Yogi Berra supposedly said, "It's tough making predictions, especially about the future." He was right. However, there is an out for forecasters trying to predict long-term medical consequences of the Fukushima nuclear facility accident: The final reckoning will take about 50 years; they are unlikely to be around to be judged wrong.
With this reassurance in mind, we think the public deserves an estimate of likely outcomes of radiation released when the March 11, 2011, earthquake and tsunami caused multiple meltdowns of nuclear fuel at the plant.
Fukushima has understandably reignited debate and concern regarding cancer risks from radiation. A year after the accident, many people still won't travel to Japan. Sushi sales have taken a hit. And yet the Japanese government says that even those who lived near the reactor have little to worry about. Who's right?
Humans are exposed to radiation every day. About 50% comes from natural sources, including the cosmos, the sun and our planet. The other 50% is from man-made sources. Physicians contribute to more than 80% of the man-made radiation by ordering X-rays, CT scans and the like. Other sources of man-made radiation include smoke detectors, exit signs and cigarette smoking. Our food and water are also naturally radioactive. And each of us, because we contain these radionuclides, is also radioactive.
In general, we don't think much about the inherent risks of such exposures. For example, if your doctor sends you for a CT scan, you may get a radiation dose about seven times greater than you would in a year from most natural or man-made sources. However, few people decline a CT scan because of the risk of radiation-induced cancer. But when we read of a spike in the amount of radiation in the water in Tokyo, we get scared.
One important element that we have to consider to assess cancer risks associated with an accident like Fukushima is our baseline risk for developing cancer. All of us, unfortunately, have a substantial risk of developing cancer in our lifetime. For example, a 50-year-old male has a 42% risk of developing cancer during his remaining life; it's almost the same for a 10-year-old. This risk only decreases when we get much older and only because we are dying of other causes.
It's true that excess radiation exposure can increase our cancer risk above baseline levels; it's clear from studies of the survivors of the 1945 atomic bombings of Hiroshima and Nagasaki, of people exposed to radiation in medical and occupational settings, and of people exposed to radon decay products in mines and home basements. When it comes to exposures like that of Fukushima, the question is: What is the relative magnitude of the increased risk from Fukushima compared to our baseline cancer risk? Despite our fears, it is quite small.
The basis of this estimate are data learned from the A-bomb survivors, from people exposed to radiation from the Chernobyl accident 25 years ago and from other medical and occupational exposures. The explosion of the Chernobyl reactor spread radiation around the world. The distressing news is that several thousand cases of thyroid cancer developed, almost all in children who drank iodine-131 contaminated milk within one to two months after the accident and did not receive iodine tablets to prevent absorption of radioactive iodine. Fortunately, thyroid cancer is usually readily treated and seldom leads to death.
But there is also good news from Chernobyl. After intensive study of hundreds of thousands of people, there are no convincing data of increased leukemia or other cancers, even among the 500,000 cleanup workers who received the highest doses. It may be too soon for a final call, but so far the situation looks favorable.
Now for Fukushima. The kind of radiation was similar to Chernobyl, but about four to 10 times less was released. And there are other important differences. Most of the radiation released (about 80%) was blown offshore by winds, where it was diluted by air and sea. Consequently, exposures received by Fukushima workers and the public are quite low, including among the 20,000 or more workers decommissioning the facility and the approximately 100,000 evacuees. This doesn't mean there will be no future radiation-caused cancers, as some claim. But because there may be so few cancers, it is unlikely any epidemiological investigations will detect an increase in Japan or elsewhere that can be directly attributed to Fukushima.
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.
By Robert Peter Gale, a visiting professor of hematology at Imperial College London, involved with the aftermath of the Chernobyl and Fukushima accidents and F. Owen Hoffman, an expert in radiation risk assessment working in Oak Ridge, Tenn.