Iodine-129, Iodine-127 and Cesium-137 in seawater from the North Sea and the Baltic Sea

In this study, new data are presented for the iodine isotopes (¹²⁷I, ¹²⁹I and their isotopic ratios) and Cesium (¹³⁷Cs) in water samples of the North Sea and the Baltic Sea in 2005 and 2009. This study supplements and extends the study of Michel et al. (2012). Iodine isotopes were separated from their matrix by using an anion exchange method and were determined by applying ICP-MS and AMS. ¹³⁷Cs in seawater was determined after cesium ion exchange procedure enrichment by gamma-spectrometry. The concentrations of ¹²⁷I in seawater of the North and Baltic Sea are fairly constant in each Sea with averages of (44 ± 2) and (21 ± 1) ng g^-1, respectively, depending on the salinity. However, large variations of ¹²⁹I concentrations in these areas were detected, which decreased along the French, Belgian, Dutch, German, and Danish shores. ¹²⁹I/¹²⁷I isotope ratios in the Baltic Sea are about 10 times lower than in the North Sea in 2009. The highest isotopic ratios (2.7 × 10^-6) was detected in the English Channel east of the nuclear reprocessing plant at Cap de la Hague. The results confirm the result of our early study that the sources of ¹²⁹I in the North Sea are primarily the nuclear reprocessing facilities at Sellafield (UK) and La Hague (F), and that in the Baltic Sea the inflow of water from North Sea through the Danish Straits dominates the occurrence of ¹²⁹I. In 2009, the activity concentration of ¹³⁷Cs was at least 6 times higher in the Baltic Sea (37 Bq m^-3) than in the North Sea (5.9 Bq m^-3), due to release of ¹³⁷Cs from sediments in the Baltic Sea, which were contaminated by the Chernobyl accident and - to a minor degree - the atmospheric explosions of atomic bombs. The results are discussed by comparing the results of our previous work and the current study demonstrating the continuing disequilibrium of ¹²⁹I/¹²⁷I atomic ratio in the environmental compartments.

Iodine-129 and iodine-127 in European seawaters and in precipitation from Northern Germany

In order to obtain a comprehensive survey on the consequences of the marine (129)I discharges from the European reprocessing plants La Hague and Sellafield, the distribution of (129)I and (127)I in surface waters of the North Sea, the English Channel, the Irish Sea, and the Northeast Atlantic was studied using accelerator mass spectrometry for (129)I and ICP-MS for (127)I. Samples of seawater were taken in the German Bight in May, September, and November 2005 and in the entire North Sea and the English Channel in August 2005. Further samples were obtained from the Irish Sea in June and August 2006 and from Arctic waters between Spitsbergen and Southern Norway in September 2005. (129)I is a conservative tracer in seawater. The concentrations of (127)I are relatively constant with exceptions of coastal areas with high biological activity and of areas influenced by influx from rivers and the Baltic Sea. The variability of the (129)I/(127)I isotopic ratios is exclusively determined by admixture of (129)I released from the reprocessing facilities Sellafield and La Hague to the seawater. The (129)I/(127)I ratios were between 4 × 10(-9)and 3 × 10(-6): at least 3 orders of magnitude higher than the natural equilibrium isotopic ratio 1.5 × 10(-12). (129)I/(127)I ratios of a few times 10(-10) were only found in seawater from the Indian Ocean and from the Pacific at Hawaii. Comparison of the results obtained for seawater with those of a measurement of airborne iodine species and with iodine isotopes in precipitation in Northern Germany demonstrates the transfer of (129)I and (127)I from the sea into the atmosphere and the dominating role of the marine discharges for the atmospheric fallout of (129)I in Western Europe. The results are discussed with the goal to estimate the relevance of the marine discharges for the contamination of the continental areas.