Dietary items as possible sources of ¹³⁷Cs in large carnivores in the Gorski Kotar forest ecosystem, Western Croatia

The mountain forest ecosystem of Gorski Kotar is distant from any significant sources of environmental pollution, though recent findings have revealed that this region is among the most intense ¹³⁷Cs contaminated area in Croatia. Therefore, the aim of this study was to investigate ¹³⁷Cs and ⁴⁰K load in three large predator species in the mountain forest ecosystem. Radionuclides mass activities were determined by the gamma-spectrometric method in the muscle tissue of brown bear (47), wolf (7), lynx (1) and golden jackal (2). The highest ¹³⁷Cs mass activity was found in lynx (153 Bq kg⁻¹), followed by brown bear (132 Bq kg⁻¹), wolf (22.2 Bq kg⁻¹), and golden jackal (2.48 Bq kg⁻¹). Analysis of 63 samples of dietary items suggests that they are not all potentially dominant sources of ¹³⁷Cs for wildlife. The most important source of radionuclides for the higher parts of the food-chain from the study area were found to be the mushroom species wood hedgehog (Hydnum repandum), with a transfer factor TF of 5.166, and blueberry (Vaccinium myrtillus) as a plant species (TF = 2.096). Food items of animal origin indicated higher mass activity of radionuclides and therefore are possible moderate bioindicators of environmental pollution. The results also revealed that possible unknown wild animal food sources are a caesium source in the study region, and further study is required to illuminate this issue. - Highlights: • Radionuclide mass activities were determined by the gamma-spectrometric method. • The highest ¹³⁷Cs mass activity in brown bear was 132, wolf 22.2 and lynx 153 Bq kg⁻¹. • The best bioindicators are a wood hedgehog (TF = 5.166) and blueberry (TF = 2.096).