A Map of Fukushima's Radiation Risks

Jocelyn is a staff writer for Science magazine.

A new map from the U.S. Department of Energy (DOE) shows the long-term radiation risks to people living near Japan's ailing Fukushima Daiichi nuclear plant.

DOE-sponsored aerial surveys began measuring radiation around the plant about 1 week after the reactor was hit by a tsunami on 11 March. The maps released before, however, have been reporting current radiation levels. Now DOE has projected what the first-year dose would be to people living around the plant up to about 80 kilometers away (see map). The analysis, released on 18 April, takes into account the fact that radiation levels are slowly falling—mainly due to the decay of iodine-131, which has a half-life of 8 days. It shows the high end of external exposures—what people would receive if they didn't evacuate after the accident and didn't follow advice to stay indoors.

In the red swath of land northwest of the plant where weather deposited a lot of fallout, potential exposures exceed 2000 millirems/year. That is the level at which the U.S. Department of Homeland Security would consider relocating the public. The area includes the places outside the 20 kilometer evacuation zone where Japanese officials advised that people evacuate last week. (Yesterday, Japan announced it will begin enforcing a ban on entering the evacuation zone itself.)

Although 2000 millirems over 1 year isn't an immediate health threat, it's enough to cause roughly one extra cancer case in 500 young adults and one case in 100 1-year-olds, says Owen Hoffman, a radiation risk expert with SENES Oak Ridge Inc. in Oak Ridge, Tennessee. Still, there are parts of the world—in Guarapari, Brazil for example—where natural background radiation levels are even higher. Also worth keeping in mind is that the normal disease rate is much higher: four in 10 people will eventually develop cancer without exposure to extra radiation, Hoffman notes.

Japanese officials will need to decide whether people should be allowed to return to these areas (and hot spots with even higher radiation levels) and explain the risks, says Hoffman. "It depends on how much hardship is associated [with long-term evacuation]. They will have to balance social and economic considerations against future health risks."

*This item has been amended to confirm that DOE-sponsored aerial surveys began measuring radiation around the plant about 1 week after the reactor was hit by a tsunami, not 10 days.

Posted in Asia, Climate Japan Quake 2011