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As if recovering from an earthquake and tsunami weren’t enough to deal with, residents of Japan now find themselves worrying about the health risks of radiation exposure, as workers struggle to gain control of the Fukushima Dai-ichi nuclear plant.
At a news conference on March 15, Japan's Chief Cabinet Secretary Yukio Edano said radiation levels near the quake-battered Fukushima Dai-ichi plant reached as high as 400 millisieverts (mSv) an hour. According to the World Nuclear Association, levels above 350 mSv were cause for relocating residents after Chernobyl.
This has many Americans uneasy, too. Even though radiation experts say there is no threat to the U.S. -- radiation would dissipate in the Pacific -- NPR reported today that potassium iodide pills, which counteract some of the effects of radiation, are selling out.
No matter where you live or how you spend your day, you are exposed to harmless levels of radiation every day of your life. According to the U.S. Nuclear Regulatory Commission, the average American is exposed to about 620 mrems, or 6.2 mSv, a year. And the biggest sources are not the things you tend to fear, like your computer or TV, but the natural world.
Radioactive elements are found naturally in soil, rocks, the water we drink, the food we eat, the air we breathe, and even our bones. The most common culprit is radon gas. When naturally occurring uranium breaks down in rocks, soil and water, it rises up from the ground into the air and into homes through cracks in the foundation. If you own a house, you’ve likely had your home tested for radon. And if you haven’t, you should. (Learn more about radon’s risks here). The other big chunk of our annual radiation exposure comes largely from medical procedures like CT scans, X-rays and nuclear medicine.
Radiation deposits energy into bodily tissue and can cause cell damage. The body parts most sensitive to radiation exposure are the thyroid gland and bone marrow. As such, high levels of radiation exposure can lead to an increased risk of thyroid and bone cancers, as well as leukemia, which affects bone marrow. According to the World Nuclear Association, exposure to 100 mSv of radiation a year is the lowest level known to increase the risk of cancer. If that sounds cryptic, it’s because not everyone who is exposed to that amount will get cancer -- kind of like those centenarians who smoked nearly every day of their very long life. That means the 40 or so workers trying to get the Fukushima plant under control, while not in any imminent danger, may be at greater risk of cancer in their lifetime.
Taking potassium iodide pills just before or after exposure could limit their risk. The pill floods the thyroid gland with so much iodine that the body is unable to absorb any of the harmful radioactive forms of iodine released in a nuclear accident.
Massive radiation exposure (roughly 1,000 mSv or more) within a short period of time can lead to acute radiation syndrome (ACS) or radiation poisoning. Radiation from x-rays and other medical devices is typically too low to cause ARS, though some cancer treatments can lead to symptoms. ARS symptoms may include nausea, vomiting, diarrhea, sunburn-like skin damage and hair loss; their severity depend on how much radiation your body has absorbed.
High levels of radiation can kill a person within hours, days or months. According to the Radiation Effects Research Foundation, which studied the health effects of radiation on Japan’s atomic bomb survivors, exposure to 5,000 mSv of radiation or more can lead to death within a week. A chest X-ray, for comparison, yields roughly 0.1 mSv of radiation.
Here are a few more sources of radiation, along with the level of radiation exposure they emit:
TVs or computer screens with cathode ray tube (CRT) technology: 1 mrem or 0.001 mSv per year (Note: flat-screens do not use this type of technology and do not produce x-rays.)
Food and water: 40 mrem or 0.04 mSv per year
Cigarettes (one-and-a-half pack a day habit): 1,300 mrem or 1.3 mSv per year
Airport full body scanner: 0.005 mrem or 0.000005 mSv per scan
Mammogram: 72 mrem or 0.07 mSv for two images
Full-body CT scan: 1,000 mrem or 1 mSv per scan
As you can see, even the sources of radiation that we fear give off well below the levels known to cause health risks. Still, if you want to lower your exposure, your best bet is to test for radon, quit smoking and avoid unnecessary medical tests.