Editing Perchlorate (section)

==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>