As it decays, uranium also produces radon, a colourless, odorless, radioactive gas that's all around us. Some places have more uranium and radon than others.
In central Montana, people visit underground health mines in the belief that large doses of radon can cure arthritis and other ailments.
Why is radon dangerous?
Simply put, radiation can cause cancer. Like all radioactive substances, radon emits high-energy waves and particles that can bombard the cells in your body.
Small amounts of radiation are generally harmless, which is why the occasional x-ray should not be a problem. But larger or long-term doses of radiation can damage your DNA, the genetic material in your cells.
Breathing in radon can expose your lung cells to dangerous levels of radiation. If the DNA in lung cells get too damaged, the cells can turn cancerous and start dividing out of control.
The United States Environmental Protection Agency roughly estimates that radon causes roughly 21,000 fatal cases of lung cancer in the U.S. each year, making it the second-leading cause of lung cancer after smoking. By comparison, about 124,000 people die each year from lung cancer caused by cigarette smoke.
Read: How cancer is treated
It's hard to know exactly how many lung cancer cases can be linked to radon, partly because many people breathe both cigarette smoke and radon on a daily basis. But one thing is clear: The two are more dangerous in combination than they are alone.
In some places, radon can leach into the water supply. A report from the National Academy of Sciences estimated that the risk from radon in water was far lower than the radon in air, although it could contribute to stomach cancer risk. When radon-laced water is used in homes, some of it can be released into the air as well.
How much radon is too much?
There's no single cut-off between safe and dangerous levels of radon. But the EPA has come up with a guideline for homeowners.
If the radon level in your home is above 4 Becquerel per cubic metre of air (Bq/m3, a measure of radiation), you should do something about it. If the levels are between 2 and 4 Bq/m3, consider having the level reduced. Levels below 2 Bq/m3 don't require any action because it's difficult to reduce radon levels to lower than 2Bq/m3.
The average home has about 1.3 Bq/m3 of radon. Such levels aren't enough to worry about, but under the right conditions, they could make you sick.
Read: Risk factors for cancer
According to the EPA, a nonsmoker who was exposed to average levels of radon for a lifetime would have a 1 in 500 risk of developing lung cancer. At 4 Bq/m3, the risk jumps to about 3.5 in 500.
Do I need to have my home tested?
You can't predict how much radon will be in your home unless you have it checked. People who live on the third floor or higher in an apartment building can be confident that their levels are low, but the EPA and the Surgeon General recommend testing for everyone else.
Radon gas enters homes from below, through cracks in the foundations and floors.You'll want to check the lowest living space in your home, but if you have an unfinished basement you may also want to check that if you spend much time in it or if your forced-air heating system uses that air.
Radon can be distributed very unevenly, so even if your next-door neighbour has safe levels of radon, your house could have a high level.
How can I test my home for radon?
There are two basic ways to check the radon levels in your home: You can buy a testing kit and do it yourself, or you can hire a professional to check it for you.
(In some places, you may be able to get free or subsidised test kits through your local or state health department.)
If you plan to do it yourself, the first step is choosing a kit. You can buy an inexpensive model at a hardware store or over the Internet for $50 or less.
Read: Each cancer tumour is totally unique
The cheaper products will be passive devices that don't need any power to operate. Using a charcoal canister, alpha-track detector, a charcoal liquid scintillation device, or other type of technology, the devices sample the air.
After the recommended time has passed the quickest tests take 48 hours, the longest more than 90 days you send the kit to a laboratory for results.If you're doing a quick test with a passive device, you should run the test at least twice to make sure you get an accurate reading.
You can do the two tests simultaneously or do the second test right after the first in the same spot.The more expensive active models record radon levels continuously.
If there's a sudden spike or drop in radon levels that could affect the final results, you'll know it. Some active models are especially designed so they aren't thrown off by drafts or other types of interference.
Do-it-yourself kits can give accurate readings, but only if you follow the directions carefully. When using a passive kit, it's especially important to make sure that the room is free of drafts.
Close doors and windows 12 hours before you start testing and keep them closed until the test is finished. Put the device at least 20 inches above the floor, and make sure it's not near any exterior walls.
You should conduct the test on the lowest floor or two or your house where people spend large amounts of time. You don't need to test an unfinished basement that's mainly used for storage.
If you decide to hire a professional to measure your radon levels, check with your state radon office for a list of qualified radon testing companies.
How can I reduce radon in my home?
Levels above 4 Bq/m3 definitely should be addressed, and between 2 and 4Bq/m3, you may want to take action. Not only will you be protecting your family's health, you'll also be avoiding potential problems down the road if you ever sell your house.
You won't need any major renovations to take care of radon, but it's not a do-it-yourself project, either. You'll have to hire a qualified contractor to do the job.
You can contact your state radon board for a list of contractors or find one on your own. If possible, find a contractor who has been certified or licensed by either the National Radon Safety Board or the National Environmental Health Association.
Ideally, you should avoid conflicts of interest by hiring different contractors for testing your radon levels and fixing the problem. If the same contractor does both jobs, you may have to sign a waiver showing that you're aware of the potential conflict.
Download: The WHO radon handbook
The remedy for radon depends on the structure of your home. In most cases, sealing any cracks or other gaps in the foundation is the first step.
The contractor may also install underground pipes and an exhaust fan to expel radon before it can seep into your home. Whatever you need to do to get radon out of your house, it's a relatively inexpensive project with a potentially huge payoff.
You may have heard that radon can escape from granite counter tops, but you don't necessarily need to make plans to remodel your kitchen. Some exotic kinds of granite may emit higher levels, however, according to experts quoted in the New York Times.
If you have granite counter tops and are worried about radon leakage, get them tested. If tests show that the levels are low but your home has high radon levels in general, the standard radon remedies will be far more effective than tearing out your counter tops.
If you are planning any new construction, there are inexpensive radon-resistant construction techniques that can seal out or ventilate radon from the beginning.
How often does a home need to be checked for radon?
If your radon levels are below 2 Bq/m3 and if you've taken the right steps to get an accurate reading you may not need to ever check again, but there are exceptions: If your unfinished basement becomes a living space, you'll want to check it for radon.
You may also want to check again if your foundation has undergone any major changes, perhaps because of a renovation, an earthquake, or shifting ground. If you're selling your house, a prospective buyer may request that you measure radon levels again even if you've already done the test.
Should I test my water too?
If you have a radon problem in your house, you may want to find out if your water is contributing a significant amount to the level in your air. There are no federal drinking-water standards for radon yet, but your local water supplier may have figures available.
If not, you can have your water tested. If you get your drinking water from a well, the EPA recommends testing your water.
Radon is a silent killer. Could it be in your home?
Less invasive cancer treatment Novalis Tx™ Radiosurgery comes to SA hospitals
Is your cotton shirt 'killing the earth'?
Image: Radon from iStock
Environmental Protection Agency. Home buyers and sellers guide to radon. 2007.
Environmental Protection Agency. A citizens guide to radon: The guide to protecting yourself and your family from radon. 2008.
Frumkin H and JM Samet. Radon. CA: A cancer journal for clinicians. 2001. 51(6): 337.
National Safety Council. Frequently asked questions about radon.
NAS Risk Assessment of Radon in Drinking Water.
"Murphy, Kate. "What's Lurking in Your Countertop?" New York Times, July 24, 2008.