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

Abstract Despite the common incorporation of iodine in the biological cycle and occurrence of huge contamination of the radioactive isotope 129 I 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 129 I and 127 I 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 129 I and inductively coupled plasma mass spectroscopy (ICP-MS) for 127 I. 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 129 I − / 129 IO 3 − and 127 I − / 127 IO 3 − 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 129 I and 127 I 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.