137Cs concentration in surface waters of Far Eastern seas: Results of expeditionary research in 2018

Based on the results of expeditionary research carried out during the 82nd cruise of the RV “Akademik M. A. Lavrentyev” (01.06.2018–20.07.2018), the assessment of current levels of concentration activity of technogenic radionuclide 137Cs in surface waters of Far Eastern seas is given. The studies were carried out in the northwestern part of the Sea of Japan, the southern part of the Sea of Okhotsk, the coastal waters of the Pacific Ocean near the Kamchatka Peninsula, and the western part of the Bering Sea. Activity of 137Cs in seawater samples was determined by sorption method using two series-connected adsorbers with subsequent measurement of 137Cs content via its gamma-emitting daughter radionuclide 137mBa. Sorption efficiency was assessed by the difference in activity on the first and second adsorbers. A comparative analysis of contamination levels of water areas studied was made. It was revealed that 137Cs volumetric activity in surface water of the Sea of Japan varied from (2.9 ± 0.1) to (5.1 ± 0.3) Bq·m−3, in the Sea of Okhotsk – from (1.8 ± 0.1) to (2.3 ± 0.1) Bq·m−3, and in the Bering Sea – from (1.7 ± 0.1) to (3.1 ± 0.1) Bq·m−3. The maximum 137Cs concentrations were registered in the Sea of Japan, which might be due to its isolation from other water areas and presence of secondary sources of radionuclide intake. In general, contamination of adjacent water areas is insignificant, and fluctuations in concentrations occur within technogenic isotopes global background in the marginal seas of the Pacific Ocean.