Indoor environment factor · measured in Bq/m³
Radon
Also: Rn-222, radon gas
A naturally occurring radioactive gas released from uranium in soil and rock that seeps into buildings through the ground. It is the second leading cause of lung cancer after smoking and the largest source of ionising radiation most people receive. Measured in becquerels per cubic metre.
Why it matters indoors
Radon is a noble gas with no colour, smell or taste, formed by the radioactive decay of radium in the ground. It enters buildings through cracks and joints in floors and walls in contact with soil, and accumulates where ventilation is low — basements and ground floors in winter above all. Its decay products attach to dust and are inhaled; their alpha radiation damages lung tissue.
Where it comes from indoors
The ground beneath the building is the dominant source; building materials (granite, some concretes) and well water contribute a small share. Concentrations depend on local geology, the construction of the floor slab, and the pressure difference that draws soil gas indoors — which is why levels vary tenfold between neighbouring houses.
Health effects
Lung cancer is the established outcome; risk rises roughly linearly with long-term concentration, with no threshold, and is many times higher for smokers because the two exposures multiply. No other health effect is established at residential levels.
Exposure limits
| Jurisdiction | Value | Basis | Source |
|---|---|---|---|
| World Health Organization | 100 Bq/m³ reference level; not above 300 Bq/m³ where 100 cannot be reached | annual average | WHO Handbook on Indoor Radon 2009 |
| European Union | reference level not higher than 300 Bq/m³ | annual average, dwellings and workplaces | Directive 2013/59/Euratom |
Slovak, UAE and Hong Kong values are being compiled in the indoor air quality limits table.
How it is measured
Passive track-etch detectors exposed for one to three months give the reliable long-term average that guidelines refer to; electronic monitors give continuous readings and show the effect of ventilation and weather. A single short measurement is not enough — levels change with season and even time of day.
What the studies report
12 of 69 Findings — those with the strongest study design.
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Lung cancer | other 0.14 (0.10–0.18) per 100 Bq/m3 | — | combined analysis of onco-epidemiological studies of indoor radon: excess relative risk of lung cancer estimated from geographically aggregated data and from a meta-analysis of case-control studies | F-1649 Combined analysis of onco-epidemiological tudies of the rela… (2020) | machine |
| Natural ventilation | mean 46 | apartment occupants · apartment | continuous measurement of radon-222 and CO2 with meteorological parameters in one occupied apartment (about 27 m2) in Ljubljana, Slovenia, 3-15 October, under recorded ventilation schedules (frequent, poor, none), followed by CONTAM 3.4 transient simulations of design ventilation rates | F-0482 Dovjak et al. Analysis of Ventilation Efficiency as Simultaneous Control o… (2022) | machine |
| — | difference 26.7 | residential occupants · dwelling | analysis of long-term radon tests in 42,051 Canadian residential properties across 2,034 communities, comparing urban and rural community types with property metrics (building design, floorplan size, construction year) and groundwater well data | F-0607 Khan Rural communities experience higher radon exposure versus ur… (2024) | machine |
| — | difference 37 | residential occupants · dwelling in a small town or village | analysis of long-term radon tests in 42,051 Canadian residential properties across 2,034 communities, comparing urban and rural community types with property metrics (building design, floorplan size, construction year) and groundwater well data | F-0608 Khan Rural communities experience higher radon exposure versus ur… (2024) | machine |
| — | difference 44 | residential occupants · dwelling in a small town or village | analysis of long-term radon tests in 42,051 Canadian residential properties across 2,034 communities, comparing urban and rural community types with property metrics (building design, floorplan size, construction year) and groundwater well data | F-0609 Khan Rural communities experience higher radon exposure versus ur… (2024) | machine |
| — | other 15,000 | waterworks staff · groundwater treatment plant (process hall) | measurement of radon release from water into indoor air at Finnish groundwater treatment plants: radon in water before and after each process unit and radon in the indoor air of pump rooms and process halls | F-0610 Tyrväinen Radon transport to indoor air in groundwater plants as a by-… (2023) | machine |
| — | other 19,000 | waterworks staff · groundwater treatment plant (process hall) | measurement of radon release from water into indoor air at Finnish groundwater treatment plants: radon in water before and after each process unit and radon in the indoor air of pump rooms and process halls | F-0611 Tyrväinen Radon transport to indoor air in groundwater plants as a by-… (2023) | machine |
| — | share-above 15.0 | residential occupants · dwelling | indoor radon survey in southwest and south Greenland: 524 passive detectors deployed, 495 returned and 459 used for analysis in detached and semi-detached homes in Nuuk, Qaqortoq and Narsaq, with house characteristics and dose assessment | F-0614 Hansen Indoor radon survey in Greenland and dose assessment (2023) | machine |
| — | share-above 5.2 | residential occupants · dwelling | indoor radon survey in southwest and south Greenland: 524 passive detectors deployed, 495 returned and 459 used for analysis in detached and semi-detached homes in Nuuk, Qaqortoq and Narsaq, with house characteristics and dose assessment | F-0615 Hansen Indoor radon survey in Greenland and dose assessment (2023) | machine |
| — | share-above 3.2 | residential occupants · dwelling | indoor radon survey in southwest and south Greenland: 524 passive detectors deployed, 495 returned and 459 used for analysis in detached and semi-detached homes in Nuuk, Qaqortoq and Narsaq, with house characteristics and dose assessment | F-0616 Hansen Indoor radon survey in Greenland and dose assessment (2023) | machine |
| — | the supporting values are in the supplementary material; the sentence carries its own test statistics | residential occupants · dwelling with a crawl space | indoor radon survey in southwest and south Greenland: 524 passive detectors deployed, 495 returned and 459 used for analysis in detached and semi-detached homes in Nuuk, Qaqortoq and Narsaq, with house characteristics and dose assessment | F-0617 Hansen Indoor radon survey in Greenland and dose assessment (2023) | machine |
| — | mean 113 | residential occupants · dwelling | population-weighted analysis of two Swedish national indoor radon surveys (8,992 dwellings in 1990 and 1,819 in 2008, both representative of Swedish dwellings), with an estimate of lung cancer cases preventable by lowering radon | F-0618 Lung cancer risk from radon exposure in dwellings in Sweden:… (2015) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. Rows are re-checked by a person over time. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
Identifiers
- Molecular formula
- Rn
- IUPAC name
- radon
- CAS Registry Number
- 10043-92-2 · PubChem · CTD
- InChIKey
- SYUHGPGVQRZVTB-UHFFFAOYSA-N
- MeSH
- D011886
- SMILES
[Rn]
In the literature
- Jelle Development of a model for radon concentration in indoor air (2012). The Science of the total environment. doi:10.1016/j.scitotenv.2011.11.052 CKB 0375
- Yoon Indoor radon exposure and lung cancer - a review of ecological studies (2016). Annals of occupational and environmental medicine. doi:10.1186/s40557-016-0098-z CKB 0392
- Kim Attributable risk of lung cancer deaths due to indoor radon exposure (2016). Annals of occupational and environmental medicine. doi:10.1186/s40557-016-0093-4 CKB 0391
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.
Cite this page
Coridum Research. Radon. Coridum Knowledge G-0047, 16 September 2026. https://coridum.com/k/G-0047/