How Does Radon Induce Lung Cancer?
If inhaled, airborne radon decay products become deeply lodged or trapped in the lungs, where the alphas radiate and penetrate the cells of the mucous membranes, bronchi, and other pulmonary tissues.
The ionizing radiation energy affecting the bronchial epithelial cells is believed to initiate the process of the carcinogenesis. Although, radon-related lung cancers are mainly seen in the upper airways, radon increases the incidence of all historical types of lung cancer, including small cell carcinoma, adenocarcinoma, and squamous cell carcinoma.
What is The Evidence?
More is known about the health risk of radon exposure than almost any other human carcinogen. In fact, the University of Iowa College of Public Health recently compiled a bibliography of radon epidemiology research that took 192 pages just to list!
These include extensive studies of thousands of underground miners, carried out over more than 50 years worldwide, that have consistently shown an increase in lung cancer occurrence with exposure to radon progeny.
Miner studies have produced some interesting findings. For example, 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 that high exposures over short periods. Non-smoking miners were observed to have a significant increased risk, even after controlling for, or in the absence of other mine exposures such as asbestos, silica, diesel fumes, arsenic, chromium, nickel, and ore dust. An added synergic effect between radon exposure and cigarette smoking was also found.
The NAS has repeatedly concluded that it is reasonable to extrapolate from the miner data to a residential situation and in doing so, consider that the effective doses per unit of exposure for people in homes is approximately 30% less than for the miners.
Residential studies have yielded similar findings. The Iowa Residential Radon Study completed in May of 2000 determined that even at the EPA Action Level of 4 pCi/L, an approximate 50 percent excess lung cancer risk was found among the women in the study after correcting for the impact of smoking. A 2002 residential study conducted in northeast Spain yielded similar results. Even at concentrations far below official guideline levels, the Spanish study found that radon might lead to a 2.5-fold rise in the risk of lung cancer.
Exposures of animals further confirm that radon and its progeny cause lung cancer. Health effects observed in animals exposed to radon include lung carcinomas, pulmonary fibrosis, emphysema, and a shortening of life span. The incidence of respiratory tract tumors increased with an increase in cumulative exposure. Exposure to ore dust and diesel fumes simultaneously with radon did not increase the incidence of lung tumors above that produced by radon progeny exposures alone. In a study of rats exposed to radon progeny, it was observed that the risk of lung cancer was elevated at exposure levels similar to those found in homes.
Facts About Lung Cancer
- Lung cancer is the leading cause of cancer deaths in the United States.
- Lung cancer kills more Americans each year than breast, prostate and colorectal cancers combined.
- Lung cancer kills more women each year than breast cancer.
- Lung cancer kills 85% of newly diagnosed patients within five years.
- Approximately 50% of the people diagnosed with lung cancer have never smoked or are former smokers.
- Lung cancer gets few of the research dollars because of the perception it is self-inflicted by smoking.
- In 2003, approximately $1,740 was spent on research per lung cancer death, compared with: $13,649 per breast cancer death, $10,560 per prostate cancer death and $4,581 per colorectal cancer death.