[en] The aim of this work was to calculate the values of the ²³⁴U/²³⁸U activity ratio in natural environment (water, sediments, Baltic organisms and marine birds from various regions of the southern Baltic Sea; river waters (the Vistula and the Oder River); plants and soils collected near phosphogypsum waste heap in Wislinka (Northern Poland) and deer-like animals from Northern Poland. On the basis of the studies it was found that the most important processes of uranium geochemical migration in the southern Baltic Sea ecosystem are the sedimentation of suspended material and the vertical diffusion from the sediments into the bottom water. Considerable values of the ²³⁴U/²³⁸U are characterized for the Vistula and Oder Rivers and its tributaries. The values of the ²³⁴U/²³⁸U activity ratio in different tissues and organs of the Baltic organisms, sea birds and wild deer are varied. Such a large variation value of obtained activity ratios indicates different behavior of uranium isotopes in the tissues and organisms of sea birds and wild animals. This value shows that uranium isotopes can be disposed at a slower or faster rate. The values of the ²³⁴U/²³⁸U activity ratio in the analyzed plants, soils and mosses collected in the vicinity of phosphogypsum dumps in Wislinka are close to one and indicate the phosphogypsum origin of the analyzed nuclides. Uranium isotopes ²³⁴U and ²³⁸U are not present in radioactive equilibrium in the aquatic environment, which indicates that their activities are not equal. The inverse relationship is observed in the terrestrial environment, where the value of the of the ²³⁴U/²³⁸U activity ratio really oscillates around unity. (author)