Iodide and iodate (129I and 127I) in surface water of the Baltic Sea, Kattegat and Skagerrak

Despite the common incorporation of iodine in the biological cycle and occurrence of huge contamination of the radioactive isotope 129I in the Baltic Proper, Skagerrak and Kattegat, there is no data on chemical speciation of iodine in these waters. We here present first time data on iodine isotopes 129I and 127I species as iodide and iodate in surface seawater samples collected from 16 locations in August 2006 and 19 locations in April 2007 in the Baltic Proper, Skagerrak and Kattegat. After extensive separation methods, the isotopes concentrations were determined using accelerator mass spectrometry (AMS) technique for the 129I and inductively coupled plasma mass spectroscopy (ICP-MS) for 127I. High concentrations of both isotopes species were found in the Skagerrak–Kattegat basins, whereas the values in the Baltic Proper are low for both species. The ratios of 129I−/129IO3− and 127I−/127IO3− significantly increase from south to central Baltic Sea, and iodide (both isotopes) appears as the predominant inorganic iodine species along the Baltic Sea. The results show insignificant change in 129I and 127I speciation and suggest that reduction of iodate and oxidation of iodide in Skagerrak and Kattegat may be a slow process. Additionally, the positive correlation between salinity and iodide and iodate (both isotopes) may reflect effective control of Skagerrak water mass on iodine distribution in surface water of the Baltic Sea.

► Speciation of 129I and 127I in surface water of the Baltic Proper, Skagerrak and Kattegat.
► Reduction of iodate and oxidation of iodide in Skagerrak and Kattegat may be a slow process.
► Reduction of iodate to iodide seems to be relative fast process in surface water of the southern Baltic Sea.
► Oxidation conditions of the surface water are not exerting a marked effect on the iodine speciation in the studied basins.