Experts: minimal radiation risk from Japan nuclear crisis
Posted on April 8, 2011
In this article:
- Information about Japan's nuclear crisis
- Everyday background radiation
- Radiation exposure risk information
- Potassium iodide
Radiation is invisible but can be very powerful — and thus very mysterious to many of us. So it’s understandable that recently, some Californians have wondered whether they should take precautions against possible radiation exposure from Japan’s nuclear crisis.
Many inquire about taking potassium iodide, a supplement/medication that can help protect a key gland from a very specific kind of radiation. The Japanese government has distributed this substance to some people living near the tsunami-damaged Fukushima nuclear plants.
The consensus among a variety of U.S. public-health officials at the federal, state and local levels is that there is no need for concern about dangerous radiation exposure here from the Japanese nuclear emergency, and no need to take potassium iodide — a drug that can pose some health risks of its own.
The federal Nuclear Regulatory Commission has stated that Japan’s nuclear crisis presents no danger to California, according to the California Department of Public Health, which monitors the situation in partnership with other agencies.
The Japanese government has evacuated residents within several miles of the damaged Fukushima plant, which has leaked radiation following the March 11 earthquake and tsunami. But America’s west coast is approximately 5,000 miles away, and radiation dissipates over long distances.
At present, all data from state and federal sources show that harmful levels of radiation won’t reach California, according to state public health officials. California's public health department reports that radiation from Japan is expected to be thousands of times less than daily background radiation from natural and human-made sources.
Everyday background exposure
So just what amount of background radiation are we exposed to, where does it come from – and what level of radiation poses a health concern?
The sun and stars contribute to our background radiation, as do radioactive materials such as uranium, tritium and radon found in the earth’s soil, water and air. Radon tests in your basement or crawl space are designed to detect especially elevated levels emitted from the soil, which may heighten lung-cancer risk when breathed over the long term.
Consumer products and activities such as cigarettes, building materials and commercial air travel can also contribute to radiation exposure. The highest human-made source for most people is medical imaging tests like CT scans or nuclear medicine scans, which have revolutionized health care and help on a daily basis to save and improve lives.
The average American is exposed to approximately 620 millirem of radiation each year, half from natural background and half from human-made sources. A millirem is a dose of “ionizing” radiation, an energetic form of radiation that can cause changes in living cells. While it is true that high doses of radiation can increase the risk of developing cancer, the dose of radiation from natural background or from a medical imaging study does not pose a significant health risk.
A round-trip, coast-to-coast U.S. flight results in a dose of approximately 5 millirem from the increased exposure to cosmic radiation. A typical chest x-ray results in a dose of about 10 millirem, or about twelve days worth of natural background radiation. A typical mammogram involves about 40 millirem. More extensive and less common tests involve somewhat more radiation exposure; a head CT scan is about 200 millirem and a chest CT is about 700 millirem.
According to the U.S. Environmental Protection Agency or EPA, the radiation from Japan detected by California monitors so far is thousands of times below levels of concern.
"The risk to Californians from the damaged reactors in Japan is expected to remain low," says Jerrold Bushberg, director of health physics programs and clinical professor of radiology and radiation oncology at UC Davis Health System. "Even if higher levels of radioactive material were to be released from the damaged reactors, it would be hard to imagine a release so catastrophic that it would pose a significant risk to people on the west coast of the U.S."
Sources for ongoing health information about Japan’s nuclear crisis:
Bushberg is an expert on the biological effects and safety of ionizing and non-ionizing radiation, and serves as an expert to international and national advisory bodies on radiation exposure. The risks from radiation exposure depend on two major factors, he says: how high the dose is, and whether the dose was received acutely (over a short period of time like minutes or hours) or occurred gradually over weeks and years.
The adverse health effects from acute high doses can range from mild effects, such as skin reddening, to serious effects such as a significantly increased risk of developing cancer or even death. For example, the extremely high radiation doses experienced by some firefighters and other first-responders early on the scene at the 1986 Chernobyl nuclear power plant accident caused prompt radiation sickness within less than an hour, and were eventually fatal.
A whole-body dose of 500 rem (500,000 millirem) received all at one time would be fatal for about half the people exposed – even with advanced medical care. That’s a dose equal to performing more than 400 CT scans of the entire body all at the same time.
An acute high-level radiation exposure that is not lethal will cause an increase in the cancer risk for that individual. While very high doses of radiation can cause a substantial increase in cancer risk, Bushberg says the risks from lower level exposures (like those from a CT scan or background radiation) are very small.
For example, a person receiving a high dose of 100 rem (100,000 millirem) to their whole body would increase their lifetime fatal cancer risk from 23 percent (the average risk in the US population) to 28 percent. However, much smaller exposures (like an abdominal CT scan or three years of background radiation exposure) might increase one’s cancer risk by approximately 0.04 percent (from 23 percent to 23.04 percent).
CT scanning has quite literally revolutionized the practice of medicine, enabling clinicians to detect and monitor many types of life-threatening cancer, as well as other diseases, and to assess the extent of injuries.
While we know that any increase in risk from small radiation exposures like this are very low, we cannot calculate it precisely, Bushberg says. The risk will depend on many factors such as a person’s age, gender and preexisting health conditions, just to name a few. The actual change in cancer risk for a particular individual from a low radiation dose may be a little more or less (including zero) than the example given above.
"There is no doubt that for radiation used in medically indicated imaging procedures, the health benefits far outweigh the risks," Bushberg says. For example, CT scanning has quite literally revolutionized the practice of medicine, enabling clinicians to detect and monitor many types of life-threatening cancer, as well as other diseases, and to assess the extent of injuries. In some cases, CT has helped patients avoid higher-risk procedures such as exploratory surgery.
"We constantly seek new ways to minimize radiation exposure while maximizing health benefits," Bushberg added.
Potassium iodide (KI)
Individuals should not take KI unless directed to do so by public-health officials or at the direction of their physician.
In certain nuclear emergencies, potassium iodide (KI) tablets may be recommended to individuals if there is a significant risk of environmental contamination and public exposure to radioactive iodine.
Radioactive iodine (or radioiodine) can be released into the air after a radiological or nuclear event, where it can be breathed into the lungs. In most cases, once radioactive iodine has entered the body, the thyroid gland quickly absorbs it. If enough radioiodine is absorbed into the thyroid gland it can then cause thyroid gland injury. Taking KI shortly before or soon after exposure to radioiodine acts to block the radioactive iodine from being taken into the thyroid gland, and thus protect it from injury.
However, it is also important to know that KI does not protect parts of the body other than the thyroid from radioactive iodine, and is not effective for any other radioactive elements other than radioiodine. Taking KI may be harmful for some people, resulting in potentially serious side effects — and if radioactive iodine is not present, then taking KI only exposes one to the risks, and does not provide any benefit or protection.
"Individuals should not take KI unless directed to do so by public-health officials or at the direction of their physician," Bushberg says.
The EPA monitors for radioactivity through a national network of radiation monitoring stations. Scientists are tracking the location of radioactive iodine released from the power plant in Japan. According to the U.S. Centers for Disease Control and Prevention: “At this time, CDC does not recommend that people in the United States take potassium iodide (KI) or iodine supplements in response to the nuclear power plant explosions in Japan.” To visit the CDC website, click http://emergency.cdc.gov/radiation/japan/ki.asp.
Posted on April 8, 2011