Characteristics of Radon-222

Fate and Transport

Monitoring in the Environment


Measurement Methods

Control and Prevention

Harmful Effects

Absorption, Distribution and Organic Sites of Toxicity

Radon Dose

Radon Biomarkers

Risk Assessment

Molecular Action and Genetic Effects

Radon for Skeptics

Radon for Children

Risk Assessment

Radon Prevalence and Public Health Impact

Risk Estimates

Who’s at Risk

Radon Prevalence and Public Health Impact

Natural sources contribute significant quantities of radiation toward the total radiation exposure that humans receive. The majority of this natural radiation is harmless to humans in the ambient environment. However, radon, a large component of the natural radiation that humans are exposed to (greater than sixty percent), can pose a threat to the public health when radon gas accumulates in poorly ventilated residential and occupational settings.

According to the Office of the Surgeon General: “Indoor radon gas is a serious health problem in our nation that can be addressed by individual action. Unless people become aware of the danger radon poses, they will not act. Millions of homes are estimated to have elevated radon levels. Fortunately, the solution to this problem is straight-forward. Like the hazards from smoking, the health risks of radon can be reduced.”

Radon accounts for more than half of our total average annual exposure to radiation, about 200 of 360 millirem per year. Radon, although not always publicized as a tremendous public health concern (in the way that drunk driving is), ranks highly among other preventable causes of death, including drunk driving, drowning, and fires. Additionally, the death risk to the average person from radon gas at home is 1,000 times higher than the risk from any other carcinogen or toxin regulated by the FDA or EPA. For these reasons, research must be conducted to evaluate certain subgroups that have elevated risks and technology must be developed and implemented in order to limit exposure to dangerous levels of radon and its harmful progeny.

The most recent National Academy of Science (NAS) report on radon, The Health Effects of Exposure to Radon (the BEIR VI Report, published in 1999), estimated that about 14 percent of the 164,100 lung cancer deaths in the United States each year are attributable to exposure to radon - correlating to approximately 15,000 to 22,000 lung cancer deaths each year. 160 of these deaths have been attributed to radon dissolution exposure in ingested water, and 700 deaths from exposure in outdoor air (mostly exposure from mines). The majority of the radon caused deaths occur from inhalation of radon and radon progeny. The average number of years of life expectancy lost per death from lung cancer is about fifteen. In a second NAS report published in 1999 on radon in drinking water, the NAS estimated that about 89 percent of the fatal cancers caused by radon in drinking water were due to lung cancer from inhalation of radon released to indoor air, and about 11 percent were due to stomach cancer from consuming water containing radon.

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Risk Estimates

  • For a lifetime exposure at the EPA recommended guideline of 4 pCi/L, the EPA estimates
  • that the risk of developing lung cancer is 1 to 5%, depending on whether a person is a nonsmoker, former smoker, or smoker. The National Research Council estimates the risk as 0.8 to 1.4%.
  • The overall risk of radon exposure is related not only to its average level in the home, but also to the occupants and their lifestyles.

Factors that influence the risk of lung cancer from radon exposure:

  • age
  • duration of exposure
  • time since initiation of exposure
  • cigarette smoking
  • other carcinogenic exposures
  • gender
  • physical condition
  • genetic tendency either to resist or be affected by internal radiation exposure
  • geographic location – The upper Midwest has the most intense environmental radon concentration due to glacial deposits 10,000 years ago. View the EPA radon hazard zones in the “Sources of Radon” section for more information

Certain characteristics of the residence and environmental factors will play a role in determining the indoor radon concentrations. The highest radon levels are typically found in the lowest level of the house. If well water is the major source of radon, upper floors can be affected more than lower floors because of dissolution of radon from the water. Radon levels are elevated in colder climates (winter) rather than in more mild temperatures (summer and spring).

The risk of lung cancer associated with lifetime inhalation of radon in air at a concentration of 1 Bq m-3 was estimated on the basis of studies of underground miners. The values were based on risk projections from three follow-up studies: BEIR IV (National Research Council 1988), NIH (1994) and BEIR VI (National Research Council 1998). These three reports used data from 4 to 11 cohorts of underground miners in seven countries and developed risk projections of 1.0 x 10-4, 1.2 x 10-4, and 1.3 x 10-4 per unit concentration in air (1 Bq m-3), respectively. The three values were for a mixed population of smokers and nonsmokers. The risk of lung cancer (discussed in two reports of the National Research Council and one of the National Institutes of Health) posed by lifetime exposure to radon (222Rn) in water at 1 Bq m-3 was calculated to be 1.3 x 10-8.

As already stated, an increase in the number of radiation particles that pass through the human body correlates to an increase in the chance of developing cancer. Therefore, the risk to people is proportional to the length of exposure and the radon concentration in air (linear, no-threshold hypothesis). However, the radon risk begins to level off for extremely high concentrations, like for miners, because more lung cells are killed off by the radiation (rather than becoming cancerous) and some radiation is wasted on the already killed cells (the "inverse exposure-rate effect"). But at lower concentrations, like in residences, every emitted particle will have an impact.

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Who’s at Risk

This is a list of occupations that have the potential for high 222Rn progeny exposure:

  • Mine workers, including uranium, hard rock, and vanadium
  • Workers remediating radioactive contaminated sites, including uranium mill sites and mill tailings
  • Workers at underground nuclear waste repositories
  • Radon mitigation contractors and testers
  • Employees of natural caves
  • Phosphate fertilizer plant workers
  • Oil refinery workers
  • Utility tunnel workers
  • Subway tunnel workers
  • Construction excavators
  • Power plant workers, including geothermal power and coal
  • Employees of radon health mines
  • Employees of radon balneotherapy spas (waterborne 222Rn source)
  • Water plant operators (waterborne 222Rn source)
  • Fish hatchery attendants (waterborne 222Rn source)
  • Employees who come in contact with technologically enhanced sources of naturally occurring radioactive materials
  • Incidental exposure in almost any occupation from local geologic 222Rn sources

As early as the 16th century, two scientists, Paracelsus and Agricola, discovered and described a wasting disease present in many miners. In 1879, this condition was identified as lung cancer by Herting and Hesse in their investigation of miners from Schneeberg, Germany. Radon itself was discovered some 20 years later by Rutherford. Eventually, an increase in the incidence of lung cancer among miners was linked to radon daughter exposure in mines. Miners are particularly at risk of developing lung cancer for two reasons:

1.) miners are constantly being exposed to large quantities of radon. Radon is formed from the radioactive decay of radium and uranium. The latter two elements are naturally occurring elements in certain rocks and soils and will lead to excessive buildup of radon in the confined spaces of mines.

2.) miners are constantly being exposed to other chemicals, compounds, and particulate matter that have also shown an association with lung cancer incidence. Underground uranium mines found throughout the world, including the western United States and Canada, pose the greatest risk because of their high concentration of radon daughters in combination with silica dust, diesel fumes, and, typically, cigarette smoke. Iron ore, potash, tin, fluorspar, gold, zinc, and lead mines also have significant levels of radon. It is also important to note that in the past, it was not uncommon to use the tailings from these mines as fill on which to build homes, schools, and other structures, leading to elevated levels of radon in these indoor environments.

Geographic and Residential Risks
The amount of radon emanating from the earth and concentrating inside homes varies considerably by region and locality, and is greatly affected by the residential structure as well as soil and atmospheric conditions. Nearly every state in the United States has dwellings with measured radon levels above acceptable limits. The EPA estimates that 6% of American homes (approximately 6 million) have concentrations of radon above 4 pCi/L. Areas of the country that are likely to have homes with elevated radon levels are those with significant deposits of granite, uranium, shale, and phosphate, which are all high in radium content and, therefore, potential sources of radon gas. However, due to the many determinants of indoor radon levels, local geology alone is an inadequate predictor of risk. The only way to determine indoor radon concentration is by testing. Other factors that predispose homes to elevated levels of radon include soil porosity, foundation type, location, building materials used, entry points for soil gas, building ventilation rates, and source of water supply. Further research is being conducted on ways to predict which homes are most likely to have significant levels of radon.

Risk for Smokers
Apart from the results of very limited in-vitro and animal experiments, the only source of evidence on the combined effect of the 2 carcinogens (cigarette smoke and radon) was the National Academy of Science (NAS) data collected from 6 of miner studies. Analysis of that data indicated a synergistic effect of the two exposures acting together, which was characterized as submultiplicative (i.e., less than the anticipated effect if the joint effect were the product of the risks from the two agents individually, but more than if the joint effect were the sum of the individual risks). The risk of lung cancer from radon exposure is estimated to be approximately 10 -15 times greater for persons who smoke cigarettes in comparison with those who have never smoked. According to the NAS Committee on the Biological Effects of Ionizing Radiation (BEIR VI), a breakdown of the contribution of smoking and radon exposure to lung cancer deaths in the United States illustrates that of every 100 persons who died of lung cancer, approximately 93 were current or former smokers, whereas 7 had never smoked. However, it is important to remember that the lung cancer incidence among non-smokers is much lower than among smokers. Radon in homes causes 11% of lung cancer deaths among ever-smokers, but 23% among never-smokers. Therefore, increasing the radon levels presents a much higher relative risk to non-smokers. For example, increasing the radon concentration from 1.5 pCi/L to 4 pCi/L, the cancer risk for a non-smoker increases 100%, but only 42% for a smoker. Although there is no sure explanation for the synergistic effect of radon exposure and smoking, the predominant hypothesis is that smokers have a higher potential retention of deposited radon progeny due to increased mucus production and alterations in mucociliary clearance.

Risk estimates at 4 pCi/L for an average human lifetime (74 years):

1.) For people who never smoke:

  • 2/1000 (Citizen’s Guide to Radon, US EPA,1992)
  • 7/1000 (report from the National Academy of Sciences)

2.) For current smokers:

  • 3/100 (EPA 1992 and recent NAS report)

3.) For former smokers:

  • the risk is between the risks for smokers and those who have never smoked.

* note - The estimates above assume one spends 70% of one’s time indoors at home breathing 4 pCi/L. Short times spent in a region with higher radon (a basement) will not be important.
* note - If the average radon inhaled is higher, the risk is greater. If the average radon inhaled is lower, the risk is less.

Radon Level If 1,000 People Who Smoked Were Exposed to This Level Over a Lifetime... The Risk of Cancer From Radon Exposure Compares to... What To Do: STOP SMOKING and...
20 pCi/L About 250 men or 143 women could die of lung cancer
> 100 times the risk of drowning Consider fixing between 2 and 4 pCi/L
8 pCi/L About 132 men or 66 women could die of lung cancer > 100 times the risk of dying in a home fire Consider fixing between 2 and 4 pCi/L
4 pCi/L
About 66 men or 33 women could die of lung cancer > 100 times the risk of dying in an airplane crash Consider fixing between 2 and 4 pCi/L
2 pCi/L About 33 men or 16 women could die of lung cancer > 2 times the risk of dying in a car crash Consider fixing between 2 and 4 pCi/L
1.0 pCi/L About 16 men or 8 women could die of lung cancer (Average indoor radon level) (Reducing radon levels below 2 pCi/L is difficult)
0.4 pCi/L About 8 men or 4 women could die of lung cancer (Average outdoor radon level)

*pCi/L: picocuries per liter. If you are a former smoker, your risk might be lower.

Radon Risk Evaluation Chart if You Have Never Smoked
Radon Level If 1,000 People Who Smoked Were Exposed to This Level Over a Lifetime... The Risk of Cancer From Radon Exposure Compares to... What To Do: STOP SMOKING and...
20 pCi/L About 33 men or 20 women could die of lung cancer > 2 times the risk of being killed in a violent crime Consider fixing between 2 and 4 pCi/L
8 pCi/L About 13 men or 8 women could die of lung cancer Consider fixing between 2 and 4 pCi/L
4 pCi/L
About 6.4 men or 4 women could die of lung cancer > 10 times the risk of dying in an airplane crash Consider fixing between 2 and 4 pCi/L
1.0 pCi/L About 1.6 men or 1 woman could die of lung cancer The risk of dying in a home fire (Average indoor radon level) (Reducing radon levels below 2 pCi/L is difficult)
0.4 pCi/L Less than 1 person could die of lung cancer (Average outdoor radon level)

*pCi/L: picocuries per liter.
If you are a former smoker, your risk might be higher.

Risk for Women and Men
The effect of radon exposure on lung cancer risk in women might be different from that in men because of differing lung dosimetry or other factors related to gender (the risk model was developed using epidemiological studies in male miners). Women have displayed lower rates of lung cancer incidence than males, even after stratifying the analysis to control for smoking history. In 1999, the National Academy of Sciences calculated the lifetime risks of exposure to Radon-222 at home for each Becquerel/m3 (0.007 pCi/L) in air:

Lung cancer risks from exposure to Radon-222 at 1 Bq/m3
Ever-Smokers Never-Smokers
Men 3.1 x 10-4 0.59 x 10-4
Women 2.0 x 10-4 0.40 x 10-4
1.6 x 10-4

Risk for Children and Elderly

Data on the effects of radiation in children is rather limited, however, several studies have showed that children are more susceptible to radon exposure than adults. Children have different lung architecture and breathing patterns, resulting in a somewhat larger dose of radiation to the respiratory tract. Children also have longer latency periods in which to develop cancer. Hofmann reported that the radon dose was strongly dependent on age, with a maximum value reached at about the age of 6 years. Despite these findings, no conclusive data exists on whether children are at greater risk than adults from radon. Because of the latency time for cancer to develop and the cumulative nature of radon risk through time, there is very little possibility that someone could get lung cancer from radon before age 35, although exposures before that age contribute to the risk at later ages. The relative risk from domestic radon exposure is also higher for children because they spend more time at home and/or the basement. On average, children spend 70% more time in the house than adults.
Studies regarding the rates of translocation in a person show that there exists an exponential increase in the number of translocation with an increase in age. Characterized by the formula:2.8 + 0.0025 x (age)2

It has been hypothesized that decreased efficiency in DNA repair mechanisms is a function of age. Therefore, as a person gets older, their DNA becomes more unstable and abnormalities persist through the cell cycling process because of a lack of repair capabilities. For this reason, alpha particle exposure at later life stages can have greater potential for causing genomic changes. However, individuals of this age are probably too old to die of the associated tumor progression (cancer endpoints take many years [usually >15] to manifest themselves).

Risk for Individuals with Preexisting Respiratory Conditions
Populations that may be more susceptible to the respiratory effects of radon and radon progeny are people who have chronic respiratory diseases, including asthma, emphysema, and fibrosis. People with chronic respiratory disease often have reduced expiration efficiency and increased residual volume (i.e., greater than normal amounts of air left in the lungs after normal expiration). Therefore, radon and its progeny would be resident in the lungs for longer periods of time, increasing the risk of damage to the lung tissue. Additionally, persons who have existing lung lesions may be more susceptible to the tumor-causing effects of radon.

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