People in a room containing radon will inhale this gas along with its solid daughters, such as polonium, which may be aptly thought of as "radioactive dust." Radon and polonium produce alpha radiation when they decay. The alpha particles are not energetic enough to pass through a person's outer skin, but when released within the lungs they easily penetrate the unprotected lining and pass through the living cells. In the process of doing this, the alpha particles damage the cells in a way that can cause some of them to become cancerous. The other forms of radiation produced by the decay of radon and its daughters, beta particles and gamma rays, have no significant adverse health effects when released inside the lungs. It is by now well established that radon and its daughters can cause lung cancer. Ironically, very little of the damage done is caused by radon directly because this gas is usually exhaled before it has a chance to decay. Far more hazardous is the polonium which will stick to the lung's lining where it will stay until it decays. It is still appropriate, however, to characterize this health hazard as the "radon problem" because, being a gas, radon can readily escape from the ground and work its way into buildings where it then decays into polonium and other daughters. If radon were a solid element it would stay in the ground and cause no health problems. It has been suggested that drinking water containing radon may cause stomach cancer, but this effect has not been conclusively demonstrated and is, in any case, a very minor risk in comparison to that of radon-induced lung cancer.
Radon is the second leading cause of lung cancer in the U.S. after smoking. Not everyone who has been exposed to radon will develop lung cancer, but for those who do, the time between first exposure and onset of the disease may be many years. People who smoke (or who inhale second-hand smoke) and are also exposed to high levels of radon have a much greater chance of developing lung cancer because the two carcinogens (tobacco and radon) acting together have a more-than-additive effect. This arises from the tendency of radon daughters to adhere to the microscopic, air-borne dust from smoke which permeates a room and is inhaled by smokers and non-smokers alike. Thus, more of the daughters will come into contact with the lungs than would be the case in absence of smoke. The United States Environmental Protection Agency (US EPA) estimates that between 10 and 15 percent of all lung cancer deaths in the U.S. are attributed directly to radon alone or radon in combination with smoking. This amounts to between 700 and 1300 deaths in Ohio each year.
There is no safe level of radon, just different levels of risk. It is, unfortunately, impossible to avoid radon completely. In outdoor air the average radon concentration is about 0.4 pCi/l, and inside U.S. homes the average is about 1.3 pCi/l. It is technologically feasible to reduce indoor indoor levels to that of the outside air but it would be prohibitively expensive. Instead the US EPA specified an "action level" of 4 pCi/l, and recommends that buildings with an annual average radon concentration above this level be remediated immediately to reduce it to 2 pCi/l or less. Remediation of buildings with radon concentrations between 2 and 4 pCi/l is less urgent but should be considered at some point in the future. It is important to understand that the 4 pCi/l action level is not based on health risk considerations but rather strictly on what is reasonably affordable in remediation.
The US EPA has estimated the risk of developing lung cancer for people who have spent a lifetime in houses with a given average concentration of indoor radon. These estimates assume that people spend about 75 % of their time at home. The estimates are presented in the tables on the previous page. (Click here to go there).