¹²⁹I in Swedish rivers: Distribution and sources

We analyzed the concentration of ¹²⁹I in the water of 26 rivers covering most of the runoff from Sweden, with the aim of assessing current contamination levels, distribution patterns and potential sources in freshwater systems of northern Europe. The results show relatively high values (up to 1.4×10⁹ atoms l^-1), steeply decreasing levels with increasing latitude and a positive correlation with Cl concentration and other chemical parameters. The ¹²⁹I concentrations observed in south Sweden are probably the highest ever recorded in rivers without any direct discharge from a nuclear installation. The strong latitudinal dependence suggests a northward dilution and possibly depletion of the isotope and a transport from a source located to the south. The most plausible source of the ¹²⁹I in the studied rivers is atmospheric fallout of ¹²⁹I emitted either by atmospheric discharges from the nuclear reprocessing facilities at Sellafield (England) and La Hague (France) or by volatilization from seawater contaminated by the same sources. The question is now whether and at what rate the ¹²⁹I concentration in Nordic watersheds will increase further if discharges from nuclear reprocessing continue.