What are the Potential Health Effects from Exposure to Increased Radon Levels?
At levels normally encountered in the environment, radon exposure causes no acute or subacute health effects, no irritating effects, and has no warning signs.
- The primary adverse health effect of exposure to increased levels of radon is lung cancer.
- For lung cancer to develop may take years.
- For smokers, exposure to elevated radon levels increases their already heightened lung cancer risk.
Children exposed to radon will have higher estimated radiation doses than will adults. This is due to the differences in lung shape and size and children’s faster respiration rate, all of which increase children’s risk of adverse health effects from radon exposure.
Due to radon progeny’s charged state and solid nature, they tend to attract dust particles. The progeny can be inhaled either as free particles (i.e., the unattached fraction) or attached to airborne particulates (i.e., the attached fraction). The attached fraction is 2-3 orders of magnitude more carcinogenic. The smaller the dust particle, the deeper into the lungs it can travel and deposit, together with the radon progeny it carries (ATSDR 2009).
Epidemiologic studies of miner cohorts have reported increased frequencies of chronic, nonmalignant lung diseases such as
- Chronic interstitial pneumonia, and
- Pulmonary fibrosis,
all of which increased as cumulative exposure to radiation and cigarette smoking increased (ATSDR 2009).
Researchers have studied the prevalence of radon-induced lung cancer in mining and residential populations. In miners, statistically significant increases in lung cancer have been observed, exceeding 465 WLM (Roscoe et al. 1989) and in residential populations exceeding an average 14.65 pCi/L.
As charged particles, the unattached radon progeny can adhere to lung fluid or the respiratory epithelium. But the attached fraction is what clings more effectively to the respiratory epithelium. Through mucociliary action, those progeny floating unattached in lung fluid are rapidly cleared from the respiratory tract. And because of the alpha particles’ short track length, only the fluid is exposed to any released radiation, with no adverse health effects.
- When progeny transform within the lungs and their energy deposits in tissue (and not fluid), the genetic material of cells lining the airways can be damaged. If a cell lives but repair is incomplete, lung cancer can develop (NRCC 1999).
- Attached progeny preferentially deposit in the bronchi, the site of most lung cancers.
- The total amount of energy deposited in successive transformations of the progeny is several times that produced in the initial radon decay.
An exact systematic description of how cancers form as a result of exposure to radiation is only partially understood. Cancer is a monoclonal disease that starts as a single cell with heritable damage to the deoxyribonucleic acid (DNA); this damage confers a proliferative advantage relative to normal cells (Iannaccone 1987). Most of the lung cancers associated with radon are bronchogenic, with all histologic types represented.
Smaller lungs and faster respiration rates in children generally results in higher estimated radiation doses to children’s lungs relative to adults.
Cigarette smoking and radon decay products synergistically influence lung cancer risk in a supra-additive manner. Miner studies found that if smoking started before occupational radon exposure, the effect was submultiplicative, or, if these occurred in the opposite order, more-than-multiplicative (ATSDR 2009).
The analysis of results from thirteen European residential case-control studies showed an increase in lung cancer risk proportionate to the unit increase in radon concentration, similar in lifelong nonsmokers and cigarette smokers (ATSDR 2009).
The lung cancer risk for cigarette smokers may be up to 25 times greater than that of nonsmokers exposed to high residential radon levels (up to 10.8 pCi/L) (Darby et al. 2005, 2006).
The lung cancer risk due to radon exposure is second only to that of smoking (Alberg 2007; Copes 2007; EPA 2009a).
- Although the synergistic mechanism(s) of cigarette smoking and radon exposure are unknown, the combination’s adverse health effects are well known.
Among both smoking and nonsmoking populations of underground miners, small-cell carcinoma occurs at a higher frequency in the initial years following exposure compared with the pattern of similar histologic types in the general population. This is believed due to the high levels of radon exposure underground, but could be due in part to high-level silica dust exposure.
Other types of lung cancers seen in radon exposed miners include
- Large cell carcinoma, and
- Squamous cell carcinoma.
No evidence supports the suggestion that environmental radon exposure is causally associated with adverse reproductive effects.
- Lung cancer is the only established human health effect currently associated with exposure to increased radon levels.
- The risk of lung cancer due to radon exposure is second only to that of smoking.
- Children have higher estimated radiation doses due to the differences in their lung shape and size, and their higher respiration rates compared with adults.
- Smokers are also exposed to radon and have a higher risk for lung cancer than do nonsmokers.