From weapons tests to destructive accidents at power plants, human nuclear activity has contaminated the Earth with radioactive material. These unstable particles can spread long distances and remain in the environment for hundreds of years, accumulating in plants and the bodies of animals.
In Germany, for example, scientists have long known that the wild boars roaming forests in the country’s south contain high levels of radioactive cesium. Boars hunted in certain areas must be tested for radiation, and some have been deemed unsafe to eat.
Previously, researchers considered radioactive material from the Chernobyl nuclear power plant explosion to be the primary source of the boars’ radiation exposure. The 1986 disaster in Ukraine released radioactive material that spread over 40 percent of Europe, as well as parts of Asia, Africa and North America.
But according to a new study, published late last month in the journal Environmental Science and Technology, fallout from weapons testing decades before Chernobyl still contributes significantly to the levels of radioactive cesium in the boars.
“The fact that the radiation from those nuclear tests is still present, even when compared to Chernobyl, is noteworthy,” Michael Fiederle, a radiation researcher at the University of Freiburg in Germany who did not contribute to the study, tells the New York Times’ Christopher F. Schuetze.
“My mind was blown when I realized how relevant this source of radioactive contamination in general still is,” Georg Steinhauser, a co-author of the study and radiochemist at the Vienna University of Technology in Austria, says to the Washington Post’s Kasha Patel.
During the second half of the 20th century, countries around the world regularly carried out tests of nuclear bombs, detonating more than 2,000 nuclear explosions between 1945 and 1996. Roughly half of these tests were conducted by the United States, according to the United Nations (U.N.). These began with the Trinity Test in 1945, depicted in the movie Oppenheimer.
Aboveground nuclear tests shot radioactive materials high into the upper atmosphere, and these particles were spread by wind and weather patterns before returning to Earth via precipitation or by simply falling to the ground, per the Environmental Protection Agency. A 1963 treaty between the U.S, the United Kingdom and the Soviet Union banned atmospheric nuclear testing, though France and China continued such tests afterward, according to the U.N.
While these tests have now wound down, some of the radioactive material released from them has persisted in the environment. To measure the effects of these tests on wild boars today, the authors of the new study measured the ratio of the cesium-135 isotope to the cesium-137 isotope in samples of wild boar meat. A high ratio would indicate a high proportion of radioactive cesium from weapons tests, while a low ratio would be a sign of exposure to material from Chernobyl.
The researchers collected meat from 11 parts of the southern German state of Bavaria between 2019 and 2021. Their analysis revealed that contamination due to nuclear testing made up between 10 and 68 percent of the radioactive material in the tested samples. Not only that, but the total contamination levels in 88 percent of the samples exceeded regulatory limits for food products in Germany—with some meat exceeding the limit by as much as a factor of 25. In about a quarter of the samples, contamination from nuclear tests alone was enough to make the meat unsafe for humans, per the study.
While contamination levels in other animal species have declined since the Chernobyl accident, they’ve remained high for wild boars. Steinhauser tells the New York Times that the boars’ habit of eating deer truffles, which are neglected by other animals, could be part of the reason why. These mushrooms grow inches below the ground and absorb cesium from the soil, making them more contaminated than some other natural food sources. When wild boars consume the truffles in winter, their radioactivity levels increase, per the Post.
Rebecca Abergel, a nuclear chemist at the University of California, Berkeley, who was not involved in the study, tells the Post that she was not surprised by the findings. It has been “known for decades that significant isotope contamination throughout the planet is a result of weapons contamination,” she says to the publication.