Radionuclides and mercury in the salt lakes of the Crimea

⁹⁰Sr concentrations, resulting from the Chernobyl NPP accident, were determined in the salt lakes of the Crimea (Lakes Kiyatskoe, Kirleutskoe, Kizil-Yar, Bakalskoe and Donuzlav), together with the redistribution between the components of the ecosystems. The content of mercury in the waters of the studied reservoirs was also established. Vertical distributions of natural radionuclide activities (²³⁸U, ²³²Th, ²²⁶Ra, ²¹⁰Pb, ⁴⁰K) and anthropogenic ¹³⁷Cs concentrations (as radiotracers) were determined in the bottom sediments of the Koyashskoe salt lake (located in the south-eastern Crimea) to evaluate the longterm dynamics and biogeochemical processes. Radiochemical and chemical analysis was undertaken and radiotracer and statistical methods were applied to the analytical data. The highest concentrations of ⁹⁰Sr in the water of Lake Kiyatskoe (350.5 and 98.0 Bq/m³) and Lake Kirleutskoe (121.3 Bq/m³) were due to the discharge of the Dnieper water from the North-Crimean Canal. The high content of mercury in Lake Kiyatskoe (363.2 ng/L) and in seawater near Lake Kizil-Yar (364 ng/L) exceeded the maximum permissible concentration (3.5 times the maximum). Natural radionuclides provide the main contribution to the total radioactivity (artificial and natural combined) in the bottom sediments of Lake Koyashskoe. The significant concentration of ²¹⁰Pb in the upper layer of bottom sediments of the lake indicates an active inflow of its parent radionuclide—gaseous ²²²Rn from the lower layers of the bottom sediment. The average sedimentation rates in Lake Koyashskoe, determined using ²¹⁰Pb and ¹³⁷Cs data, were 0.117 and 0.109 cm per year, respectively.