By Sean Henahan, Access Excellence

ATHENS, GA (9/8/96) Serious long-term genetic consequences are evident in the wildlife near the site of the world's worst nuclear reactor disaster in Chernobyl, Ukraine.

Scientists at the University of Georgia analyzed the DNA of some 400 crucian carp and found significant genetic changes in individuals many generations removed from the massive release of radioactivity in 1986. The work was funded by the University of Georgia and the U.S. Department of Energy.

"We theorize that unequal amounts of DNA were passed on to the daughter cells of fish at some point, leaving genetic information in offspring in places where it shouldn't be," said Dr. Cham Dallas, a toxicologist in UGA's College of Pharmacy.

While numerous genetic changes were found in the DNA of many of the carp, the team found no morphologic alterations. Years ago, some researchers theorized that a severe nuclear accident like the one at Chernobyl would cause such severe genetic damage that animals would be born showing drastic changes in appearance. So far, the Chernobyl accident has not borne that out, the researchers note.

Just why is unclear, though Dallas speculates that the animals who received the worst genetic injuries from the accident probably did not survive to pass traits on to their offspring. The carp in the study, rather than being obviously damaged by their rearranged DNA, seem to be completely healthy.

"The most impressive thing to me is that we didn't see more changes than we did," said Dallas. "It just shows the amazing resilience of nature."

The scientists chose to study fish because they knew that nearly all radionuclides -products of a nuclear reaction -- go into the bottom sediments when they fall on rivers or lakes. From there, the radionuclides are taken up by fish. Dallas and the scientists looked at 400 carp from 12 ponds in contaminated areas of the Ukraine some 20-30 kilometers from the site of the Chernobyl explosion.

The researchers used methods such as flow cytometry to assess the possible relationships between the chronic lifetime exposure to contaminants and variation in the cellular DNA content of fish. Analysis of whole blood from the fish showed clear evidence of aneuploidy -- extra DNA that does not belong in the genetic makeup of the fish. (Careful comparison with several fish species from unpolluted environments have made the alterations in DNA obvious, since aneuploidy has not been found in them.)

The appearence of aneuploidy is strong evidence of radioactive pollution, Dallas said, because in a companion study of some 2,000 bass from clean areas examined in the U.S., not a single case of aneuploidy was discovered. That makes it less likely that the DNA changes in the carp in the ponds near Chernobyl are the result of some natural process.

"We also measured the coefficient of variation, in which 10,000 blood cells from each fish were compared to each other to look for changes in DNA content," said Dallas.

There were also clear differences in the carp in their ploidy -- the number of chromosomes. Two populations with completely different ploidy were found. While differences in ploidy do occur in nature, it is also known to be altered by environmental factors. So far, only high levels of radiocesium have been positively identified in the ponds, but work is underway to identify other radioactive pollutants. (The issue of which radionuclides are in the pond is important. Radiocesium, for example, has a half-life of only 30 years, while plutonium, another product of the meltdown, has a half-life of 76,000 years.)

Dallas is working on human studies in the area as well, and he points out that studying the effects on human beings is much easier, because when people become sick, they go to the hospital -- essentially self-selecting themselves for study. Animals, on the other hand, often show no effects of exposure to radioactivity that can be detected easily. Most animals studied so far in the vicinity of the Chernobyl accident show no outward changes over many generations in the decade since the accident. Only by sampling and intensive, often difficult tests can researchers be certain what changes have occurred in DNA.

The University of Georgia scientists, who have a major ongoing research effort in the area, have with others established the first baseline of what has occurred both to humans and wildlife because of the accident. What they have found has often been unexpected. Other scientists involved with the study came from the U.S. Fish and Wildlife Service; UGA's Savannah River Ecology Laboratory in Aiken, S.C.; and from the International Research and Development Agency in Kiev, Ukraine.

"For instance, there are probably two million people in the contaminated areas, and only a few thousand are actually sick from diseases than can be reasonably linked to the high levels of radioactive contaminants. We really don't know why this is yet," said Dallas.

One reason is clearly the discovery that patterns of long-term radiation effects were somewhat dependent on the winds on the day the explosion occurred in the reactor. Some areas not far from the plant (which is still in operation) are virtually pollution-free, while others some distance away may never be opened to resettlement. Also, the decay of short-lived radionuclides left some areas reasonably safe that at first had been quite polluted by fallout.

Before the accident, the land around Chernobyl was largely used for forestry and agriculture. An area of flat, poorly drained landscapes, it has extensive wetlands, ponds and rivers. Dallas notes that because of this use, there could be some runoff from agricultural chemicals or pesticides that might contribute to some of the DNA damage to the fish. Still, the evidence of damage from radioactivity is compelling, though further studies will be required to determine with certainty the causes and potential outcomes.

The research will be published in October 1996 issue of the journal Ecotoxicology.