Editing Chloride (section)

==Occurrence in nature==
In nature, chloride is found primarily in seawater, which has a chloride ion concentration of 19400&nbsp;mg/liter.<ref>{{Cite web|title=Chloride and Salinity|url=https://www.ldeo.columbia.edu/edu/k12/snapshotday/activities/2011/Classroom%20HS%20activity/chloride%20conversion/Chloride%20and%20Salinity.pdf|date=8 September 2011|access-date=8 January 2023|website=colombia.edu}}</ref> Smaller quantities, though at higher concentrations, occur in certain inland seas and in subterranean [[brine well]]s, such as the [[Great Salt Lake]] in [[Utah]] and the [[Dead Sea]] in Israel.<ref>{{cite book |last1=Greenwood |first1=N. N. |title=Chemistry of the elements |date=1984 |publisher=Pergamon Press |location=Oxford [Oxfordshire] |isbn=9780750628327 |edition=1st}}</ref> 
Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground. Some chloride-containing minerals include [[halite]] (sodium chloride [[NaCl]]), [[sylvite]] (potassium chloride [[KCl]]), [[bischofite]] (MgCl<sub>2</sub>∙6H<sub>2</sub>O), [[carnallite]] (KCl∙MgCl<sub>2</sub>∙6H<sub>2</sub>O), and [[kainite]] (KCl∙MgSO<sub>4</sub>∙3H<sub>2</sub>O). It is also found in evaporite minerals such as [[chlorapatite]] and [[sodalite]].

===Role in biology===
Chloride has a major physiological significance,<ref>{{Cite journal|title=Chloride ions in health and disease|journal=Bioscience Reports|last1=Raut|first1=Satish|volume=44|issue=5|doi=10.1042/BSR20240029
|year=2024|at=BSR20240029|language=en|pmc=11065649|pmid=38573803}}</ref> which includes regulation of [[osmotic pressure]], electrolyte balance and acid-base homeostasis. Chloride is present in all [[body fluid]]s,<ref>{{Cite journal|title=The distribution of total body chloride in man|journal=Journal of Clinical Investigation|last1=Deane|first1=Norman|volume=31|last2=Ziff|first2=Morris|issue=2|doi=10.1172/JCI102592|year=1952|at=p. 201, Table 1|language=en|pmc=436401|pmid=14907900|last3=Smith|first3=Homer W.}}</ref> and is the most abundant extracellular [[anion]] which accounts for around one third of [[extracellular fluid]]'s [[tonicity]].<ref>{{cite journal |last1=Berend |first1=Kenrick |last2=van Hulsteijn |first2=Leonard Hendrik |last3=Gans |first3=Rijk O.B. |title=Chloride: The queen of electrolytes? |journal=European Journal of Internal Medicine |date=April 2012 |volume=23 |issue=3 |pages=203–211 |doi=10.1016/j.ejim.2011.11.013 |pmid=22385875}}</ref><ref>{{cite journal |last1=Rein |first1=Joshua L. |last2=Coca |first2=Steven G. |title="I don't get no respect": the role of chloride in acute kidney injury |journal=American Journal of Physiology. Renal Physiology |date=1 March 2019 |volume=316 |issue=3 |pages=F587–F605 |doi=10.1152/ajprenal.00130.2018 |pmid=30539650 |issn=1931-857X |pmc=6459301}}</ref>

Chloride is an essential [[Electrolyte#Physiological importance|electrolyte]], playing a key role in maintaining cell [[Homeostasis#Overview|homeostasis]] and transmitting [[action potentials]] in neurons.<ref>{{cite journal |title=Molecular Structure and Physiological Function of Chloride Channels |url=http://physrev.physiology.org/content/82/2/503 |journal=Physiological Reviews |date=2002-04-01 |issn=0031-9333 |pmid=11917096 |pages=503–568 |volume=82 |issue=2 |doi=10.1152/physrev.00029.2001 |first1=Thomas J. |last1=Jentsch |first2=Valentin |last2=Stein |first3=Frank |last3=Weinreich |first4=Anselm A. |last4=Zdebik}}</ref> It can flow through [[chloride channels]] (including the [[GABAA|GABA<sub>A</sub>]] receptor) and is transported by [[KCC2]] and [[NKCC2]] transporters.

Chloride is usually (though not always) at a higher extracellular concentration, causing it to have a negative [[reversal potential]] (around −61&nbsp;mV at 37&nbsp;°C in a mammalian cell).<ref>{{cite web |title=Equilibrium potentials |url=http://www.d.umn.edu/~jfitzake/Lectures/DMED/IonChannelPhysiology/MembranePotentials/EquilibriumPotentials.html |website=www.d.umn.edu}}</ref> Characteristic concentrations of chloride in model organisms are: in both ''E. coli'' and budding yeast are 10–200&nbsp;[[molar concentration|mM]] (dependent on medium), in mammalian cells 5–100&nbsp;mM and in [[blood plasma]] 100&nbsp;mM.<ref>{{cite web|url = http://book.bionumbers.org/what-are-the-concentrations-of-different-ions-in-cells/|title =Cell Biology by the Numbers: What are the concentrations of different ions in cells? |website =book.bionumbers.org|first1= Ron|last1= Milo|first2= Rob |last2=Philips|access-date=24 March 2017}}</ref>

Chloride is also needed for the production of [[hydrochloric acid]] in the stomach.<ref>{{cite web|url=http://www.med.umich.edu/1libr/aha/aha_schlorid_crs.htm |access-date=30 April 2010 |url-status=dead |archive-url=https://web.archive.org/web/20090331211149/http://med.umich.edu/1libr/aha/aha_schlorid_crs.htm |archive-date=31 March 2009 |title=Blood (Serum) Chloride Level Test}}</ref>

The concentration of chloride in the blood is called [[serum chloride]], and this concentration is regulated by the [[kidneys]]. A chloride ion is a structural component of some proteins; for example, it is present in the [[amylase]] enzyme. For these roles, chloride is one of the essential [[dietary mineral]]s (listed by its element name ''chlorine''). [[Serum (blood)|Serum]] chloride levels are mainly regulated by the kidneys through a variety of transporters that are present along the [[nephron]].<ref>{{cite journal |last1=Nagami |first1=Glenn T. |title=Hyperchloremia – Why and how |journal=Nefrología (English Edition) |date=1 July 2016 |volume=36 |issue=4 |pages=347–353 |doi=10.1016/j.nefro.2016.04.001 |pmid=27267918 |url=https://www.revistanefrologia.com/en-hyperchloremia-why-how-articulo-S021169951630025X |language=en |issn=2013-2514|doi-access=free }}</ref> Most of the chloride, which is filtered by the [[Glomerulus (kidney)|glomerulus]], is reabsorbed by both [[Proximal tubule|proximal]] and [[distal tubule]]s (majorly by proximal tubule) by both active and passive transport.<ref>{{cite journal |last1=Shrimanker |first1=Isha |last2=Bhattarai |first2=Sandeep |title=Electrolytes |url=https://pubmed.ncbi.nlm.nih.gov/31082167/ |website=StatPearls |publisher=StatPearls Publishing |date=2020|pmid=31082167 }}</ref>

===Corrosion===
[[Image:NaCl polyhedra.png|thumb|right|The structure of sodium chloride, revealing the tendency of chloride ions (green spheres<!--even though both spheres are equiv-->) to link to several cations.]]
The presence of chlorides, such as in seawater, significantly worsens the conditions for [[pitting corrosion]] of most metals (including stainless steels, aluminum and high-alloyed materials). Chloride-induced corrosion of steel in concrete leads to a local breakdown of the protective oxide form in alkaline concrete, so that a subsequent localized corrosion attack takes place.<ref>{{cite book |last1=Criado |first1=M. |title=Handbook of Alkali-Activated Cements, Mortars and Concretes |publisher=Woodhead Publishing |isbn=978-1-78242-276-1 |pages=333–372 |chapter-url=https://www.sciencedirect.com/science/article/pii/B9781782422761500137 |language=en |chapter=13. The corrosion behaviour of reinforced steel embedded in alkali-activated mortar|date=January 2015 |doi=10.1533/9781782422884.3.333 }}</ref>

===Environmental threats===
Increased concentrations of chloride can cause a number of ecological effects in both aquatic and terrestrial environments. It may contribute to the acidification of streams, mobilize radioactive soil metals by ion exchange, affect the mortality and reproduction of aquatic plants and animals, promote the invasion of saltwater organisms into previously freshwater environments, and interfere with the natural mixing of lakes. Sodium chloride has been shown to change the composition of microbial species at relatively low concentrations, hinder the [[denitrification]] process, a microbial process essential to [[nitrate]] removal and the conservation of water quality, and inhibit the [[nitrification]] and respiration of organic matter.<ref>{{cite book |last1=Kaushal |first1=S. S. |title=Encyclopedia of Inland Waters |publisher=Academic Press |isbn=978-0-12-370626-3 |pages=23–29 |language=en |chapter=Chloride|date=19 March 2009 }}</ref>