137Cesium i myrsamhällen i Gävleborgs län 24 år efter Tjernobylolyckan

Abstract: 24 years have passed since the Chernobyl accident when radionuclides were spread over large areas of Europe, including the Scandinavian countries. Today, measurable activities of 137Cs are still observed in many Swedish ecosystems. Ants (belonging to the order Hymenoptera) are social insects which collect organic material from a large area around their nests. This study focuses on the 137Cs activity in ant nests and the cesium accumulation in these nests. The aims were (1) to estimate the 137Cs fall-out in 1986, (2) estimate the radiation exposure of ants and (3) find how 137Cs is distributed in an ant hill. Seven ant hills (occupied by the species Formica polyctena) were studied near the village of Hille, situated north of the city of Gävle in central Sweden. The hills were located in coniferous forest stands. Samples of ants and material from different vertical layers in the ant hills 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 radioactive fall-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 of radioactivity. The top layer (0-2 cm) was divided in two separate samples by using a sieve with a 2 mm mesh size. The fine material contained soil particles and spruce needles. The coarse material contained twigs and pine needles. The 137Cs activity was always higher in the fine material samples than in the coarse samples. The activity increased by depth. Ants, the coarse top layer and stump material had low activities compared to the other layers. The radiation exposure of the ants and ant hills was estimated by a model. An average exposure and a worst case scenario were estimated. The radiation exposure varied between 0,1 and 8 μGy/hour.