Distribution and sources of 129I in rivers of the Baltic region

Abstract

The concentration of 129I was measured in 54 river waters discharging into the Baltic Sea from Sweden, Finland, Estonia, Latvia, Lithuania, Poland and Germany. Sample collection was performed during a well-bracketed time interval (June–July 1999), thus allowing comparison of the rivers over a wide latitude range without the effect of long temporal spread. Although there is no direct input of anthropogenic 129I in the watersheds, the concentration of the isotope is about two to three orders of magnitude higher than the expected pre-nuclear era natural values in the rivers of Finland and northern Sweden, and in the rivers of southern Sweden, Lithuania, Estonia, Latvia, Poland and Germany; the 129I concentration may reach five orders of magnitude higher. Furthermore, there are significant correlations between the 129I concentration and latitude and/or distance from the North Sea and between 129I and Cl. These findings suggest seawater as a main source of 129I to the rivers through atmospheric transport. Of the many chemical parameters investigated, the pH may account for some of the variability in 129I concentrations of the rivers. The contribution from nuclear weapon tests and the Chernobyl accident to the riverine 129I is insignificant compared to the releases from the nuclear fuel reprocessing facilities. The total flux of 129I by rivers to the Baltic Sea and related basins represents minor amounts of the isotope pool in these marine waters. External radioactivity hazards from 129I are considered to be negligible in the Baltic region. However, as the main 129I intake to the human body is likely through water, due to the large amount of daily water consumption, more concern should be given to internal radioactivity hazard that may be associated with the isotope's localized elevated concentration in the human organs.