Epsilon Archive for Student Projects

Abstract

The fallout from the Chernobyl nuclear accident resulted in large deposits of caesium, iodine
and strontium as well as noble gases in various parts of Sweden. 137Cs has a radioactive halflife
of about 30 years and is therefore one of few radio-fission products remaining in
measurable quantities in the Swedish soil. Radiocaesium behaves similarly to potassium in
soil-plant systems and is easily absorbed by plants. It is important to understand how 137Cs
behaves in different ecosystems in order to minimize the risk toward humans.

The aim of this study was to determine how potassium fertilization influences radiocaesium
content in different forest plants and fungi. Potassium fertilizer was spread once in 1992 with
approximately 200 kg KCl per ha. The method of determining the 137Cs activity concentration
involved collecting forest plants and fungi samples from the sites used in previous studies.
These samples were then placed in a High-Purity Germanium Coaxial Photon Detector to
accurately determine the 137Cs activity concentration levels. The results from this study were
compared with results from earlier studies made on the same sites between the years of 1992
and 2005. This comparison was carried out in order to observe and estimate any long-term
trends.

The results show that there is a large variation in the 137Cs activity concentration levels for the
eight different fungi species found and analysed. Cortinarius semisanguineus, Cortinarius
cinnamomeus and Rozites caperata were found to be the fungi species with the highest 137Cs
activity concentration levels. Taking the previous years into account, the majority of the fungi
species show a decrease in 137Cs activity concentration for the potassium fertilized area,
which would mean that it is possible to use potassium fertilization in order to reduce the 137Cs
activity concentration uptake in fungi.

With regard to plant species, it was determined that heather is the plant that shows the highest
137Cs activity concentration levels. When comparing the levels of 137Cs in the plant species
with those found in previous studies it clearly shows that the use of potassium fertilization as
a countermeasure reduces the 137Cs activity concentration uptake in all plant species
measured.