What do the Fukushima exposures really mean? A rough estimate is that for a 50-year-old male working at the Fukushima nuclear facility, his lifetime risk of cancer might increase from 42% to 42.2%. The magnitude of this increased risk is comparable to the added risk of living in Denver (where background radiation is higher because of the altitude and radionuclides in the Rocky Mountains) versus New York City for 10 to 15 years, or smoking one pack of cigarettes a day for one to two years. The Japanese public will, of course, get far less radiation.
Why are people still frightened given the relatively small risks of radiation from Fukushima? Mostly because governments and scientists have done a poor job of explaining radiation to the public. Until now, most reports compare doses of radiation or contamination with radiation of foodstuffs, without discussing the risk associated with these exposures. The implication is that if the estimated dose is below the dose or concentration used for comparison, there is no cause for concern. People are typically unconvinced by this argument.
Instead, radiation exposure and dose should be expressed using estimates about the risk of cancer in later life. This can be calculated in a few different ways. For example, a person's lifetime risk of cancer regardless of cause; or, after an accident like Fukushima, the total and/or excess numbers of cancers anticipated in an exposed population over its lifetime. Because these risk estimates are uncertain, a range of estimates should be given to reflect what we know and don't know about the chance that radiation exposure might lead to more cancers in later life.
People deserve direct, credible and intelligible answers. The challenge is to place this risk into context to help people weigh the importance of a risk and decide whether a future exposure is acceptable. Equally important is the ability to compare risk with potential alternatives and with potential benefits (like whether to have a CT scan). It is especially important to acknowledge that our risk estimates may change as our knowledge improves.
Like any complex technology, caution using nuclear energy is essential. But no one should cancel a trip to Japan or stop eating sushi because of the Fukushima accident.
Robert Peter Gale, a visiting professor of hematology at Imperial College London, is involved with the aftermath of the Chernobyl and Fukushima accidents. F. Owen Hoffman is an expert in radiation risk assessment working in Oak Ridge, Tenn.