"The actual radiation suffered by the populations is little known," said André Giordan, the director of the Didactic Science and Epistemology Laboratory at the University of Geneva. "It is therefore very difficult to quantify the health effects of the Chernobyl accident."
Poor recordkeeping and corruption also prevented the accurate registration of the 600,000 so-called liquidatorsthe workers who helped put out the fire and entomb the smoldering nuclear plant in the spring of 1986. Significant international efforts by the United Nations and others have been underway to better understand public and worker exposure, and the possible effects on their health.
A report published in the journal Nuclear Energy last year predicted that 4,400 people would develop thyroid cancer as a result of the Chernobyl accident, leading to 1,000 premature deaths. Most cases can be cured by surgically removing the thyroid and treating patients with tablets of thyroxin hormone for the rest of their lives.
So far, only three people have died from Chernobyl-induced thyroid cancer, according to Ted Lazo, the deputy head of radiation protection at the Nuclear Energy Agency in Paris. There is no evidence yet of an increase in other cancers, such as leukemia.
"This is not to say that the populations still living in contaminated territories are healthy," Lazo said. "It seems pretty clear that, in general, the health of these people has deteriorated and continues to do so."
In Hiroshima and Nagasaki, it took, in some cases, 20 to 30 years to detect certain cancers.
But studies of Hiroshima and Nagasaki victims may not be applicable to predicting the effects of Chernobyl. While the victims of those atomic bombs were exposed to radiation in a blinding flash, the people of Chernobyl have lived with chronic exposurealbeit at a lower dose ratefor years. The danger of such radiation is difficult to assess and is the topic of ongoing research.
There are many noncancer health concerns, too.
In a major study of children born in 1994 to mothers who had lived 186 miles (300 kilometers) from Chernobyl and had been exposed to radioactive fallout, researchers found never before observed "germ line" mutations: changes in the DNA of sperm and eggs.
"Genetic defects may remain hidden for several generations," Adler said. "We have to expect more [of them] in the future."
Fear of the effects of radiation had a significant effect. Around 200,000 women reportedly aborted fetuses after being exposed to radioactive fallout, fearing that the children would have birth defects. So far, no such birth defects have been observed.
There is evidence that the Chernobyl disaster has led to increases in cardiovascular and gastrointestinal diseases, diabetes, and disorders of bone and connective tissue. Some of these diseases may be linked to stress.
"A number of stresses are most likely contributing to the current degradation [of] public health," Lazo said. "Exposure to radiation and other toxic substances is a fact and probably is part of this biological and complex problem. But these are certainly not the only major contributors to public health decline. The people living in these territories feel that they and their children are, in some sense, doomed."
Radiation doses in the area are still a dozen times higher than normal. Unable to make ends meet elsewhere, several hundred former residents have returned to Chernobyl, which once had a population of 120,000. Thousands more are shuttled into the so-called exclusion zone to work on the gradual powering down of the plant.
Reactor 4 has been sealed. However, some experts have warned that nuclear fuel trapped in its remains could cause the structure to deteriorate, and radiation to be released once again.
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