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What is Radon
Radon is a colourless, odourless, radioactive gas. It comes from the radioactive decay of radium, which in turn comes from the radioactive decay of uranium. Uranium acts as a permanent source of radon and is found in small quantities in all soils and rocks, although the amount varies from place to place. It is particularly prevalent in granite areas but not exclusively so. Radon levels vary not only between different parts of the country but even between neighbouring buildings. 
Radon in the soil and rocks mixes with air and rises to the surface where it is quickly diluted in the atmosphere. Concentrations in the open air are very low. However, radon concentration in soil-gas can be very high, typically from less than 10 000 to 100 000 Bq/m3. Entry of this radon-bearing air into living spaces is the main reason for elevated indoor radon concentrations. Mineral building materials also emit radon. Radon that enters enclosed spaces, such as buildings, can reach relatively high concentrations in some circumstances.
When radon decays it forms tiny radioactive particles called radon daughters which may be breathed into the lungs. If formed in air, these particles may be inhaled and some will be deposited in the lungs. The radiation emitted by them as they decay can give a high dose to lung tissues and damage them. Being exposed to radon and its decay products increases the risk of developing lung cancer. In addition, smoking and exposure to radon are known to work together to greatly increase the risk of developing lung cancer. It is important however to confirm that whilst radon causes lung cancer the majority of lung cancer risk is caused by smoking.
In addition to the risk from radon in air it is now recognised that some private water supplies contain levels of radon which should also be controlled. However, it is important to recognise that radon in water presents a far smaller health hazard than radon in air, both in term of the numbers of people exposed to high levels, and in terms of the risks to the most exposed individuals. Tap water supplied by public utilities is usually treated and poses no risk to the user. However it is advisable to have water from private bore holes in radon affected areas tested, and if necessary treated.
Radon is classified by International Agency for the Research on Cancer as known human carcinogen (IARC Group 1). Radon is second only to tobacco smoking as a cause of lung cancer. Two types of cancer risk estimations have been applied for ionising radiation, including lung cancer from α-radiation of radon and radon daughters. Absolute risk estimation assumes the risk to be a product of radon exposure level and dose/response, and it is usually expressed as a unit risk, i.e. lifetime probability per lifetime exposure. For radon the lung cancer unit risk estimate is 3-6*10-5 Bq/m3 (Pershagen et al. 1994). Relative risk estimation assumes that the additional cancer risk of radon depends on the background lung cancer levels. Because the background level depends strongly on tobaccos smoking, consequentially the additional lung cancer risk caused by radon also depends on smoking. Epidemiological evidence gives support to the relative risk model. For every additional Bq/m3 the lung cancer increases by 0.14% of its background incidence. Multiplying this relative unit risk by the European population weighed average radon concentration of 65 Bq/m3 results in an estimate that radon in the indoor air accounts for about 9 % of all lung cancer cases and consequently about 2 % of all cancer in Europe. (Darby et al. 2005). Besides lung cancer radon is not known to cause other health effects. 
Total estimated number of annual lung cancer incidence attributable to radon exposure in EU-Europe (plus Albania, Croatia, Switzerland and Norway) is about 21 000. This makes radon second to only tobacco as a cause of lung cancer. Direct comparison between the countries is not possible, because lung cancer incidence depends almost linearly on the total population. It is, however, interesting to compare the
Environmental and Occupational Guidelines and Standards
Radon concentrations in the ambient air vary significantly in time and space, typically around the order of magnitude of 10 Bq/m3. Similar levels would be desirable but are not achievable in the indoor air. WHO Air Quality Guidelines (2000) does not recommend any guideline value for radon, but suggests that remedial measures should be considered for buildings where the radon progeny concentrations exceed 100 Bq/m3 as an annual average. 
National indoor air radon guidelines are rather similar across Europe. The guideline values and respectively the preventive actions have gradually become stricter over the past decades. Differences, therefore, depend mainly on the year when the guideline came into effect. The Finnish regulation here is give as an example: Current national radon guideline value (action value) for older buildings is 400 Bq/m3 and design criterion for all new buildings is 200 Bq/m3. 400 Bq/m3 is also set as an action value for all workplaces and as a limit value for all schools and day care centres.
- Radiation Act (592/1991) chapter 12 Natural radiation, section 45-49 latest amendment 22.12.2005
- Radiation Decree (1512/1991) chapter 7 Natural radiation, section 26-28 (pursuant to the Radiation Act); latest amendment 29.12.2005/1264
- Ministry for Social Affairs and Health Order on the Upper Limits for Radon Concentration in Places of Residence (944/1992) (pursuant to Radiation Act section 48 and Radiation Decree)
Of all indoor air contaminants radon is the most unpredictable. Even at extremely high concentrations it is not detectable by the senses, it is of natural origin and penetrates into the building from the ground underneath. In spite of these obstacles, and thanks to large randomised surveys and harmonised monitoring methods, the levels of radon as well as its large (country averages) and small (building statistics) scale distributions are probably better known and more reliably comparable between the different regions of Europe than those of any other indoor air contaminant. Table 126.96.36.199 demonstrates that there are fivefold differences between the country averages and that the maximum levels may exceed country median values by more than three orders of magnitude. Distribution of the exposure to and risk of radon within the population is the most skewed of all common indoor air contaminants. 
Because the radon level in any existing or new building is still quite difficult to estimate without actual measurement, most of the buildings with radon levels that exceed the guideline values are still unknown to the owners, occupants and national authorities, and, thus, outside of any remedial programmes. Pointing out all buildings which do not meet the guideline values would require monitoring of almost every building, renovating all detected non-compliance buildings would require convincing millions of building owners and occupants of the necessity of the work and costs, and finally, actually accomplishing these tasks would still reduce the lung cancer risks of radon only marginally, because most of the radon induced lung cancers are caused by indoor air radon concentrations which do meet the current guidelines.
These facts clearly point out that the most effective radon mitigation policies will focus on new buildings and buildings undergoing major renovations, and would aim at reducing all indoor radon levels, also those that are otherwise well below, e.g., 200 or even 100 Bq/m3.
- ERF for long-term indoor exposure to radon and lung cancer
- An Overview of Radon Surveys in Europe. Joint Research Centre, 2005. ISBN 92-79-01066-2
- In Heande (password-protected)
radon, indoor air, air pollutant, uranium, lung cancer