Editing Thorium (section)

==Hazards and health effects==
[[File:PSM V74 D233 Thorium radioactive incandescent gas mantle placed above plant seeds.png|thumb|alt=Thorium mantle installed over a small sprout of grass|Experiment on the effect of radiation (from an unburned thorium gas mantle) on the germination and growth of [[timothy-grass]] seed]]

===Radiological===

Natural thorium decays very slowly compared to many other radioactive materials, and the emitted [[alpha radiation]] cannot penetrate human skin. As a result, handling small amounts of thorium, such as those in gas mantles, is considered safe, although the use of such items may pose some risks.<ref name="epa">{{cite web|title=Thorium: Radiation Protection|date=August 2000 |url=http://www.epa.gov/radiation/radionuclides/thorium.html|archive-url=https://web.archive.org/web/20061001225000/http://www.epa.gov/radiation/radionuclides/thorium.htm|publisher=United States Environmental Protection Agency|access-date=27 February 2016|archive-date=1 October 2006}}</ref> Exposure to an aerosol of thorium, such as contaminated dust, can lead to increased risk of [[cancer]]s of the [[lung]], [[pancreas]], and [[blood]], as lungs and other internal organs can be penetrated by alpha radiation.<ref name="epa" /> Internal exposure to thorium leads to increased risk of [[liver]] diseases.<ref name="arpansa" />

The decay products of <sup>232</sup>Th include more dangerous radionuclides such as radium and radon. Although relatively little of those products are created as the result of the slow decay of thorium, a proper assessment of the radiological toxicity of <sup>232</sup>Th must include the contribution of its daughters, some of which are dangerous [[gamma radiation|gamma]] emitters,<ref>{{cite web|url=http://gonuke.org/ComprehensiveTeachingToolkits/Radiation%20Protection/ChSCC_RP/Columbia%20Basin%20RPT-111/Supplementary%20materials/natural-decay-series.pdf |title=Natural Decay Series: Uranium, Radium, and Thorium |publisher=Argonne National Laboratory |year=2005 |archive-url=https://web.archive.org/web/20160817010031/http://gonuke.org/ComprehensiveTeachingToolkits/Radiation%20Protection/ChSCC_RP/Columbia%20Basin%20RPT-111/Supplementary%20materials/natural-decay-series.pdf |archive-date=17 August 2016 |access-date=30 September 2017}}</ref> and which are built up quickly following the initial decay of <sup>232</sup>Th due to the absence of long-lived nuclides along the decay chain.{{sfn|Stoll|2005|p=35}} As the dangerous daughters of thorium have much lower melting points than thorium dioxide, they are volatilised every time the mantle is heated for use. In the first hour of use large fractions of the thorium daughters <sup>224</sup>Ra, <sup>228</sup>Ra, <sup>212</sup>Pb, and <sup>212</sup>Bi are released.<ref>{{cite journal |title=Radioactivity released from burning gas lantern mantles |first1=J. W. |last1=Luetzelschwab |first2=S. W. |last2=Googins |date=1984 |journal=Health Phys. |volume=46 |issue=4 |pages=873–881 |pmid=6706595 |doi=10.1097/00004032-198404000-00013|bibcode=1984HeaPh..46..873L }}</ref> Most of the radiation dose by a normal user arises from inhaling the radium, resulting in a radiation dose of up to 0.2&nbsp;[[sievert|millisieverts]] per use, about a third of the dose sustained during a [[mammogram]].<ref>{{cite journal |last1=Huyskens |first1=C. J. |last2=Hemelaar |first2=J. T. |last3=Kicken |first3=P. J. |date=1985 |title=Dose estimates for exposure to radioactivity in gas mantles |journal=Sci. Total Environ. |volume=45 |pages=157–164 |pmid=4081711|bibcode=1985ScTEn..45..157H |doi=10.1016/0048-9697(85)90216-5 |s2cid=39901914 |url=https://research.tue.nl/nl/publications/dose-estimates-for-exposure-to-radioactivity-in-gas-mantles(0c586a27-db9f-44ac-b8a8-ef94155f9c6a).html }}</ref>

Some [[nuclear safety]] agencies make recommendations about the use of thorium mantles and have raised safety concerns regarding their [[Gas mantle#Safety concerns|manufacture]] and disposal; the radiation dose from one mantle is not a serious problem, but that from many mantles gathered together in factories or landfills is.<ref name="arpansa">{{cite web|archive-url=https://web.archive.org/web/20071014211034/http://arpansa.gov.au/RadiationProtection/Factsheets/is_lantern.cfm |url=http://arpansa.gov.au/RadiationProtection/Factsheets/is_lantern.cfm |title=Radioactivity in Lantern Mantles |publisher=[[Australian Radiation Protection and Nuclear Safety Agency]] |archive-date=14 October 2007 |access-date=29 September 2017}}</ref>

===Biological===
Thorium is odourless and tasteless.<ref>{{cite web|url=https://www.atsdr.cdc.gov/toxprofiles/tp147.pdf|title=Toxicological Profile for Thorium|publisher=Agency for Toxic Substances and Disease Registry U.S. Public Health Service|date=1990|page=4|access-date=5 September 2016|archive-date=21 October 2004|archive-url=https://web.archive.org/web/20041021114032/https://www.atsdr.cdc.gov/toxprofiles/tp147.pdf|url-status=live}}</ref> The chemical toxicity of thorium is low because thorium and its most common compounds (mostly the dioxide) are poorly soluble in water,<ref name="Schneckenstein">{{cite report|last1=Merkel |first1=B. |last2=Dudel |first2=G. |display-authors=etal |year=1988 |archive-url=https://web.archive.org/web/20130108094057/http://www.geo.tu-freiberg.de/~merkel/schneckenstein.PDF |archive-date=8 January 2013 |url=http://www.geo.tu-freiberg.de/~merkel/schneckenstein.PDF |title=Untersuchungen zur radiologischen Emission des Uran-Tailings Schneckenstein |publisher=Sächsisches Staatsministerium für Umwelt und Landesentwicklung |language=de}}</ref> precipitating out before entering the body as the hydroxide.{{sfn|Stoll|2005|p=34}} Some thorium compounds are chemically moderately [[toxic]], especially in the presence of strong complex-forming ions such as citrate that carry the thorium into the body in soluble form.{{sfn|Stoll|2005|p=35}} If a thorium-containing object has been chewed or sucked, it loses 0.4% of thorium and 90% of its dangerous daughters to the body.<ref name="Poljanc" /> Three-quarters of the thorium that has penetrated the body accumulates in the [[skeleton]]. Absorption through the skin is possible, but is not a likely means of exposure.<ref name="epa" /> Thorium's low solubility in water also means that excretion of thorium by the kidneys and faeces is rather slow.{{sfn|Stoll|2005|p=35}}

Tests on the thorium uptake of workers involved in monazite processing showed thorium levels above recommended limits in their bodies, but no adverse effects on health were found at those moderately low concentrations. No chemical toxicity has yet been observed in the [[tracheobronchial tract]] and the lungs from exposure to thorium.{{sfn|Stoll|2005|p=34}} People who work with thorium compounds are at a risk of [[dermatitis]]. It can take as much as thirty years after the ingestion of thorium for symptoms to manifest themselves.<ref name="Emsley2011" /> Thorium has no known biological role.<ref name="Emsley2011" />

===Chemical===
Powdered thorium metal is pyrophoric: it ignites spontaneously in air.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}} In 1964, the [[United States Department of the Interior]] listed thorium as "severe" on a table entitled "Ignition and explosibility of metal powders". Its ignition temperature was given as 270&nbsp;°C (520&nbsp;°F) for dust clouds and 280&nbsp;°C (535&nbsp;°F) for layers. Its minimum explosive concentration was listed as 0.075&nbsp;oz/cu ft (0.075&nbsp;kg/m<sup>3</sup>); the minimum igniting energy for (non-submicron) dust was listed as 5&nbsp;[[Joule|mJ]].<ref>{{cite report|url=http://apps.dtic.mil/dtic/tr/fulltext/u2/b270510.pdf|archive-url=https://web.archive.org/web/20160803175920/http://www.dtic.mil/dtic/tr/fulltext/u2/b270510.pdf|url-status=live|archive-date=3 August 2016|title=Explosibility of metal powders|first1=M. |last1=Jacobson |first2=A. R. |last2=Cooper |first3=J. |last3=Nagy |publisher=[[United States Department of the Interior]] |year=1964 |access-date=29 September 2017}}</ref>

In 1956, the [[Sylvania Electric Products explosion]] occurred during reprocessing and burning of thorium sludge in [[New York City]], United States. Nine people were injured; one died of complications caused by [[third-degree burns]].<ref name="AP">{{cite news |agency=Associated Press |url=https://news.google.com/newspapers?nid=1129&dat=19560703&id=eSgNAAAAIBAJ&sjid=BmwDAAAAIBAJ&pg=4985,347025 |title=Nine Injured in Atomic Lab Blasts |newspaper=[[Pittsburgh Post-Gazette]] |year=1956 |page=2 |access-date=29 September 2017 |archive-date=16 March 2020 |archive-url=https://web.archive.org/web/20200316201104/https://news.google.com/newspapers?nid=1129&dat=19560703&id=eSgNAAAAIBAJ&sjid=BmwDAAAAIBAJ&pg=4985%2C347025 |url-status=live }}</ref><ref>{{cite news |agency=Associated Press |url=https://news.google.com/newspapers?nid=888&dat=19560703&id=n6RSAAAAIBAJ&sjid=M3YDAAAAIBAJ&pg=7412,1311234 |title=No Radiation Threat Seen in A-laboratory Blast |newspaper=[[The St. Petersburg Times (Russia)|The St. Petersburg Times]] |date=1956 |page=2 |access-date=29 September 2017 |archive-date=16 March 2020 |archive-url=https://web.archive.org/web/20200316213830/https://news.google.com/newspapers?nid=888&dat=19560703&id=n6RSAAAAIBAJ&sjid=M3YDAAAAIBAJ&pg=7412%2C1311234 |url-status=live }}</ref><ref name="Newsday">{{cite news|last=Harrington|first=M.|url=http://www.newsday.com/columnists/glenn-gamboa/2.1091/sad-memories-of-56-sylvania-explosion-1.451270|title=Sad Memories of '56 Sylvania Explosion|work=[[New York Newsday]]|date=2003|archive-url=https://web.archive.org/web/20120204183944/http://www.newsday.com/columnists/glenn-gamboa/2.1091/sad-memories-of-56-sylvania-explosion-1.451270|archive-date=4 February 2012|access-date=29 September 2017}}</ref>

===Exposure routes===
Thorium exists in very small quantities everywhere on Earth although larger amounts exist in certain parts: the average human contains about 40&nbsp;[[microgram]]s of thorium and typically consumes three micrograms per day.<ref name="Emsley2011" /> Most thorium exposure occurs through dust inhalation; some thorium comes with food and water, but because of its low solubility, this exposure is negligible.{{sfn|Stoll|2005|p=35}}

Exposure is raised for people who live near thorium deposits or radioactive waste disposal sites, those who live near or work in uranium, phosphate, or tin processing factories, and for those who work in gas mantle production.<ref name="ATSDR">{{cite web |url=http://www.atsdr.cdc.gov/toxfaqs/tfacts147.pdf |title=Thorium ToxFAQs |publisher=[[Agency for Toxic Substances and Disease Registry]] |access-date=29 September 2017 |archive-date=5 June 2012 |archive-url=https://web.archive.org/web/20120605122824/http://www.atsdr.cdc.gov/toxfaqs/tfacts147.pdf |url-status=live }}</ref> Thorium is especially common in the [[Tamil Nadu]] coastal areas of India, where residents may be exposed to a naturally occurring radiation dose ten times higher than the worldwide average.<ref>{{cite web |url=http://www.dae.gov.in/iandm/minesback.htm |title=Compendium of Policy And Statutory Provisions Relating To Exploitation of Beach Sand Minerals |publisher=Department of Atomic Energy |access-date=19 December 2008 |archive-url=https://web.archive.org/web/20081204114125/http://www.dae.gov.in/iandm/minesback.htm |archive-date=4 December 2008 }}</ref> It is also common in northern [[Brazil]]ian coastal areas, from south [[Bahia]] to [[Guarapari]], a city with radioactive monazite sand beaches, with radiation levels up to 50 times higher than world average background radiation.<ref>{{cite journal|journal=An. Acad. Bras. Ciênc.|year=1981|volume=53|issue=4|pages=683–691|pmid=7345962 |title=Measurements of environmental radiation exposure dose rates at selected sites in Brazil |author1=Pfeiffer, W. C.|author2=Penna-Franca, E.|author3=Ribeiro, C. C.|author4=Nogueira, A. R.|author5=Londres, H.|author6=Oliveira, A. E.}}</ref>

Another possible source of exposure is thorium dust produced at weapons testing ranges, as thorium is used in the guidance systems of some missiles. This has been blamed for a high incidence of birth defects and cancer at [[Salto di Quirra]] on the Italian island of [[Sardinia]].<ref>{{cite news |url=https://www.abc.net.au/news/2019-01-29/sardinia-military-weapons-testing-birth-defects/10759614 |title=Italian military officials' trial ignites suspicions of links between weapon testing and birth defects in Sardinia |last=Alberici |first=Emma |date=29 January 2019 |website=ABC News |publisher=Australian Broadcasting Corporation |access-date=29 January 2019 |archive-date=29 January 2019 |archive-url=https://web.archive.org/web/20190129165810/https://www.abc.net.au/news/2019-01-29/sardinia-military-weapons-testing-birth-defects/10759614 |url-status=live }}</ref>