Agency for Toxic Substances and Disease Registry Radon Toxicity Physiologic Effects
The primary adverse health effect of exposure to radon daughters is lung cancer.
Radon exposure causes no acute or subacute health effects, no irritating effects, and has no warning signs at levels normally encountered in the environment. The only established human health effect associated with residential radon exposure is lung cancer. Epidemiological studies of miner cohorts have reported increased frequencies of chronic, nonmalignant lung diseases such as emphysema, pulmonary fibrosis, and chronic interstitial pneumonia, all of which increased with increasing cumulative exposure to radiation and with cigarette smoking.
The synergistic mechanism(s) of cigarette smoking and radon exposure are not known, although the adverse health effects of the combination are clear.
Epidemiological studies and a recent study of groundwater radon and cancer mortality have found no association with extrapulmonary cancers, such as leukemias and gastrointestinal cancers. This is expected on the basis of studies of the radium-dial painter population. Evidence is also lacking that environmental radon exposure is causally associated with adverse reproductive effects.
Radon progeny can be inhaled either as free particles or attached to dust. Attached progeny preferentially deposit in the bronchi, the site of most lung cancers.
Because of their charged state and solid nature, radon progeny rapidly attach to most available surfaces, including walls, floors, clothing (as in the case of "Worker A"), and airborne particulates. Radon progeny can be inhaled, therefore, either as free, unattached particles or attached to airborne dust. Smaller dust particles can deposit radon progeny deep in the lungs. Because they are ionized, the progeny tend to attach to the respiratory epithelium. Through mucociliary action, the progeny are eventually cleared from the respiratory tract, but because of their short half-life, they can release alpha particles before being removed. The total amount of energy deposited by the progeny is several hundred times that produced in the initial decay of radon. When these emissions occur within the lungs, the genetic material of cells lining the airways can be damaged, resulting in lung cancer.
The risk of lung cancer due to radon exposure is thought to be second only to that of smoking. The synergism between cigarette smoking and radon places the large population of current and former smokers at particularly high risk for lung cancer. Although the net consequence of cigarette smoking and exposure to radon decay products has been clearly demonstrated in smokers, the mechanism of interaction is still unclear.
Most of the lung cancers associated with radon are bronchogenic, with all histologic types represented. However, small-cell carcinoma occurs at a higher frequency among both smoking and nonsmoking populations of underground miners in the initial years after exposure, compared to the pattern of histologic types in the general population. Other types of lung cancers seen in radon-exposed miners are squamous cell carcinoma, adenocarcinoma, and large-cell carcinoma.
If the patient's daughter described in the case study were pregnant, would the fetus be at risk from maternal exposure to airborne radon?
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The patient's husband developed mesothelioma as a result of
asbestos exposure when he worked in the shipyards. What role might radon have played in the development of this condition?
