Mad about Science: The radioactive ‘wild boar paradox’

By Zach Hagadone
Reader Staff

By now, pretty much everyone should be at least familiar with the disaster that befell the Chernobyl Nuclear Power Plant on April 26, 1986, when its Reactor No. 4 exploded and released enough radioactive contamination that health experts theorize it may have been responsible for elevated global rates of cancer.

Many people may also already know about the “exclusion zone,” an area of about 1,000 square miles established around the power plant in which very few — if any — human inhabitants remain. 

Being located near the abandoned city of Pripyat in northern Ukraine, Chernobyl’s surroundings were always rich in wildlife and have remained so, despite the legacy of the 1986 explosion. Plants, animals and insects of many varieties survived the initial bombardment of radiation, which peaked at about 20,000 roentgens per hour (exposure to more than 200 roentgens will cause serious radiation sickness and upwards of twice that will likely result in death). 

Not only that, but species have been returning to the area for years, both on their own and with the help of rewilding efforts.

The presence of so much contaminated flora and fauna has for decades provided scientists with the unique opportunity to study the short- and long-term effects of high- and low-level chronic radiation exposure. Though mutations and birth defects are elevated among the lifeforms in the zone, exposed animals have experienced steady declines in the radioactive contamination in their bodies, as the various chemicals spewed by the meltdown have either dissipated or progressed toward their half-life. 

That hasn’t been the case with the boars, however, which have consistently registered high levels of the cesium-137 isotope in particular. Cesium-137 is a byproduct of nuclear fission and has a half-life of about 30 years, which means the isotopes expelled by Reactor No. 4 should be more than half decayed by now — having been in the environment for nearly 40 years.

Yet the boars remain as contaminated as if they had just received a relatively healthy dose.

The phenomenon stumped researchers for years — even more so as heavily irradiated boars were discovered roaming the wilds of southern Germany, bearing enough radioactive contamination to make them unsafe to eat. (Which is a big deal in pork-loving Deutschland.)

It wasn’t too much of a stretch to assume that the fallout from Chernobyl had affected German boars, considering that the release of material from the power plant — which included heavy amounts of radioactive iodine-131, cesium-137 and strontium — landed on more than 40% of Europe.

Still, the idea that the boars alone were retaining high levels of contamination 807 miles west of the site of the disaster and almost 40 years later remained a mystery.

That changed in 2023, when radioecologist Bin Feng proposed another theory: Maybe the boars weren’t contaminated by Chernobyl alone, but also absorbing fallout from the nuclear weapons testing that took place in the decades before the Chernobyl disaster?

As an August 2023 article from the American Association for the Advancement of Science pointed out, 500 of the 2,000 nuclear bombs tested during the Cold War were detonated in the atmosphere, scattering contamination far and wide that settled, then sank into soils.

Researchers in the study looked at the meat from 48 boars in Bavaria and found that a whopping 88% were too contaminated to pass German food safety regulations.

With the level of contamination established, the scientists narrowed in on the precise isotopes in play, and thereby uncovered the smoking gun. Both cesium-137 and cesium-135 were present in the boars’ meat, but those isotopes are created in different amounts depending on if they came from a nuclear reactor or a nuclear weapon. Further analysis of the samples showed anywhere from 10% to 99% of the cesium present came from nuclear bomb detonations.

But that seemed strange, too, considering that the height of atmospheric nuclear weapons testing was in the 1960s — 20 years older even than the Chernobyl contamination.

To answer why 21st-century German boars were full of almost-60-year-old radioactive fallout, researchers looked at the animals’ diet — specifically, truffles.

The theory goes something like this: Cesium from the bomb blasts settled on the forest floors around Europe, then sank further and further with rainfall, sealing it in underground layers. Fungi have extremely large and complex root structures, which are also especially receptive to absorbing the constituent elements in their environment.

The truffles of the Bavarian woods — just as the mushrooms in the timberlands surrounding Pripyat — tapped into those lower layers of contamination and have been transporting the cesium from more than half a century ago back to the surface, where it’s been gobbled up by the boars. 

While other animals that don’t rely on mushrooms as a foodstuff have spent the past several decades sloughing off Chernobyl contamination generation after generation, the boars have been basically sucking Cold War bomb waste out of the ground with a fungal straw. Which is just as disgusting as it sounds, and a good reminder that even if we think our radioactive sins are buried, they have a way of resurfacing.

Stay curious 7B (and maybe skip the wild Bavarian bacon).

Regular columnist Brenden Bobby will be back next week.