Half-Century Trends of Radioactivity in Fish from Danish Areas of the North Sea, Kattegat, and Baltic Sea

Abstract

This work reports comprehensive time-series datasets over the past 50 years for natural (210Po) and anthropogenic (134Cs and 137Cs) radionuclides in three fish species (cod, herring and plaice) from Danish marine area covering the North Sea, Kattegat, and Baltic Sea. Impact from the global fallout of atmospheric nuclear weapons testing, radioactive discharges from the European nuclear reprocessing plants (Sellafield and La Hague) and release from Chernobyl accident are clearly detected in the fish samples. While 210Po concentrations in each fish species demonstrated comparable levels across the three regions without notable temporal trends, significantly higher median 210Po concentration was observed in the lower trophic level fish, namely herring and plaice, compared to cod. In contrast, 137Cs concentrations in all three species steadily decrease over time after the Chernobyl-attributed peaks in late 1980s in the entire study area, whereas 137Cs always demonstrated higher concentrations in cod than herring and plaice. Our calculated concentration factors (CFs) for 137Cs in this work indicate that the mean CFs for 137Cs over the past 50 years are significant different across the three species, following the order of cod < herring < plaice. Based on the time-series data, ecological half-lives (Teco) of 137Cs in fish of the coastal regions of Denmark were estimated to evaluate the long-term impact of anthropogenic radioactive contamination in different regions. Our results indicate no significant difference in Teco across different fish species, whereas the weighted mean Teco for the fish in Baltic Sea (29.3 ± 3.9) is significantly longer than those of North Sea (29.3 ± 3.9) and Kattegat (29.3 ± 3.9), reflecting the strong ‘memory effect’ of the Baltic Sea due to it slow water renewal. However, dose assessment demonstrated that the contribution of natural radionuclide 210Po to ingestion dose is 1-2 order of magnitude higher compared to that of 137Cs.

Keywords: 210Po, 134Cs, 137Cs, Temporal variation, fish, Dose assessment