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

Abstract 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.