An international team of scientists has linked Soviet atmospheric nuclear tests in the 1940's and '50's to genetic mutations in people living downwind of the blasts at the time. But there is no evidence that the radiation from the explosions has actually caused disease.
Between 1949 and 1956, the Soviet Union exploded four nuclear bombs above ground in Kazakhstan before a 1963 treaty banned such tests.
Now, a study in the journal "Science" shows a compelling connection between the blasts and elevated genetic mutations in families who lived up to 100 kilometers away.
A Russian, Kazakh, Finnish, and British team examined blood samples from three generations of families that were alive during all or part of the time the blasts occurred. They compared the genetic material in the blood with DNA from Kazakh families who lived in an uncontaminated region further away at the same time.
Research leader Yuri Dubrova of the University of Leicester in England says the first generation in the contaminated area had nearly twice the rate of genetic mutations as its more distant counterparts. That's the generation who lived through all four explosions. "So what you've got here, you've got a window of exposure to relatively high levels of ionizing radiation starting from 1949 up to the end of the 1950's," says Mr. Dubrova.
The double mutation rate in this first generation may seem proof enough of the physical effect of nuclear radiation. But Mr. Dubrova's group found evidence in their children they consider stronger. The second generation near the nuclear test site also had higher mutation rates than their more distant counterparts, but not as high as their parents, and the rate declined the later the individuals were born. Mr. Dubrova says this reflects their exposure to fewer explosions. "This correlation perfectly corresponds to the improvement in the radiological situation in this area, basically providing quite strong evidence that what we actually found is, indeed, activity to ionizing radiation," he says.
The findings support a controversial study six years ago in which Mr. Dubrova linked mutations to fallout from the 1986 Chernobyl nuclear power reactor explosion. That study was a revelation because Japanese who survived the 1945 U.S. atomic bombing at the end of World War II had shown no such mutations.
But the study was criticized because it compared people living near Chernobyl with people living in Britain. This new study is an effort to overcome that deficiency by analyzing more comparable populations. Yuri Dubrova is also following up on the Chernobyl findings with an improved study now underway in Ukraine.
Yet, what these mutations mean for health is a mystery. The director of radiation cancer research at the University of Maryland, William Morgan, says the genetic material studied has no known physical function. "We don't know what any of the consequences of these particular mutations [are]. They are not specific genes. But all genomic change has some potential not to be good," says Mr. Morgan.
Mr. Morgan says animal studies show that continuous low doses of radiation cause some genetic mutations that are passed to the next generation. He notes that the Soviet nuclear tests were a similar situation in which radiation was chronic, so he does not rule out the possibility that they may have contributed to disease. "A lot of us are becoming more aware now that long term, continuous exposures are probably different from where you just get a quick flash, if you will, when you go to the doctor's you get an x-ray, you are irradiated," he says. "But it's different when you are continuously exposed because it looks like at different times during development you are more sensitive."
Mr. Morgan suggests that the differences in the term of exposure may account for the reason genetic mutations have never been seen in Japanese atomic bomb survivors.