Ecosystem modelling in exposure assessments of radioactive waste in coastal waters

Full text: Environmental transport and fate of radioactive isotopes in a brackish water bay of the Baltic Sea, was investigated in this study by using an ecosystem modelling approach. The purpose was to develop a method to assess the exposures to humans and to other organisms in the environment in case of discharges from an underground repository for radioactive operational waste. The radionuclides considered are long-lived, have high environmental mobility and bioavailability and pose a potential threat to living organisms for an extensive period of time. In the model, the radionuclide transport is tightly associated with a site-specific carbon flow model based on general ecological principles, that identifies and quantifies the main flows and storages of energy in the ecosystem, both in the physical environment and in the food web. In the model, the radionuclides are introduced into the food web via photosynthesising organisms. C-14 is assumed to assimilate in proportion to its presence compared to other carbon isotopes in the water while transfer factors are used in the initial uptake of other radionuclides. The trophic transfer in the food web are presumed to follow the flow of energy between the ecosystem compartments and to be proportional to the rate of predominant ecological processes, such as respiration, consumption and excretion. Modelling results demonstrates that this approach provides a method that allows evaluation of several scenarios. For instance, it is possible to compare the influence of different abiotic and biotic processes, such as accumulation pattern, excretion rates and water exchange, on radionuclide accumulation and transfer between the compartments of the ecosystem. This technique has potential to be a powerful tool in safety assessments of radioactive waste. (author)