Michaela Rehle/Reuters
- A high percentage of Germany's wild boars are radioactive while other animals in the region are not.
- Scientists have a surprising theory about what makes them so radioactive.
- A new study found that fallout from nuclear weapons and Chernobyl make a potent combination.
Wild boars have long been a problem in Germany, digging up graves, destroying crops, and attacking people. But what puzzles scientists is something they call the "wild board paradox."
The boars continue to be more radioactive than other animals in the area, even though their levels of radioactivity should have decreased over time.
Researchers long believed the cause was the deer truffles they ate, contaminated by the Chernobyl accident in 1986.
But fallout from nuclear weapons tests decades ago may also have contaminated the truffles, according to a new study published in the journal Environmental Science & Technology.
The researchers tested boar meat for the radioactive isotope cesium-137, a fission product. Cesium-137 has a 30-year half-life — the time it takes for the radioactive material to decay by half. But in some locations, boars' cesium-137 levels were staying about the same.
The researchers found boar-meat contamination linked to atmospheric weapons from the 1950s and '60s. The isotopes from the weapons and Chernobyl interacting may be the cause, one of the study's authors, Bin Feng, told Vice.
"The sources mixed together, and became a new source that can get stronger," he said. "This is the reason, we think, why the cesium contamination is so strong and persistent."
The wild boar paradox
In 1986, an explosion at the Chernobyl Nuclear Power Plant in Ukraine killed two people immediately and thousands more from radiation poisoning and radioactive fallout after.
The fallout spread for hundreds of miles, including to Bavaria in southeastern Germany, depositing radioactive material into the soil and the forest animals that lived there.
Many forest animals in the area showed high levels of radioactive cesium after the accident. Over time, rainfall and other effects, in addition to nuclear decay, lessened the amount of cesium the animals and plants absorbed. Contamination in many species declined. But not in the wild boars.
While prized for their meat, many German boars are too radioactive to eat, generations later. Hunters must have any boars they kill tested for radioactivity.
In 2014, The Telegraph reported that roughly one in three exceeded regulatory levels. The new study found 88% of the meat samples they tested were unsafe.
The trouble with truffles
The likely culprit is the deer truffle, which grows underground and accumulates radioactive cesium. Wild boars root them out, especially during the colder months when other food sources are scarce.
For a 2009 study, researchers tested Bavarian truffles that were about 6 inches or less underground and found that they were far more contaminated than ferns, berry bushes, and beech nuts.
When boars' stomachs contained even a small amount of truffles, they were responsible for three-quarters of the radiocesium they ingested.
Even though it's been decades since the tests and power plant accident, cesium is still slowly seeping deeper into the soil.
Deer truffles that are over a foot underground that nuclear weapons previously contaminated are now absorbing cesium from Chernobyl. In turn, boars that eat these truffles will accumulate cesium in their organs and tissues.
The study's authors used a gamma-ray detector to test 48 wild boar meat samples for cesium-137 and cesium-135 levels. Based on the ratio of the different isotopes of cesium, the scientists could tell whether the material was from Chernobyl or the older atmospheric nuclear weapons tests.
All the affected meat samples had contamination from both, with the weapons contributing between 10% and 68% of the cesium in the unsafe boars. In about a quarter of the samples, the amount of cesium-137 from weapons fallout alone exceeded the European regulatory limit.
"Just because they took place 60 years ago doesn't mean that they no longer impact the ecosystem," Feng and a co-author, Georg Steinhauser, told the BBC.