Chernobyl caesium still lingers in Czech forests — scientists have turned it into a scientific tool

Radioactive caesium-137, released into the atmosphere after the 1986 Chernobyl nuclear disaster, can still be detected in Czech forest ecosystems nearly forty years later. That's according to the Research Institute for Landscape, whose experts have spent more than two decades monitoring the element's behaviour at over 250 coniferous forest sites across the country.

Modern analytical methods now allow scientists to detect caesium even at extremely low concentrations — a capability that not only helps track the radionuclide itself but also reveals how other trace elements and pollutants move through forest ecosystems. Researchers analysed samples of soil, humus, mosses, grasses and spruce needles, compiling a unique dataset on how substances travel through the forest.

Humus as a long-term trap

It turns out caesium behaves differently in forests than most other elements: it naturally accumulates in humus — the topsoil layer made up of decomposed organic matter — where it can remain for a very long time.

"Our biomonitoring results show that caesium is retained extraordinarily well within forest ecosystems. Natural processes concentrate it primarily in the humus, where it becomes part of a long-term cycle between soil and biomass. This gives us a better understanding not just of caesium's behaviour, but of how forest ecosystems function as a whole," explains Ivan Suchara, head of the biomonitoring department at the Research Institute for Landscape.

Chernobyl's legacy still detectable

Research into caesium-137 — a radionuclide produced by the fission of uranium and plutonium during nuclear weapons tests or the operation of nuclear power plants — has given scientists key insights into how substances move through nature. This isotope, previously unknown in the natural environment, entered Europe's ecosystems mainly as a result of the 1986 Chernobyl disaster.

Although forty years have passed since the catastrophe, the movement of radioactive caesium in some forest ecosystems can still be measured: the isotope has a half-life of 30.2 years, meaning its mass is halved only every thirty years. Scientists have found that caesium penetrates the soil very slowly and circulates for a long time between soil, roots and vegetation.

"The forest environment functions as an extremely effective retention system. Caesium isn't quickly washed away here — it remains part of natural biological cycles. This is valuable information both for assessing environmental risks and for long-term monitoring of environmental quality," notes Ivan Suchara.

Fungi — nature's caesium accumulators

Scientists paid particular attention to fungi: certain species accumulate caesium far more readily than other organisms, and this applies to both stable and radioactive forms of the element.

This is precisely why fungi have become one of the most important indicators of radionuclide contamination. Their ability to concentrate caesium explains why, after the Chernobyl disaster, elevated radioactivity levels were recorded in some parts of Europe specifically in mushrooms, and later in game meat. That said, the concentration of radioactive caesium in the fruiting bodies of forest mushrooms is so low that eating them poses no radiation risk under normal consumption.

According to researchers, studying caesium today serves not only to assess the consequences of nuclear accidents but has also become a valuable tool for understanding how soils, forests and ecosystems function overall. Data gathered in Czech forests helps specialists predict the movement across the landscape not just of radionuclides, but of other trace elements and pollutants as well.

"Radioactive caesium is an example of a radionuclide that lets us observe landscape processes over a timescale of decades. Thanks to this, we gain valuable insight into how soils and forests work, and how well they can respond to different kinds of stress," Ivan Suchara concludes.

Around Prague, based on reporting by ekolist.cz