Thesis: In the event of accidental releases from nuclear installations, radionuclides including iodine radioactive isotopes and mainly iodine-131 are susceptible to be emitted in environment. The circumstances of releases have generally been such that iodine is released in gaseous and particulate form. Following its emission into the atmosphere, iodine is eventually deposited on surfaces in wet or dry deposition. Then, 131I can accumulate in the thyroid gland, which can cause diseases in humans via ingestion. To understand, assess and predict the impact of iodine in environment, it's necessary to study its wet and dry deposition. The absence of robust data on the dry deposition velocities (Vd) of iodine in gaseous elemental form (I2) as a function of meteorological parameters and surface properties causes uncertainties on models up to three orders of magnitude. In this thesis, an original methodology for I2 dry deposition velocity determining was developed. It's based on short-term (30 minutes to 1 hour) emissions of stable iodine (127I) as I2 form in atmosphere in the absence of precipitation in the middle of a grassland. The influence of meteorological parameters and surface properties on Vd have been studied. Then, the dry deposition model of gases based on electrical analogy has been adapted to iodine. Finally, the model was validated under different meteorological conditions by long-term (30 days) measurements of the transfers into grass of 129I as I2 form emitted by Orano La Hague plant.