inhibition of thyroidal radioiodide uptake in humans | journal = [[Environmental Health Perspectives]] | volume = 110 | issue = 9 | pages = 927–937 | url = http://www.ehponline.org/docs/2002/110p927-937greer/abstract.html | format = free online | pmid=12204829 | pmc=1240994}}</ref> The EPA converted this dose into a [[reference dose]] of 0.0007&nbsp;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 {{convert|70|kg|abbr=on}} and consumes {{convert|2|L|abbr=on}} of drinking water per day over a lifetime.<ref>{{cite web |url=http://www.epa.gov/fedfac/pdf/perchlorate_guidance.pdf |title=Perchlorate Guidance (Memorandum) |publisher=EPA |date=January 26, 2006}}</ref>{{Update inline|reason=EPA removed the cited 2006 ref from its website; various new studies have been published since 2006 |date=May 2017}}

In 2006, a study 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. The authors also indicated that they did not originally normalize their findings for creatinine, which would have essentially accounted for fluctuations in the concentrations of one-time urine samples like those used in this study.<ref>{{cite journal | title = Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States |author1=Benjamin C. Blount |author2=James L. Pirkle |author3=John D. Osterloh |author4=Liza Valentin-Blasini |author5=Kathleen L. Caldwell |name-list-style=amp | journal = [[Environmental Health Perspectives]] | volume = 114 | issue = 12 | year = 2006 | doi = 10.1289/ehp.9466 | pmid=17185277 | pages = 1865–71 | pmc = 1764147}}</ref> 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, any remaining association between the results and perchlorate intake disappeared.<ref name="Tarone1">{{cite journal |author=Tarone|year=2010 |title=The Epidemiology of Environmental Perchlorate Exposure and Thyroid Function: A Comprehensive Review |journal=Journal of Occupational and Environmental Medicine |issue=June |pmid=20523234 |doi=10.1097/JOM.0b013e3181e31955 |volume=52 |pages=653–60|s2cid=2090190 |display-authors=etal}}</ref> Soon after the revised Blount Study was released, Robert Utiger, a doctor with the Harvard Institute of Medicine, testified before the US Congress and stated: "I continue to believe that that reference dose, 0.007 milligrams per kilo (24.5&nbsp;ppb), which includes a factor of 10 to protect those who might be more vulnerable, is quite adequate."<ref name="Testimony">{{cite web |title=Perchlorate: Health and Environmental Impacts of Unregulated Exposure |url=http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=110_house_hearings&docid=f:38495.wais |publisher=United States Congress |access-date=15 April 2012}}</ref>

In 2014, a study was published, showing that environmental exposure to perchlorate in pregnant women with hypothyroidism is associated with a significant risk of low IQ in their children.<ref name="UK">{{Cite journal |last1=Taylor |first1=Peter N. |last2=Okosieme |first2=Onyebuchi E. |last3=Murphy |first3=Rhian |last4=Hales |first4=Charlotte |last5=Chiusano |first5=Elisabetta |last6=Maina |first6=Aldo |last7=Joomun |first7=Mohamed |last8=Bestwick |first8=Jonathan P. |last9=Smyth |first9=Peter |last10=Paradice |first10=Ruth |last11=Channon |first11=Sue |last12=Braverman |first12=Lewis E. |last13=Dayan |first13=Colin M. |last14=Lazarus |first14=John H. |last15=Pearce |first15=Elizabeth N. |date=November 2014 |title=Maternal Perchlorate Levels in Women With Borderline Thyroid Function During Pregnancy and the Cognitive Development of Their Offspring: Data From the Controlled Antenatal Thyroid Study |journal=The Journal of Clinical Endocrinology & Metabolism |language=en |volume=99 |issue=11 |pages=4291–4298 |doi=10.1210/jc.2014-1901 |issn=0021-972X |pmid=23706508|s2cid=32482599 |doi-access=free }}</ref>

===Lung toxicity===
Some studies suggest that perchlorate has pulmonary toxic effects as well. Studies have been performed on rabbits where perchlorate has been injected into the trachea. The lung tissue was removed and analyzed, and it was found that perchlorate injected lung tissue showed several adverse effects when compared to the control group that had been intratracheally injected with saline. Adverse effects included inflammatory infiltrates, alveolar collapse, subpleural thickening, and lymphocyte proliferation.<ref>{{cite journal |author1=Wu F. |author2=Chen H. |author3=Zhou X. |author4=Zhang R. |author5=Ding M. |author6=Liu Q. |author7=Peng KL. | year = 2013 | title = Pulmonary fibrosis effect of ammonium perchlorate exposure in rabbit | journal = Arch Environ Occup Health | volume = 68 | issue = 3| pages = 161–5 | doi = 10.1080/19338244.2012.676105 | pmid = 23566323 |bibcode=2013ArEOH..68..161W |s2cid=205941484 }}</ref>

===Aplastic anemia===
In the early 1960s, [[potassium perchlorate]] used to treat [[Graves' disease]] was implicated in the development of [[aplastic anemia]]—a condition where the [[bone marrow]] fails to produce new [[blood cell]]s in sufficient quantity—in thirteen patients, seven of whom died.<ref name=NRC>{{cite book |author=National Research Council |chapter=Perchlorate and the thyroid |title=Health implications of perchlorate ingestion |publisher=[[National Academies Press]] |location=Washington, D.C. |year=2005 |pages=[https://archive.org/details/healthimplicatio00nati/page/7 7] |isbn=978-0-309-09568-6 |chapter-url=https://books.google.com/books?id=EMX4ZTF6pusC&pg=PA7 |author-link=United States National Research Council |url=https://archive.org/details/healthimplicatio00nati/page/7 }} Retrieved on April 3, 2009 through [[Google Book Search]].</ref> 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.<ref>{{cite book |author=Clark, J. J. J. |chapter=Toxicology of perchlorate |editor=Urbansky ET |title=Perchlorate in the environment |publisher=Kluwer Academic/Plenum Publishers |location=New York |year=2000 |pages=19–20 |isbn=978-0-306-46389-1 |chapter-url=https://books.google.com/books?id=aN1nV174zVIC&pg=PA19}} Retrieved on April 3, 2009 through [[Google Book Search]].</ref>

==Regulation in the U.S.==

===Water===
In 1998, perchlorate was included in the U.S. EPA [[Safe Drinking Water Act#Unregulated contaminants|Contaminant Candidate List]], primarily due to its detection in California drinking water.<ref>EPA (1998-03-02). "Announcement of the Drinking Water Contaminant Candidate List." ''Federal Register,'' {{usfr|63|10274}}</ref><ref name="Kucharzyk"/>

In 2002, the EPA completed its draft toxicological review of perchlorate and proposed an [[reference dose]] of 0.00003 milligrams per kilogram per day (mg/kg/day) based primarily on studies that identified neurodevelopmental deficits in rat pups. These deficits were linked to maternal exposure to perchlorate.<ref name="greer" />

In 2003, a [[United States District Court for the Central District of California|federal district court]] in California found that the [[CERCLA|Comprehensive Environmental Response, Compensation and Liability Act]] applied, because perchlorate is ignitable, and therefore was a "characteristic" hazardous waste.<ref>''Castaic Lake Water Agency v. Whittaker,'' 272 F. Supp. 2d 1053, 1059–61 (C.D. Cal. 2003).</ref>

Subsequently, the U.S. National Research Council of the [[National Academy of Sciences]] (NAS) reviewed the health implications of perchlorate, and in 2005 proposed a much higher reference dose of 0.0007&nbsp;mg/kg/day based primarily on a 2002 study by Greer ''et al.''<ref name="greer">{{cite journal | vauthors = Greer MA, Goodman G, Pleus RC, Greer SE | title = Health effects assessment for environmental perchlorate contamination: the dose response for inhibition of thyroidal radioiodine uptake in humans | journal = Environmental Health Perspectives | volume = 110 | issue = 9 | pages = 927–937 | date = September 2002 | pmid = 12204829 | pmc = 1240994 | doi = 10.1289/ehp.02110927 }}</ref> During that study, 37 adult human subjects were split into four exposure groups exposed to 0.007 (7 subjects), 0.02 (10 subjects), 0.1 (10 subjects), and 0.5 (10 subjects) mg/kg/day. Significant decreases in iodide uptake were found in the three highest exposure groups. Iodide uptake was not significantly reduced in the lowest exposed group, but four of the seven subjects in this group experienced inhibited iodide uptake. In 2005, the [[Reference dose|RfD]] proposed by NAS was accepted by EPA and added to its integrated risk information system (IRIS).

# The NAS report described the level of lowest exposure from Greer ''et al.'' as a "no-observed-effect level" ([[NOEL]]). However, there was actually an effect at that level although not statistically significant largely due to small size of study population (four of seven subjects showed a slight decrease in iodide uptake).
# Reduced iodide uptake was not considered to be an adverse effect, even though it is a precursor to an adverse effect, [[hypothyroidism]]. Therefore, additional safety factors, would be necessary when extrapolating from the point of departure to the RfD.
# Consideration of data uncertainty was insufficient because the Greer, ''et al.'' study reflected only a 14-day exposure (=acute) to healthy adults and no additional safety factors were considered to protect sensitive subpopulations like for example, breastfeeding newborns.

Although there has generally been consensus with the Greer ''et al.'' study, there has been no consensus with regard to developing a perchlorate RfD. One of the key differences results from how the point of departure is viewed (i.e., NOEL or "lowest-observed-adverse-effect level",  [[LOAEL]]), or whether a benchmark dose should be used to derive the RfD. Defining the point of departure as a NOEL or LOAEL has implications when it comes to applying appropriate safety factors to the point of departure to derive the RfD.<ref>{{cite web | title = EPA's Perchlorate Drinking Water Preliminary Remediation Goal (Prg). | url = http://www.epa.gov/region10/pdf/sites/euclid/eroad-perchlorate-memo-071307.pdf | archive-url = https://web.archive.org/web/20170303012904/http://www.epa.gov/region10/pdf/sites/euclid/eroad-perchlorate-memo-071307.pdf | archive-date = 3 March 2017 | work = Office of Environmental Health Assessments | publisher = Washington State Department of Health | date = 13 July 2007 }}</ref>

In early 2006, EPA issued a "Cleanup Guidance" and recommended a [[Drinking Water Equivalent Level]] (DWEL) for perchlorate of 24.5&nbsp;μg/L.{{Citation needed|date=December 2020}} Both DWEL and Cleanup Guidance were based on a 2005 review of the existing research by the [[National Academy of Sciences]] (NAS).<ref name="NAS1">{{cite book |title=Health Implications of Perchlorate Ingestion |author=Committee to Assess the Health Implications of Perchlorate Ingestion, National Research Council |year=2005 |publisher=The National Academies Press |location=Washington, DC |isbn=978-0-309-09568-6 |url=https://archive.org/details/healthimplicatio00nati |doi=10.17226/11202 }}</ref>

Lacking a federal drinking water standard, several states subsequently published their own standards for perchlorate including Massachusetts in 2006{{citation needed|date=November 2017}} and California in 2007. Other states, including Arizona, Maryland, Nevada, New Mexico, New York, and Texas have established non-enforceable, advisory levels for perchlorate.{{citation needed|date=May 2017}}

In 2008, EPA issued an interim [[Safe Drinking Water Act#Health advisories|drinking water health advisory]] for perchlorate and with it a guidance and analysis concerning the impacts on the environment and drinking water.<ref name="EPA-perchlorate">{{cite web |url=https://www.epa.gov/dwstandardsregulations/perchlorate-drinking-water |title=Perchlorate in Drinking Water |author=<!--Not stated--> |date=2017-03-31 |website=Drinking Water Contaminants—Standards and Regulations |publisher=EPA}}</ref> California also issued guidance{{when|date=November 2017}} regarding perchlorate use.<ref>{{cite web |url=http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Perchlorate.aspx |title=Perchlorate in Drinking Water |date=2012-12-07 |website=Drinking Water Systems |publisher=California Department of Public Health |location=Sacramento, CA |archive-date=2013-02-06 |archive-url=https://web.archive.org/web/20130206064109/http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Perchlorate.aspx}}</ref> Both the [[United States Department of Defense|Department of Defense]] and some environmental groups voiced questions about the NAS report,{{citation needed|date=November 2017}} but no credible science has emerged to challenge the NAS findings.{{citation needed|date=November 2017}}

In February 2008, the U.S. [[Food and Drug Administration]] (FDA) reported that U.S. toddlers on average were being exposed to more than half of EPA's safe dose from food alone.<ref>{{cite journal |last1=Renner |first1=Rebecca |date=2008-03-15 |title=Perchlorate In Food |journal=Environ. Sci. Technol. |volume=42 |issue=6 |page=1817 |doi=10.1021/es0870552|pmid=18409597 |bibcode=2008EnST...42.1817R |doi-access=free }}</ref> In March 2009, a [[Centers for Disease Control]] study found 15 brands of infant formula contaminated with perchlorate and that combined with existing perchlorate drinking water contamination, infants could be at risk for perchlorate exposure above the levels considered safe by EPA.

In 2010, the [[Massachusetts Department of Environmental Protection]] set a 10 fold lower RfD (0.07&nbsp;μg/kg/day) than the NAS RfD using a much higher uncertainty factor of 100. They also calculated an Infant drinking water value, which neither US EPA nor [[CalEPA]] had done.<ref name="ma">{{cite journal | vauthors = Zewdie T, Smith CM, Hutcheson M, West CR | title = Basis of the Massachusetts reference dose and drinking water standard for perchlorate | journal = Environmental Health Perspectives | volume = 118 | issue = 1 | pages = 42–48 | date = January 2010 | pmid = 20056583 | pmc = 2831965 | doi = 10.1289/ehp.0900635 }}</ref>

On February 11, 2011, EPA determined that perchlorate meets the [[Safe Drinking Water Act]] criteria for regulation as a contaminant.<ref name="EPA-perchlorate"/><ref>EPA (2011-02-11). "Drinking Water: Regulatory Determination on Perchlorate." {{usfr|76|7762}}</ref> The agency found that perchlorate may have an adverse effect on the health of persons and is known to occur in [[public water system]]s with a frequency and at levels that it presents a public health concern. Since then EPA has continued to determine what level of contamination is appropriate. EPA prepared extensive responses to submitted public comments.<ref>[http://www.regulations.gov/#!searchResults;rpp=10;po=0;s=EPA-HQ-OW-2008-0692 EPA-HQ-OW-2009-0297] "Docket ID" for EPA</ref>{{better source needed|date=November 2017}}

In 2016, the [[Natural Resources Defense Council]] (NRDC) filed a lawsuit to accelerate EPA's regulation of perchlorate.<ref>{{cite web |title=Regulatory Update At-A-Glance |url=https://www.amwa.net/update-glance/regulatory-update-glance |access-date=2019-04-04 |publisher=Association of Metropolitan Water Agencies |location=Washington, DC |archive-date=2019-04-06 |archive-url=https://web.archive.org/web/20190406015412/https://www.amwa.net/update-glance/regulatory-update-glance |url-status=dead }}</ref>

In 2019, EPA proposed a [[Maximum Contaminant Level]] of 0.056&nbsp;mg/L for public water systems.<ref>EPA (2019-06-26). "National Primary Drinking Water Regulations: Perchlorate." Proposed Rule. ''Federal Register.'' {{usfr|84|30524}}.</ref>

On June 18, 2020, EPA announced that it was withdrawing its 2011 regulatory determination and its 2019 proposal, stating that it had taken "proactive steps" with state and local governments to address perchlorate contamination.<ref>{{cite web |title=Perchlorate in Drinking Water; Final Action |url=https://www.epa.gov/sdwa/perchlorate-drinking-water |date=2020-06-18 |publisher=EPA}}</ref> In September 2020 NRDC filed suit against EPA for its failure to regulate perchlorate, and stated that 26 million people may be affected by perchlorate in their drinking water.<ref>{{cite news |last=Slisco |first=Aila |title=EPA Sued For Not Regulating Rocket Fuel Chemical in Drinking Water |url=https://www.msn.com/en-us/news/us/epa-sued-for-not-regulating-rocket-fuel-chemical-in-drinking-water/ar-BB18GT1p |date=2020-09-04 |work=Newsweek}}</ref> On March 31, 2022, the EPA announced that a review confirmed its 2020 decision.<ref>{{cite web |title=EPA Announces Plan to Protect the Public from Perchlorate in Drinking Water |url=https://www.epa.gov/newsreleases/epa-announces-plan-protect-public-perchlorate-drinking-water |publisher=U.S. Environmental Protection Agency |access-date=18 April 2022 |date=March 31, 2022}}</ref> Following the NRDC lawsuit, in 2023 the [[United States Court of Appeals for the District of Columbia Circuit|US Court of Appeals for the DC Circuit]] ordered EPA to develop a perchlorate standard for public water systems.<ref>{{cite magazine |last=Erickson |first=Britt E. |title=Court orders EPA to regulate perchlorate in drinking water |url=https://cen.acs.org/environment/pollution/Court-orders-EPA-regulate-perchlorate-drinking-water/101/web/2023/05 |date=2023-05-11 |magazine=Chemical and Engineering News |publisher=American Chemical Society}}</ref> EPA stated that it will publish a proposed standard for perchlorate in 2025, and issue a final rule in 2027.<ref>{{cite web |title=Perchlorate in Drinking Water |url=https://www.epa.gov/sdwa/perchlorate-drinking-water |date=2024-01-05 |publisher=EPA}}</ref>

==Covalent perchlorates==
Although typically found as a non-coordinating anion, a few [[metal complex]]es are known. [[Hexaperchloratoaluminate]] and [[tetraperchloratoaluminate]] are strong [[oxidising agent]]s.

Several perchlorate esters are known.<ref name=":0">{{Cite journal |last1=Markov |first1=P. O. |last2=Yashin |first2=N. V. |last3=Averina |first3=E. B. |date=2022 |title=Covalent Organic Perchlorates: Synthesis and Properties |url=https://link.springer.com/10.1134/S2634827622600153 |journal=Reviews and Advances in Chemistry |language=en |volume=12 |issue=3 |pages=178–193 |doi=10.1134/S2634827622600153 |s2cid=257355136 |issn=2634-8276|url-access=subscription }}</ref> For example, [[methyl perchlorate]] is a high energy material that is a strong [[alkylating agent]]. [[Chlorine perchlorate]] is a covalent inorganic analog.

==Safety==
As discussed above, iodide is competitor in the thyroid glands.  In the presence of reductants, perchlorate forms potentially explosive mixtures. The [[PEPCON disaster]] destroyed a production plant for [[ammonium perchlorate]] when a fire caused the ammonium perchlorate stored on site to react with the aluminum that the storage tanks were constructed with and explode.

==References==
{{reflist}}

==External links==
* [https://web.archive.org/web/20050907022215/http://lab.nap.edu/nap-cgi/discover.cgi?term=perchlorate&restric=NAP NAS Report: The Health Effects of Perchlorate Ingestion]
* [http://www.nrdc.org/media/pressreleases/050110.asp NRDC's criticism of NAS report]
* [http://environmentcalifornia.org/envirocalif.asp?id2=15344&id3=CE& Environment California report] {{Webarchive|url=https://web.archive.org/web/20100609191142/http://environmentcalifornia.org/envirocalif.asp?id2=15344&id3=CE& |date=2010-06-09 }} (Executive Summary with link to full text)
* [http://www.sciencenews.org/articles/20060812/fob2.asp Macho Moms: Perchlorate pollutant masculinizes fish: Science News Online, August 12, 2006] {{Webarchive|url=https://web.archive.org/web/20080220230204/http://www.sciencenews.org/articles/20060812/fob2.asp |date=February 20, 2008 }}
* [https://www.newscientist.com/blog/space/2008/08/phoenix-discovery-may-be-bad-for-mars.html?DCMP=ILC-hmts&nsref=specrt10_bar New Scientist Space Blog: Phoenix discovery may be bad for Mars life]
* [http://www.yourlawyer.com/practice/news.htm?story_id=5959&topic=Perchlorate State Threatening to Sue Military over Water Pollution] {{Webarchive|url=https://web.archive.org/web/20051109052234/http://yourlawyer.com/practice/news.htm?story_id=5959&topic=Perchlorate |date=2005-11-09 }}, [[Associated Press]], May 19, 2003.
* [http://www.spacedaily.com/news/fuel-02h.html Health Effects of Perchlorate from Spent Rocket], ''SpaceDaily.com'', July 11, 2002.
* [http://www.serdp.org/Research/upload/WP_FS_1280.pdf Dept of Defense, Dept of Energy, and US Environmental Protection Agency's Strategic Environmental Research and Development Program, Elimination of Perchlorate Oxidizers from Pyrotechnic Flare Compositions, 2009] {{Webarchive|url=https://web.archive.org/web/20070806070236/http://www.serdp.org/Research/upload/WP_FS_1280.pdf |date=2007-08-06 }}

{{Perchlorates}}
{{Thyroid therapy}}
{{Thyroid hormone receptor modulators}}

[[Category:Perchlorates| ]]
[[Category:Endocrine disruptors]]
[[Category:Non-coordinating anions]]
[[Category:Oxidizing agents]]
[[Category:Pyrotechnic oxidizers]]