Editing Radon (section)

== Health risks ==
{{Main|Health effects of radon}}

=== In mines ===
{{sup|222}}Rn decay products have been classified by the [[International Agency for Research on Cancer]] as being [[carcinogenic]] to humans,<ref>{{cite web |access-date=2008-06-26 |url=http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp |archive-url=https://web.archive.org/web/20031213030702/http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp |url-status=dead |archive-date=2003-12-13 |title=Known and Probable Carcinogens |publisher=[[American Cancer Society]]}}</ref> and as a gas that can be inhaled, lung cancer is a particular concern for people exposed to elevated levels of radon for sustained periods. During the 1940s and 1950s, when safety standards requiring expensive ventilation in mines were not widely implemented,<ref>{{cite book |title=A Century of X-rays and Radioactivity in Medicine |author=Mould, Richard Francis |date=1993 |isbn=978-0-7503-0224-1 |publisher=CRC Press}}</ref> radon exposure was linked to lung cancer among non-smoking miners of uranium and other hard rock materials in what is now the Czech Republic, and later among miners from the Southwestern US<ref>{{Unbulleted list citebundle|{{Cite news |issn=0040-781X |title=Uranium Miners' Cancer |magazine=Time |access-date=2008-06-26 |date=1960-12-26 |url=http://www.time.com/time/magazine/article/0,9171,895156,00.html |archive-url=https://web.archive.org/web/20090115070225/http://www.time.com/time/magazine/article/0,9171,895156,00.html |url-status=dead |archive-date=January 15, 2009 }}|{{cite news |url=http://www.irsn.fr/FR/Larecherche/publications-documentation/Publications_documentation/BDD_publi/DRPH/LEADS/Documents/IRPA10-P2A-56.pdf |author=Tirmarche M. |author2=Laurier D. |author3=Mitton N. |author4=Gelas J. M. |title=Lung Cancer Risk Associated with Low Chronic Radon Exposure: Results from the French Uranium Miners Cohort and the European Project |access-date=2009-07-07 |archive-date=December 19, 2021 |archive-url=https://web.archive.org/web/20211219230252/https://www.irsn.fr/FR/Larecherche/publications-documentation/Publications_documentation/BDD_publi/DRPH/LEADS/Documents/IRPA10-P2A-56.pdf |url-status=dead }}|{{Cite journal |doi=10.1001/jama.1989.03430050045024 |volume=262 |last1=Roscoe |first1=R. J. |last2=Steenland |first2=K. |last3=Halperin |first3=W. E. |last4=Beaumont |first4=J. J. |last5=Waxweiler |first5=R. J. |title=Lung cancer mortality among nonsmoking uranium miners exposed to radon daughters| journal=[[Journal of the American Medical Association]] |date=1989-08-04 |pmid=2746814 |issue=5 |pages=629–633}}}}</ref> and [[South Australia]].<ref>{{Cite journal |jstor = 3553403 |title = Radon Daughter Exposures at the Radium Hill Uranium Mine and Lung Cancer Rates among Former Workers, 1952–87 |last1 = Woodward |first1 = Alistair |date = 1991-07-01 |journal = [[Cancer Causes & Control]] |doi = 10.1007/BF00052136 |pmid = 1873450|volume = 2 |issue = 4 |pages = 213–220 |last2 = Roder |first2 = David |last3 = McMichael |first3 = Anthony J. |last4 = Crouch |first4 = Philip |last5 = Mylvaganam |first5 = Arul|s2cid = 9664907 }}</ref> Despite these hazards being known in the early 1950s,<ref>{{cite news |title = Uranium mine radon gas proves health danger (1952) |url = https://www.newspapers.com/clip/3853075/uranium_mine_radon_gas_proves_health/ |newspaper = The Salt Lake Tribune |date = 27 September 1952 |page = 13 |access-date = 2015-12-22}}</ref> this [[occupational hazard]] remained poorly managed in many mines until the 1970s. During this period, several entrepreneurs opened former uranium mines in the US to the general public and advertised alleged health benefits from breathing radon gas underground. Health benefits claimed included relief from pain, sinus problems, asthma, and arthritis,<ref>{{Unbulleted list citebundle|{{cite news |title = Radon gas mine health benefits advertisement (1953) |url = https://www.newspapers.com/clip/3869275/radon_gas_mine_health_benefits/ |newspaper = Greeley Daily Tribune |date = 27 March 1953 |page = 4 |access-date = 2015-12-22}}|{{cite web |title = Clipping from The Montana Standard |url = https://www.newspapers.com/clip/3869277/the_montana_standard/ |website = Newspapers.com |access-date = 2015-12-22}}}}</ref> but the government banned such advertisements in 1975,<ref>{{cite web |title = Government bans Boulder mine ads about radon health benefits (1975) |url = https://www.newspapers.com/clip/3869269/government_bans_boulder_mine_ads_about/ |website = Newspapers.com |access-date = 2015-12-22}}</ref> and subsequent works have debated the truth of such claimed health effects, citing the documented ill effects of radiation on the body.<ref>{{cite journal |last=Salak |first=Kara |author2=Nordeman, Landon |year=2004 |title=59631: Mining for Miracles |url=http://ngm.nationalgeographic.com/ngm/0401/feature7/index.html |url-status=dead |journal=National Geographic |publisher=National Geographic Society |archive-url=https://web.archive.org/web/20080124233142/http://ngm.nationalgeographic.com/ngm/0401/feature7/index.html |archive-date=January 24, 2008 |access-date=June 26, 2008}}</ref>

Since that time, ventilation and other measures have been used to reduce radon levels in most affected mines that continue to operate. In recent years, the average annual exposure of uranium miners has fallen to levels similar to the concentrations inhaled in some homes. This has reduced the risk of occupationally-induced cancer from radon, although health issues may persist for those who are currently employed in affected mines and for those who have been employed in them in the past.<ref name="Darby05">{{cite journal |author=Darby, S. |author2=Hill, D. |author3=Doll, R. |date=2005 |title=Radon: a likely carcinogen at all exposures |journal=[[Annals of Oncology]] |volume=12 |issue=10 |pages=1341–1351 |doi=10.1023/A:1012518223463 |pmid=11762803 |doi-access=free}}</ref> As the relative risk for miners has decreased, so has the ability to detect excess risks among that population.<ref name="UNSCEAR06">{{cite web |url=http://www.unscear.org/unscear/en/publications/2006_1.html |title=UNSCEAR 2006 Report Vol. I |publisher=United Nations Scientific Committee on the Effects of Atomic Radiation UNSCEAR 2006 Report to the General Assembly, with scientific annexes}}</ref>
[[File:Uranium waste near Rifle, Colorado.jpg|thumb|A tailing pond near [[Rifle, Colorado]]. Waste from uranium mining has been allowed to settle and is exposed to the atmosphere, leading to the release of radon gas into the air and decay products into the groundwater.<ref name="OLM" />]]
Residues from processing of uranium ore can also be a source of radon. Radon resulting from the high radium content in uncovered dumps and [[Uranium tailings|tailing]] ponds<ref name="USPHS90" /> can be easily released into the atmosphere and affect people living in the vicinity.<ref>{{cite journal
 | url= http://www.rad-journal.org/helper/download.php?file=../papers/RadJ.2016.03.041.pdf
 | title= Radon exhalation of the uranium tailings dump Digmai, Tajikistan
 | author1= Schläger, M. |author2=Murtazaev, K. |author3= Rakhmatuloev, B. |author4= Zoriy, P.|author5= Heuel-Fabianek, B.
 | year= 2016
 | journal= Radiation and Applications
 | volume=1 |pages=222–228
 | doi=10.21175/RadJ.2016.03.041
 | doi-access=free
}}</ref> The release of radon may be mitigated by covering tailings with soil or clay, though other decay products may leach into [[groundwater]] supplies.<ref name="OLM">{{Cite web|url=https://www.energy.gov/lm/articles/uranium-mining-and-milling-near-rifle-colorado |website=Office of Legacy Management |via=[[Energy.gov]] |date=April 19, 2016 |title=Uranium Mining and Milling near Rifle, Colorado }}</ref>

Non-uranium mines may pose higher risks of radon exposure, as workers are not continuously monitored for radiation, and regulations specific to uranium mines do not apply. A review of radon level measurements across non-uranium mines found the highest concentrations of radon in non-metal mines, such as [[phosphorus]] and [[salt mines]].<ref>{{Cite journal |last=Chen |first=Jing |date=April 2023 |title=A Review of Radon Exposure in Non-uranium Mines—Estimation of Potential Radon Exposure in Canadian Mines |journal=Health Physics |language=en |volume=124 |issue=4 |pages=244–256 |doi=10.1097/HP.0000000000001661 |issn=1538-5159 |pmc=9940829 |pmid=36607249}}</ref> However, older or abandoned uranium mines without ventilation may still have extremely high radon levels.<ref>{{Cite journal |last1=Miklyaev |first1=Petr S. |last2=Petrova |first2=Tatiana B. |last3=Maksimovich |first3=Nikolay G. |last4=Krasikov |first4=Alexey V. |last5=Klimshin |first5=Aleksey V. |last6=Shchitov |first6=Dmitriy V. |last7=Sidyakin |first7=Pavel A. |last8=Tsebro |first8=Dmitriy N. |last9=Meshcheriakova |first9=Olga Yu. |date=2024-02-01 |title=Comparative studies on radon seasonal variations in various underground environments: Cases of abandoned Beshtaugorskiy uranium mine and Kungur Ice Cave |url=https://linkinghub.elsevier.com/retrieve/pii/S0265931X23002394 |journal=Journal of Environmental Radioactivity |volume=272 |pages=107346 |doi=10.1016/j.jenvrad.2023.107346 |pmid=38043218 |bibcode=2024JEnvR.27207346M |issn=0265-931X}}</ref>

In addition to lung cancer, researchers have theorized a possible increased risk of [[leukemia]] due to radon exposure. Empirical support from studies of the general population is inconsistent; a study of uranium miners found a correlation between radon exposure and [[chronic lymphocytic leukemia]],<ref>{{cite journal |pmid=16759978 |title=Incidence of leukemia, lymphoma, and multiple myeloma in Czech uranium miners: a case-cohort study |last1=Rericha |first1=V. |last2=Kulich |first2=M. |last3=Rericha |first3=R. |last4=Shore |first4=D. L. |last5=Sandler |first5=D. P. |date=2007 |volume=114 |journal=[[Environmental Health Perspectives]] |issue=6 |pmc=1480508 |pages=818–822 |doi=10.1289/ehp.8476}}</ref> and current research supports a link between indoor radon exposure and poor health outcomes (i.e., an increased risk of lung cancer or childhood [[leukemia]]).<ref name="Nunes-2022">{{Cite journal |last1=Nunes |first1=Leonel J. R. |last2=Curado |first2=António |last3=da Graça |first3=Luís C. C. |last4=Soares |first4=Salete |last5=Lopes |first5=Sérgio Ivan |date=2022-03-25 |title=Impacts of Indoor Radon on Health: A Comprehensive Review on Causes, Assessment and Remediation Strategies |journal=International Journal of Environmental Research and Public Health |volume=19 |issue=7 |pages=3929 |doi=10.3390/ijerph19073929 |issn=1661-7827 |pmc=8997394 |pmid=35409610 |doi-access=free}}</ref> Legal actions taken by those involved in nuclear industries, including miners, millers, transporters, nuclear site workers, and their respective unions have resulted in compensation for those affected by radon and radiation exposure under programs such as the [[compensation scheme for radiation-linked diseases]] (in the United Kingdom)<ref>{{Cite book |last= |first= |url=https://books.google.com/books?id=shCh5KzE7xEC&q=%22compensation+scheme+for+radiation+linked+diseases%22&pg=PA20 |title=The Redfern Inquiry into human tissue analysis in UK nuclear facilities |date=2010-11-16 |publisher=The Stationery Office |isbn=9780102966183 |location= |pages= |language=en |quote= |via=}}</ref> and the [[Radiation Exposure Compensation Act]] (in the United States).<ref>{{cite web |last1= |date=July 21, 2004 |title=An Overview of the Radiation Exposure Compensation Program |url=http://www.gpo.gov/fdsys/pkg/CHRG-108shrg25152/html/CHRG-108shrg25152.htm |access-date=August 28, 2024 |website=www.gpo.gov |publisher=United States Senate and the U.S. Government Printing Office}}</ref>

=== Domestic-level exposure ===
Radon has been considered the second leading cause of lung cancer in the United States and leading environmental cause of cancer mortality by the EPA,<ref>{{cite web |date=February 27, 2024 |title=Health Risk of Radon |url=https://www.epa.gov/radon/health-risk-radon |access-date=August 15, 2024 |website=[[Environmental Protection Agency]]}}</ref> with the first one being [[smoking]].<ref>{{cite journal |vauthors=Schabath MB, Cote ML |date=October 2019 |title=Cancer Progress and Priorities: Lung Cancer |journal=Cancer Epidemiol Biomarkers Prev |volume=28 |issue=10 |at=Radon |doi=10.1158/1055-9965.EPI-19-0221 |pmc=6777859 |pmid=31575553}}</ref> Others have reached similar conclusions for the United Kingdom<ref name="Darby05" /> and France.<ref name="Catelinois">{{cite journal |author=Catelinois O. |author2=Rogel A. |author3=Laurier D. |last4=Billon |first4=Solenne |last5=Hemon |first5=Denis |last6=Verger |first6=Pierre |last7=Tirmarche |first7=Margot |date=2006 |title=Lung cancer attributable to indoor radon exposure in france: impact of the risk models and uncertainty analysis |journal=[[Environmental Health Perspectives]] |volume=114 |issue=9 |pages=1361–1366 |doi=10.1289/ehp.9070 |pmc=1570096 |pmid=16966089|bibcode=2006EnvHP.114.1361C }}</ref> Radon exposure in buildings may arise from subsurface rock formations and certain building materials (e.g., some granites).<ref name="Todorovic">{{Cite book |last1=Todorović |first1=N. |title=Radon: geology, environmental impact and toxicity concerns |last2=Nikolov |first2=J. |last3=Petrović Pantić |first3=T. |last4=Kovačević |first4=J. |last5=Stojković |first5=I. |last6=Krmar |first6=M. |date=2015 |publisher=Nova Science Publishers, Inc. |isbn=978-1-63463-742-8 |editor-last1=Stacks |editor-first1=Audrey M. |pages=163–187 |chapter=Radon in Water - Hydrogeology and Health Implication}}</ref> The greatest risk of radon exposure arises in buildings that are airtight, insufficiently ventilated, and have foundation leaks that allow air from the soil into basements and dwelling rooms.<ref name="RECR" /> In some regions, such as [[Niška Banja]], Serbia and [[Ullensvang]], Norway, outdoor radon concentrations may be exceptionally high, though compared to indoors, where people spend more time and air is not dispersed and exchanged as often, outdoor exposure to radon is not considered a significant health risk.<ref>{{Cite journal |last1=Čeliković |first1=Igor |last2=Pantelić |first2=Gordana |last3=Vukanac |first3=Ivana |last4=Krneta Nikolić |first4=Jelena |last5=Živanović |first5=Miloš |last6=Cinelli |first6=Giorgia |last7=Gruber |first7=Valeria |last8=Baumann |first8=Sebastian |last9=Quindos Poncela |first9=Luis Santiago |last10=Rabago |first10=Daniel |date=2022-01-07 |title=Outdoor Radon as a Tool to Estimate Radon Priority Areas—A Literature Overview |journal=International Journal of Environmental Research and Public Health |volume=19 |issue=2 |pages=662 |doi=10.3390/ijerph19020662 |issn=1661-7827 |pmc=8775861 |pmid=35055485 |doi-access=free}}</ref>

Radon exposure (mostly radon daughters) has been linked to lung cancer in case-control studies performed in the US, Europe and China. There are approximately 21,000 deaths per year in the US (0.0063% of a population of 333 million) due to radon-induced lung cancers.<ref name="epa">{{cite web |url=http://www.epa.gov/radon/pubs/citguide.html |title=A Citizen's Guide to Radon |date=October 12, 2010 |work=www.epa.gov |publisher=[[United States Environmental Protection Agency]] |access-date=January 29, 2012}}</ref><ref>{{Cite web |url=https://www.census.gov/quickfacts/fact/table/US/PST045221.html |title=QuickFacts |date=2022-07-01 |work=www.census.gov |publisher=[[United States Census Bureau]] |access-date=2023-03-08}}</ref> In Europe, 2% of all cancers have been attributed to radon;<ref name="Ngoc-2022">{{Cite journal |last1=Ngoc |first1=Le Thi Nhu |last2=Park |first2=Duckshin |last3=Lee |first3=Young-Chul |date=2022-12-21 |title=Human Health Impacts of Residential Radon Exposure: Updated Systematic Review and Meta-Analysis of Case–Control Studies |journal=International Journal of Environmental Research and Public Health |volume=20 |issue=1 |pages=97 |doi=10.3390/ijerph20010097 |doi-access=free |issn=1661-7827 |pmc=9819115 |pmid=36612419}}</ref> in [[Slovenia]] in particular, a country with a high concentration of radon, about 120 people (0.0057% of a population of 2.11 million) die yearly because of radon.<ref>{{Unbulleted list citebundle|{{Cite web|title=Žlahtni plin v Sloveniji vsako leto kriv za 120 smrti|url=https://www.24ur.com/novice/preverjeno/zlahtni-plin-v-sloveniji-vsako-leto-kriv-za-120-smrti.html|access-date=2021-11-02|website=www.24ur.com|language=sl}}|{{Cite web |url=https://www.stat.si/StatWeb/en/News/Index/9212 |date=2021-01-01 |title=Population, Slovenia, 1 January 2021 |publisher=Republic of Slovenia Statistical Office (Source: SURS) |access-date=2023-03-08 |work=www.stat.si |archive-date=2022-01-11 |archive-url=https://web.archive.org/web/20220111171853/https://www.stat.si/StatWeb/en/News/Index/9212 |url-status=dead }}}}</ref> One of the most comprehensive radon studies performed in the US by epidemiologist [[R. William Field]] and colleagues found a 50% increased lung cancer risk even at the protracted exposures at the EPA's action level of 4&nbsp;pCi/L. North American and European pooled analyses further support these findings.<ref name=RECR>{{Cite report|archive-url=https://web.archive.org/web/20100528010149/http://deainfo.nci.nih.gov//advisory/pcp/pcp08-09rpt/PCP_Report_08-09_508.pdf |url=http://deainfo.nci.nih.gov//advisory/pcp/pcp08-09rpt/PCP_Report_08-09_508.pdf |title=Reducing Environmental Cancer Risk&nbsp;– What We Can Do Now |publisher=US Department of Health and Human Services |chapter=Exposure to Environmental Hazards from Natural Sources |pages=89–92 |date=April 2010 |archive-date=May 28, 2010}}</ref> However, the conclusion that exposure to low levels of radon leads to elevated risk of lung cancer has been disputed,<ref>{{Unbulleted list citebundle|{{cite journal |last=Fornalski |first=K. W. |author2=Adams, R. |author3=Allison, W. |author4=Corrice, L. E. |author5=Cuttler, J. M. |author6=Davey, Ch. |author7=Dobrzyński, L. |author8=Esposito, V. J. |author9=Feinendegen, L. E. |author10=Gomez, L. S. |author11=Lewis, P. |author12=Mahn, J. |author13=Miller, M. L. |author14=Pennington, Ch. W. |author15=Sacks, B. |author16=Sutou, S. |author17=Welsh, J. S. |pmid=26223888 |title=The assumption of radon-induced cancer risk |year=2015 |journal=Cancer Causes & Control |doi=10.1007/s10552-015-0638-9 |issue=26 |volume=10 |pages=1517–18|s2cid=15952263 }}|{{cite journal |last=Becker |first=K. |pmid=19330110 |title=Health Effects of High Radon Environments in Central Europe: Another Test for the LNT Hypothesis? |year=2003 |journal=[[Nonlinearity in Biology, Toxicology and Medicine]] |issue=1 |volume=1 |pages=3–35 |pmc=2651614|doi=10.1080/15401420390844447 }}|{{cite journal |author=Cohen B. L. |title=Test of the linear-no threshold theory of radiation carcinogenesis for inhaled radon decay products |journal=[[Health Physics (journal)|Health Physics]] |volume=68 |issue=2 |year=1995 |pmid=7814250 |url=http://www.phyast.pitt.edu/%7Eblc/LNT-1995.PDF |doi=10.1097/00004032-199502000-00002 |pages=157–74|s2cid=41388715 }}}}</ref> and analyses of the literature point towards elevated risk only when radon accumulates indoors<ref name="Nunes-2022" /> and at levels above 100&nbsp;Bq/m<sup>3</sup>.<ref name="Ngoc-2022" />

Thoron (<sup>220</sup>Rn) is less studied than {{Sup|222}}Rn in regards to domestic exposure due to its shorter half-life. However, it has been measured at comparatively high concentrations in buildings with earthen architecture, such as traditional [[Timber framing#Half-timbering|half-timbered houses]] and modern houses with [[clay]] wall finishes,<ref>{{Cite journal|first1=Stefanie |last1=Gierl |first2=Oliver |last2=Meisenberg |first3=Peter |last3=Feistenauer |first4=Jochen |last4=Tschiersch |doi=10.1093/rpd/ncu076 |title=Thoron and thoron progeny measurements in German clay houses |journal=[[Radiation Protection Dosimetry]] |volume=160 |date=April 17, 2014 |issue=1–3 |pages= 160–163|pmid=24743764 }}</ref> and in regions with thorium- and [[monazite]]-rich soil and sand.<ref name="Ramola-2020">{{Cite journal |last1=Ramola |first1=R.C. |last2=Prasad |first2=Mukesh |date=December 2020 |title=Significance of thoron measurements in indoor environment |url=https://linkinghub.elsevier.com/retrieve/pii/S0265931X20306998 |journal=Journal of Environmental Radioactivity |language=en |volume=225 |pages=106453 |doi=10.1016/j.jenvrad.2020.106453|pmid=33120031 |bibcode=2020JEnvR.22506453R }}</ref> Thoron is a minor contributor to the overall radiation dose received due to indoor radon exposure,<ref>{{Cite journal |last=Chen |first=Jing |date=2022 |title=Assessment of thoron contribution to indoor radon exposure in Canada |journal=Radiation and Environmental Biophysics |volume=61 |issue=1 |pages=161–167 |doi=10.1007/s00411-021-00956-0 |issn=0301-634X |pmc=8897316 |pmid=34973065|bibcode=2022REBio..61..161C }}</ref> and can interfere with {{Sup|222}}Rn measurements when not taken into account.<ref name="Ramola-2020" />

==== Action and reference level ====
WHO presented in 2009 a recommended reference level (the national reference level), 100&nbsp;Bq/m<sup>3</sup>, for radon in dwellings. The recommendation also says that where this is not possible, 300&nbsp;Bq/m<sup>3</sup> should be selected as the highest level. A national reference level should not be a limit, but should represent the maximum acceptable annual average radon concentration in a dwelling.<ref>{{Cite book|url=http://whqlibdoc.who.int/publications/2009/9789241547673_eng.pdf |date=2009 |title=WHO Handbook on Indoor Radon |publisher=World Health Organization |archive-date=March 4, 2012 |archive-url=https://web.archive.org/web/20120304001907/http://whqlibdoc.who.int/publications/2009/9789241547673_eng.pdf |isbn=978-92-4-154767-3}}</ref>

The actionable concentration of radon in a home varies depending on the organization doing the recommendation, for example, the EPA encourages that action be taken at concentrations as low as 74&nbsp;Bq/m<sup>3</sup> (2&nbsp;pCi/L),<ref name="EPA radon">{{cite web |title =Radiation Protection: Radon |publisher=[[United States Environmental Protection Agency]] |date=November 2007 |url=http://www.epa.gov/radiation/radionuclides/radon.html |access-date =2008-04-17}}</ref> and the [[European Union]] recommends action be taken when concentrations reach 400&nbsp;Bq/m<sup>3</sup> (11&nbsp;pCi/L) for old houses and 200&nbsp;Bq/m<sup>3</sup> (5&nbsp;pCi/L) for new ones.<ref>{{cite web |url=http://www.euro.who.int/__data/assets/pdf_file/0006/97053/4.6_-RPG4_Rad_Ex1-ed2010_editedViv_layouted.pdf |title=Radon Levels in Dwellings: Fact Sheet 4.6 |date=December 2009 |publisher=European Environment and Health Information System |access-date=2013-07-16 }}</ref> On 8 July 2010, the UK's Health Protection Agency issued new advice setting a "Target Level" of 100&nbsp;Bq/m<sup>3</sup> whilst retaining an "Action Level" of 200&nbsp;Bq/m<sup>3</sup>.<ref name="HPA radon">{{cite web |title=HPA issues new advice on radon |publisher=[[UK Health Protection Agency]] |date=July 2010 |url=http://www.hpa.org.uk/NewsCentre/NationalPressReleases/2010PressReleases/100708Newadviceonradon/ |archive-url=https://web.archive.org/web/20100714170654/http://www.hpa.org.uk/NewsCentre/NationalPressReleases/2010PressReleases/100708Newadviceonradon/ |url-status=dead |archive-date=2010-07-14 |access-date=2010-08-13}}</ref> Similar levels (as in the UK) are published by Norwegian Radiation and Nuclear Safety Authority (DSA)<ref>{{Cite web|title=Radon mitigation measures|url=https://dsa.no/en/radon/radon-mitigation-measures|access-date=2021-07-12|website=DSA|language=no}}</ref> with the maximum limit for schools, kindergartens, and new dwellings set at 200&nbsp;Bq/m<sup>3</sup>, where 100&nbsp;Bq/m<sup>3</sup> is set as the action level.<ref>{{Cite web|url=https://www2.dsa.no/publication/strategy-for-the-reduction-of-radon-exposure-in-norway.pdf|title=Strategy for the reduction of radon exposure in Norway, 2010|accessdate=14 March 2023|archive-date=20 November 2021|archive-url=https://web.archive.org/web/20211120103812/https://www.dsa.no/publication/strategy-for-the-reduction-of-radon-exposure-in-norway.pdf|url-status=dead}}</ref>

==== Inhalation and smoking ====
Results from epidemiological studies indicate that the risk of lung cancer increases with exposure to residential radon. A well known example of source of error is smoking, the main risk factor for lung cancer. In the US, cigarette smoking is estimated to cause 80% to 90% of all lung cancers.<ref>{{cite web |title=What Are the Risk Factors for Lung Cancer? |url=https://www.cdc.gov/cancer/lung/basic_info/risk_factors.htm |website=Centers for Disease Control and Prevention |access-date=3 May 2020 |date=18 September 2019}}</ref>

According to the EPA, the risk of lung cancer for smokers is significant due to [[Synergy|synergistic]] effects of radon and smoking. For this population about 62 people in a total of 1,000 will die of lung cancer compared to 7 people in a total of 1,000 for people who have never smoked.<ref name="epa" /> It cannot be excluded that the risk of non-smokers should be primarily explained by an effect of radon.

Radon, like other known or suspected external risk factors for lung cancer, is a threat for smokers and former smokers. This was demonstrated by the European pooling study.<ref name="bmj38308">{{cite journal |doi=10.1136/bmj.38308.477650.63 |pmid=15613366 |pmc=546066 |title=Radon in homes and risk of lung cancer: Collaborative analysis of individual data from 13 European case-control studies |journal=BMJ |volume=330 |issue=7485 |pages=223 |year=2005 |last1=Darby |first1=S. |last2=Hill |first2=D. |last3=Auvinen |first3=A. |last4=Barros-Dios |first4=J. M. |last5=Baysson |first5=H. |last6=Bochicchio |first6=F. |last7=Deo |first7=H. |last8=Falk |first8=R. |last9=Forastiere |first9=F. |last10=Hakama |first10=M. |last11=Heid |first11=I. |last12=Kreienbrock |first12=L. |last13=Kreuzer |first13=M. |last14=Lagarde |first14=F. |last15=Mäkeläinen |first15=I. |last16=Muirhead |first16=C. |last17=Oberaigner |first17=W. |last18=Pershagen |first18=G. |last19=Ruano-Ravina |first19=A. |last20=Ruosteenoja |first20=E. |last21=Rosario |first21=A. Schaffrath |last22=Tirmarche |first22=M. |last23=Tomášek |first23=L. |last24=Whitley |first24=E. |last25=Wichmann |first25=H.-E. |last26=Doll |first26=R. }}</ref> A commentary<ref name="bmj38308" /> to the pooling study stated: "it is not appropriate to talk simply of a risk from radon in homes. The risk is from smoking, compounded by a synergistic effect of radon for smokers. Without smoking, the effect seems to be so small as to be insignificant."

According to the European pooling study, there is a difference in risk for the [[Histology|histological]] subtypes of lung cancer and radon exposure. [[Small-cell lung carcinoma]], which has a high correlation with smoking, has a higher risk after radon exposure. For other histological subtypes such as [[adenocarcinoma]], the type that primarily affects non-smokers, the risk from radon appears to be lower.<ref name="bmj38308" /><ref>{{cite web |first=R. William |last=Field |location=Charleston, South Carolina |url=https://www.aarst.org/images/PCPanelRadonTest.pdf |title=President's Cancer Panel, Environmental Factors in Cancer: Radon |date=December 4, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20130829005508/http://www.aarst.org/images/PCPanelRadonTest.pdf |archive-date=August 29, 2013 |publisher=The American Association of Radon Scientists and Technologists (AARST)}}</ref>

A study of radiation from post-[[mastectomy]] [[radiotherapy]] shows that the simple models previously used to assess the combined and separate risks from radiation and smoking need to be developed.<ref>{{cite journal |last1=Kaufman |first1=E. L. |last2=Jacobson |first2=J. S. |last3=Hershman |first3=D. L. |last4=Desai |first4=M. |last5=Neugut |first5=A. I. |date=2008 |title=Effect of breast cancer radiotherapy and cigarette smoking on risk of second primary lung cancer |journal=[[Journal of Clinical Oncology]] |volume=26 |issue=3 |pages=392–398 |doi=10.1200/JCO.2007.13.3033 |pmid=18202415|doi-access=free }}</ref> This is also supported by new discussion about the calculation method, the [[linear no-threshold model]], which routinely has been used.<ref>{{cite journal |doi=10.1093/rpd/ncq141 |title=Review and evaluation of updated research on the health effects associated with low-dose ionising radiation |date=2010 |last1=Dauer |first1=L. T. |last2=Brooks |first2=A. L. |last3=Hoel |first3=D. G. |last4=Morgan |first4=W. F. |last5=Stram |first5=D. |last6=Tran |first6=P. |journal=[[Radiation Protection Dosimetry]] |volume=140 |issue=2 |pages=103–136 |pmid=20413418}}</ref>

A study from 2001, which included 436 non-smokers with lung cancer and a control group of 1649 non-smokers without lung cancer, showed that exposure to radon increased the risk of lung cancer in non-smokers. The group that had been exposed to tobacco smoke in the home appeared to have a much higher risk, while those who were not exposed to passive smoking did not show any increased risk with increasing radon exposure.<ref>{{cite journal |last1=Lagarde |first1=F. |last2=Axelsson |first2=G. |last3=Damber |first3=L. |last4=Mellander |first4=H. |last5=Nyberg |first5=F. |last6=Pershagen |first6=G. |date=2001 |title=Residential radon and lung cancer among never-smokers in Sweden |journal=Epidemiology |volume=12 |issue=4 |pages=396–404 |doi=10.1097/00001648-200107000-00009 |jstor=3703373 |pmid=11416777|s2cid=25719502 |doi-access=free }}</ref>

==== Absorption and ingestion from water ====
The effects of radon if ingested are unknown, although studies have found that its biological half-life ranges from 30 to 70 minutes, with 90% removal at 100 minutes. In 1999, the US [[National Research Council (United States)|National Research Council]] investigated the issue of radon in drinking water. The risk associated with ingestion was considered almost negligible;<ref>[http://www.nap.edu/openbook.php?isbn=0309062926 Risk Assessment of Radon in Drinking Water]. Nap.edu (2003-06-01). Retrieved on 2011-08-20.</ref> Water from underground sources may contain significant amounts of radon depending on the surrounding rock and soil conditions, whereas surface sources generally do not.<ref>{{cite web |url=http://water.epa.gov/lawsregs/rulesregs/sdwa/radon/basicinformation.cfm |title=Basic Information about Radon in Drinking Water |access-date=2013-07-24 }}</ref> Radon is also released from water when temperature is increased, pressure is decreased and when water is aerated. Optimum conditions for radon release and exposure in domestic living from water occurred during showering. Water with a radon concentration of 10<sup>4</sup>&nbsp;pCi/L can increase the indoor airborne radon concentration by 1&nbsp;pCi/L under normal conditions.<ref name="Thad. Godish 2001" /> However, the concentration of radon released from contaminated groundwater to the air has been measured at 5 orders of magnitude less than the original concentration in water.<ref>{{Cite web |last=Johnson |first=Jan |date=28 October 2019 |title=Answer to Question #13127 Submitted to "Ask the Experts" |url=https://hps.org/publicinformation/ate/q13127.html |access-date=2024-09-23 |website=Health Physics Society}}</ref><!--The ocean surface only carries about {{val|e=-4}} <sup>226</sup>Ra, where measurements of <sup>222</sup>Rn concentration have been 1% over various continents.<ref name="agupubs.onlinelibrary.wiley.com" />--> 

Ocean surface concentrations of radon exchange within the atmosphere, causing <sup>222</sup>Rn to increase through the air-sea interface.<ref name="agupubs.onlinelibrary.wiley.com">{{Cite journal|url=https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JC080i027p03828|doi=10.1029/JC080i027p03828|title=Radon 222 from the ocean surface|year=1975|last1=Wilkening|first1=Marvin H.|last2=Clements|first2=William E.|journal=Journal of Geophysical Research|volume=80|issue=27|pages=3828–3830|bibcode=1975JGR....80.3828W}}</ref> Although areas tested were very shallow, additional measurements in a wide variety of coastal regimes should help define the nature of <sup>222</sup>Rn observed.

=== Testing and mitigation ===
{{Main|Radon mitigation}}
[[File:Radon detector.jpg|alt=radon detector|thumb|A digital radon detector]]
[[Image:Radon test kit.jpg|thumb|A radon test kit]]
There are relatively simple tests for radon gas. In some countries these tests are methodically done in areas of known systematic hazards. Radon detection devices are commercially available. Digital radon detectors provide ongoing measurements giving both daily, weekly, short-term and long-term average readouts via a digital display. Short-term radon test devices used for initial screening purposes are inexpensive, in some cases free. There are important protocols for taking short-term radon tests and it is imperative that they be strictly followed. The kit includes a collector that the user hangs in the lowest habitable floor of the house for two to seven days. The user then sends the collector to a laboratory for analysis. Long term kits, taking collections for up to one year or more, are also available. An open-land test kit can test radon emissions from the land before construction begins.<ref name="epa" /> Radon concentrations can vary daily, and accurate radon exposure estimates require long-term average radon measurements in the spaces where an individual spends a significant amount of time.<ref>{{cite web |url=https://hps.org/publicinformation/ate/q10299.html |title=Answer to Question #10299 Submitted to "Ask the Experts" |last=Baes |first=Fred |website=Health Physics Society |access-date=2016-05-19}}</ref>

Radon levels fluctuate naturally, due to factors like transient weather conditions, so an initial test might not be an accurate assessment of a home's average radon level. Radon levels are at a maximum during the coolest part of the day when pressure differentials are greatest.<ref name="Thad. Godish 2001" /> Therefore, a high result (over 4&nbsp;pCi/L) justifies repeating the test before undertaking more expensive abatement projects. Measurements between 4 and 10&nbsp;pCi/L warrant a long-term radon test. Measurements over 10&nbsp;pCi/L warrant only another short-term test so that abatement measures are not unduly delayed. The EPA has advised purchasers of real estate to delay or decline a purchase if the seller has not successfully abated radon to 4&nbsp;pCi/L or less.<ref name="epa" />

Because the half-life of radon is only 3.8 days, removing or isolating the source will greatly reduce the hazard within a few weeks. Another method of reducing radon levels is to modify the building's ventilation. Generally, the indoor radon concentrations increase as ventilation rates decrease.<ref name="USPHS90" /> In a well-ventilated place, the radon concentration tends to align with outdoor values (typically 10&nbsp;Bq/m<sup>3</sup>, ranging from 1 to 100&nbsp;Bq/m<sup>3</sup>).<ref name="epa" />

The four principal ways of reducing the amount of radon accumulating in a house are:<ref name="epa" /><ref name="WHO291">{{cite web |author=World Health Organization |title=Radon and cancer, fact sheet 291 |url=https://www.who.int/mediacentre/factsheets/fs291/en/index.html |author-link=World Health Organization}}</ref>
* Sub-slab depressurization (soil suction) by increasing under-floor ventilation;
* Improving the ventilation of the house and avoiding the transport of radon from the basement into living rooms;
* Installing a radon sump system in the basement;
* Installing a positive pressurization or positive supply ventilation system.

According to the EPA, the method to reduce radon "...primarily used is a vent pipe system and fan, which pulls radon from beneath the house and vents it to the outside", which is also called sub-slab depressurization, active soil depressurization, or soil suction.<ref name="epa" /> Generally indoor radon can be mitigated by sub-slab depressurization and exhausting such radon-laden air to the outdoors, away from windows and other building openings. "[The] EPA generally recommends methods which prevent the entry of radon. Soil suction, for example, prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe, or pipes, to the air above the home where it is quickly diluted" and the "EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently".<ref name="epa.gov">{{cite web | url = http://www.epa.gov/radon/pubs/consguid.html#reductiontech| title = Consumer's Guide to Radon Reduction: How to fix your home| access-date = 2010-04-03| publisher = EPA}}</ref>

[[Positive pressure ventilation|Positive-pressure ventilation]] systems can be combined with a [[heat exchanger]] to recover energy in the process of exchanging air with the outside, and simply exhausting basement air to the outside is not necessarily a viable solution as this can actually draw radon gas into a dwelling. Homes built on a crawl space may benefit from a radon collector installed under a "radon barrier" (a sheet of plastic that covers the crawl space).<ref name="epa" /><ref>{{cite book |url=https://books.google.com/books?id=bspdQ8H2yUcC&pg=PT46 |page=46 |title=Building radon out a step-by-step guide on how to build radonresistant homes |publisher=DIANE Publishing |isbn=978-1-4289-0070-7}}</ref> For crawl spaces, the EPA states that "[a]n effective method to reduce radon levels in crawl space homes involves covering the earth floor with a high-density plastic sheet. A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors. This form of soil suction is called submembrane suction, and when properly applied is the most effective way to reduce radon levels in crawl space homes."<ref name="epa.gov" />