Technetium-99 in biota samples collected along the Finnish coast in 1999

The aim of the study was to develop a method for analysing 99Tc at STUK, and to establish whether 99Tc can be detected in Finnish coastal waters. Samples of Fucus vesiculosus, Myriophyllum spp., Macoma baltica, Mytilus edulis, Saduria entomon and seawater were collected at more than 30 stations along the western and southern coasts of Finland for 99Tc analysis. Small amounts of 99Tc were observed in all the Fucus samples collected; the activity concentrations ranged from 1.6 to 11.6 Bq kg–1 dry wt. The highest concentrations were found in two samples taken from the northernmost stations in the Quark, probably for biological reasons. Due to the low salinity of the water, Fucus vesiculosus is very slow-growing and small in this area, which is at the extreme limit of its permanent distribution range in the Baltic Sea. In seawater and in all the other biota samples, the concentration of 99Tc was below the detection limit, which supports the use of Fucus as an indicator organism for 99Tc in the marine environment. Global fallout from atmospheric nuclear weapons tests carried out in the 1950s and 1960s is certainly the most important source of 99Tc detected in Fucus on the Finnish coast. In addition, the samples were analysed for gamma-emitting radionuclides.