<div>Today, 33 years after the Chernobyl accident, long-term dynamics of
radio-cesium in the environment becomes the most relevant issue. Study
of bottom sediments in lakes and reservoirs provide insight in
understanding long-term dynamics of radionuclides strongly bound to
sediment particles such as 137Cs. With this in mind, in 2018 a number of
cores of bottom sediments were collected in the deep parts of Lake
Glubokoe, Lake Azbuchin and Cooling Pond in the close vicinity of the
Chernobyl NPP and in Schekino reservoir (Upa River) in Tula region of
Russia. All these water bodies were contaminated as a result of the
accident in 1986. The collected bottom sediment cores were sliced in
2-cm layers, dried and passed through 2-mm sieve, after which analyzed
for 137Cs using γ-spectrometry. The obtained 137Cs vertical
distributions in sediments accumulation zones of the water bodies
suggest that almost no vertical mixing of sediments has occurred, and
the 137Cs peaks are well-defined and not diffuse ones. Assuming that
sediment accumulation rates after the accident were more or less
uniform, layers of bottom sediments can be attributed to certain time of
sedimentation. With 137Cs activity concentration in a given layer of
bottom sediments corresponding to 137Cs concentration on suspended
matter at that point in time, we were able to obtain the dynamics of
particulate 137Cs activity concentrations from 1986 to 2018. Using the
experimental values of the distribution coefficient Kd, changes in the
dissolved 137Cs activity concentrations in the above water bodies have
been estimated for the period of 32 years after the accident. The
estimates of dissolved 137Cs concentrations seem to be in reasonable
agreement with monitoring data. By and large, the general trend of the
particulate and dissolved 137Cs and 241Am activity concentrations in all
water bodies are consistent with the semi-empirical “diffusional”
model. This research was supported by Science and Technology Research
Partnership for Sustainable Development (SATREPS), Japan Science and
Technology Agency (JST)/Japan International Cooperation Agency (JICA)
(JPMJSA 1603) and by bilateral project No. 18-55-50002 of Russian
Foundation for Basic Research (RFBR) and Japan Society for the Promotion
of Science (JSPS).</div>