The Health Risk of Radon Gas
Radon is a class A known human carcinogen.
Alpha particles from the radon decay products can damage lung tissue.
Lung cancer is the main health effect from radon exposure.
How Does Radon Induce Cancer?
If inhaled, radon decay products (polonium-218 and polonium-214, solid form), unattached or attached to the surface of aerosols, dusts, and smoke particles, become deeply lodged or trapped in the lungs, where they can radiate and penetrate the cells of mucous membranes, bronchi, and other pulmonary tissues. The ionizing radiation energy affecting the bronchial epithelial cells is believed to initiate the process of carcinogenesis. Although radon-related lung cancers are mainly seen in the upper airways, radon increases the incidence of all histological types of lung cancer, including small cell carcinoma, adenocarcinoma, and squamous cell carcinoma. Lung cancer due to inhalation of radon decay products constitutes the only known risk associated with radon. In studies done on miners, variables such as age, duration of exposure, time since initiation of exposure and especially the use of tobacco have been found to influence individual risk. In fact, the use of tobacco multiplies the risk of radon-induced lung cancer enormously.
What is the Evidence?
More is known about the health risk of radon exposure to humans than about most other human carcinogens. This knowledge is based on extensive epidemiological studies of thousands of underground miners, carried out over more than fifty (50) years worldwide, including miners in the United States and Canada. In addition to the miner data, experimental exposures of animals confirm that radon and its decay products can cause lung cancer.
The research on lung cancer mortality in miners exposed to radon progeny is substantial and consistent. Studies of thousands of miners, some with follow-up periods of thirty (30) years and more, have been conducted in metal, fluorspar, shale, and uranium mines in the United States, Canada, Australia, China, and Europe. These studies have consistently shown an increase in lung cancer occurrence with exposure to radon decay products, despite differences in study populations and methodologies.
The miner studies produced some interesting findings.
At equal cumulative exposures, low exposures in the range of EPA’s 4 pCi/L action level over longer periods produced greater lung cancer risk than high exposures over short periods.
Increased lung cancer risk with radon exposure has been observed even after controlling for, or in the absence of, other mine exposures such as asbestos, silica, diesel fumes, arsenic, chromium, nickel, and ore dust.
Increased lung cancer risk has been observed in miners at relatively low cumulative exposures in the range of EPA’s 4 pCi/L action level (Sevc Kunz, Tomasik et al, Health Physics 54(1):27-46,1988; Mulles Wheeler et al, Proceedings of International Conference on Occupation Radiation Safety in Mining, Vol. 1, Canadian Nuclear Association; Radford and St. Clair Renard, New England Journal of Medicine310(23):1485-1494, 1984;Woodward, Roder et al, “Cancer Causes and Control” 2:213-220, 1991).
Nonsmoking miners exposed to radon have been observed to have an increased risk of lung cancer.
What About Smoking and Radon Exposure?
Some people ask whether the lung cancer deaths attributed to radon exposure actually may be the result of smoking. A 1989 study by researchers from the National Institute for Occupational Safety and Health, the Centers for Disease Control, the Harvard School of Public Health, and the University of California at Davis demonstrated a greatly incased lung cancer risk in nonsmoking uranium miners exposed to high radon concentrations: compared to typical non-smoking populations, these miners had nine (9) to twelve (12) times the risk of developing lung cancer (Roscoe et al, JAMA 262(5): 629-633, 1989).
