Radioactive caesium and strontium can remain in the environment for decades after a release. Jonas Lystrup Andresen’s PhD research shows that insects and other arthropods play a key role in how these substances circulate through ecosystems.
Forty years after the Chernobyl accident, significant levels of radioactivity are still present in the Ukrainian environment. Radioactive substances that remain biologically available can be taken up by plants, fungi and animals, allowing them to continue circulating through ecosystems for decades after a radioactive release.
Insects and other arthropods are an extremely important group of animals. They break down dead organic matter, recycle nutrients and serve as food for a wide range of other animals. Yet researchers still know relatively little about the role these small animals play in the movement of radioactive substances through ecosystems.
Fact box: Arthropods
In his PhD research, Jonas Lystrup Andresen investigated how radioactive caesium and strontium are absorbed, excreted and transferred between organisms.
“We know that radioactive substances can remain in the environment for many years after a release. But to understand the long-term consequences, we also need to understand how these substances move through food chains,” says Andresen.
Where do the radioactive substances go?
In his PhD, Andresen studied the levels of radioactive caesium and strontium in different groups of arthropods, such as millipedes and butterflies. He combined fieldwork in the Chernobyl area with controlled laboratory experiments.
He investigated how radioactive substances were absorbed, stored and excreted throughout the development of several insect species, from the larval stage to adulthood. This made it possible to study both how radioactive isotopes move through food chains in nature and which biological processes influence uptake and excretion in different species.
Millipedes stood out
Andresen’s results revealed substantial differences between the animal groups. Millipedes stood out clearly, with much higher concentrations of both radioactive caesium and strontium than any of the other groups examined.
“Millipedes live in close association with soil and decaying plant material. These are environments where radioactive substances can remain for a long time after a release,” Andresen explains.
The findings suggest that food chains linked to the decomposition of dead organic matter may be particularly important for the circulation of radioactive substances in nature.
Radioactivity increased during the summer
The amount of radioactive strontium changed throughout the animals’ growing season. Concentrations increased in both herbivorous and predatory arthropods over the course of the summer. The results show that both season and diet can influence how much radioactivity the animals contain.
“It is not only where the animals live that matters. What they eat and the time of year we study them can also be highly important,” says Andresen.
Photo: Shutterstock
What happens when a larva becomes an adult?
Andresen also investigated what happens to radioactive substances when insects undergo complete metamorphosis from larva to adult. In such insects, large parts of the larval body are broken down before being rebuilt. During this process, substances acquired through food may either be retained in the body or excreted.
He studied this process in blowflies, parasitoid wasps, cabbage white butterflies and black soldier flies.
Laboratory experiments showed that concentrations of radioactive caesium were greatly reduced during development from larva to adult insect.
Strontium behaves differently
The picture was more complex for radioactive strontium. Strontium is chemically similar to calcium, which some arthropods require in larger amounts to build and harden their exoskeleton. In some species, calcium is also used in egg production.
The experiments showed that the uptake and excretion of strontium were closely linked to the insects’ calcium requirements. Black soldier flies tended to accumulate strontium, whereas cabbage white butterflies excreted a larger proportion during development.
“The results show that the physiology of different species can have a major influence on how radioactive substances are absorbed and stored,” says Andresen.
This also means that animals feeding on insect larvae may be exposed to different levels of radioactivity than animals feeding on adult insects.
Small animals, major importance
Andresen’s research shows that arthropods play an important role in the transport of radioactive substances through nature. At the same time, this role varies considerably among species, food sources and life stages.
The results particularly highlight the importance of food chains associated with fungi, soil and dead organic matter.
“If we are to understand how radioactive contamination affects nature over time, we must also understand what happens in the small food chains. Insects and other arthropods are an important part of that picture,” he concludes.
Jonas Lystrup Andresen will defend his PhD "The Influence of Arthropods on Radionuclide Cycling" Thursday 19 November, 2026. Trial lecture and public defense are open to all.