Baseline levels of natural radioactivity in the bottom sediments of the East Siberian and Laptev Seas and assessment of the associated risks

The paper summarises the results of gamma-spectrometric determination of the activity concentration of the major natural radionuclides (²²⁶Ra, ²³²Th, and ⁴⁰K) in the surface bottom sediments (84 samples) and a single sample of ferromanganese nodules collected in the East Siberian Sea and the Laptev Sea in 2008–2020. Radium equivalent activity, external and internal hazard, and gamma activity concentration indices were calculated in order to assess the natural pollution and risk level of radionuclides. Activity concentrations ranged 16.5–70.4 (mean 31.0) Bq kg⁻¹ of ²²⁶Ra, 21.4–77.9 (mean 40.2) Bq kg⁻¹ of ²³²Th, and 298–991 (mean 543) Bq kg⁻¹ of ⁴⁰K for the East Siberian Sea samples. The Laptev Sea samples exhibited ranges 15.5–54.0 (mean 32.9) Bq kg⁻¹ of ²²⁶Ra, 23.1–66.4 (mean 41.8) Bq kg⁻¹ of ²³²Th, and 328–546 (mean 441) Bq kg⁻¹ of ⁴⁰K. In the case of the ferromanganese nodule sample, the measured activity concentrations were 262 ± 42 Bq kg⁻¹ of ²²⁶Ra, 137 ± 35 Bq kg⁻¹ of ²³²Th, and 323 ± 45 Bq kg⁻¹ of ⁴⁰K. The activity concentrations of natural radionuclides in the sediments were found to be in close proximity to the global average. Activity concentrations of ²²⁶Ra and ²³²Th in ferromanganese nodules were 8 and 3 times higher, respectively. The subsequent radiological risk assessment indicated that the observed values for the sediments were below the specified threshold values. The values for the ferromanganese nodule sample exceeded these thresholds indicating a potential radiological hazard associated with mining of such deposits.