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 ^-/ ¹²⁹IO ₃ ^- and ¹²⁷I ^-/ ¹²⁷IO 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 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.