Temporal and geographical distributions of 99Tc in inshore waters around Ireland following increased discharges from Sellafield

In anticipation of increased discharges of 99Tc from Sellafield to the north-eastern Irish Sea, a study of the concentrations of this radionuclide in inshore waters around Ireland was undertaken. Using Fucus vesiculosus as a bio-indicator, the geographical distribution of 99Tc around the Irish coastline was mapped and temporal variations at some key sites were studied. Comparison with earlier studies shows that, although the absolute concentrations have increased, the geographical distribution of 99Tc has remained unchanged since the mid-1980's. The distribution closely follows that observed for 137Cs, with the highest concentrations being found along the north-east coast. The concentrations recorded at two sites were compared with monthly discharge figures from Sellafield and a transit time for 99Tc was estimated. This was found to be consistent with a similar estimate for radiocaesium. A semi-empirical model was fitted to the time-series data for the Balbriggan sampling site and a value of 17 months deduced for the mean bioavailability time. The concentration factor, Fucus:water, was also determined at the same site. Finally, the radiological significance of the increased rate of discharge of 99Tc was assessed from the perspective of an Irish seafood consumer. (author)