Concentrations of ¹²⁹I along a transect from the North Atlantic to the Baltic Sea

Large amounts of iodine-129 were, and still are, released to the environment from nuclear facilities, in particular from two reprocessing facilities located at the east coast of the North Atlantic Ocean (Sellafield and La Hague). The main transport path of the releases from the two facilities is towards Northern Europe and further into the Arctic Ocean. Here we present data of ¹²⁹I concentrations observed along a transect from the Baltic Sea to the North Atlantic in 1999. Concentration of ¹²⁹I in surface water samples are several orders of magnitude higher than the natural background level, with the highest enrichment found in the Skagerrak basin. Three profiles taken in the Baltic Sea show an increase of ¹²⁹I with depth. Preliminary inventory calculations suggest that the major source of ¹²⁹I in the Baltic Sea is via marine input from the North Sea. So far concentrations of this isotope do not constitute a source of environmental hazard.