This is a subpage of Environmental radioactivity.
See the story of Eben Byers for details of one very nasty case which involved a product called Radithor which contained 1 mCi (40 MBq) of 226Ra and 1 mCi of 228Ra per bottle. Radithor was taken by mouth and as radium is a calcium mimic it has a very long biological halflife in bone.
Residues from the oil and gas industry often contain radium and its daughters. The sulfate scale from an oil well can be very radium rich. It is the case that the water inside an oil field is often very rich in strontium, barium and radium while seawater is very rich in sulfate so if water from an oil well is discharged into the sea or mixed with seawater the radium is likely to be brought out of solution by the barium/strontium sulfate which acts as a carrier precipitate.
The majority of the dose is caused by the decay of the polonium (218Po) and lead (214Pb) daughters from 222Rn. It is the case that by controlling the daughters that the dose to the skin and lungs can be reduced by at least 90%. This can be done by wearing a dust mask, and wearing a suit to cover the entire body. Note that exposure to smoke at the same time as radon and radon daughters will increase the harmful effect of the radon. In uranium miners radon has been found to be more carcinogenic in smokers than in non-smokers.
On average, there is one atom of radon in 1 x 1021 molecules of air. Radon can be found in some spring waters and hot springs. The towns of Misasa, Japan, and Bad Kreuznach, Germany boast radium-rich springs which emit radon. Unsurprisingly, Radium Springs, New Mexico does too.
Radon exhausts naturally from the ground, particularly in certain regions, especially but not only regions with granitic soils. Not all granitic regions are prone to high emissions of radon, for instance while the rock which Aberdeen is on is very radium rich the rock lacks the cracks required for the radon to migrate. In other near by areas of Scotland (to the north of Aberdeen) and in Cornwall/Devon the radon is very able to leave the rock.
Radon is a decay product of radium which in turn is a decay product of uranium. It is possible to get maps of average radon levels in houses, these maps assist in the planning of radon mitigation measures for homes.
Note that while high uranium in the soil/rock under a house does not always lead to a high radon level in air, a positive correlation between the uranium content of the soil and the radon level in air can be seen.
Radon is related to Indoor air quality as it blights many homes. (See "Radon in Houses" below.)
The radon (222Rn) released into the air decays to 210Pb and other radioisotopes, the levels of 210Pb can be measured. It is important to note that the rate of deposition of this radioisotope is very dependent on the season. Here is a graph of the deposition rate observed in Japan (M. Yamamoto et al., Journal of Environmental Radioactivity, 2006, 86, 110-131).
Well water can be very radon rich, the use of this water inside a house is an additional route allowing radon to enter the house. The radon can enter the air and then be a source of exposure to the humans, or the water can be consumed by humans which is a different exposure route.
The water, oil and gas from a well often contains radon. The radon decays to form solid radioisotopes which form coatings on the inside of pipework. In an oil processing plant the area of the plant where propane is processed is often one of the more contaminated areas of the plant as radon has a similar boiling point as propane.
Because uranium minerals emit radon gas, and their harmful and highly radioactive daughter products, uranium mining is considerably more dangerous than other (already dangerous) hard rock mining, requiring adequate ventilation systems if the mines are not open pit. During the 1950s, a significant number of American uranium miners were Navajo Indians, as many uranium deposits were discovered on Navajo reservations. A statistically significant subset of these miners later developed small-cell lung cancer, a type of cancer usually not associated with smoking, after exposure to uranium ore and radon-222, a natural decay product of uranium. The radon, which is produced by the uranium, and not the uranium itself has been shown to be the cancer causing agent.  Some survivors and their descendants received compensation under the Radiation Exposure Compensation Act in 1990.
Currently the level of radon in the air of mines is normally controlled by law. In a working mine, the radon level can be controlled by ventilation, sealing off old workings and controlling the water in the mine. The level in a mine can go up when a mine is abandoned, it can reach a level which is able to cause the skin to become red (a mild radiation burn). The radon levels in some of the mines can reach 400 to 700 kBq m-3.
A common unit of exposure of lung tissue to alpha emitters is the Working level month (WLM), this is where the human lungs have been exposed for 170 hours (a typical month worth of work for a miner) to air which has 3.7 kBq of 222Rn (in equilibrium with its decay products). This is air which has the alpha dose rate of 1 working level (WL). It is estimated that the average person (general public) is subject to 0.2 WLM per year, which works out at about 15 to 20 WLM in a lifetime. According to the NRC 1 WLM is a 5 to 10 mSv lung dose (0.5 to 1.0 rem), while the OECD consider that 1 WLM is equal to a lung dose of 5.5 mSv, the ICRP consider 1 WLM to be a 5 mSv lung dose for professional workers (and 4 mSv lung dose for the general public). Lastly the UN (UNSCEAR) consider that the exposure of the lungs to 1 Bq of 222Rn (in equilibrium with its decay products) for one year will cause a dose of 61 μSv. This overview of the working level month is based upon the book by Jiří Hála and James D. Navratil (ISBN 80-7302-053-X).
In humans a relationship between lung cancer and radon has been shown at exist (beyond all reasonable doubt) for exposures of 100 WLM and above. By using the data from several studies it has been possible to show that an increased risk can be caused by a dose as low as 15 to 20 WLM. Sadly these studies have been difficult as the random errors in the data are very large. It is likely that the miners are also subject to other effects which can harm their lungs while at work (for example dust and diesel fumes).
A.R. Denman, J.P. Eatough, G. Gillmore and P.S. Phillips, Assessment of Health Risks To Skin and Lung Of Elevated Radon Level in Abandoned Mines, Health Physics, 2003, 85, 733.
G.K. Gillmore, P. Phillips, A. Denman, M Sperrin and G. Pearse, Ecotoxicology and Environmental Safety, 2001, 49, 281.
Radioactivity, ionizing radiation and Nuclear Energy, Jiří Hála and James D. Navratil, Chapter 8 (Radioactivity and ionizing radiation in the environment), ISBN 80-7302-053-X.
J.H. Lubin and J.D. Boice, Journal Natl. Cancer Inst., 1997, 89, 49. (Risks of indoor radon)
N.M. Hurley and J.H. Hurley, Environment International, 1986, 12, 39. (Lung cancer in uranium miners as a function of radon exposure).
The danger of radon exposure in dwellings was discovered in 1984 by Stanley Watras, an employee at the Limerick nuclear power plant in Pennsylvania. Mr. Watras set off the radiation alarms (see Geiger counter) on his way into work for two weeks straight while authorities searched for the source of the contamination. They were shocked to find that the source was astonishingly high levels of Radon in his basement and it was not related to the nuclear plant. The risks associated with living in his house were estimated to be equivalent to smoking 135 packs of cigarettes every day.
Depending on how houses are built and ventilated, radon may accumulate in basements and dwellings. The European Union recommends that action should be taken starting from concentrations of 400 Bq/m3 for old houses, and 200 Bq/m3 for new ones.
The National Council on Radiation Protection and Measurements (NCRP) recommends action for any house with a concentration higher than 8 pCi/L (300 Bq/m³).
The United States Environmental Protection Agency recommends action for any house with a concentration higher than 148 Bq/m3 (given as 4 pCi/L). Nearly one in 15 homes in the U.S. has a high level of indoor radon according to their statistics. The U.S. Surgeon General and EPA recommend all homes be tested for radon. Since 1985, millions of homes have been tested for radon in the U.S.
By adding a crawl space under the ground floor, which is subject to forced ventilation the radon level in the house can be lowered.