Transfer of radionuclides and dose assessment to ants and anthills in a Swedish forest ecosystem

In forest ecosystems soil organisms are important for immobilization, translocation and recycling of radionuclides. Still, there is a lack of studies on the role of insects such as ants in the turnover of radionuclides and how radioactivity affects an ant community. In this study seven anthills were sampled in an area that was heavily contaminated after the fallout from the Chernobyl accident. Samples of ant and anthill materials were taken from different depths of the anthills as well as from the surrounding soil and the activity concentrations of ¹³⁷Cs were determined. In addition, a radiation dose assessment was performed for ants and anthills using the ERICA tool. The deposition of ¹³⁷Cs in 1986 in the study area was calculated back to be on average 110,500 Bq m^-2. The averaged data for all the seven locations investigated indicate that the level of ¹³⁷Cs activity concentrations in the anthill's material increased with depth of the anthill being highest at the depth 50-65 cm. The concentration in the upper layers (0-2 cm) and of the ants showed significant correlations with the deposition upon multivariate analysis. The concentration ratio (CR) defined as the ratio between the mass activity for ¹³⁷Cs density in ants (Bq kg^-1 d.w.) and mass activity density in soil (Bq kg^-1 d.w.) was determined to be in the range of 0.04-0.14. Also, the transfer factor (TF) defined as the ratio between the mass activity for ¹³⁷Cs density in ant (Bq kg^-1 d.w.) and to the unit area activity density (in Bq m^-2 d.w.) was determined for ¹³⁷Cs to be 0.0015 m² kg^-1 d.w. The assessed radiation doses were found to be a 4.9 μGy h^-1 which is below international reference levels for non-human biota.