On the distribution and inventories of radionuclides in dated sediments around the Swedish coast

Publication date: Available online 4 October 2017
Source:Journal of Environmental Radioactivity
Author(s): Grzegorz Olszewski, Pål Andersson, Patric Lindahl, Mats Eriksson
The activity concentrations and distribution of ¹³⁷Cs, ²³⁸Pu, ^239+240Pu, ²⁴¹Am, and ²¹⁰Pb was determined by the analysis of six sediment cores from the Baltic Sea and Kattegat. The chronology of the sediment cores has been used to evaluate the origin and time trend of the radionuclide sources in these sediments. The sediment cores were dated with a ²¹⁰Pb model and the results were validated with fallout peaks, assumed to originate from the global nuclear weapons testing and the Chernobyl accident. Source identification, using the isotopic and radionuclide activity ratios, showed that the Chernobyl accident is the main source of ¹³⁷Cs in the Baltic Sea; for ^239+240Pu and ²⁴¹Am the dominant source was shown to be fallout from nuclear weapons tests. For ²³⁸Pu and ²⁴¹Am the Chernobyl accident had a significant impact on the direct fallout into the Baltic Proper, with up to a 65% contribution in the sediment slices dated to 1986. In these sediment slices the maximum activity ratios of ²³⁸Pu/^239+240Pu and ²⁴¹Am/^239+240Pu were 0.314 ± 0.008 and 1.29 ± 0.06, respectively. The ratios clearly deviate from the corresponding ratios for global nuclear weapons fallout (around 0.028 and 0.54, respectively). Calculated inventories were 63–175 Bq·m⁻² for ^239+240Pu, 2.8–7.8 for ²³⁸Pu Bq·m⁻² and 0.92–44.4 kBq·m⁻² for ¹³⁷Cs. Different fallout patterns for ¹³⁷Cs and plutonium isotopes from the Chernobyl accident were confirmed through depth profiles analyses. The maximum inventory of ¹³⁷Cs was observed in the Bothnian Sea, while Chernobyl-derived plutonium was found to be mostly present in Northern Baltic Proper. The radionuclides distribution in the depth profiles shows how contaminated water affects the sediment as it passes sampling stations according to the current circulation pattern in the Baltic Sea. Additionally, the effect of increased activity concentrations from of river discharges in the most contaminated area in the Bothnian Sea was observed.



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