Features of ^(90)Sr behavior in Crimean lakes with different salinity of their water environment

The comparative study of technogenic ^(90)Sr behavior features in Crimea lakes’ ecosystems with different levels of salinity was carried out in 2016-2021.Two sources of ^(90)Sr input were identified for all the studied lakes:the primary source concerned with atmospheric fallout immediately after the Chernobyl NPP accident and the secondary long-term input of this radionuclide by waterway.The half-life of the ^(90)Sr concentration in the water of the hypers aline Lake Sasyk-Sivash was estimated to vary from 0.8 to 1.1 years after the closure of the North Crimean Canal(NCC).Biogeochemical processes in the lake under the absence of the secondary source of the radionuclide input were shown to decrease in the ^(90)Sr residence time in the water column by 131 times.For brackish water bodies,a significant factor influencing the radionuclide concentration in ecosystems of lakes was the pH of their water,while for hypers aline lakes the level of water salinity was the main factor determining ^(90)Sr behavior.The concentration of ^(90)Sr in bottom sediments of studied lakes depended mainly on this radionuclide concentration in a water environment.Calculated ^(90)Sr distribution factors(Kd) for studied lakes’ bottom sediments varied in a range of n·10^(0)÷n·10^(2) for hypersaline lakes and of n·10^(1)÷n·10^(2) for lakes with brackish waters.Due to the closure of the NCC,the ^(90)Sr redistribution took place in lake ecosystems only under the geochemical processes within the water bodies themselves.The results obtained in this work are of particular importance as a starting point or a basis for further radioecological studies of the Crimean inland waters after the reopening of the NCC and the Dnieper waters re-entering the territory of Crimea in 2022after the 8 years of their absence.

Radionuclides and mercury in the salt lakes of the Crimea

^99Sr 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 long- term 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 ^99Sr in the water of Lake Kiyatskoe （350.5 and 98.0 Bq/m^3） and Lake Kirleutskoe （121.3 Bq/m^3） 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.

Radiochemoecological Monitoring of the Salt Lakes of the Crimea

1 Introduction The salt lakes of the Crimea contain the practically inexhaustible sources of salts of sodium,magnesium,bromine and other chemical elements(Ponizovskii,1965),being the potential powerful raw materials base for the

Radioactive source terms for the Fukushima nuclear accident

A large amount of radioactivity was released into the environment after the Fukushima nuclear accident （FNA） in Japan in 2011. This radioactivity had a significant impact on the global environment, and there was much public concern about its effects. The subsequent assessment of the FNA and the environmental remediation required are proving to be long and complicated tasks. The assessments are based on the radioactive source terms for the FNA, which determine the level of damage caused by the nuclear accident. We investigated the radioactive source terms from three aspects： the amount and composition of the radionuclides; the activity and atomic ratio of the radionuclides; and comparison with other historical events. The total amount of radioactivity, excluding the radioactive noble gases （85Kr and 133Xe）, released by the FNA was about 10% of that released by the Chernobyl nuclear accident in 1986 and 〈1%o of the global fallout from the atmosphere nuclear explosion. However, the FNA was the most serious nuclear accident in terms of radioactive pollution of the marine environment. The recovery actions carried out after the FNA have been evaluated and the environmental impacts of the FNA are discussed.