(Fucus serratus and Fucus vesiculosus)
SSM perspective
Background
The marine environment receives discharges from nuclear facilities around the world as well as in Sweden. The brown seaweeds, Fucus serratus and Fucus vesiculosus, are important organisms in the marine ecosystem both due to their ecological importance but also due to it is well known ability to accumulate contaminants and thereby usefulness in environmental monitoring as a bio indicator. Bio indicators provide information on levels and variations of elements, like for example radionuclides, in the marine environment. By studying the elemental and radionuclide composition in brown algae over a time period it is possible to gain an increased understanding on processes affecting transfer and accumulation in the marine environment. In this study SSM supported additional analyses of radionuclides and stable metals in brown algae collected every second month at the same site on the Swedish west coast since 1967, which has resulted in a unique dataset covering over fifty years. The data set is useful in order to understand the fate of radionuclide discharges in the marine environment, in risk assessments and in case of emergency situations to provide background levels of relevant radionuclides. The project also contributes to the development of analysis techniques in environmental samples.
Results
This project has resulted in the completion of a unique half-century[1]long time series of concentrations of radionuclides and metals in brown sea weed on the Swedish west coast. Sea weed samples for the whole time period is also saved in a sample bank. For some radionuclides the whole time period is covered, while for others and for the stable elements parts of the time series are covered. Peaks and variations in the time series are described, compared with discharges and explained, which gives valuable information on how currents transfer radionuclides in the marine environment and on the time-scale for such processes. Analysis capacity for Pu and Am isotopes has been developed. Long-term changes as well as seasonal variations in concentrations is described and discussed. This has provided better information about long-term processes and seasonal variations for different radionuclides in both Fucus serratus and Fucus vesiculosus. The study also shows that the brown algae could be important for the monitoring of emissions of naturally occurring radioactive materials (NORM) from the offshore oil and gas industry by systematically studying long-term and seasonal variations of the content of 228Ra and in the future also 226Ra and 210Pb.
The method development part of the project includes a modernisation of the methods used for the extraction and separation of actinides and the preparation of alpha spectroscopy sources. In addition, a method for the analysis of Pu isotopes in seaweed has been fully developed.
The project has also demonstrated the value of access to long time series of regularly collected samples of algae for other analyses than of radionuclides. Measurements on Fucus samples has also made it possible to describe time trends for a number of heavy metals like lead and cadmium. It has demonstrated a decrease of mercury levels, probably an effect of the gradual phasing out of mercury in Sweden and other countries and an increase of the concentrations of gadolinium, which most likely is a consequence of the increased use of gadolinium[1]based contrast agents for MR imaging in our hospitals. The metal analyses contributes to assessment of transport routes for radionuclides generated in new radiation sources, such as gadolinium isotopes from the European Spallation Source (ESS).
The project has given new knowledge about the function and capacity of Fucus as a bioindicator especially regarding the degree of seasonal variations for various radionuclides and stable elements.
Relevance
The project’s relevance for SSM is high as it is connected to several areas. Among other things, SSM participates in the OSPAR convention as a representative for Sweden, where, among other things, 238Pu is included among the key nuclides that the member states report. Sweden has chosen not to report 238Pu. For the Swedish part, the current project provide knowledge about how the levels of 238Pu have developed in the marine environment over the past 50 years and thereby increase the ability to make a correct decision regarding monitoring and reporting according to the OSPAR convention for radioactive substances. Furthermore, the project has increased knowledge of how radioactive substances are spread and accumulated in the marine environment and thus become a tool for improving transport and dose models and thereby risk assessments for humans and the environment. The results will contribute to knowledge that the authority needs in order to make well-founded decisions and to maintain and develop national and international competence.
Need for further research
The sample bank can be used for further studies of radionuclides, stable elements, long-term transfer and accumulation in the marine environment. By completing the time series for important radionuclides and study potential correlations and connections in present dataset further understanding of the influence from nuclear facilities and from the offshore oil and gas industry (NORM) on the marine environment could be gained.
Maintaining the sample bank as a historical archive and continuing the analyses and collection of samples is valuable for the possibilities of further studies in general of marine transfer and accumulation processes on a long-term time scale.