Health Risks

How does radon induce cancer?

Radon decay product, polonium-218 and polonium-214, when inhaled, attached or unattached to the surfaces of dusts, aerosols, and smoke particles, become deeply lodged and trapped in the lungs, where they radiate and can penetrate the cells of mucous membranes, bronchi, and other lung tissues.

The process of carcinogenesis is believed to be initialized from the ionizing radiation energy affecting the bronchial epithelial cells. Radon-related lung cancers are generally seen in the upper airways, but radon increases the frequency of all histological types of lung cancer, including: Adenocarcinoma, small cell carcinoma, and squamous cell carcinoma.

Lung cancer resulting from the inhalation of radon decay products is the only known risk associated with radon. In the studies done on uranium miners, variables such as age, time of exposure, time since the initiation of exposure, and the use of tobacco have been found to greatly influence individual risk. Smoking tobacco multiplies the risk of radon induced lung cancer by an average of 10 times.

What is the evidence?

More is known about the risk of radon exposure in humans than about most other group 1, or human carcinogens. This is based on extensive epidemiological studies of thousands of miners, conducted over more than 50 years world-wide, including miners in the US and Canada. Experimental testing exposing animals to radon confirms that radon decay products can cause lung cancer.

The research on lung cancer mortality is substantial and consistent in miners exposed to radon progeny. Studies of thousands of miners, some with follow-up periods of thirty years or more, have been conducted in mines, mining metal, fluorspar, shale, and uranium in the US, Canada, China, Australia and Europe. These studies are consistent in showing an increase in lung cancer occurrences from exposure to radon decay products, despite the differences in study populations and methodologies. The miner studies produced some interesting findings.

Equal at exponential exposures, lower exposures in the range of the 4 pCi/L action level over longer periods of time produced greater health risk than higher exposures over short periods of time.
Increased lung cancer risk with radon exposure has been observed, even after the absence of other mine exposures such as asbestos, diesel fumes, silica, arsenic, nickel, chromium, and ore dust.
Increased health risk has been observed in miners at relatively low cumulative exposures, in the range of the EPAs 4 pCi/L action level.
Nonsmoking miners exposed to radon, and radon decay products, have been observed to have an increased risk of lung cancer.

Animal experiments have confirmed the carcinogenicity of radon, and have provided understanding into the nature of the exposure-response relationship, as well as the modifying effects of the radon exposure rate. To date, these animal studies that were conducted in the US and France, have produced several relevant findings.

The Observed health effects in animals exposed to radon and its decay products include lung carcinomas, emphysema, pulmonary fibrosis, and a shortened life-span.
The frequency of respiratory tract tumors increased with an increase in cumulative exposure, and with a decrease in rate of exposure.
An increased frequency of respiratory tract tumors was observed in rats at cumulative exposures as low as 20 working level months (WLM).
The exposure to diesel fumes, or ore dust simultaneously with radon did not increase the occurrence of lung tumors above that produced by radon progeny exposures alone.
The lifetime lung-tumor risk coefficients that were detected in animals, are similar to the life-time lung cancer risk coefficients observed in human studies.
An observation made in a study of rats exposed to radon decay products and uranium ore dust simultaneously, was that the risk of lung cancer was elevated at exposure levels proportionate to those found in homes, and the risk decreased in proportion to a decrease in the exposure of radon decay products.

In 1988, a panel of world experts assembled by the World Health Organizations International Agency for Research on Cancer, came to a consensus that there is sufficient evidence to conclude that radon, and radon decay products, cause cancer in humans and in laboratory animals.

Is occupational exposure to radon concentrations comparable to residential exposure?

Because questions have been raised about the suitability of using the epidemiological studies of miners as a foundation for estimating the risk radon poses to the general population, the EPA appointed the National Academy of Sciences (NAS) to investigate the difference between underground miners and the general public, in the doses they receive per unit exposure due to inhaled radon decay products.

The NAS report concluded that it is respectable to extrapolate from the miner data to a residential situation, but that the effective doses per unit of exposure for the general public in their homes is about 30% less than that of the miners. In its analysis, the NAS considered variables including the breathing rate of underground miners in comparison to that of people at home, the amount and type of dust to which the radon decay particles would attach, and the presence of women and children in the homes.

The EPA has adjusted its residential health risk estimates accordingly. The result is still considerable the EPA now estimates that approximately fourteen thousand (14,000) lung cancer deaths are due to residential radon exposures in the United States per year, with an uncertainty range of 7,000 to 30,000 lung cancer deaths. As more data is collected about residential radon exposures, the health risk estimates may be adjusted further. Enough data exists now to be able to say with certainty that thousands of preventable lung cancer deaths each year in the United States are due to residential exposure to radon indoors.

To answer important questions about radons effect on women and children, more information about residential exposure to radon is needed. Although children have been reported to be at higher risk than adults for developing certain types of cancers from radiation, currently theres no evidence that radon exposure places children at any higher risk. Some miner and animal studies indicate that for the same total amount of exposure, a lower exposure over a longer time is more hazardous than a shorter, higher exposure, therefore, these findings increase concerns about radon exposures in homes. Epidemiological case control studies are in progress in the US and Europe, and the pooled results should enhance the understanding of the health risk of residential exposure to radon.

What about smoking tobacco and radon exposure?

Some people ask whether the lung cancer mortality attributed to the exposure of radon may actually be the result of smoking. A 1989 study demonstrated a greatly increased lung cancer risk in non-smoking uranium miners exposed to elevated radon concentrations: compared to typical non-smoking populations, and generally these miners had 9-12 times the risk of developing lung cancer.

Evidence observed from some of the epidemiological studies of underground miners, primarily in US uranium miners, indicate that radon exposure and smoking may have a collaborative relationship. Either smoking tobacco or radon exposure can increase the risk of developing lung cancer; however, exposure to both greatly increases that risk.

Your chances of developing lung cancer from radon mostly depends on:

The concentration of radon in your home
How much time you spend in your home
If you are a smoker, or have ever smoked.

Radon Publications: A Citizens Guide to Radon The Guide to Protecting Yourself and Your Family From Radon. EPA. Environmental Protection Agency, n.d. Web.

Source URL: http://www.epa.gov/radon/pubs/citguide.html