By Dennis Normile | Science (sciencemag.org) | Link to article
The general public avoided exposure to high levels of radioactivity, but questions linger about the long-term effects of contamination.
FUKUSHIMA, JAPAN—At 5 p.m. sharp, Mitsuru Itou watches as a technician steps inside a quartet of orange traffic cones and black-and-yellow traffic bars marking a “keep out” area in a gravel lot. Holding a radiation meter at his waist, the technician waits for the instrument to stabilize. Then every 30 seconds for the next 2½ minutes he recites the count. Itou, a supervisor with the Public Health and Welfare Office of Fukushima Prefecture, correctly predicts that the readings will average 1.6 microsieverts per hour. “That’s what [the radiation] has come down to for some time now,” he says. The results are phoned in to a disaster center, which posts them to its Web site. This ritual is repeated every hour at seven locations across the prefecture to track environmental radiation from the Fukushima Daiichi nuclear power plant, 63 kilometers southeast of Fukushima city. The measured levels range from two to 1000 times normal background radiation—and residents, officials, and scientists wonder what that may mean for public health.
The magnitude-9.0 earthquake and tsunami on 11 March knocked out nuclear fuel cooling systems at the power plant. In the days that followed, overheating triggered hydrogen explosions that spewed radioisotopes into the air. Radiation spiked 4 days after the first explosion, according to measurements here and at other ground-monitoring sites hastily set up after the earthquake. Since then, radiation levels have ebbed as short-lived radionuclides, such as iodine-131 with a half-life of 8 days, decay into stable isotopes.
Across Fukushima and neighboring prefectures, small amounts of cesium-134 and cesium-137, isotopes with half-lives of 2 and 30 years respectively, lie on the ground. Cleanup workers have stripped contaminated topsoil from some schoolyards, and remediation or permanent evacuation is likely for the worst areas. But for much of the prefecture, “we’re stuck, there are no practical countermeasures,” says Hisashi Katayose, a Fukushima official in charge of radiation monitorin.