As workers struggle with Japan's damaged Fukushima nuclear power plant, the potential risk that more radiation will be released remains unknown. But the unfolding events since Friday's earthquake have given public health officials time to plan ahead, unlike what occurred after the 1986 Chernobyl accident. And that means they can minimize people's exposure to radiation, says a scientist who has studied that disaster.
The most significant health effect from Chernobyl was a steep rise in children with thyroid cancer--more than 6000 cases, according to a recent United Nations report. To lessen the chances of such an increase, people living near the plant are reportedly being given potassium iodide tablets. The idea is to flood the thyroid with iodine and block any inhaled or ingested radioactive iodine-131 from entering the thyroid. But "timing is critical," says Fred Mettler, a radiology professor emeritus at the University of New Mexico who led an international team that investigated health effects from the accident. If taken 1 day before an exposure, the pills are 80% effective, he says; if taken during the point of exposure, 100% effective; 8 hours later, 30%. (Except for pregnant women, there's not much reason for adults over 20 to take the tablets, Mettler adds, because their cancer risk is low.)
At Chernobyl, iodine-131 also got into the food supply via milk from cows that had fed in pastures tainted with radioactive iodine. Japan can avoid this consequence by barring cows from grazing in contaminated pastures, he said, or by storing any milk products or cheese for 80 days until the radioactivity is gone.
Another risk is cesium-137, which can also be spewed into the air from a nuclear plant. Its half-life is 30 years. In Chernobyl, it entered the food chain through soil and ended up in meat, berries, and mushrooms. One solution is to plow up a half-meter or more of soil, Mettler says. But the isotope also leaves the body within 2 months, so another option is to feed livestock clean food for a few months before slaughter, Mettler says. (People who accidentally ingest radioactive cesium are sometimes given a chemical called Prussian blue that binds to the cesium and helps the body to excrete it. But taking pills for weeks cuts exposure only by 50%, and levels in Japan will likely be too low to warrant such a step, Mettler says.)
Japan is also minimizing people's exposure by evacuating the area 20 kilometers around the plant and advising people living within 10 kilometers outside that area to stay indoors. Those steps will reduce their exposure to both gamma rays (which are attenuated by walls) and to airborne radioactive particles.
The bottom line, Mettler says, is that radiation levels measured by monitors don't equate with what actually enters people's bodies. "The trick is to keep people from being exposed."