The exposure cutoff for the evacuated areas is an estimated 20 millisieverts per year. (A sievert is a unit of ionizing radiation equal to 100 rems; a rem is a dosage unit of x-ray and gamma-ray radiation exposure.) That is more radiation than the typical U.S. resident is exposed to in an average year, but not that much more, Caracappa says. Taking into account natural background radiation, medical procedures and other sources, people in the U.S. encounter an average of about 6.5 millisieverts per year. Although that extra exposure can increase cancer risk, the effect is very small. A 20-millisievert-per-year exposure might increase the odds of getting cancer by a few thousandths of a percent.
The early cleanup workers faced a higher dose, with the risk of acute radiation sickness, resulting in nausea, low blood cell counts and neurological issues. It usually only occurs when someone has been exposed to about one sievert of radiation over a relatively short period of time. So far, no one has been reported to have suffered this illness from the Fukushima accident. Even the early cleanup workers had exposures that were estimated to be about 500 to 600 millisieverts.
Even the concerns about radiation-contaminated food have likely been exaggerated. Although it is possible cesium could get into the food supply, it is not as likely to accumulate as readily as iodine, Caracappa notes. And simple screening—with Geiger counters and the like—of soil, food and seafood can pick up radiation at low levels (so low, in fact, that the lower-end readings indicate contamination that not likely to be harmful). "It's not like some chemical contaminants—it's not invisible" to our screening methods, Caracappa says.
These reassurances notwithstanding, the authorities will monitor the area for ongoing health risks. A study launched last year will track some 360,000 children from the Fukushima Prefecture over 20 years to look for long-term health effects. A thyroid-screening program has so far detected no malignancies that required additional examination. The prefecture's health officials have also created more comprehensive surveys to get a sense of the entire population's health and well-being.
Even if the Fukushima Daiichi power plant's accident has not proved as dangerous as it was originally feared to be, other risks may be worse than commonly appreciated. Potentially even more dangerous than radioactive isotopes, Higley suggests, might be the debris and scattered chemicals left in the wake of the earthquake and tsunami. "You have shredded buildings, you have industrial parks, petroleum sites," she says. Even in an average suburban neighborhood, the known carcinogens kept around the home, "when it's shredded and dumped on the countryside," it can create another risk that could be much more difficult to detect than cesium.
The physical effects of the earthquake have extended beyond the Fukushima Prefecture as well. As Garfield notes, last summer many nuclear power plants remained closed—and electricity rationing is still a major issue. "It's very indirect, but not insignificant," Garfield says. For those who are just on the edge of health, less heating, air-conditioning, lighting and even reduced mass transit, can be enough to push some of them into illness or even death, he notes.
Perhaps more immediately evident, the earthquake and tsunami left many survivors disconnected from their standard medical care. A region that was known for its aging population, Fukushima Prefecture was especially vulnerable to a disaster that would sever residents from simple health support, such as heart medication and physicians familiar with their medical histories.