Thesis: Initially emitted in the environment by atmospheric nuclear weapons tests, tritium (3H) is one of the main radionuclide released by nuclear facilities. It is present in all environmental media in several different forms, bound to organic matter (OBT) or in free forms (HT, HTO, CH3T). Furthermore, 3H follows the same dynamics of incorporation and degradation in living organisms as the hydrogen and is quickly balanced with the surrounding environment. Numerous studies have shown disequilibrium of OBT/HTO in different environmental compartments and matrices. This research work aims to explain the variability of 3H concentrations and the origin of disequilibrium of OBT/HTO based on the persistence hypothesis. In this study, a multi-scale approach was used, focusing on the role of delayed transfer of organic matter between natural compartments. The main results have established the ranges of HTO concentrations in several rivers that are not influenced by atmospheric releases from nuclear facilities, and also identified key environmental parameters linked to the observed variability. The results also made it possible to understand the origin of OBT using statistical analyses. The results tend to confirm that atmospheric nuclear tests led to areas of persistence of OBT, and can lead to significant disequilibrium between bound and free forms. Moreover, the study of a sediment core has shown a peak of OBT at depth, in all likelihood from the global fallout associated with atmospheric nuclear weapons tests. Also, a study site impacted by industrial releases of tritium for the last fifty years has confirmed the persistence of OBT in organic matter, especially in abiotic matrices.