On the eve of the 10th anniversary of history's worst nuclear power plant disaster, scientists report that a group of children 120 miles away who were born eight years after a reactor exploded near Chernobyl, Ukraine, have twice as many mutations in their DNA as do other children.
Although researchers have long known that radiation can permanently damage DNA, this study by scientists in Russia and England offers the first evidence that people can pass such mutations to their children.
The findings lend support to a scenario advanced by nuclear apocalyptics and sci-fi writers alike: Genetic alterations wrought by escaped radiation can become part of the human legacy, woven into the fabric of a generation that did not even exist when the disaster took place.
The researchers say they do not know if the mutations will affect the health of the children, who otherwise appeared normal. Using DNA fingerprinting, the investigators analyzed stretches of DNA that have no known biological function but are nonetheless vulnerable to mutations, thus serving as a chemical sentinel of change within a person's genome, or genetic makeup.
"We cannot predict the impact of this increase in mutations on the health of future generations," said the study's lead author, Yuri Dubrova, a geneticist at the Vavilov Institute of General Genetics in Moscow. He is currently a visiting professor at the University of Leicester in England, where he collaborated on the study with biologist Alec Jeffreys, a pioneer in DNA fingerprinting techniques.
Still, the scientists cannot rule out harmful health effects of mutations either. "The implication is if there's an effect seen in this part of the genome, then there are also likely to be effects seen in parts of the genome that have a more direct bearing on human health," said David Hillis, a radiation biologist at the University of Texas. He said the mutations documented were so pronounced as to be "surprising" and "unexpected."
Indeed, some researchers viewed the study as groundbreaking for detecting human genetic alterations in the absence of outright disease or injury. "My concern is that radiation protection standards do not take into account this kind of impact," said Pennsylvania State University geographer Judith Johnsrud, who has studied radiation exposures at Chernobyl.
For the most part, she said, safety thresholds for radiation exposure are based on the risk of an individual developing cancer at any given dosage. But this study, she said, suggests that "subtle but significant" effects occur in the children of adults exposed to relatively low doses over a long period.
The new study appears today in the journal Nature, which is also publishing an analysis of voles, a category of small rodents, living near the shut-down Chernobyl reactor. Surprisingly, the vole population appears to be thriving, even though the animals are so radioactive they exceed the scale of a Geiger counter.
"The bottom line is there are no monsters" as a result of the radiation, said the vole study's lead author, biologist Robert Baker of Texas Tech University.
The explosion and subsequent burning of Reactor 4 of the Chernobyl Nuclear Power Plant on April 26, 1986, released a host of radioactive chemicals into the environment, resulting in the evacuation of 135,000 people within 18 miles of the plant.
More than 30 people were killed by the explosion, and estimates of the death toll from acute radiation illnesses range widely, but generally number in the thousands. Researchers have documented a rise in thyroid cancer and congenital malformations among people living near the reactor, but the effects of low-level radiation over a long period of time are less well understood.
Dubrova and colleagues focused on 79 families living about 120 miles north of Chernobyl in Belarus. Collecting blood from children born in 1994 and their parents, they analyzed so-called "mini-satellite" DNA fragments. They then gauged the extent of mutations from parent to child--in effect, the number of DNA fragments that were "misspelled" in the process of being transmitted via sperm and egg to the next generation.
A number of mutations in these stretches of DNA would be expected to occur spontaneously from one generation to the next in any population. Taking that into account, the researchers performed similar DNA fingerprinting analyses on 109 "control" families in England. Compared with the English children, the children born in Belarus had twice as many mutations in their DNA, the researchers found.
Other researchers have questioned the findings, given that studies of the children of the survivors of atomic bomb blasts in Hiroshima and Nagasaki were not found to harbor such a high mutation rate. But Dubrova counters that the radiation from the bombs was such a large dose in such a short time that it has little bearing on those exposed to radioactive pollutants deposited in the environment by the Chernobyl explosion.
"Our data simply indicate that for some part of the human genome, the mutation rate is higher following this accident," Dubrova said.
Some researchers have also questioned whether the mutations were in fact caused by radiation, given the large number of other pollutants emitted by Reactor 4. But Dubrova said that among the children of Belarus, the mutation rate was higher in regions where the soil was most contaminated with radioactive cesium, suggesting a link.
If the radiation is the cause of the increased mutations, said Tore Straume, a biophysicist at the Lawrence Livermore Laboratory, it will be important for scientists to know more about the exact doses that the parents received. The doses that the Belarus parents were presumably exposed to are lower than those that could be expected to induce inherited mutations, given experiments in lab animals, he said.
"My guess," said Hillis, "is that the whole story of the mechanisms behind the mutations isn't understood."