Despite how widespread and dangerous it is, radon rarely makes headlines. Most of us have heard more about the cancer-causing effects of sun exposure or grilled meat than about the dangers of radon. Considering that it accounts for more than half of the average annual dose of radiation that U.S. residents receive, perhaps radon hasn't gotten the attention it deserves.
Radon-222 is a naturally occurring radioactive gas. It forms during the decay of uranium-238, another radioactive substance that occurs naturally in the earth. The radioactivity of substances like radon and uranium is the result of instability of the atomic nucleus. The number of protons and neutrons in the nucleus of a radioactive atom is not in the proportion it needs to be in order to be stable. In the process of correcting this imbalance, radioactive elements cast off radiation in the form of particles or rays and in so doing are themselves transformed into other elements or more stable forms of the same elements. Sometimes these new elements, the products of radioactive decay, are stable, but often they too are unstable and undergo further decay. Radon-222 forms during the fifth of 14 steps in uranium-238's decay process.
Because radon is a gas, it can easily enter the body by being breathed in, and thus poses greater health risks to humans than many other radioactive elements. Often it seeps from the ground through cracks in the foundations of homes and buildings. In well-ventilated areas, it dissipates quickly. However, in enclosed basements, it can accumulate in concentrations high enough to be harmful to residents or workers who breathe the contaminated air.
Although much of the radon that humans breathe in is exhaled before it can have adverse effects, some radon atoms stay in the lungs where they undergo further radioactive decay. At each of the nine decay steps between radon-222 and the non-radioactive lead-206, radiation is released, increasing the risk of cancer to exposed tissue. Experts estimate that radon is responsible for between 15,000 and 22,000 lung cancer deaths each year in the U.S. However, a few simple steps can greatly reduce radon exposure. These include testing buildings for radon contamination and, if necessary, sealing foundations and/or ventilating basements.