Among the legacies left by the Soviet Union in the Central Asian nations is a nuclear test site in Kazakhstan that has contaminated the region with radiation for years. Now, an international research team has found that radiation from the site affected the genes of people living nearby, as well as the genes of their offspring. RFE/RL correspondent Margot Buff explores the implications of this discovery, and reveals why the researchers are hesitant to raise alarm.
Prague, 21 February 2002 (RFE/RL) -- The Soviet Union performed more than 400 nuclear tests at its Semipalatinsk test site in Kazakhstan between 1949 and 1989.
The blasts filled the surrounding region with ionizing radiation similar to the fallout from the bombs dropped on Hiroshima and Nagasaki in Japan in World War II, and from the meltdown at Ukraine's Chornobyl nuclear power plant in 1986. The radiation hit residents of the rural Beskaragai district most intensely between 1949 and 1956, when the Soviets detonated four surface explosions at the site.
The radiation in the region has since faded to almost normal levels, and the heightened risk of cancer linked to radiation exposure has diminished as well. But researchers say the effects of the nuclear testing are still lingering in the children and grandchildren of the people who live near Semipalatinsk.
A study in a recent issue of "Science" magazine -- published by the American Association for the Advancement of Science -- shows that analysis of the DNA of adults exposed to nuclear fallout at the time of the tests passed on genetic mutations to their children. The children, in turn, passed on mutations to their children.
Geneticist Yuri Dubrova of the University of Leicester in England says the mutations he and his colleagues identified in the study do not necessarily imply a health risk for the people involved, however. In fact, he says, they are genetic changes of which the subjects themselves are unaware.
"Mutation in these genes is absolutely irrelevant to the health status of these children," Dubrova says. "So we are talking about some sort of mutations which you cannot spot unless you go and analyze these children using our sophisticated ways of molecular genetics."
These methods involved collecting blood samples from 40 three-generation families living near the Semipalatinsk test site. The researchers from Britain, Finland, and Kazakhstan also tested a control group of 28 families in the non-contaminated rural area of Taldy Kurgan. Both groups were matched by year of birth, ethnicity, occupation, and whether or not they were smokers.
All members of the first generation studied were living near the test site during the nuclear tests between 1949 and 1956, and received the heaviest doses of radiation. Members of the second generation were born throughout the 1960s. By comparing the DNA of parents and children, scientists found that the number of new mutations -- or newly occurring genetic features -- in the oldest members of the test group was nearly 100 percent greater than the rate in the control group. These mutations were inherited by the second generation.
But the team found that the rate of new abnormalities passed to the third generation was only 50 percent higher than in the non-contaminated group. The third generation inherited all of the mutations from their parents and grandparents, but the number of new mutations decreased with each generation.
The research also showed that the rate of mutation was higher for people born earlier. That is, someone from the second generation who was born in 1960 was exposed to more intense radiation than someone born in 1970, when the lingering radiation had dissipated further. So the effect of radiation on the subject's sperm or eggs -- called germ cells -- resulted in more mutations in his or her children if the parent had experienced greater exposure.
From the decreasing rates of mutation that match the decreasing amounts of radiation in the environment, the researchers concluded that exposure to continuous, low-level radiation results in genetic changes in the germ line, or family line.
Determining the health implications of these changes is more difficult. One reason is that the genetic tests were performed on so-called "junk DNA," genetic material with no known function but which is frequently used for testing.
But Dubrova also says it may be possible to extrapolate the health implications from the existence of mutations in the junk DNA: "But what does it mean? It means that mutation rate is up in this particular part of the genome [the complete gene complement of an organism], and one might expect that it may also be up in other parts of genome, including essential genes, the mutation of which may also affect cancer rate, malformation and mortality among the offspring of irradiated parents. But this is only a guess. And we don't know exactly to what extent our results may be extrapolated to other genes."
Another researcher who participated on the Semipalatinsk study, Maj Fulten of the University of Warwick in England, explains one difficulty in identifying health problems in a genetic study. Tracking genes over several generations requires that the older family members still be living and that they have reproduced successfully, so these subjects are unlikely to show major health effects.
"These families were selected where all the three people in the three generations were living in the same area, and still living there, so they hadn't migrated, and also they were 'good' families in as much as there had to be at least two children in each generation. So they were selected in that way, and therefore we haven't selected families where there is genetic disease," Fulten says.
Dubrova says much more research is needed to determine what these genetic changes mean for the exposed population, and whether, as he says, changes in the "junk DNA" imply changes in more critical parts of the genome. He says researchers are trying to organize a collection of blood samples from people living near the Chornobyl nuclear power plant in Ukraine. Similarly, the genetic effects of radiation from other sources, including functioning nuclear power plants, is not yet known.
But the Semipalatinsk study provides a stepping stone for future research, not only in the findings but also in the DNA itself. Fulten says the blood samples will be available for future use.
"We have set up a biobank, so we have cells and DNA stored. So if even more sensitive technologies are appearing in the future, researchers can get the same samples again, because it was terribly difficult to get the samples," Fulten says.
This mean that although the radiation levels from nuclear tests at Semipalatinsk have returned to nearly normal, future projects will be able to investigate the effects of fallout on the residents who were alive at the time of the Soviet tests.
Dubrova says the most important move to protect the local population from radiation has long been made. He praises the 1963 Limited Test Ban Treaty, in which the U.S., the Soviet Union and Britain agreed to halt the most dangerous forms of nuclear testing.
"In 1963, when both governments signed the Moscow treaty, the testing in atmosphere and aboveground came to an end, which in turn resulted in a drastic improvement of radiological situation in this area, and therefore in decreasing the amount of exposure of these people to ionizing radiation," Dubrova says.
The study ends with a dual conclusion. Radiation from the test site resulted in genetic mutations in exposed families. But the decline in the rate of genetic mutations over three generations shows that the ban on nuclear testing worked to decrease the risk.