Almost four decades after the nuclear power plant accident in Prypiat, Ukraine, the animals of Chernobyl continue to fascinate researchers. Among these survivors in one of the most contaminated regions of Europe, the wild boar stands out as an enigmatic species and one of the most radioactive species at Chernobyl.
Solving the mystery. Experts now have a new clue about these animals and know why their radioactivity is higher than that of other species. Surprisingly, the reason has less to do with the nuclear disaster itself and more to do with something that happened well before.
The study that solved this mystery analyzed a population of 48 wild boars in Bavaria, Germany. The findings were published in the journal Environmental Science & Technology.
More radioactive? Despite this new discovery, there’s still much to learn about the animals of Chernobyl. One of the most interesting enigmas is that of the wild boars. To understand why, we need to talk about one of the most contaminating radioactive isotopes, cesium-137 (Cs-137).
The half-life of this isotope is just over 30 years, which means that half of the atoms in the material will have disintegrated in that time. Technically, the concentration of cesium in the food chain should be reduced because the atoms tend to leach into the soil or be washed into rivers.
As a result, the level of radioactivity in animals such as deer or roe deer has notably decreased in the area. However, this decrease hasn’t occurred in wild boar populations. Quite the opposite: Their radiation levels have remained almost constant, which isn’t in line with the expected decrease implied by the half-life of Cs-137. This is known as the “wild boar paradox.”
Nuclear testing and radioactive truffles. This particularity of Chernobyl’s wild boars lies in the cesium-135 (Cs-135) isotope. The research team solved this mystery by focusing on the origin of the radiation rather than its levels. They discovered that this other cesium isotope was responsible for the phenomenon. Cs-135 has a much longer half-life compared to Cs-137, which explains why the reduction had been smaller.
The presence of Cs-135 is more difficult to detect compared to other isotopes. According to the research team, each type of nuclear accident has its own unique “fingerprint.” While experts estimate that 90% of the Cs-137 in Europe came from the Chernobyl accident, this isn’t the case for Cs-135. In this case, 68% of the Cs-135 can be traced back to the nuclear tests conducted during the Cold War.
Depth matters. The diet of wild boars has been a crucial factor in understanding the reason behind their radiation levels. These animals feed on a type of truffle (Elaphomyces) that grows underground, at depths of 8 to 16 inches.
To clarify, radioactive cesium has partly been leaking into the soil of the area year after year. At a rate of a few millimeters per year, the cesium (from both nuclear testing and accidents) has been gradually reaching these depths, contaminating the fungi that serve as a food source for the wild boars.
A look into the future. The study suggests that the high levels of radioactivity in wild boars are unlikely to decrease in the near future. This sets them apart from other similar animals like deer or roe deer.
The higher radiation in these animals has caused hunters to avoid capturing them, leading to a potential increase in wild boar populations. While the radiation levels may decrease over generations as the wild boars expand across central Europe, this process could take decades.
This article was written by Pablo Martínez-Juarez and originally published in Spanish on Xataka.
Image | Joachim Reddemann / Кирилл Пурин
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