Measuring Chernobyl's fallout

April 27, 2006
How many people died because of the Chernobyl nuclear-reactor explosion, which spewed radiation across northern Europe? Twenty years after the accident, the death toll remains in dispute.
This month, the World Health Organization estimated “up to” 9,000 people died or will die of cancer because of the incident, which unfolded in the early morning hours of April 26, 1986. The number was 6,700 to 38,000 in a recent report published in a peer-reviewed journal, from the Lyon, France-based International Agency for Research on Cancer, an agency governed by the WHO and 16 member nations. Greenpeace International, which opposes nuclear power, published its own report, based partly on papers from former Soviet nations. Greenpeace estimates the death toll is between 93,000 and 200,000, including cancer deaths and other illnesses like immunity disorders.
The wide range reflects lingering uncertainty about the health effects of such disasters. In the case of Chernobyl, the initial blast, and efforts to contain it, killed 31 people. But, through the air, food and water, the fallout exposed roughly 600,000 residents and relief workers to very high doses of radiation, and six million more to lower but still severe doses. Potentially hundreds of millions more were exposed to radiation at some level, which is why some researchers study all 570 million Europeans at the time of the accident.
All the Chernobyl studies base death tolls on the health effects from the bombings of Hiroshima and Nagasaki — where most people suffered acute, short-term exposure. And even those bombings remain poorly understood: Although survivors have been closely tracked for most of the subsequent six decades, important data were lost in the first years after the 1945 bombings. Other information on radiation’s effects, from U.S. veterans involved in atomic testing and from medical patients who receive radiation treatments, also reflects short-term, high-dose exposure and therefore isn’t fully applicable to Chernobyl.
“There is a very big controversy on the effects of low doses of radiation,” Elisabeth Cardis, head of the radiation institute at the International Agency for Research on Cancer, told me. Her group’s estimate of deaths (between 6,700 and 38,000) has such a wide range because it relied in part on data from the Japan bombings, an imperfect model. (Her agency has looked for more reliable statistics on the effects of radiation — it recently studied 400,000 nuclear-industry workers and found that their cancer risk was reasonably well-predicted by the models based on Hiroshima and Nagasaki survivors.)
Because of this great uncertainty, the WHO didn’t count any possible deaths from low-dose exposure, focusing instead on the six million people closest to Chernobyl. “Any time you’re looking at numbers that have to do with low-dose radiation, it’s speculative” because of the dearth of studies on the health effects of low-dose radiation, WHO spokesman Gregory Hartl told me.
An announcement last September from the Chernobyl Forum, a group including the WHO, the International Atomic Energy Agency — the U.N.’s nuclear-energy agency — and six other U.N. agencies put the death toll at 4,000, though it only looked at the 600,000 people who were most exposed. Michael Repacholi, manager of WHO’s radiation program, said at the time, “the sum total of the Chernobyl Forum is a reassuring message.” That initial announcement sparked criticism for excluding millions of people who were also exposed. Since then, WHO has also acknowledged the possibility of up to 5,000 more deaths that may be attributable to Chernobyl.
Keith Baverstock, a former WHO researcher who studies radiation at the University of Kuopio in Finland, told me in an email, “There is no excuse for the WHO/IAEA ignoring these fatal cancers” outside the immediate vicinity of Chernobyl. He added, “If we cannot believe that WHO tells us the truth about health issues it is a pretty poor outlook for public health.”
Greenpeace, sparked by the September announcement, brought together more than 50 scientists — mostly from Belarus, Ukraine and Russia, the most-affected nations — to write a report compiling papers published in regional medical journals. Ivan Blokov, leader of Greenpeace’s Chernobyl project and an editor of the report, told me that the report is “scientifically based,” with no political statements.
However, the report relied heavily on some questionable methods. It assumed that Chernobyl was responsible for an overall increase in cancer rates, but Chernobyl’s effect on those rates is difficult to isolate from other factors, such as changes in smoking rates and improvements in the diagnosis of cancer. Also, researchers wanted to estimate how many people exposed to Chernobyl radiation developed cancer other than thyroid cancer, which usually isn’t fatal. To do so, they studied how cancer rates rose in post-war Hiroshima and Nagasaki, and looked at the ratio of thyroid cancers to other cancers in those cases. They applied a similar ratio for Chernobyl. But Japan’s overall cancer rates differ from Europe’s — Japan has a higher rate of stomach cancer but a lower rate of lung cancer, for instance — so it’s not clear the same ratios would hold true.
Mikhail Malko, a contributor to the Greenpeace report and a researcher at the Joint Institute of Power and Nuclear Research in Minsk, Belarus, outlined the ratios method to me in an email. “According to my assumption, ratios of radiation risks have to be similar for all ethnic groups of humans,” he wrote, acknowledging that this is a weakness of his approach. Dr. Cardis said she needed to study Dr. Malko’s approach further, but based on her initial analysis, she called it “interesting,” but “fairly crude.” The WHO’s Mr. Hartl, meanwhile, dismissed the Greenpeace report, saying Greenpeace “took the reports that we rejected.”

Share this:


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.