This research examines the dynamics of radioactive discharges in brackish water ecosystems, emphasising their distribution and accumulation in the Baltic Sea in the vicinity of the Swedish nuclear research facility, Studsvik. Since 1959, Studsvik has produced liquid radioactive waste, which includes 60Co, 90Sr, 137Cs, 152Eu and different plutonium isotopes. The contaminated liquid waste undergoes purification at Studsvik's treatment facility. However, it is difficult to eliminate all radioactive substances, thus, the final liquid waste will carry significant amounts of radionuclides. Strictly controlled, aquatic dis-charges of radionuclides have been conducted, with documentation and over-sight from the Swedish Radiation Safety Authority.
When creating risk assessments and dispersion models, knowledge about the environmental behaviour of different pollutants is essential.
The aim of this thesis is to determine the faith of the discharges and to evaluate the reliability of the reported discharge data. For Paper I, sediment cores from the vicinity of Studsvik were collected and dated. Analysis of sediment cores indicated that notable quantities of 60Co, 137Cs, and 152Eu have been maintained in the closest bay, although a significant amount has also dispersed into the Baltic Sea. In Paper II, the total discharges of plutonium from Studsvik were reconstructed based on the plutonium in one dated core. The isotope signatures of 238Pu, 239Pu, 240Pu, 241Pu, 242Pu, and 244Pu show the origin of the plutonium in the examined area and reveal traces of the Swedish nuclear program in the 1960s and 1970s.
In Paper III, deposition maps were constructed to visualise the radionuclides' behaviour and mobility. The results suggest that cesium has the greatest mobility of the radionuclides studied. The studies also indicate that europium is less mobile compared to cobalt. Furthermore, the Chornobyl accident, 1986, continues to be the largest 137Cs source in the examined region.
The upward transfer of local radioactive discharges through the food chain is of particular interest. In Paper IV, measurements were conducted on the skeletons of three white-tailed eagles, (Haliaeetus albicilla). The plutonium signature suggests that Global Fallout, GF, rather than local discharges, is the main source. The activity levels of 60Co, 137Cs, and 152Eu were below Minimal Detection Activity, MDA, while the activity level of 90Sr, was highest in the bones of an eagle found dead in northern Sweden.
The results of this study highlight the importance of incorporating site-specific variables into risk assessments and dispersion models to improve emergency preparedness and environmental monitoring initiatives.