Earth has many ways to kill us. We keep on the lookout, and rightly so, for volcanic eruptions, earthquakes, landslides, flooding, cosmic impacts, climate change and falling rocks on the highway. Should we still worry about radon?
You remember radon—that radioactive gas that comes up from the soil and collects in basements and ground floors, sometimes in well water. Radon is a prominent villain in the United States, blamed for tens of thousands of deaths from lung cancer. Like asbestos, radon was looked at more kindly when it was new, and today it too is more feared than it deserves.
To the geologist, radon is interesting, not worrisome. For one thing, radon starts with uranium, which is worth knowing about for its energy content and its important role in the Earth's heat budget.
Uranium turns to lead via a long, slow cascade of nuclear decay, and radon sits at an important point in that process. Not only does the radon nuclide decay quickly, with a half-life less than four days, but the next four nuclides in the cascade decay with a combined half-life less than an hour. In other words, radon packs a powerful dose of radioactivity, and because it is a gaseous element, it can drift out of the minerals where it forms into the air. Thus it's a good signal of uranium, even for buried deposits.
Radon loves fractures because they set it free. Solid mineral grains are a pretty good trap for gases, but break the grains and the gas escapes. So just having rocks rich in uranium is not enough—they must be fractured, too. Earthquake faults are often a strong source of radon for that reason, and changes in radon emissions are a well-known simple indicator of seismic stress and deep ground movement.
Radon is relatively high in uranium-rich rocks such as ancient granites, high-organic shales and coal beds. (Coal burning is a major source of uranium pollution, and the boom in natural gas from shale may have an effect on household radiation budgets.) The US map of potential radon reflects this geological factor.
The Radon Hazard
The government has set reasonable radon limits that protect mine workers and other occupations with unusually high exposures. The Environmental Protection Agency urges the rest of us to test our homes and take measures against moderate radon levels, while admitting that good research is still needed.
High radon levels, unless they are truly extreme, are not an urgent threat. Lowering radon levels is simple and fairly cheap. If the EPA's policy is excessive, it's a pretty benign excess.
Nevertheless, radon is a background risk to the average American who doesn't smoke. Consider a well-conducted study published in the June 2000 American Journal of Epidemiology. Press releases trumpeted its result—if you were an Iowa women who'd lived for 15 years in a home with radon levels above the EPA's "action level," you faced an estimated excess lung cancer risk of 50 percent! (More recent studies give similar results.) But your actual odds of dying from lung cancer due to home radon exposure above the action level, if you don't smoke and if you spend 70 percent of your total time indoors at home, is about 1 in 100,000 per year, with a large statistical uncertainty.
Among smokers, radon has a substantial additive effect in raising the risk of lung cancer. High radon is not such a negligible risk for smokers.
If you care about the hazard of household radon, the authorities will help you investigate your risk and find someone to fix it for you. And you'll keep following the painstaking, expensive research needed to quantify this public health threat.
Making Friends with Radon
There are still reminders around of times when radon was desirable. Early in the 20th century, radiation was a full-blown health fad, and natural sites with high radiation were sought out for their curative powers. And at least two abandoned mines in Montana are reborn as old-fashioned radon centers—complete with glowing testimonials, so to speak—the Free Enterprise Health Mine in Boulder and the Merry Widow Health Mine in Basin.
But I think I'd rather be pampered in traditional Austrian spa luxury and hot water at Bad Gastein while I take my radon therapy. The medical patter is more persuasive there, and they seem to serve food.
PS: Frozen radon, which condenses into solid form at a relatively balmy –71°C, must be quite a sight. Evidently it glows with a bright phosphorescence from its own radioactivity, turning yellow through orange to red as it is cooled further.