Selected anthropogenic and natural radioisotopes in the Barents Sea and off the western coast of Svalbard

The Murmansk Marine Biological Institute (MMBI) performed high-latitude expeditions to the Barents Sea during 2007-2009 where a scientist from the Radiation and Nuclear Safety Authority (STUK) participated. The aim of the expeditions was to study and map the current radiological situation throughout the Barents Sea. In the expeditions, samples of seawater, sediment and biota were collected for radioactivity studies. The (90)Sr and (137)Cs isotopes were analysed from the seawater samples and no spatial distribution in the concentrations of (90)Sr and (137)Cs was found. The sediment samples were analysed for γ-emitting isotopes. In the statistical analysis performed only the (90)Sr was found to have no spatial distribution. In the (137)Cs concentrations two areas containing higher concentrations were observed: one in the western part of Svalbard and another in Franz Victoria Trough near the Franz Josef Land archipelago. The increase in the western coast of Svalbard suggests an Atlantic influence while in the Franz Victoria Trough source regions are possibly more complex. Since (137)Cs in marine sediments mainly originates from terrestrial sources, finding higher concentrations in the northern part of the Barents Sea may also suggest a contribution of (137)Cs carried by the ocean currents and by sea ice from the outside Barents Sea. In addition to γ spectrometric measurements, the sediment samples were radiochemically analysed for (210)Pb. It was found that the unsupported fraction of (210)Pb showed significant spatial variation. The fraction of unsupported (210)Pb was reduced to 40-70% near Bear Island, Edge Island and in the Franz Josef Land archipelago. In these regions the sea is typically covered with sea ice during winter. The relatively low fraction of unsupported (210)Pb is possibly caused by blocking of wet and dry deposition of (210)Pb onto the sea by winter sea ice. In biota samples, only small traces, at the level of 0.2 Bq/kg w.w. of (137)Cs, were found. When the (137)Cs concentrations found in cod and in haddock were compared with studies done in the early 1990's an effective half-life of (137)Cs in cod and in haddock was deduced. For cod the estimated effective half-life of (137)Cs was between 5.8 and 7.5 years and for haddock between 5.3 and 9.5 years. Similarly, the concentrations of naturally occurring (210)Po and (210)Pb were from 0.1 to 0.3 Bq/kg w.w. The (210)Po/(210)Pb ratio varied from 1.8 to 30 indicating a more efficient bioaccumulation of (210)Po than its precursor (210)Pb. The dose to humans eating Barents Sea fish was estimated. Even for people consuming large quantities of Barents Sea fish the annual dose was found to be below 20 μSv. The effective dose from anthropogenic (137)Cs was found to be less than 1% compared to the dose caused naturally occurring (210)Po and (210)Pb.