Why Europe’s boars still hold radioactivity surprises scientists

Spoiler alert: It’s because they eat deer truffles

BERLIN — Although scientists have long known that flora and fauna in central Europe still carry traces of radiation stemming from the 1986 meltdown at the Chernobyl nuclear power plant in Ukraine, a new study on wild boars roaming the forests of Bavaria in southern Germany has turned up unexpected findings about the radiation present in their tissue.

The peer-reviewed study, published this past week in the journal Environmental Science & Technology, found in the boars high levels of radiation that the researchers believe come from nuclear weapons tests in the atmosphere carried out long before the Chernobyl meltdown. It also answers a question that has stumped researchers and hunters: Why is the radiation in the wild boar population relatively high, when most other wildlife is uncontaminated, many generations after the accident? (Spoiler: It’s because they eat deer truffles.)

The findings were so unexpected that when Georg Steinhauser, the paper’s lead researcher, and a colleague first saw the results, they thought there had been a mistake. “That can’t be right; that’s not possible,” Steinhauser recalled his colleague exclaiming.

Given that radiation from the Chernobyl accident temporarily contaminated large swaths of Ukraine, Belarus, Russia, and central Europe, flora and fauna there have since been regularly tested to determine whether they are safe for human consumption. And Martin Steiner, a scientist at the German Federal Office for Radiation Protection who was not involved in the study, said in an interview that he and his colleagues had long known that significant radiation from mid-20th-century nuclear weapons testing remained in the environment.

But the newly published study, by researchers from Leibniz University in Hanover, Germany, and the Vienna University of Technology, provides a more concrete way of quantifying the extent to which the radiation from the testing persists in boars today.

The research used a method involving the ratio of two cesium isotopes to analyze the carcasses of boars killed by hunters across Bavaria from 2019 to 2021. That relatively new method of analysis allowed the team to better understand what was behind the higher levels of contamination in wild boars in central Europe.

In Bavaria, boar hunted in certain areas must be tested for radioactivity, and German health guidelines allow for the human consumption of such meat if the radiation is under 600 becquerels per kilogram. Torsten Reinwald, a spokesperson for the German Hunting Association, said in an interview that, overall, “We have no indication that meat from wild boar in Germany is contaminated with significant radioactivity.”

But some of the boars tested in the new study carried far higher radioactivity levels, with the contamination ranging from 370 to 15,000 becquerels per kilogram of meat.

And given that nuclear reactors and nuclear weapons leave slightly different contamination signatures — with distinct ratios of cesium-135 to cesium-137 isotopes — the researchers determined that a surprising amount of radiation present in the tested boars stemmed from nuclear testing in the 1950s and 1960s.

After the first nuclear weapons test in New Mexico in 1945, the United States, its allies, China, and the Soviet Union kept testing atomic weapons by detonating them above ground, leading to heavy atmospheric nuclear pollution that spread around the globe.

In all, the world’s nuclear powers conducted more than 500 atmospheric tests before moving them underground to try to limit the spread of radioactivity. The new study’s findings indicate how the many decades of above-the-ground detonations continue to have ramifications.

“The fact that the radiation from those nuclear tests is still present, even when compared to Chernobyl, is noteworthy,” Michael Fiederle, a University of Freiburg professor who studies radiation and was not involved in the research, said in an interview. He also described the method of sourcing radiation by looking at cesium isotopes as promising.

As for why wild boars in southern Germany bear more traces of such radiation than other animals do, Steinhauser said that a crucial element to the mystery was a fungus — elaphomyces, or deer truffles — that boars dig up and eat but other wildlife ignore.

Although many other edible fauna are no longer significantly contaminated, the truffles, which grow inches below earth’s surface, store radiation particularly well.

Depending on the soil composition and how deep the truffles are, the fungi can be exposed to water containing decades-old radiation both from the nuclear tests and the Chernobyl disaster, making them a particularly rich source of radiation.