When you think of great survivors in the animal kingdom, your mind might not immediately go to the humble pig, but maybe it should. In the wild, pigs are extremely durable — they can thrive in almost any environment — and they’re well-known for being able and willing to eat just about anything.

These two traits alone should earn them some respect as highly adaptable creatures. The problem is, those same characteristics make them a nuisance, certainly in the U.S., where feral hogs are now considered a highly destructive invasive species.  

In Europe, though, especially in Bavaria, Germany, the meat of the hairy, tusked wild boar (Sus scrofa) is more than a delicacy; it is one of the most popular forms of game meat. This makes feral pigs a favorite quarry among hunters in that part of the world.

Unfortunately, over the last several years, the inherent hardiness of those hogs has made them especially resistant to one of the most destructive forces in the world — and brought to light a problem that is both a mystery and something of a menace. In short, a significant portion of the German wild boar population — more than one in three, according to research going back nearly a decade — is radioactive.

German hunters who kill a wild boar are supposed to submit it to authorities for testing. Often, the meat of the pig is deemed too radioactive for human consumption and must be destroyed. The situation has led many hunters to stop harvesting wild boars altogether, giving rise to a new problem: the proliferation of these feral pigs. Over the past several years, that pig population has increasingly pushed wild boars out of the realm of wild-game delicacy and into the same arena of invasive species that the U.S. is currently dealing with.

But what makes these wild German boars so radioactive in the first place? For several years, scientists thought they knew, but the real reason behind these “hot” hogs was something far more insidious and long-lasting.

What Is the Wild Boar Paradox?

Since about 1986, researchers believed that they understood why pigs maxed out the Geiger counter on radiation. They tended to register for high levels of a certain radioactive isotope known as cesium-137 — an isotope associated with nuclear reactors, among other things. And in 1986, one particular nuclear reactor emitted a whole bunch of cesium-137 into the atmosphere.

The Cause of Radioactive Isotopes in Wild Boars

That reactor? Chernobyl, the Ukrainian nuclear power plant that suffered an explosion and partial meltdown of its core, resulting in the worst nuclear disaster in history. Thanks to prevailing winds and weather patterns, cesium-137 fallout drifted several hundred miles across Europe.

Unsafe Levels of Radiation in European Animals

For many years thereafter, plenty of wild European animals besides pigs were deemed to be contaminated by that fallout, especially in the vicinity of Chernobyl. You wouldn’t have wanted to eat any of those creatures unless you were prepared to absorb unsafe levels of radiation and accept the health risks that might entail. Over time, though, as the cesium-137 from Chernobyl dispersed, the radiation levels of most animals within the massive fallout zone dropped to less-than-dangerous levels.

Lasting Effects of Radiation in Boars

Curiously, that didn’t happen with wild boars. The stomach and tissue samples of the boars that researchers tested still continued to exhibit unsafe levels of cesium isotopes. Why were pigs still so irradiated when other animals in the same habitats were not? It was a conundrum, one so profound and mystifying that it came to be known in some scientific circles as the “wild boar paradox.” 

Read More: Have Chernobyl Mutations Rewired Evolution?

Why Are Germany’s Wild Boars Still Radioactive?

Eventually, scientists thought they had it figured out. For several years now, researchers have been able to conclusively link wild boars’ excessive radioactivity to their diet. It turns out that feral pigs go hog-wild for a certain type of truffle — they rely on it as a major food source at certain times of the year — and that truffle tends to absorb high levels of radioactive cesium.

How Wild Boar Diet Contributes to Radioactivity

But even though wild boars like to root out those radioactive truffles, more than 30 years after the Chernobyl disaster, researchers still should have seen some declines in the wild pigs’ contamination levels. Why didn’t they?

Recently, that answer was determined: the truffles, and therefore the wild pigs, also had high ratios of cesium-135, another isotope, but much longer lasting than the cesium-137 that came from Chernobyl.

Read More: Military Action In Radioactive Chernobyl Could Be Dangerous For People And The Environment

Nuclear Weapon Testing and Cesium-135 Contamination

In an August 2023 study published in Environmental Science & Technology, the authors concluded that the cesium-135 contamination was the result of years of 20th-century nuclear weapons tests. These tests dated at least as far back as the 1960s, but were still accounting for anywhere from 10 to nearly 70 percent of the radioactive contamination that scientists were finding in the wild boar population.

Environmental Challenges of Radioactive Isotopes

Although various international bans and agreements have curbed the testing of such weapons of mass destruction, the isotopes never signed any treaty, of course. While contamination from Chernobyl will continue to abate — cesium-137 has a half-life of about 30 years — cesium-135 will live on in the environment for quite a bit longer: It has a half-life of about 2.3 million years.  

Ongoing Concerns for Hunting Bavarian Wild Boar Meat

So, between the lingering residuals of nuclear tests and the Chernobyl disaster, Bavaria’s boars will continue to remain under watch, a potential vector for nuclear contamination for as long as pigs continue to root for those truffles.

Hunters who don’t wish to expose themselves or their customers to radioactive danger will need to keep submitting their wild hogs for testing for the foreseeable future. Make no mistake: It will be a long while before cesium contamination ceases to be a problem for wild boars and a longer while yet before the people who love to eat them will be able to pig out — without fear of fallout.

Read More: Nuclear Warfare’s Past, Present and Future