Radiation fallout from bomb testing causes mutations in 'junk DNA' with no perceived health effects, researchers say

Thursday, February 7th 2002, 12:00 am

By: News On 6

WASHINGTON (AP) _ Two generations of families living downwind from a Soviet atomic bomb test site experienced a higher-than-normal level of DNA mutation, but the effects have no known health effects, researchers report.

A study appearing Friday in the journal Science gives compelling evidence that low-dose radiation from atomic bomb fallout can have long-term genetic effects, but it is not clear that there are any health consequences from these DNA changes, experts say.

A group of European researchers led by Yuri E. Dubrova of the University of Leicester took blood samples from 40 families in an area of Kazakhstan not far from the Semipalatinsk site where the former Soviet Union conducted atomic bomb tests.

For a control group, the researchers took blood samples from 28 families in a geographically similar region of Kazakhstan that had not been exposed to radiation from the tests.

Members of the study group and the control group were matched by year of birth, occupation and ethnicity.

The researchers then checked DNA of the two groups for evidence of mutations that could have been passed from one generation to another.

For the generation exposed to radiation from bomb tests in 1949, 1951, 1953 and 1956, the study found a mutation rate that was about 80 percent higher than in the corresponding generation in the control group which was not exposed.

In the children of the exposed generation, the researchers found a mutation rate about 50 percent greater than in the control group.

All of the mutations were found in what is known as ``junk DNA,'' bits of genetic material that have no known function.

``These are mutations, but not in critical genes and there is not anything that we can correlate with a health effect,'' said Dr. William F. Morgan, director of the Radiation Oncology Research Laboratory at the University of Maryland, Baltimore.

Morgan, who reviewed the study for Science, said the findings give new understanding of how ionizing radiation, such as from an atomic bomb and its fallout, can affect successive generations.

Most of what is known about such radiation effects comes from survivors of the atomic bombs dropped on Japan during World War II. Those survivors were exposed to a single, severe dose of radiation. No inherited mutations were found in that group, said Morgan, but it was rare that both parents in the Japanese bombings were equally exposed.

In the new study, he said, ``they are finding that if you live in an environment that is contaminated where you are continuously exposed, then you start to see these increases'' in mutations.

Dubrova and his colleagues found that rate of mutations declined with the passage of time once the bomb tests stopped. They said this suggests that the 1963 treaty banning aboveground nuclear weapons testing ``has been effective in reducing genetic risk to the affected population.''

Morgan said the findings are consistent with animal studies that showed low-level, chronic exposure to radiation, such as from the fallout of bomb tests, can cause some genetic mutations that are passed to the next generation.

Such mutations, he said, can be traced to radiation exposure affecting sperm at a critical phase of its development.

The mutations that pass to the next generation originate ``predominantly on the male side'' of reproduction, Morgan said.

In an earlier study, Dubrova found similar mutations among families exposed to fallout from the 1986 nuclear power plant accident at Chernobyl in the Ukraine. Deaths of about 8,000 people in the Ukraine, Russia and Belarus have been blamed on the incident, but another 200,000 are thought to live in areas still contaminated.

Dubrova's Chernobyl study, published in Nature in 1996, found that children of men living in the contaminated area of Belarus had about twice the number of mutations of a comparison group in Britain. Many researchers said that study was flawed.

But Morgan said the new study in Kazakhstan supports Dubrova's earlier findings.