The Truly Wild Life Around Chernobyl
Many animals are in evolutionary overdrive
At first glance, the glistening marshes of Glebokye Lake in Ukraine appear to be paradise. Wild boars stomp by, roe deer leap through the waist-high grass and myriad herons and swans feed in the shallows. Look on the horizon, though, and the skyline of Pripyat, a ghost city abandoned by 45,000 people, is visible. So is the red-and-white-striped tower of the Chernobyl nuclear power station's infamous Reactor 4, which exploded nine years ago. Paradise? Not even close. Glebokye is one of the most radioactive lakes in the world.
There is no disputing that the worst nuclear disaster in history was a human tragedy. But paradoxically, it is providing scientists with a unique opportunity to study how life adapts to extreme adversity. For more than two years, researchers affiliated with the University of Georgia's Savannah River Ecology Laboratory--armed with respirators, dosimeters and protective clothing--have gone to Ukraine to study Chernobyl's flourishing wildlife. On a recent trip, they allowed a U.S. News reporter unprecedented access to observe their work. "All your life you're told of the dangers of radiation, and here are all these organisms living with it," says team leader Ronald Chesser. "How are they managing to survive?"
One clue is being revealed this week at a meeting of the Society for the Study of Evolution in Montreal. Robert Baker of Texas Tech University in Lubbock, and a member of Chesser's group, is presenting startling evidence that Chernobyl field mice are undergoing an extremely rapid rate of evolution. Indeed, he says the amount of evolutionary change in some animal species since the accident is greater than would normally occur in 10 million years.
Life altering. Investigating how small creatures such as Chernobyl field mice are adapting and evolving is part of an emerging scientific discipline called evolutionary toxicology--the study of how radioactive and chemical pollutants alter the life course of species. "Man is deflecting the path of evolution; 200 years from now, we may be living with organisms that are genetically quite different from today's," says John Bickham of Texas A&M University at College Station.
Few predicted a swift comeback of wildlife around the Chernobyl plant. Flaws in the reactor's design combined with judgment errors by the operators caused an explosion on April 26, 1986, which belched into the atmosphere at least 10 times the amount of radiation released by the atomic bomb dropped on Hiroshima in 1945. More than 5 million acres of prime farmland were contaminated, and more than 160,000 people were forced to abandon their homes. The accident also caused nearly 1,500 acres of the surrounding forest to die almost immediately. (Pine trees have large chromosomes that are particularly sensitive to radiation.) Soviet researchers noted steep declines in wild animals and die-offs of small insects and worms living in the forest litter. Cattails with two and three "heads" became common.
Today, much of the original radioactivity has disappeared. Contaminants with short half-lives, such as radioiodine, have completely decayed and longer-lived ones, such as plutonium, radiocesium and radiostrontium, have settled deep into soils, says Richard Wilson, a physicist at Harvard University and a Chernobyl expert. However, high surface radioactivity remains in patches, and contaminants still circulate within the food chain. Mushrooms and berries set Geiger counters screaming. And boars, deer and mice captured in the zone have taken up radiocesium in their muscles and radiostrontium in their bones.
The abundance of wildlife is a puzzle, given what is known about the biological effects of radiation. Indeed, high-tech probing of the cells of animals from the region challenges the conventional wisdom that animals cannot tolerate a high rate of genetic change. Here's why: Extensive studies from Hiroshima and cold war laboratories have shown that radiation breaks chromosomes and the strands of the DNA double helix, which contain the blueprints for making the body's proteins (graphic, above). Most of the time, genetic damage signals a cell to die a programmed death, or else it enlists repair enzymes to restore the genetic code. Problems arise when genetic mistakes aren't fixed or are repaired incorrectly, and persist as mutations. In the body, such genetic errors can lead to birth defects in offspring and cancer. More subtly, mutations can cause cells to produce faulty proteins, such as those important for immunity.
While Chernobyl mice don't look like "mutants," on closer inspection, they have many breaks in their DNA strands and a phenomenally high mutation rate. Baker and Ron Van Den Bussche at Texas Tech analyzed DNA from five voles--a type of field mouse--captured within the contaminated zone and compared it with DNA from voles living outside the zone. To search for signs of genetic mutation, they read the code of a gene called cytochrome b that, because it is passed down directly from mother to offspring and changes slowly, is used by scientists as a sort of "genetic clock" for estimating genetic relatedness. As expected, the voles from the area outside the zone had essentially the same cytochrome b gene. But among the Chernobyl voles, the gene sequences as well as the proteins from all five animals were different. Indeed, the differences in the genes between two Chernobyl voles were greater than those normally found between mice and rats, two species that diverged about 15 million years ago.
How adaptable? During mammalian evolution, the rate of spontaneous mutation of one letter in the genetic code has been estimated at 1 in a billion per generation, says David Hillis, who studies molecular evolution at the University of Texas at Austin. But at Chernobyl, the mutation rate in the cytochrome b gene is 1 in 10,000. The important question now is whether rapid mutation observed in the cytochrome b gene is also occurring in other genes. "If that kind of high mutation rate can be tolerated across the entire genome," says Hillis, "it would indicate that mammals in particular are a whole lot more resilient than anyone ever guessed."
Still, the full impact on the mice of this rapid rate of mutation is far from clear. While populations seem to thrive in the Chernobyl environment, individual mice may be living on the edge of their ability to adapt to stress or paying a price with shorter life spans, says Chesser. His lab is now investigating whether Chernobyl mice have had to maximize their resistance to cancer by keeping a well-known tumor suppressor gene called p53 turned on full throttle.
People from the region are clearly paying a heavy price for the accident as cancer and other disorders related to genetic mutations are rising in those who received the heaviest doses. Last month, scientists reported in the journal Nature that rates of thyroid cancer in Ukrainian children have climbed fivefold overall and 30-fold in those who lived nearest to Chernobyl. Higher rates of spontaneous abortion and birth defects have been documented in Belarus, but it's not clear that radiation exposure is the primary cause, says Martin Cherniack, an associate professor of medicine and international health at Yale University. Researchers also expect at least a small increase in leukemias and other cancers to show up over the years, but that, too, may be hard to trace to the Chernobyl accident.
The human toll triggers a conflict of emotions for Chesser. "The research potential is very exciting, but I also feel the sadness of all the people who were betrayed," he says. The picturesque landscape near Chernobyl will be repopulated in the coming years, but more by genetically adapted plants, insects and field mice than by people.
CHERNOBYL'S ASSAULT ON GENES Scientists now know a great deal about the ways that radiation can cause genetic mutations. 1. Radiation release. In 1986, an accident at a Chernobyl reactor caused the release of tons of radioactive materials. 2. Food consumption. Radioactive cesium and strontium are taken up by plants and once eaten, become incorporated in animals' muscle and bones. 3. Cell death. Radiation bombards DNA inside animal cells, causing chromosomes to break and, usually, cells to die. 4. DNA damage. Radiation can also break apart DNA strands. 5. Gene repair. DNA is often repaired, but inaccurate restoration can lead to gene mutations that are passed on to new generations of cells. 6. Cancer's origin. Some mutations release the brakes that normally control cell division. Cancer may develop. 7. Inherited mutations. Mutations in egg and sperm cells can be passed to the animal's offspring. Sometimes that causes birth defects. Harmful defects can hasten the death of offspring, but some "defects" may benefit an offspring's chance of survival.
CHERNOBYL'S FUTURE What to do with Reactor 4? Two reactors continue to operate at Chernobyl--one in a building just next to the shoddily housed remains of the 1986 explosion. Because of Ukraine's entrenched nuclear bureaucracy and a desperate need for energy and employment, the new nation has resisted closing the Chernobyl station in spite of experts' fears of another nuclear accident.
In April, after years of pressure from abroad and from environmentalists at home, Ukraine's President Leonid Kuchma announced that he is committed to shutting down the facility by the year 2000. A month later, the government signed an agreement with a consortium of Western companies to replace the station with a new gas-powered plant. But the deal could still fall through. Laying Chernobyl to rest will be a thorny and expensive problem for many years.
A shutdown would immediately soothe qualms about the two operating reactors. True, some new safety features have been added to these units. But since the breakup of the Soviet Union, parts, money for maintenance, and qualified nuclear workers all have become scarce. "These reactors are aging, and they're not operating under anything approaching Western standards of safety," says David Schwarzbach, a nuclear policy expert at the Natural Resources Defense Council in Washington, D.C.
Containment. Properly entombing the station, however, will be a long-term challenge. The bowels of burnt-out Reactor 4 were filled with a molten mix of radioactive materials that solidified into eerily beautiful multicolored masses. This "chernobylite," as well as tons of contaminated dust, will remain radioactive for hundreds of thousands of years. No one knows yet how to safely contain this debris for such a long period of time, and contamination of ground water is a growing threat. The existing shelter, constructed hastily nine years ago, already has holes in it; radioactive dust can escape, rain can enter, and birds nest inside. Experts recommend building a new earthquake-resistant shelter designed to stand 100 years.
Who will pay? Ukrainian officials are asking for $4 billion in aid to get these Chernobyl-related projects started. The World Bank and the European Bank for Reconstruction and Development are evaluating the nation's energy needs and are expected to update the current offer of $800 million with a new aid package this fall.
This story appears in the July 17, 1995 print edition of U.S. News & World Report.