137Cesium i myrsamhällen i Gävleborgs län 24 årefter Tjernobylolyckan

Abstract: 24 years have passed since the Chernobyl accident when radionuclides were spread over largeareas of Europe, including the Scandinavian countries. Today, measurable activities of 137Csare still observed in many Swedish ecosystems.Ants (belonging to the order Hymenoptera) are social insects which collect organic materialfrom a large area around their nests. This study focuses on the 137Cs activity in ant nests andthe cesium accumulation in these nests. The aims were (1) to estimate the 137Cs fall-out in1986, (2) estimate the radiation exposure of ants and (3) find how 137Cs is distributed in an anthill. Seven ant hills (occupied by the species Formica polyctena) were studied near the villageof Hille, situated north of the city of Gävle in central Sweden. The hills were located inconiferous forest stands. Samples of ants and material from different vertical layers in the anthills were collected. Soil near the ant hills and in a nearby arable field was collected as well.The 137Cs activity in the samples was measured. A model was used to estimate the radioactivefall-out in 1986. The 137Cs within the sampling area was estimated at 90 000 Bq/m2 or higher.These results agree with other studies in the same area.The different ant hill layers showed an increasing vertical trend with respect to the amount ofradioactivity. The top layer (0-2 cm) was divided in two separate samples by using a sievewith a 2 mm mesh size. The fine material contained soil particles and spruce needles. Thecoarse material contained twigs and pine needles. The 137Cs activity was always higher in thefine material samples than in the coarse samples. The activity increased by depth. Ants, thecoarse top layer and stump material had low activities compared to the other layers. Theradiation exposure of the ants and ant hills was estimated by a model. An average exposureand a worst case scenario were estimated. The radiation exposure varied between 0,1 and 8μGy/hour.