Soviet Nuclear Tests Altered DNA, Study Says
Aboveground nuclear tests conducted by the Soviet Union from the 1940s until the early 1960s appear to have altered the DNA of people who were living near the test site and exposed to fallout, new research indicates.
People living near the Semipalatinsk testing site in Kazakhstan passed mutations along to their children at a rate that was almost double what is normal, according to the new study, published in the journal Science.
The study, conducted by scientists in Britain, Kazakhstan and Finland, looked only at selected pieces of DNA chosen as markers. It does not directly show that the people affected were more likely to suffer diseases such as cancer as a result.
But the findings underscore the risks borne by civilian populations living near testing sites during the early years of the Cold War.
Other studies have documented increased rates of medical problems in the region, including birth defects and stillbirths, said Nailya Dyusembayeva, head of the Medico-Genetic Center in the Kazakh city of Karaganda.
Between 1949 and 1989, the Soviet Union conducted 470 nuclear tests at the Semipalatinsk site in the far eastern part of Kazakhstan. Before 1963, when the Soviet Union, United States and Britain signed a treaty banning all but underground tests, many of the explosions were conducted aboveground.
As much as 85% of the fallout exposure came from four large surface tests conducted between 1949 and 1956.
The United States also conducted aboveground tests but primarily on isolated islands in the South Pacific.
Residents of the region near the Soviet test site were, over the years, exposed to radiation from fallout that was several times greater than the average exposure of survivors of the atomic bomb dropped on Hiroshima, Japan, said Robert Ullrich, a professor at Colorado State University in Fort Collins and an expert in radiation-induced cancer. Genetic abnormalities of the sort seen in Kazakhstan have not been found in the Hiroshima population, Ullrich added.
To see whether radiation from the Soviet tests had left a measurable mark on the DNA of local residents, geneticist Yuri Dubrova of the University of Leicester in England and colleagues collected blood samples from 40 families living in the Beskaragai region near the test site, which was exposed to particularly high levels of fallout.
Blood was taken from three generations; all members of the oldest generation were alive at the time of the most contaminating blasts.
Dubrova and colleagues analyzed eight small pieces of DNA in the grandparents, children and grandchildren to see if any mutations had occurred and had been passed on to the next generation.
For comparison, the scientists also studied 28 three-generation families living in a similar rural region of Kazakhstan that had not been exposed to fallout.
The grandparents exposed to radiation passed on almost twice as many mutations to their children as did the grandparents from the unexposed area, the scientists found.
The second generation, many of whom had also been exposed to the most serious blasts, also passed on more mutations than normal.
Dubrova and colleagues also found that the rate of mutations appeared to be linked to the amount of exposure--implying that the nuclear tests, and not some other unknown factor, were indeed to blame.
Scientists knowledgeable about the biological effects of radiation said that the study’s findings are significant and important, albeit not altogether surprising.
“The population was exposed to a pretty high dose of radiation,” Ullrich said.
The doubled mutation rate fits well, he said, with what has been found in studies on animals exposed to radiation.
But the medical significance of the types of changes detected by Dubrova and colleagues is unclear, scientists said. The DNA regions that were tracked by the team are not in genes but in structures known as “mini-satellites”--areas of the genome where short bits of DNA are repeated over and over. Mini-satellites were chosen for the study because they tend to mutate faster than normal genes.
Changes in mini-satellites are not of themselves likely to be harmful. “Logic tells you that if you see something going on at one part of the genome you may also expect the same sort of thing is happening all over the place,” Dubrova said. But, he added “this is only a guess.”
Scientists and activists in Russia and Kazakhstan say the many health problems found in the region do not appear to be going away.
Moreover, other studies, including research done on animals exposed to radiation from the accident at the Chernobyl nuclear power station in Ukraine, suggest that the effects of radiation can cause rates of congenital abnormalities to persist through many generations, said Alexei Yablokov, president of the Ecological Policy Center of Russia.
In lab experiments, scientists have detected a genetic instability that persists over many generations, said Tom Hei, professor of radiation oncology and public health at Columbia University. The cause is not well understood.
“Maybe it is true that now the rate of inherited mutations is declining, but the research I conducted with my colleagues and the situation around Semipalatinsk testing grounds is far from being anywhere normal,” Dyusembayeva said.
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Sergei L. Loiko of The Times’ Moscow Bureau contributed to this report.
