Long-term study of 99Tc in the marine environment on the Swedish west coast

Abstract

The activity concentration of 99Tc in brown seaweed ( Fucus vesiculosus and Fucus serratus) and seawater were analysed in samples collected in 1991, 1995 and 2001 at several stations along the Swedish west coast. In addition to these locations, a well-defined site (Särdal, 56.76 °N, 12.63 °E) was included with 99Tc activity concentration data in seaweed from 1967 to 2000. Over the years, the major source of 99Tc in the coastal waters of western Sweden has been the radioactive liquid discharge from the nuclear fuel reprocessing plant in Sellafield (UK) transported via ocean currents in the North Sea. The 99Tc activity concentration in seaweed at the Särdal site increased from approximately 30 Bq kg -1 up to 230 Bq kg -1 (dry weight) between 1997 and 2000 due to the Sellafield EARP (Enhanced Actinide Removal Plant) discharges in 1995–1996, yielding an approximate transport time of 4–5 years between the Irish Sea and the Kattegat. Due to the very sharp gradient in 99Tc concentration between the Baltic Sea and the North Sea, 99Tc is presently one of the best transit tracers for the recent ventilation events in the Baltic Sea.