Determination of control levels of radionuclides ensuring acceptable environmental risk in the Barents Sea water and bottom sediments
To assess the radioecological situation, criteria were developed ensuring acceptable environmental risk - control levels of radionuclides in the components of the natural ecosystem. The method was applied to evaluate the control levels of technogenic radionuclides in the Barents Sea water and bottom sediments. If these levels are not exceeded, marine biota is considered protected from radioactive contamination. Local concentration factors of ¹³⁷Cs, ⁹⁰Sr, and ²³⁹Pu in the Barents Sea biota were estimated using the data of long-term observations. Moreover, the reference organisms were selected - a fish (cod), mollusc (mussel), aquatic plant (fucus), and marine mammal (harp seal). The values of ¹³⁷Cs, ²³⁹Pu, and ⁹⁰Sr concentration factors were, respectively, as follows (L·kg⁻¹): in fish, 93, 262, and 12; in molluscs, 51, 1,180, and 21; in aquatic plants, 69, 732, and 19; and in marine mammals, 63, 222, and 14. The values of the water-sediment distribution coefficients of ¹³⁷Cs, ²³⁹Pu, and ⁹⁰Sr were 426, 189,600, and 443 L·kg⁻¹, respectively. For most radionuclides and the reference organisms from the Barents Sea, the values of radionuclide concentration differ from the global average reference values. For the period of 1992-2020, there is no pronounced temporal trend for the concentration factors of all technogenic radionuclides in the Barents Sea fish; this indicates the establishment of equilibrium in the distribution of radioactivity between the components of the Arctic marine ecosystem. The control levels of radionuclides were as follows: in the Barents Sea water (Bq·L⁻¹), 115 for ¹³⁷Cs, 439 for ⁹⁰Sr, and 0.124 for <sup>239,240</sup>Pu; in the Barents Sea bottom sediments (kBq·kg⁻¹ fresh weight), 48.9 for ¹³⁷Cs, 194 for ⁹⁰Sr, and 23.6 for <sup>239,240</sup>Pu. The contamination index for both water and bottom sediments of the Barents Sea was calculated using the monitoring data and reference levels. In 2006-2020, its values were several orders of magnitude lower than 1 and did not tend to increase or decrease. In terms of marine biota protection, the main contributor to the contamination index for the Barents Sea water is <sup>239,240</sup>Pu (up to 75 %) while the main contributor to the contamination index for the Barents Sea bottom sediments is ¹³⁷Cs (up to 90 %). To date, the ratio of the contributions of technogenic radionuclides to the contamination index for the Barents Sea water and bottom sediments is stable.