I-129 in Swedish rivers: distribution and sources

We analyzed the concentration of I-129 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 x 10(9) atoms 1(-1)), steeply decreasing levels with increasing latitude and a positive correlation with Cl concentration and other chemical parameters. The I-129 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 I-129 in the studied rivers is atmospheric fallout of I-129 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 I-129 concentration in Nordic watersheds will increase further if discharges from nuclear reprocessing continue. (C) 2003 Elsevier Science B.V. All rights reserved.