March 23rd, 2011
05:31 PM ET
With ongoing problems at Japan’s Fukushima Daiichi nuclear plant – including the latest warning that radiation has turned up in Tokyo’s drinking water – CNN is looking at past nuclear accidents for a hint of the long-term impact.
The worst nuclear accident ever took place in 1986 when there was a massive explosion at the plant in Chernobyl, in the Ukraine region of the former Soviet Union. A team from the Fred Hutchinson Cancer Research Center in Seattle, Washington, has conducted long-term studies looking at cancer rates in the area. Scott Davis, a professor of epidemiology at the University of Washington, leads the research, including three studies of childhood cancer, one childhood leukemia study and a study now under way on breast cancer rates.
The team compares people who have the illness being studied, with people who are not sick, while estimating the amount of radiation each individual was exposed to. Through this method they estimate the increase in cancer cases that can be attributed to radiation exposure. An important part of the approach involves making estimates of each individual’s exposure; this is done through computer models and interviews with each person about his or her location and movements.
Davis has conducted three studies of childhood cancer, one specifically on childhood leukemia and is currently doing a study on breast cancer. He just returned from his latest trip to Russia and talked with CNN about his work.
CNN: How many people died because of the Chernobyl accident?
Davis: You see estimates that span a huge range, from a few hundred, to tens of thousands. I think the WHO and United Nations estimates [that about 4,000 deaths can be blamed on the accident] are pretty reasonable.
CNN: How do you sum up the health impact around Chernobyl?
Davis: The primary impact has been thyroid cancer, and to a lesser extent childhood leukemia. And of course there were acute effects to the people who were right there, related to their work [fighting the fire, cleaning up]. What’s surprising to many people, is that this is the extent of what we can say for sure.
CNN: We don’t know much about radiation’s effects in these situations? I guess no one’s running experiments where they dose people with lots of radiation.
Davis: That’s right. The environmental events that have exposed people are relatively few and are quite different: Chernobyl, Hanford [the Hanford Nuclear Reservation in Washington state, where plutonium was processed for the first atomic bombs], A-bomb survivor studies. Those are the major sources of what we know.
CNN: Aside from computer models and interviews, is there any way to measure past exposure? Does exposure to high radiation leave a signature?
Davis: That's what we'd all like to have, but there is no such thing. There’s no marker of exposure or difference in the disease…Thyroid cancer from radiation looks like thyroid cancer of any other kind. Same with other cancers.
CNN: In Japan there’s debate about how far away from the damaged reactor is safe. In Chernobyl, how far did the danger extend?
Davis: It’s a difficult answer. In Chernobyl the pattern of contamination is not uniform at all; it’s very spotty. If you look at a map… you see spots of heavy contamination, where people would have gotten heavy exposures, mixed with areas of no or very little contamination. They don’t follow a nice even pattern. It depends on precipitation patterns and other things.
CNN: Is there any point beyond which you could say was safe?
Davis: For Chernobyl, there was definitely risk beyond 30 kilometers (18.6 miles) but we don’t don’t really know how far.
CNN: 100 miles out?
Davis: It’s hard to say, but 100 miles away, it’s unlikely you’d pick up an increase in disease.
There might be a few affected individuals, but you’d never pick that up with an epidemiological study.
CNN: What are the main ways people were exposed?
Davis:For the thyroid, the worst pathway by far is through milk. Second are green and leafy vegetables, and fruits. Inhalation and water are less important.
CNN: Dr. David Brenner of Columbia University said that upwards of 90 percent of thyroid cancer cases around Chernobyl could have been avoided if authorities had simply told people to stop drinking milk. Do you agree with that?
Davis: Yes, I do.
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