Estimates from the National Research Council, the National Academy of Sciences and the U.S. Environmental Protection Agency as published in the reports "Biological Effects of Ionizing Radiation" (BEIR VI, 1998), "Risk Assessment of Radon in Drinking Water" (1999), and "EPA Assessment of Risks from Radon in Homes" (2003):
Radon works faster than the usual lung cancer - people die younger. The average age for radon-induced lung cancer is 65 years compared to 72 for all lung cancer deaths.
"Radon is likely our leading environmental cause of cancer mortality in the United States. During the past 50 years, over a million people have died nationwide from radon-related lung cancer." (Testimony from R. William Field, University of Iowa professor of occupational and environmental health and epidemiology to President's Cancer Panel in 2010.)
The passage of a single alpha particle can cause mutations of DNA and some damaged cells may become cancerous. Most cancers originate from damage to a single cell. The more radiation particles pass through the human body, the higher the chances of developing cancer. Therefore, the lung cancer risk is proportional to the radon concentration in the inhaled air and the length of exposure.
The radon risk drops off for very 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 at home, every emitted particle counts.
Radon is dangerous at any level: 70 percent of radon-attributed deaths are caused by homes with radon below 4 pCi/L, 50 percent by levels below 2 pCi/L, and only 30 percent by radon below the mean (average) level of 1.25 pCi/L. Even the low outdoor levels not harmless - NAS estimates that out of the 21,000 lung cancer deaths caused by radon each year, 800 are caused by the natural radon levels outdoors (average 0.45 pCi/L).
Smoking is by far the leading cause of lung cancer and when combined with radon, the effects are synergistic. Current smokers have about nine times the risk from radon than never-smokers or 1.5-times higher than ever-smokers.
People spend most of their time at home - on average 70%, more for children and women. The cumulative lifetime exposure to ionizing radiation from radon and the corresponding lung cancer risks to a person are dependent on the radon level:
|Radon Level (pCi/L)||Mortality risk|
|Never Smokers||Current Smokers||General Population|
Note that the death risk to the average person from radon at home is 1,000-times the risk from any other carcinogen or toxin regulated by FDA or EPA. Safety limits are normally expressed in deaths per 100,000 people but radon risks in percentages (deaths per 100 people).
Radon progeny are the tiny radioactive metal particles floating in the air, which have not yet attached to dust and plated out. Their concentration is expressed in Working Levels. 1 WL is defined as any combination of short-lived radon daughters in 1 liter of air that results in the ultimate release of 1.3x105 million electron volts of alpha energy.
Equilibrium in a closed volume constantly supplied with radon - when the rate of decay of each daughter will equal to that of the radon itself. Each pCi/L of radon will give rise (almost exactly) to 0.001 WL. In homes, the typical equilibrium fraction is 40% - there will be 0.004 WL of progeny for each pCi/L of radon. (The radon isotopes Thoron and Actinon, which may add 5-10 percent to the radiation exposure, are ignored.)
Cumulative radon daughter exposures are measured in Working Level Months (WLM) defined as an exposure of 1 WL for 170 hours (miner's work month). We assume that 70% of our time is spent indoors. Then, the cumulative annual exposure in one year per each 1 pCi/L is:
1 pCi/L x 0.004 WL/pCi/L x 0.70 x 8,760/170 WLM/WL-y = 0.144 WLM/year
Estimated risk of death from radon-attributed lung cancer per WLM for never-smokers (NS) and ever-smokers (ES), male or female, and for a population with of 53% males and 47% females:
|Risk Factors per WLM|
|Gender||Smoking Category||Risk per WLM (10-4)||Expected Life Span (years)|
|Male & Female||ES||9.68||74.2|
Example 1: a man, former smoker, exposed to 6 pCi/L for 40 years
6 x 0.144 WLM/y = 0.864 WLM/y annual exposure
x age 40 years = 34.56 WLM cumulative exposure
x risk factor 10.6x10-4 /WLM = 0.0366 = 3.7%
Example 2: a never-smoker female, exposed to 4 pCi/L during her lifetime
4 x 0.144 WLM/y = 0.576 WLM/y annual exposure
x expected lifespan 79.4 years = 45.73 WLM cumulative exposure
x risk factor 1.61x10-4 /WLM = 0.0074 = 0.74%
The risk that she will die of radon-induced lung cancer during her lifetime.
"Radon in homes causes more deaths than fires, drownings and airplane crashes combined." (EPA) However, we spend incomparably more money on preventing violent deaths than on radon mitigation in our home. And media do not inform public about radon - a fire makes better TV than a lung cancer death.
|Radon Level (pCi/L)||Population Mortality||Risk Comparison|
|20||10.5%||90||times the risk of dying by||drowning|
|4||2.3%||3||times the risk of dying in a||car crash|
(Source: EPA Citizen's Guide to Radon)
The following tables (EPA 2003) show the comparable risks for current smokers and never-smokers.
|Radon Risk If You Smoke|
|if 1,000 people who smoked were exposed to this level over a lifetime ...||The risk of cancer from radon exposure compares to ...|
|20||About 260 people could get lung cancer||250 times the risk of drowning|
|10||About 150 people could get lung cancer||200 times the risk of dying in a home fire|
|8||About 120 people could get lung cancer||30 times the risk of dying in a fall|
|4||About 62 people could get lung cancer||5 times the risk of dying in a car crash|
|2||About 32 people could get lung cancer||6 times the risk of dying from poison|
|1.3||About 20 people could get lung cancer||(Average indoor radon level)|
|0.4||About 3 people could get lung cancer||(Average outdoor radon level)|
|Radon Risk If You've Never Smoked|
|If 1,000 people who smoked were exposed to this level over a lifetime ...||The risk of cancer from radon exposure compares to ...|
|20||About 36 people could get lung cancer||35 times the risk of drowning|
|10||About 18 people could get lung cancer||20 times the risk of dying in a home fire|
|8||About 15 people could get lung cancer||4 times the risk of dying in a fall|
|4||About 7 people could get lung cancer||The risk of dying in a car crash|
|2||About 4 person could get lung cancer||The risk of dying from poison|
|1.3||About 2 people could get lung cancer||(Average indoor radon level)|
|0.4||(Average outdoor radon level)|
...I’ve never smoked a cigarette, can’t stand to be around them. ... causing my lung cancer is the fact I had radon in my home ...
... My mother, who was a non-smoking, marathon runner and in the best shape of her life was diagnosed with Stage 4 Lung cancer ... She fought for 10 months....her home has a radon level of 19.9 pCi/L.
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