Radon Risks

What is the primary organ of concern in the relationship between radiation dose from radon and risk?
The lung, and especially the bronchial epithelium of the lung, is the organ at risk from exposures to radon daughters.

Are there uncertainties in the use of equations to calculate the dose to the bronchial epithelium due to the radon daughters?
Yes. Complicating factors include the dependence of deposition in the lung (and hence dose) on the age, sex, and breathing rate of the exposed individual. There is also considerable uncertainty as to whether or not the unattached fraction will reach the tracheobronchial tree (i.e., the unattached daughters may be removed in the nasopharynx instead). There are other factors as well.

What relationship exists between the dose equivalent and exposure to the bronchial epithelium?
The following relationships between dose equivalent and exposure (in WLM) were described in NCRP Report 78 , Evaluation of Occupational and Environmental Exposures to Radon and Radon Daughters in the United States: 1 WLM = 14.2 rem (0.71 rads) in an adult male; 1 WLM = 12.6 rem (0.63 rads) in an adult female; and 1 WLM = 25 rem (1.25 rads) in a 10 year old child. The ICRP in Publication 50, Lung Cancer Risk from Indoor Exposure to Radon Daughters, also established a relationship between the exposure and the dose equivalent to the bronchial epithelium in adults. For radon daughters, one (1) WLM was equivalent to 9.5 rem indoors and 12.6 rem outdoors. For thoron daughters, one (1) WLM was equal to 2.3 rem.

If we take those numbers at face value, what conclusion can be drawn using the above relationships?
A typical yearly exposure of 0.2 WLM is essentially equivalent to a yearly dose equivalent of three (3) rem to the bronchial epithelium.

How high are the uncertainties in these relationships?
A high degree of uncertainty is associated with these numbers. Quite different values can be found elsewhere in the literature, and as new reports (with updated data) are issued.

What about the dose to the lung itself?
In some cases,the doses reported for the lung are actually the doses to the bronchial epithelium. In other cases the dose is "averaged" over the lung (There are several ways in which this might be done.). When averaging, the mean (average) dose to the total lung is approximately one-half that of the bronchial epithelium.

How is the effective dose equivalent determined for radon in the lung?
The effective dose equivalent is the dose effectively received by the whole body even if only one organ was actually irradiated. Each organ is assigned a particular "weighting factor" that determines its "importance" relative to the whole body. In this instance, once the dose equivalent to the lung has been estimated, it can be multiplied by the weighting factor (wt) of 0.12 to calculate an effective dose equivalent. As an example, if the lung received a dose equivalent of 100 rem, the effective dose equivalent to the whole body would be 12 rem (100 rem x 0.12).

What risk is associated with exposure to radon daughters?
Inhaling elevated concentrations of radon daughters increases the risk of developing lung cancer - a fatal disease usually appearing sometime after age 40.

How does this occur?
When air is inhaled, airborne particulates radon daughters will be deposited, according to size, in various parts of the respiratory system. Since radon itself is inert and unattached, it will be present in the lung for only a short period of time. The radon daughters, however, remain in the lung for longer periods of time and are thus responsible for a much larger fraction of the dose to the lung than that from radon.

What does the scientific community say about risk estimates for radon?
Organizations like the NCRP, ICRP, Environmental Protection Agency (EPA) and the Biological Effects of Ionizing Radiation (BEIR) Committee have all provided risk estimates for radon exposures. The NCRP and BEIR committees provide recommendations in this country to regulatory authorities such as the EPA. The ICRP offers recommendations on an international scale which are evaluated in the United States for their potential impact on radiation protection policy. The studies analyzed by these groups in order to derive their risk estimates were, for the most part, epidemiological studies of underground miners.

Miners? Why them?
Because the radon concentration underground is generally much higher than above the ground, and because miners spent a lot of time in those areas of elevated radon concentration.

How representative are the miner risk estimates when compared to other types of radon exposures?
Not very. There are a number of uncertainties that make a direct translation difficult, if not impossible. For example: 1) The miners were exposed to very high levels (hundreds of working level months), yet the risks are extrapolated down to low levels; 2) The exposures of the miners are uncertain - either in the mines or in their homes; 3)The studies are incomplete in that many miners in the study groups are still alive; 4) With the exception of one cohort of miners, their smoking habits are unknown; 5) The miner studies provide no evidence of the risk to women or children; 6) The breathing patterns of miners during work are different from those characteristic of the general public; and 7) The characteristics of aerosols in a mine can be quite different from those in a home.

Have other epidemiological studies produced definitive results?
No, not really. Epidemiological studies investigating the effects of radon at the environmental concentrations normally encountered typically produce mixed results. For example, in one study, the State of New Jersey compared the radon exposures of 433 case subjects and 402 controls. The result was a statistically significant increase in lung cancer risk with radon concentrations in the home. However, another study of 308 cases and 356 controls in China by the National Cancer Institute observed no increased risk associated with elevated levels of radon.

What relationship exists between smoking and lung cancer?
According to BEIR VI, of the approximately 3 million people who died in this country in 1995, 157,000 individuals died due to lung cancer (from all causes, including radon exposure and smoking). It was further estimated that 95% of the men and 90% of the women who died of lung cancer were smokers.

What relationship exists between smoking and radon?
There appears to be little argument that either smoking or radon, taken separately, can cause lung cancer. However, the combined effects of smoking and radon exposure still remain somewhat of a mystery. Nonetheless, the BEIR VI committee has stated that a synergistic effect exists (i.e., the combined risks are greater than the sum of their individual risks).

So what do we really know about the hazards associated with the inhalation of radon gas?
The studies conducted thus far have not provided a conclusive answer. The BEIR VI report indicated that the risk in homes is likely to be very small at the low exposures encountered. Also, estimating the amount of radon exposure received by an individual over a lifetime is difficult, at best.

What general conclusions did the BEIR committee reach?
The BEIR committee offered the following general comments: 1)Radon was identified as the second leading cause of lung cancer and therefore an important public health risk; 2) An estimated 10-14% of lung cancer deaths in this country - approximately 15,000 to 22,000 lung cancer deaths/year - were linked to the inhalation of radon gas (however, the committee also pointed out that due to the inherent uncertainties, the number could be as low as 3,000 or as high as 32,000 deaths); 3) Even very small exposures to radon can cause lung cancer; 4) Radon studies in homes is consistent with studies of radon health effects in mines; and 5) The lung cancer threat can be reduced by limiting the exposure to radon in homes.

Where can I get further information on the BEIR VI report?
A summary of the report is available on the EPA's Indoor Environments Division (IED) website. This website can be accessed at http://www.epa.gov/iaq. The BEIR VI summary is located athttp://www.epa.gov/iaq/radon/beirvi.html. Both an executive (technical) summary and a public summary are available for review. The report itself is available on the NAS website at http://www.nas.edu.

What does the EPA have to say about radon-induced lung cancer deaths?
The EPA estimates that between 7000 and 30,000 americans die each year of lung cancer as a result of exposure to radon gas. Their best estimate now is 14,000 deaths. Once again, however, this finding has been the subject of much debate within the scientific community.

What recommendations has the EPA provided to homeowners?
In its Citizens Guide to Radon, second edition, the EPA has set an indoor guideline level of 4 pCi/l for homeowners. This is an annual average concentration. The four (4) pCi/l value is consistent with the 0.02 WL limit employed in the Uranium Mill Tailings Remedial Action Program (UMTRAP). In general, a radon daughter concentration of one working level implies a radon concentration of 200 pCi/l (indoors). Therefore 4 pCi/l of radon is approximately equivalent to 0.02 WL (i.e. 4 pCi/l ÷ 200 pCi/WL).

What else can I do to educate myself on the radon issue?
Consider calling the National Safety Council (NSC) for information on two hotlines operated by the NSC - the National Radon Hotline and the National Radon Helpline. The NSC can be reached at 1-800-55-RADON. In addition, the Consumer Research Council (CRC) operates a Radon "Fix-It Line" (1-800-644-6999) which addresses issues related to radon and radon mitigation. And don't forget, you can always "Ask a CHP".

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