Fluoride: Difference between revisions

| Entropy = 145.58 J/mol K (gaseous)<ref>{{cite journalweb |url=http://webbook.nist.gov/cgi/cbook.cgi?ID=C16984488&Mask=1#Thermo-Gas |title=Fluorine anion |pages=1–1951 |publisher=NIST |access-date=July 4, 2012|year=1998 |last1=Chase |first1=M. W. }}</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>

*[[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>

Most fluoride salts dissolve to give the bifluoride ({{chem|HF|2|-}}) anion. Sources of true F⁻ anions are rare because the highly basic fluoride anion abstracts protons from many, even adventitious, sources. Relative [[solvation|unsolvated]] fluoride, which does exist in aprotic solvents, is called "naked". '''Naked fluoride''' is a strong [[Lewis base]],<ref>{{cite journal |last1=Schwesinger |first1=Reinhard |last2=Link |first2=Reinhard |last3=Wenzl |first3=Peter |last4=Kossek |first4=Sebastian |title=Anhydrous Phosphazenium Fluorides as Sources for Extremely Reactive Fluoride Ions in Solution |journal=Chemistry: A European Journal |volume=12 |issue=2 |pages=438–45 |year=2005 |pmid=16196062 |doi=10.1002/chem.200500838 }}</ref> and a powerful nucleophile. Some quaternary ammonium salts of naked fluoride include [[tetramethylammonium fluoride]] and [[tetrabutylammonium fluoride]].<ref name=dimagno>{{cite journal |author1=Haoran Sun |author2=Stephen G. DiMagno |name-list-style=amp | title= Anhydrous Tetrabutylammonium Fluoride | journal= [[Journal of the American Chemical Society]] | year= 2005 | volume= 127 | pages= 2050–1| doi=10.1021/ja0440497 | pmid= 15713075 | issue= 7}}</ref> [[Cobaltocenium]] fluoride is another example.<ref>{{cite journal |doi=10.1021/ja00103a045|title=Cobaltocenium Fluoride: A Novel Source of "Naked" Fluoride Formed by Carbon-Fluorine Bond Activation in a Saturated Perfluorocarbon|year=1994|last1=Bennett|first1=Brian K.|last2=Harrison|first2=Roger G.|last3=Richmond|first3=Thomas G.|journal=Journal of the American Chemical Society|volume=116|issue=24|pages=11165–11166}}</ref> However, they all lack structural characterization in aprotic solvents. Because of their high basicity, many so-called naked fluoride sources are in fact bifluoride salts. In late 2016 [[imidazolium]] fluoride was synthesized that is the closest approximation of a thermodynamically stable and structurally characterized example of a "naked" fluoride source in an aprotic solvent (acetonitrile).<ref>{{cite journal | last1 = Alič | first1 = B. | last2 = Tavčar | first2 = G. | year = 2016 | title = Reaction of N-heterocyclic carbene (NHC) with different HF sources and ratios – A free fluoride reagent based on imidazolium fluoride | journal = J. Fluorine Chem. | volume = 192 | pages = 141–146 | doi = 10.1016/j.jfluchem.2016.11.004 }}</ref> The sterically demanding imidazolium cation stabilizes the discrete anions and protects them from polymerization.<ref>{{cite journal | last1 = Alič | first1 = B. | last2 = Tramšek | first2 = M. | last3 = Kokalj | first3 = A. | last4 = Tavčar | first4 = G. | year = 2017| title = Discrete GeF5– Anion Structurally Characterized with a Readily Synthesized Imidazolium Based Naked Fluoride Reagent | journal = Inorg. Chem. | volume = 56 | issue = 16| pages = 10070–10077 | doi = 10.1021/acs.inorgchem.7b01606 | pmid = 28792216 }}</ref><ref>{{cite journal | last1 = Zupanek | first1 = Ž. | last2 = Tramšek | first2 = M. | last3 = Kokalj | first3 = A. | last4 = Tavčar | first4 = G. | year = 2018| title = Reactivity of VOF3 with N-Heterocyclic Carbene and Imidazolium Fluoride: Analysis of Ligand–VOF3 Bonding with Evidence of a Minute π Back-Donation of Fluoride | journal = Inorg. Chem. | volume = 57 | issue = 21| pages = 13866–13879 | doi = 10.1021/acs.inorgchem.8b02377 | pmid = 30353729 | s2cid = 53031199 }}</ref>

At physiological pHs, [[hydrogen fluoride]] is usually fully ionised to fluoride. In [[biochemistry]], fluoride and hydrogen fluoride are equivalent. Fluorine, in the form of fluoride, is considered to be a [[micronutrient]] for human health, necessary to prevent dental cavities, and to promote healthy bone growth.<ref name="who.int">{{cite web|last1=Fawell|first1=J. |title=Fluoride in Drinking-water|url=https://www.who.int/water_sanitation_health/dwq/chemicals/fluoride.pdf|publisher=World Health Organization|access-date=10 March 2016}}</ref> The tea plant (''[[Camellia sinensis]]'' L.) is a known accumulator of fluorine compounds, released upon forming infusions such as the common beverage. The fluorine compounds decompose into products including fluoride ions. Fluoride is the most bioavailable form of fluorine, and as such, tea is potentially a vehicle for fluoride dosing.<ref name=Chan2013>{{Cite journal|last=Chan|first=Laura|author2=Mehra, Aradhana |author3=Saikat, Sohel |author4= Lynch, Paul |title=Human exposure assessment of fluoride from tea (''Camellia sinensis'' L.): A UK based issue?|journal=Food Research International|date=May 2013|volume=51|issue=2|pages=564–570|doi=10.1016/j.foodres.2013.01.025}}</ref> Approximately, 50% of absorbed fluoride is excreted renally with a twenty-four-hour period. The remainder can be retained in the oral cavity, and lower digestive tract. Fasting dramatically increases the rate of fluoride absorption to near 100%, from a 60% to 80% when taken with food.<ref name=Chan2013 /> Per a 2013 study, it was found that consumption of one litre of tea a day, can potentially supply the daily recommended intake of 4&nbsp;mg per day. Some lower quality brands can supply up to a 120% of this amount. Fasting can increase this to 150%. The study indicates that tea drinking communities are at an increased risk of [[dental fluorosis|dental]] and [[skeletal fluorosis]], in the case where water fluoridation is in effect.<ref name=Chan2013 /> Fluoride ion in low doses in the mouth reduces tooth decay.<ref>{{Cite web | url=http://oradyne.net/fluoride-free-toothpaste/ | title=Fluoride Free Toothpaste – Fluoride (Finally!) Explained| date=2016-06-27}}</ref> For this reason, it is used in toothpaste and water fluoridation. At much higher doses and frequent exposure, fluoride causes health complications and can be toxic.

Fluoride-containing compounds, such as [[sodium fluoride]] or [[sodium monofluorophosphate]] are used in topical and systemic [[fluoride therapy]] for preventing [[Dental caries|tooth decay]], but the exact biochemical reason is unknown.{{citation needed|date=January 2023}}. They are used for [[water fluoridation]] and in many products associated with [[oral hygiene]].<ref name="mcdonagh2000">{{cite journal|author1=McDonagh M. S. |author2=Whiting P. F. |author3=Wilson P. M. |author4=Sutton A. J. |author5=Chestnutt I. |author6=Cooper J. |author7=Misso K. |author8=Bradley M. |author9=Treasure E. |author10=Kleijnen J. |year=2000 |title=Systematic review of water fluoridation |journal=[[British Medical Journal]] |volume=321 |issue=7265| pages=855–859|doi=10.1136/bmj.321.7265.855 |pmid=11021861|pmc=27492}}</ref> Originally, sodium fluoride was used to fluoridate water; [[hexafluorosilicic acid]] (H₂SiF₆) and its salt [[sodium hexafluorosilicate]] (Na₂SiF₆) are more commonly used additives, especially in the United States. The fluoridation of water is known to prevent tooth decay<ref>{{cite journal |vauthors=Griffin SO, Regnier E, Griffin PM, Huntley V |title=Effectiveness of fluoride in preventing caries in adults |journal=J. Dent. Res. |volume=86 |issue=5 |pages=410–5 |year=2007 |pmid=17452559 |doi=10.1177/154405910708600504|hdl=10945/60693 |s2cid=58958881 |hdl-access=free }}</ref><ref>{{cite journal |author1=Winston A. E. |author2=Bhaskar S. N. |title=Caries prevention in the 21st century |journal=J. Am. Dent. Assoc. |volume=129 |issue=11 |pages=1579–87 |date=1 November 1998 |pmid=9818575 |url=http://jada.ada.org/cgi/pmidlookup?view=long&pmid=9818575 |archive-url=https://archive.today/20120715143950/http://jada.ada.org/cgi/pmidlookup?view=long&pmid=9818575 |url-status=dead |archive-date=15 July 2012 |doi=10.14219/jada.archive.1998.0104 }}</ref> and is considered by the U.S. [[Centers for Disease Control and Prevention]] to be "one of 10 great public health achievements of the 20th century".<ref>{{cite web|title=Community Water Fluoridation|url=https://www.cdc.gov/fluoridation/|publisher=Centers for Disease Control and Prevention|access-date=10 March 2016}}</ref><ref>{{cite web|title=Ten Great Public Health Achievements in the 20th Century|url=https://www.cdc.gov/about/history/tengpha.htm|publisher=Centers for Disease Control and Prevention|access-date=10 March 2016|archive-url=https://web.archive.org/web/20160313072852/http://www.cdc.gov/about/history/tengpha.htm|archive-date=2016-03-13|url-status=dead}}</ref> In some countries where large, centralized water systems are uncommon, fluoride is delivered to the populace by fluoridating table salt. For the method of action for cavity prevention, see [[Fluoride therapy]]. Fluoridation of water has its critics {{crossreference|(see [[waterWater fluoridation controversy]])}}.<ref>{{cite journal |author=Newbrun E |title=The fluoridation war: a scientific dispute or a religious argument? |journal=Journal of Public Health Dentistry |volume=56 |issue=5 Spec No |pages=246–52 |year=1996 |pmid=9034969 |doi=10.1111/j.1752-7325.1996.tb02447.x}}</ref> Fluoridated [[toothpaste]] is in common use. [[Meta-analysis]] show the efficacy of 500 ppm fluoride in toothpastes.<ref>{{Cite journal|last1=Walsh|first1=Tanya|last2=Worthington|first2=Helen V.|last3=Glenny|first3=Anne-Marie|last4=Marinho|first4=Valeria Cc|last5=Jeroncic|first5=Ana|date=March 4, 2019|title=Fluoride toothpastes of different concentrations for preventing dental caries|journal=Cochrane Database of Systematic Reviews|volume=3|issue=3|pages=CD007868|doi=10.1002/14651858.CD007868.pub3|issn=1469-493X|pmc=6398117|pmid=30829399}}</ref><ref>{{Cite web|title=Remineralization of initial carious lesions in deciduous enamel after application of dentifrices of different fluoride concentrations|url=https://www.springermedizin.de/remineralization-of-initial-carious-lesions-in-deciduous-enamel-/8679072|access-date=2021-02-24|website=springermedizin.de|language=de}}</ref> However, no beneficial effect can be detected when more than one fluoride source is used for daily oral care.<ref>{{Cite journal|last1=Hausen|first1=H.|last2=Kärkkäinen|first2=S.|last3=Seppä|first3=L.|date=February 2000|title=Application of the high-risk strategy to control dental caries|url=https://pubmed.ncbi.nlm.nih.gov/10634681/|journal=Community Dentistry and Oral Epidemiology|volume=28|issue=1|pages=26–34|doi=10.1034/j.1600-0528.2000.280104.x|issn=0301-5661|pmid=10634681}}</ref>{{request quotation|date=August 2021}}

The [[European Food Safety Authority]] (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL are defined the same as in the United States. For women ages 18 and older the AI is set at 2.9&nbsp;mg/day (includesincluding pregnancy and lactation). For men, the value is 3.4&nbsp;mg/day. For children ages 1–17 years, the AIs increase with age from 0.6 to 3.2&nbsp;mg/day. These AIs are comparable to the U.S. AIs.<ref>{{cite web | title = Overview on Dietary Reference Values for the EU population as derived by the EFSA Panel on Dietetic Products, Nutrition and Allergies| year = 2017| url = https://www.efsa.europa.eu/sites/default/files/assets/DRV_Summary_tables_jan_17.pdf}}</ref> The EFSA reviewed safety evidence and set an adult UL at 7.0&nbsp;mg/day (lower for children).<ref name="EFSAtext">{{citation| title = Tolerable Upper Intake Levels For Vitamins And Minerals| publisher = European Food Safety Authority| year = 2006| url = http://www.efsa.europa.eu/sites/default/files/efsa_rep/blobserver_assets/ndatolerableuil.pdf}}</ref>

For U.S. food and dietary supplement labeling purposes, the amount of a vitamin or mineral in a serving is expressed as a percent of Daily Value (%DV). Although there is information to set Adequate Intake, fluoride does not have a Daily Value and is not required to be shown on food labels.<ref name="FedReg">{{cite web|url=https://www.gpo.gov/fdsys/pkg/FR-2016-05-27/pdf/2016-11867.pdf |title=Federal Register May 27, 2016 Food Labeling: Revision of the Nutrition and Supplement Facts Labels. FR page 33982.}}</ref>

In the higher doses used to treat [[osteoporosis]], sodium fluoride can cause pain in the legs and incomplete stress fractures when the doses are too high; it also irritates the stomach, sometimes so severely as to cause ulcers. Slow-release and [[enteric]]-coated versions of sodium fluoride do not have gastric side effects in any significant way, and have milder and less frequent complications in the bones.<ref>{{cite journal |vauthors=Murray TM, Ste-Marie LG |title=Prevention and management of osteoporosis: consensus statements from the Scientific Advisory Board of the Osteoporosis Society of Canada. 7. Fluoride therapy for osteoporosis |journal=CMAJ |volume=155 |issue=7 |pages=949–54 |year=1996 |pmid=8837545 |pmc=1335460}}</ref> In the lower doses used for [[water fluoridation]], the only clear adverse effect is [[dental fluorosis]], which can alter the appearance of children's teeth during [[Human tooth development|tooth development]]; this is mostly mild and is unlikely to represent any real effect on aesthetic appearance or on public health.<ref>{{cite book |url=http://nhmrc.gov.au/_files_nhmrc/file/publications/synopses/Eh41_Flouridation_PART_A.pdf |year=2007 |title=A systematic review of the efficacy and safety of fluoridation |author=National Health and Medical Research Council (Australia) |isbn=978-1-86496-415-8 |access-date=2010-02-21 |archive-url=https://web.archive.org/web/20091014191758/http://www.nhmrc.gov.au/_files_nhmrc/file/publications/synopses/Eh41_Flouridation_PART_A.pdf |archive-date=2009-10-14 |url-status=dead }} Summary: {{cite journal |author= Yeung CA |title= A systematic review of the efficacy and safety of fluoridation |journal= Evid.-Based Dent. |volume=9 |issue=2 |pages=39–43 |year=2008 |pmid=18584000 |doi=10.1038/sj.ebd.6400578 |doi-access=free }}</ref> Fluoride was known to enhance the measurement of bone mineral density at the lumbar spine, but it was not effective for vertebral fractures and provoked more non vertebralnonvertebral fractures.<ref>{{cite journal|last=Haguenauer|first=D|author2=Welch, V |author3=Shea, B |author4=Tugwell, P |author5=Adachi, JD |author6= Wells, G |title=Fluoride for the treatment of postmenopausal osteoporotic fractures: a meta-analysis.|journal=Osteoporosis International |date=2000|volume=11|issue=9|pages=727–38|pmid=11148800 |doi=10.1007/s001980070051|s2cid=538666}}</ref> In areas that have naturally occurring high levels of fluoride in [[groundwater]] which is used for [[drinking water]], both [[dental fluorosis|dental]] and [[skeletal fluorosis]] can be prevalent and severe.<ref>{{cite journalweb |author=World Health Organization |year=2004 |title=Fluoride in drinking-water |url=https://www.who.int/water_sanitation_health/dwq/chemicals/en/fluoride.pdf |url-status=dead |archive-url=https://web.archive.org/web/20160304082148/http://www.who.int/water_sanitation_health/dwq/chemicals/en/fluoride.pdf |archive-date=2016-03-04 |access-date=2014-02-13}}</ref>

Around one-third of the human population drinks water from groundwater resources. Of this, about 10%, approximately three hundred300 million people, obtain water from groundwater resources that are heavily contaminated with arsenic or fluoride.<ref>Eawag (2015) Geogenic Contamination Handbook – Addressing Arsenic and Fluoride in Drinking Water. C.A. Johnson, A. Bretzler (Eds.), Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland. (download: www.eawag.ch/en/research/humanwelfare/drinkingwater/wrq/geogenic-contamination-handbook/)</ref> These trace elements derive mainly from minerals.<ref>{{cite journal | last1 = Rodríguez-Lado | first1 = L. | last2 = Sun | first2 = G. | last3 = Berg | first3 = M. | last4 = Zhang | first4 = Q. | last5 = Xue | first5 = H. | last6 = Zheng | first6 = Q. | last7 = Johnson | first7 = C.A. | year = 2013 | title = Groundwater arsenic contamination throughout China | url = https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A7346| journal = Science | volume = 341 | issue = 6148| pages = 866–868 | doi = 10.1126/science.1237484 | pmid = 23970694 | bibcode = 2013Sci...341..866R | s2cid = 206548777 }}</ref> Maps locating potential problematic wells are available.<ref>[http://www.gapmaps.org Groundwater Assessment Platform]</ref>