Radionuclides in algae from Swedish coastal waters for over half a century.

Samples of Fucus serratus and Fucus vesiculosus have been regularly collected at Särdal (56.76 N, 12.63E) on the Swedish west coast since 1967, for most of the time, every two months. In 2020, sampling of Fucus spp. was extended to 44 other locations along the Swedish west, south, and east coast for comparison with Särdal data. At seven of these locations, water samples and extra samples of Fucus spp. were also taken for 3H analysis. Measurements have been performed by gamma spectrometry, or by radiochemical separation followed by low background beta measurements, alpha spectrometry or accelerator mass spectrometry. Time variations of the measured concentrations of various radionuclides (3H, 14C, 60Co, 99Tc, 129I, 131I, 134Cs, 137Cs, 236U, 238U, 239Pu, and 240Pu) are reported. The concentrations have been correlated with emissions from the nuclear fuel reprocessing facilities at Sellafield (UK) and La Hague (France). Contributions from the nuclear power plants in Ringhals and Barsebäck have also been identified, as has fallout from Chernobyl still stored mainly in the sediments and water of the Baltic Sea. In recent decades, studies have shown increasing levels of 129I and 236U and decreases in 137Cs, 99Tc, and 239 + 240Pu concentrations over time. The 14C analyses show an impact of anthropogenic 14C from activities other than atmospheric nuclear weapons tests in the 1950s and 1960s. The considerable variation in the concentration of different radionuclides over time and along the coasts warrants further studies to determine the possible origin of these radionuclides and to map background data in the event of future releases.