| Summary: | Given the importance of understanding long-term dynamics of radionuclides in the environment in general, and major gaps in the knowledge of <sup>137</sup>Cs particulate forms in Chernobyl exclusion zone water bodies, three heavily contaminated water bodies (Lakes Glubokoe, Azbuchin, and Chernobyl NPP Cooling Pond) were studied to reconstruct time changes in particulate concentrations of <sup>137</sup>Cs and its apparent distribution coefficient <i>K<sub>d</sub></i>, based on <sup>137</sup>Cs depth distributions in bottom sediments. Bottom sediment cores collected from deep-water sites of the above water bodies were sliced into 2 cm layers to obtain <sup>137</sup>Cs vertical profile. Assuming negligible sediment mixing and allowing for <sup>137</sup>Cs strong binding to sediment, each layer of the core was attributed to a specific year of profile formation. Using this method, temporal trends for particulate <sup>137</sup>Cs concentrations in the studied water bodies were derived for the first time and they were generally consistent with the semiempirical diffusional model. Based on the back-calculated particulate <sup>137</sup>Cs concentrations, and the available long-term monitoring data for dissolved <sup>137</sup>Cs, the dynamics of <sup>137</sup>Cs solid–liquid distribution were reconstructed. Importantly, just a single sediment core collected from a lake or pond many years after a nuclear accident seems to be sufficient to retrieve long-term dynamics of contamination.
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