Editing Fluoride (section)

==Occurrence==
[[File:Calcite sur fluorine (USA) 1.JPG|right|thumb|Fluorite crystals]]
[[Fluorine]] is estimated to be the 13th-most [[Abundance of elements in Earth's crust|abundant element]] in Earth's crust and is widely dispersed in nature, entirely in the form of fluorides. The vast majority is held in [[:Category:Fluorine minerals|mineral deposits]], the most commercially important of which is [[fluorite]] (CaF<sub>2</sub>).<ref name=Aigueperse/> Natural weathering of some kinds of rocks,<ref>{{cite journal |last1=Derakhshani |first1=R |last2=Raoof |first2=A |last3=Mahvi |first3=AH |last4=Chatrouz |first4=H |title=Similarities in the Fingerprints of Coal Mining Activities, High Ground Water Fluoride, and Dental Fluorosis in Zarand District, Kerman Province, Iran |journal=Fluoride |date=2020 |volume=53 |issue=2 |pages=257–267}}</ref><ref>{{cite journal |last1=Derakhshani |first1=R |last2=Tavallaie |first2=M |last3=Malek Mohammad |first3=T |last4=Abbasnejad |first4=A |last5=Haghdoost |first5=A |title=Occurrence of fluoride in groundwater of Zarand region, Kerman province, Iran |journal=Fluoride |date=2014 |volume=47 |issue=2 |pages=133–138}}</ref> as well as human activities, releases fluorides into the [[biosphere]] through what is sometimes called the [[fluorine cycle]].

===In water===
Fluoride is naturally present in groundwater, [[Fresh water|fresh]] and [[Saline water|saltwater]] sources, as well as in rainwater, particularly in urban areas exposed to air pollution.<ref>{{cite web |url= https://www.atsdr.cdc.gov/phs/phs.asp?id=210&tid=38 |title= Public Health Statement for Fluorides, Hydrogen Fluoride, and Fluorine |publisher= [[ATSDR]] |date= September 2003 }}</ref> Seawater fluoride levels are usually in the range of 0.86 to 1.4&nbsp;mg/L, and average 1.1&nbsp;mg/L<ref>{{cite web|url=http://www.env.gov.bc.ca/wat/wq/BCguidelines/fluoride/fluoridetoo-01.html|title=Ambient Water Quality Criteria for Fluoride|publisher=Government of British Columbia|access-date=8 October 2014|archive-date=24 September 2015|archive-url=https://web.archive.org/web/20150924035152/http://www.env.gov.bc.ca/wat/wq/BCguidelines/fluoride/fluoridetoo-01.html|url-status=dead}}</ref> (milligrams per [[litre]]). For comparison, [[chloride]] concentration in seawater is about 19&nbsp;g/L. The low concentration of fluoride reflects the insolubility of the [[Alkaline earth metal|alkaline earth]] fluorides, e.g., CaF<sub>2</sub>.

Concentrations in fresh water vary more significantly. [[Surface water]] such as rivers or lakes generally contains between 0.01 and 0.3&nbsp;mg/L.<ref>{{cite book|last1=Liteplo|first1=Dr R.|last2=Gomes|first2=R.|last3=Howe|first3=P.|last4=Malcolm|first4=Heath|title=FLUORIDES - Environmental Health Criteria 227 : 1st draft|date=2002|publisher=World Health Organization|location=Geneva|isbn=978-9241572279|url=http://www.inchem.org/documents/ehc/ehc/ehc227.htm#1.4}}</ref> [[Groundwater]] (well water) concentrations vary even more, depending on the presence of local fluoride-containing minerals. For example, natural levels of under 0.05&nbsp;mg/L have been detected in parts of Canada but up to 8&nbsp;mg/L in parts of China; in general levels rarely exceed 10&nbsp;mg/litre<ref name=Fawell>{{cite web|author1=Fawell, J.K.|title=Fluoride in Drinking-water Background document for development of WHO Guidelines for Drinking-water Quality|url=https://www.who.int/water_sanitation_health/dwq/chemicals/fluoride.pdf|publisher=World Health Organization|access-date=6 May 2016|ref=WHO/SDE/WSH/03.04/96|language=en|display-authors=etal}}</ref> 
* In parts of Asia the groundwater can contain dangerously high levels of fluoride, leading to serious [[Fluoride toxicity#Chronic toxicity|health problems]].<ref>{{cite journal |last1=Yadav |first1=Krishna Kumar |last2=Kumar |first2=Sandeep |last3=Pham |first3=Quoc Bao |last4=Gupta |first4=Neha |last5=Rezania |first5=Shahabaldin |last6=Kamyab |first6=Hesam |last7=Yadav |first7=Shalini |last8=Vymazal |first8=Jan |last9=Kumar |first9=Vinit |last10=Tri |first10=Doan Quang |last11=Talaiekhozani |first11=Amirreza |last12=Prasad |first12=Shiv |last13=Reece |first13=Lisa M. |last14=Singh |first14=Neeraja |last15=Maurya |first15=Pradip Kumar |last16=Cho |first16=Jinwoo |title=Fluoride contamination, health problems and remediation methods in Asian groundwater: A comprehensive review |journal=Ecotoxicology and Environmental Safety |date=October 2019 |volume=182 |pages=109362 |doi=10.1016/j.ecoenv.2019.06.045|pmid=31254856 |bibcode=2019EcoES.18209362Y |s2cid=195764865 }}</ref> 
* Worldwide, 50 million people receive water from water supplies that naturally have close to the "optimal level".<ref>{{cite web|last1=Tiemann|first1=Mary|title=Fluoride in Drinking Water: A Review of Fluoridation and Regulation Issues|url=https://www.fas.org/sgp/crs/misc/RL33280.pdf|publisher=Congressional Research Service|access-date=6 May 2016|ref=7-5700 www.crs.gov RL33280|page=3|date=April 5, 2013}}</ref>
* In other locations the level of fluoride is very low, sometimes leading to [[Water fluoridation|fluoridation]] of public water supplies to bring the level to around 0.7–1.2 ppm.
*[[Mining]] can increase local fluoride levels<ref>{{cite journal |last1=Chandio |first1=Tasawar Ali |last2=Khan |first2=Muhammad Nasiruddin |last3=Muhammad |first3=Maria Taj |last4=Yalcinkaya |first4=Ozcan |last5=Wasim |first5=Agha Arslan |last6=Kayis |first6=Ahmet Furkan |title=Fluoride and arsenic contamination in drinking water due to mining activities and its impact on local area population |journal=Environmental Science and Pollution Research |date=January 2021 |volume=28 |issue=2 |pages=2355–2368 |doi=10.1007/s11356-020-10575-9|pmid=32880840 |bibcode=2021ESPR...28.2355C |s2cid=221463681 }}</ref>

Fluoride can be present in rain, with its concentration increasing significantly upon exposure to volcanic activity<ref>{{cite journal |last1=Bellomo |first1=Sergio |last2=Aiuppa |first2=Alessandro |last3=D’Alessandro |first3=Walter |last4=Parello |first4=Francesco |title=Environmental impact of magmatic fluorine emission in the Mt. Etna area |journal=Journal of Volcanology and Geothermal Research |date=August 2007 |volume=165 |issue=1–2 |pages=87–101 |doi=10.1016/j.jvolgeores.2007.04.013|bibcode=2007JVGR..165...87B }}</ref> or atmospheric pollution derived from burning fossil fuels or other sorts of industry,<ref>{{cite journal|last1=Smith|first1=Frank A.|last2=Hodge|first2=Harold C.|last3=Dinman|first3=B. D.|title=Airborne fluorides and man: Part I|journal=CRC Critical Reviews in Environmental Control|date=9 January 2009|volume=8|issue=1–4|pages=293–371|doi=10.1080/10643387709381665}}</ref><ref>{{cite journal|last1=Smith|first1=Frank A.|last2=Hodge|first2=Harold C.|last3=Dinman|first3=B. D.|title=Airborne fluorides and man: Part II|journal=CRC Critical Reviews in Environmental Control|date=9 January 2009|volume=9|issue=1|pages=1–25|doi=10.1080/10643387909381666}}</ref> particularly [[aluminium smelter]]s.<ref>{{cite journal |last1=Arnesen |first1=A.K.M. |last2=Abrahamsen |first2=G. |last3=Sandvik |first3=G. |last4=Krogstad |first4=T. |title=Aluminium-smelters and fluoride pollution of soil and soil solution in Norway |journal=Science of the Total Environment |date=February 1995 |volume=163 |issue=1–3 |pages=39–53 |doi=10.1016/0048-9697(95)04479-K|bibcode=1995ScTEn.163...39A }}</ref>

===In plants===
All vegetation contains some fluoride, which is absorbed from soil and water.<ref name=Fawell /> Some plants concentrate fluoride from their environment more than others. All tea leaves contain fluoride; however, mature leaves contain as much as 10 to 20 times the fluoride levels of young leaves from the same plant.<ref>{{cite journal |vauthors=Wong MH, Fung KF, Carr HP |title=Aluminium and fluoride contents of tea, with emphasis on brick tea and their health implications |journal=Toxicology Letters |volume=137 |issue=1–2 |pages=111–20 |year=2003 |pmid=12505437 |doi=10.1016/S0378-4274(02)00385-5 }}</ref><ref name="pmid18078704">{{cite journal |vauthors=Malinowska E, Inkielewicz I, Czarnowski W, Szefer P |title=Assessment of fluoride concentration and daily intake by human from tea and herbal infusions |journal=Food Chem. Toxicol. |volume=46 |issue=3 |pages=1055–61 |year=2008 |pmid=18078704 |doi=10.1016/j.fct.2007.10.039}}</ref><ref>{{cite journal |vauthors=Gardner EJ, Ruxton CH, Leeds AR |title=Black tea&mdash;helpful or harmful? A review of the evidence |journal=European Journal of Clinical Nutrition |volume=61 |issue=1 |pages=3–18 |year=2007 |pmid=16855537 |doi=10.1038/sj.ejcn.1602489 |doi-access= }}</ref>