Long-time variations of radionuclides and metals in the marine environment of the Swedish west-coast studied using brown algae: (Fucus serratus and Fucus vesiculosus)

The support from SSM has made it possible to continue collecting brown algae
from the place on the Swedish west coast where regular collections began as
early as 1967. The support has also enabled more extensive analyses of
previously collected material than was possible before. This applies to both
supplementary analyses of previously reported radionuclides and analysis of
new ones. The project has also enabled a start of more comprehensive analyses
of the overall results. This has provided better information about long-term
processes and seasonal variations for different radionuclides in both toothed
wrack (Fucus serratus) and bladderwrack (Fucus vesiculosus). What is new is
that the sample material has now also been used to analyse metals, both those
with known toxic effects such as lead, cadmium and mercury, as well as those
that are of interest in assessing transport routes for radionuclides generated in
new radiation sources, such as gadolinium isotopes from the European
Spallation Source (ESS).
Regarding the long-term development of various radionuclides in the marine
environment on the Swedish west coast, the studies show rapidly increasing
levels of iodine-129, decreasing levels of cesium-137, technetium-99 and
plutonium-239+240. The carbon-14 analyses suggest a continued inflow of this
radionuclide from the North Sea. 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
radium-228 and in the future also radium- 226 and lead-210. Interesting and
hitherto unexplained variations in the beryllium-7 content in Fucus have been
made. The tritium content in Fucus and in seawater has been analysed in a
limited number of samples from 2020. No levels beyond the expected normal
ambient level for tritium have been found.
During the 10-year period 2011-2020, there was a doubling of the levels of lead
and nickel and a 50% increase in the levels of cadmium and cobalt in Fucus. For
mercury a 10-fold decrease is registered between 2011 and 2016 and then a
doubling of the concentration between 2016 and 2020. The decreasing trend for
mercury probably indicates an effect of the gradual phasing out of mercury in
Sweden and other countries. However, some businesses and companies have an
exemption for continued use. For gadolinium there is an increase with a factor of
around 5 from 2011 to 2020, most likely explained by the increased use of
gadolinium-containing contrast agents in magnetic resonance imaging in
healthcare.