Long-term effects of radiation on wildlife around Chernobyl

A fascinating article which I found through the Valuscience Blog of my friends at Magic in Stanford is titled „Is Chernobyl a Wild Kingdom or a Radioactive Den of Decay?“. The authors, Timothy Mousseau, a US-based evolutionary biologist, and Anders Møller, a Danish biologist, basically debunk the myth that already after a relatively (for standards of nuclear waste and pollution) short period of time, the „Chernobyl Exclusion Zone“ has become almost a national park’s worth of happy wildlife. The article is very long and narrative in tone, though, so here are some remarkable findings of my skimming.

Life in the zone comes at a hight cost for the individuals and species involved:

They have gathered a rising mountain of data and published dozens of papers, all suggesting that the chronic low-level radioactivity of the zone and the hot particles that find their way into the soil and food in the area cause long-term damage to the organisms that live there. In barn swallows, they found deformed beaks and eyes, tumors, damaged toes, and asymmetrical tails. (All of these changes, of course, can make the birds less successful at catching food, migrating, and breeding.) They also found high rates of dead or deformed sperm in birds nesting in the most contaminated areas, further demonstrating the reproductive cost of living in the zone. When they examined a wider sample of bird species, and then invertebrates and spiders, they found similar results: “a very strong signal of contamination effects on abundance and biodiversity,” Mousseau says. In other words, populations declined as radioactivity increased. The evidence of the damage caused by the contamination was alarming: Gathering their results on abnormalities in barn swallows for a Biology Letters paper that same year, they described the external examination of 7,700 individual birds, declaring it “the most extensive data set on abnormalities in animals ever recorded.”

So much so that it seems it requires a constant inflow of animals to sustain the populations.

Most startlingly, in 2005, Møller and Mousseau did a chemical analysis of the feathers of swallows captured in Ukraine and Denmark to identify where each bird had spent its winter migration. They compared the results with those from specimens caught in Ukraine before 1986, found in the collection of the National Museum of Natural History in Kiev, and noticed a distinct pattern. Barn swallows were now coming into the zone for the summer from a greater number of locations than before the accident. This suggested that the population of birds living in contaminated areas around Chernobyl was not sustaining itself without outside help: The area was a sink. Given the low survival and fertility rates, the population could only be propped up by constant immigration. And what is true for swallows might also be true for the other species whose presence in the zone, drawn in by the absence of humans, has seemed so remarkable.

There are of course also critics cited, but it seems much of it is due to the politics that the science either way would have direct and strong implications for. The argument sounds pretty solid and differentiated to me:

“I’ve never seen any data related to any kind of census, any kind of quantitative assessment of numbers,” Mousseau says. (Indeed, Gaschak’s assertions about the population density of large mammals in the zone are based on observational estimates.) This year, Møller and Mousseau hope to finally gather enough data to conclusively establish the density and abundance of mammal populations in the zone, returning with a team to conduct a widespread census. In the meantime, they have continued to produce attention-grabbing research on avian life. At the beginning of February, the online journal PLoS ONE published their latest paper, showing that birds they captured within the zone had brains 5 percent smaller than those they found outside it. “Microcephaly,” Møller says. “A common condition in humans in Ukraine in these contaminated areas.”

Which raises a key point: If the entire debate about the ecosystem of Chernobyl were simply about the fate of barn swallows or wild boar, the conflict might be easily dismissed as arcane bickering between biologists. But the stakes are much higher, because the animal studies may shed real light on the effects of long-term radiation exposure on humans. Post-Chernobyl, obtaining statistically significant epidemiological data on cancer was complicated by Soviet-era secrecy and disinformation and by the scattering of the hundreds of thousands of workers who participated in the cleanup and then returned to their homes across the Soviet Union.

But one of the few certainties to emerge from research into low-level radiation since 1986 is that different species react to chronic exposure in different ways. Pine trees cope less well than birch. Migrant barn swallows are apparently very radio-sensitive, resident birds less so. Winter wheat seeds taken from the Exclusion Zone in the days after the disaster and since germinated in uncontaminated soil have produced thousands of different mutant strains, and every new generation remains genetically unstable, even 25 years after the accident. Yet a 2009 study of soybeans grown near the reactor seemed to show that the plants change at a molecular level to protect themselves against radiation. No one can be certain where human beings might fall on this continuum of DNA damage and long-term adaptation. “That’s what we want to know,” Møller says. “Are we more like barn swallows or soybeans in terms of radiation-induced mutation?”

Finding the answer to this question may take decades or even centuries. The genetic effects of chronic radiation exposure on each species studied so far have often been subtle and varied and only conclusively shown after many generations. The potential genetic changes in human beings—only now producing their third generation, as the children of the liquidators themselves raise families—may take hundreds of years to fully unravel. Meanwhile, the Ukrainian government, seemingly satisfied with the anecdotal evidence of the zone-based research team, is pushing ahead with its plan to open the zone to tourism. Sergey Gaschak fears that future plans will include repopulating the Exclusion Zone at the earliest opportunity.

Some of the chemistry involved:

While iodine-131 decayed long ago and the strontium and cesium are slowly becoming less potentially lethal, the hot particles of plutonium-241 scattered across the landscape are actually decaying into an even more toxic isotope, americium-241. A more powerful emitter of alpha radiation than plutonium, americium is also more soluble and can easily find its way into the food chain. Americium-241, in turn, decays into neptunium-237, another energetic alpha emitter that has a half-life of more than 2 million years. As of yet, the long-term effect of americium-241 on animals remains largely unknown.

Datum: Mittwoch, 4. Mai 2011 19:28
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  1. 1

    Many thanks for this information.

  2. 2

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