Japan Radiation Risks: FAQ

On April 11, a month after the disaster, Japan raised the radiation alert status to its highest level, level 7 -- the same as the Chernobyl plant meltdown in Russia. It had previously been at level 5. What does this new status mean?

The reclassification doesn’t mean that the situation has gotten worse, says Henry Royal, MD, professor of radiology and associate director of the Mallinckrodt Institute of Radiology at Washington University in St. Louis. Rather, it’s acknowledging that the scope of the radiation leaked from the plant was larger than originally thought.

“The reason that the accident was reclassified was because it’s now obvious that the radioactive material has escaped the plant, particularly into the ocean. That’s why it’s been classified a level 7 as opposed to a level 5.”

An assessment released by the U.S. Department of Energy on April 7 found that beyond a 25-mile radius surrounding the plant, radiation levels were consistently below those that would require people to be evacuated. Since March 19, the report says, radiation levels have continued to decline. "The headlines are making it sound like something has gotten worse, but when you look at where people are living, the situation is getting better,” Royal says.

“Our information depends on the extent to which we’re allowed to take measurements independently on-site or close by,” Davis says.

Most of the data released by the U.S. Department of Energy is based on aerial surveillance rather than information gathered on the ground. “We can do a good job monitoring what is coming to the U.S., for example, which is important and of great concern to people here, but for the situation in Japan, we have to rely a great deal on information coming from the Japanese government," Davis says.

Isn’t it bad that radiation is leaking into the ocean?

That’s actually helpful, says Royal. “Because it’s in the ocean, the radiation gets diluted very rapidly, and it’s much less likely to affect people. Since the primary element that has been released is radioiodine, which has a very short half-life, it will go away very quickly."

What kind of radiation is coming from the plant?

There are a number of different radioactive substances that could leak from a damaged nuclear reactor. At this point, radioactive iodine (iodine-131) is the primary component of the leaked material, although there has also been some release of cesium-137.

With a half-life of just eight days, radioactive iodine quickly loses its potency and after a couple of months, is virtually gone. Cesium, however, has a half-life of 30 years, and so can pose a threat to public health for much longer.

“Even so, at Chernobyl if there were going to be major effects from cesium, we should have started seeing significant increases in solid tumors by now,” says Williams. “But 25 years later, we’re only just beginning to see the hints of possibly an increase in bladder cancers. We’re still not seeing if there was a significant impact.”

Are radiation-contaminated foods being imported from Japan?

"Based on current information, there is no risk to the U.S. food supply," the FDA states on its web site.

Could radiation from Japan's nuclear plants affect the U.S.?

No harmful amount of radiation from the Japan disaster is expected to hit the U.S., experts say.

On April 10, the U.S. Environmental Protection Agency reported that its air monitors have detected “very low levels of radioactive material in the United States consistent with estimated releases from the damaged nuclear reactors.” These findings were expected, the EPA notes, but in response, it has stepped up monitoring of precipitation, milk, and drinking water. This monitoring has also detected low levels of radioactive material, which the EPA says are “far below levels of public-health concern.”

At the University of California-Berkeley, experts in the nuclear engineering department are monitoring radiation levels in the food chain (for example, produce such as strawberries and lettuce), rain water, tap water, and milk. While they have detected elevated levels of certain radioisotopes, they confirm that these levels are still extremely low. For example, they state that “consuming 403 kg of spinach could give you a radiation dose equivalent to a roundtrip flight from San Francisco to Washington, D.C.” In fact, they note, even that risk may be overstated, because it assumes that the person is eating food contaminated at that level for a full year.

What is the best way to prevent radiation exposure?

In the event of a nuclear accident, people living near nuclear power plants generally are provided with potassium iodide pills. That's because radiation leaks tend to carry radioactive iodine. The pills load the thyroid gland with iodine and prevent uptake of radioactive molecules.

But the best way to prevent radiation exposure is to stay indoors, close the windows, and turn off external sources of air, such as air-conditioning, until the all-clear is given or until you can safely be evacuated from a contaminated area.

"Contamination from fallout comes from touching a contaminated surface, from it falling, from inhaling it, or ingesting it," Williams says. "So in case of an event, be sure to drink bottled water and eat only sealed food that has not been outside."

Should I take potassium iodide pills?

These pills can prevent radioactive iodine from collecting in the thyroid gland and causing thyroid cancer, but they don't undo all of the health effects of radiation.

Royal says there's no U.S. risk of radioactive iodine from the Japan nuclear emergency, so there is no reason to take the pills. Fortunately, if people panic and take the pills, they won't do any harm as long as they are taken as directed.

Royal notes that even if a person received enough radiation to cause radiation sickness -- 1,000 milisieverts -- the dose would increase their risk of cancer by 40%. To put this in perspective, smoking cigarettes increases cancer risk by 1,000% to 2,000%.

What are the health effects of radiation?

Radiation risks are different for people at different stages of life:

• Radiation has harmful effects on child development.
• Radiation can induce cancers that appear years after an adult is exposed.
• Elderly people's cells may have reduced ability to repair damage from radiation.

According to Lisandro Irizarry, MD, chair of emergency medicine at The Brooklyn Hospital Center in New York, symptoms of sudden (acute) radiation poisoning are nausea and vomiting. Other symptoms include fever, dizziness, disorientation, and bloody diarrhea. Symptom onset is quickest with the greatest radiation exposure.

The long-term effects of radiation exposure, Williams says, are the various cancers that can occur. The cancers most commonly associated with radiation are leukemia and cancers of the thyroid, lung, and breast.

In a year, the typical U.S. resident is exposed to 3 millisieverts of radiation, just as part of day-to-day life. By comparison, a chest X-ray is 0.02 to 0.67 millisieverts.

A person who receives a short-term dose of 1,000 millisieverts will experience radiation sickness but probably will survive. Short-term doses of 2,000 to 10,000 millisieverts have an increasing probability of causing a fatal cancer.

Is it safe to visit Japan?

That depends on whom you ask and what areas of Japan you’re talking about.

As of March 30, the U.S. State Department still advised people to defer non-essential travel to a number of regions beyond just the area of the earthquake, tsunami and radiation crisis, including Tokyo and Yokohama.

Other popular destinations, such as Kyoto, Okinawa and Osaka, are “outside the regions of concern,” according to the State Department’s warning. (For an updated alert, go to the State Department's web site.)

On the other hand, experts tell WebMD that they would not hesitate to travel to areas of Japan outside the disaster zone.

“I was supposed to go to Japan next month, but the meeting was cancelled because the organizers understandably have other things to do,” Williams says. “But I was perfectly happy to go, and I’m a bit sad that I’m not because I’ve never been to Japan. I would be absolutely fine to go.”

What does it mean for a nuclear energy plant to melt down?

"Meltdown" is not a technical term, but it vividly describes the worst-case scenario for a nuclear reactor.

Nuclear reactors generate power via controlled nuclear fission, which occurs when enough radioactive material is gathered into a critical mass. Control rods can separate the radioactive material, thus ending the nuclear reaction.

That's exactly what happened when the March 11 earthquake hit Japan. Control rods effectively halted the nuclear reactions.

This means there is no danger of a nuclear blast from Japan's damaged nuclear plants, even if fuel rods melt inside one of the containment vessels and pool into critical mass.

But the nuclear materials inside the reactors remain radioactive, which means they give off a great deal of heat. It takes days to cool these materials down, and spent fuel rods must be kept submerged in a cooling bath until their radioactivity decays and their intense temperature goes down.

If not cooled, these materials will melt. In a worst-case scenario, they could possibly melt right through the thick metal shield that contains the reactor, spilling highly radioactive materials into the environment.

When the tsunami hit Japan's Fukushima Daiichi nuclear plant, three reactors lost power. That meant serious trouble, as the pumps needed to cool the overheated reactors with water stopped running when their battery backups were exhausted.

Nuclear reactors have two main containers that keep radioactive materials from spreading outside the plant. One container is the thick-walled building surrounding each reactor. The other is a thick metal vessel that makes up the outer wall of the reactor itself.

Another radiation issue is in reactor 4, which had been shut down before the earthquake. But spent fuel rods were still cooling in the plant's rooftop pool. These fuel rods may have been exposed and may have released radiation.

One of the reactors, reactor 3, is said to be running on mixed-oxide (MOX) fuel. MOX fuel contains plutonium in far greater amounts than regular nuclear fuel and would be more toxic if released into the environment.

Could the nuclear disaster in Japan happen in the U.S.?

The U.S. has 23 nuclear reactors at 16 nuclear power plants that are designed exactly like the reactors leaking radiation in Japan.

Back in 1972, a safety official with the U.S. Atomic Energy Commission warned in a memo that the "safety disadvantages" of these reactors outweighed their advantages.

But remember, the nuclear plants in Japan were hit by an earthquake and tsunami of record proportions. This doesn't mean the aging U.S. plants are safe -- but neither does it mean they are an imminent danger.

WebMD senior reporter Daniel J. DeNoon contributed to this report.