In April 1986, a catastrophic explosion at the Chernobyl nuclear power plant released significant radiation, contaminating wildlife in multiple countries. While radiation levels in most animals have decreased over time, one exception is the wild boar, which continues to exhibit elevated radiation levels.

A recent study has resolved the “wild boar paradox,” where cesium-137 levels remained high in wild boars in Germany and Austria while decreasing in other animals. Contrary to expectations, the main source of this radiation is not the Chernobyl accident but nuclear weapons testing from the 1960s. The study, conducted by researchers including Georg Steinhauser, a radiochemist at TU Wien, highlights the surprising and ongoing relevance of nuclear weapons testing, with wild boar populations still displaying radiation levels above regulatory food limits even 60 years after the explosions.

In the past, researchers had proposed various explanations for the high cesium-137 levels in wild boars, but none were conclusive. Some believed that contamination levels were decreasing but couldn’t find evidence due to limited sample sizes. Steinhauser had previously suggested that cesium might dissolve better in wild boar fat tissue and persist longer, but subsequent research didn’t support this idea.

In their latest study, Steinhauser and his team decided to reevaluate the amount and source of cesium in wild boars. They collaborated with hunters in southern Germany, who provided wild boar meat samples, and used a gamma-ray detector to measure cesium levels.

Radioactive cesium can originate from both nuclear weapons explosions and nuclear energy production, with varying isotopic compositions such as cesium-135 and cesium-137 depending on the source. Researchers used the ratio of these isotopes to identify the radiation source. A higher cesium-137 ratio indicates nuclear weapons testing, while a lower ratio is associated with nuclear reactors.

In their analysis of nearly 50 meat samples, the researchers discovered that 88 percent exceeded Germany’s regulatory limits for radioactive cesium in food. By calculating the cesium isotope ratios in the samples, they determined that nuclear weapons testing contributed to 10 to 68 percent of the contamination.

Even in the absence of the Chernobyl accident, some wild boars would still surpass food safety limits due to current nuclear weapons tests, according to Steinhauser. This finding is remarkable because these tests occurred over 60 years ago.

Steinhauser suggests that wild boars likely consume cesium-contaminated deer truffle mushrooms during the winter when other food sources like corn and acorns are scarce. Cesium in the soil is absorbed by these mushrooms, making them a source of contamination for the boars. This also explains why radioactivity levels in wild boars are higher during the winter months. Interestingly, despite their name, deer do not show a strong preference for deer truffles.

Cesium from both nuclear weapons testing and the Chernobyl accident has permeated the soil, but Steinhauser explains that the mushrooms have absorbed the cesium primarily from the nuclear weapons testing. Cesium moves very slowly through the soil, at a rate of as little as one millimeter per year. Deer truffles, which are situated between 20 and 40 centimeters deep in the soil, have already taken in the “older” cesium from six decades ago. In contrast, the “younger” cesium from the Chernobyl incident has likely not fully integrated or is only now beginning to integrate into the soil depths where these mushrooms grow.

When the cesium from the Chernobyl incident eventually reaches the mushrooms, it could potentially lead to an increase in radioactivity levels, contrary to what was initially expected. According to Steinhauser, there is a possibility that these levels may rise rather than decline.

Steinhauser reassures that there is likely no cause for concern for humans, including consumers of wild boar meat. The consumption of “insane” quantities of the animal would be required to accumulate significant amounts of radioactive material. Furthermore, in Germany, wild boar available through stores and official channels undergo testing and regulation, ensuring safety standards are met.

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Radiochemist Ralf Sudowe, who was not part of the study, expressed surprise at some of the research’s findings. He noted that it had generally been assumed that radiocesium primarily came from the most recent radioactive releases affecting a region, such as the Chernobyl accident in Europe’s case. However, this study challenges that assumption.

Sudowe emphasized that the study highlights the importance of considering legacy sources, such as fallout from nuclear weapons tests, when assessing potential environmental consequences and health risks. This revelation was news to him, and he is a professor at Colorado State University.

Nuclear chemist Rebecca Abergel, although not part of the study, wasn’t as surprised by the significant contribution of nuclear weapons testing to contamination. She noted that it has been well-established for decades that substantial isotope contamination worldwide is a consequence of weapons testing.

However, Abergel, who is an associate professor at the University of California, Berkeley, found the study interesting because it provided a characterization of and drew attention to regional variations in contamination. Some of these differences may be attributable to localized factors like wind patterns, animal migration, or subsurface water flow.

Both Rebecca Abergel and Ralf Sudowe praised the study for its radiochemical analysis method and the ability to pinpoint the source of radiocesium. They noted that this advancement is valuable for comprehending the historical impact of weapons activity and for identifying other sources of contamination involving radioactive materials, including potential smuggling.

Sudowe emphasized that the capability to identify the source of a radioactive release plays a crucial role in addressing and remediating the environmental consequences associated with such incidents.

In summary, the study underscores the significant impact of human activities on the environment, according to Steinhauser. He emphasizes that the study does not take a stance for or against nuclear energy but highlights the importance of its responsible use.

Steinhauser sees it as a cautionary tale, emphasizing the need for careful stewardship of our environment. He underscores that once a radioactive substance is released, it cannot be undone, and nature retains the memory of such events.

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