Accumulation of technetium-99 in the Irish Sea?

An assessment has been carried out to determine the impact of continued 99Tc discharges into the Irish Sea from the nuclear fuels reprocessing plant at Sellafield. Samples of surface and bottom seawater and sediment have been collected from the Irish Sea and analysed for 99Tc. The information has been used, together with supporting data, to determine the effect of summer stratification upon the seawater concentrations and to evaluate whether sediments provide a sink for 99Tc. Hydrographic data provide clear evidence of thermal stratification of waters above the muddy sediment in the western Irish Sea. Surface water contained higher 99Tc concentrations than bottom water, and concentrations were inversely related to water salinity. This inverse relationship was not observed in the eastern Irish Sea close to Sellafield. 99Tc activities in surficial sediments were greatest (>20 Bq/kg) at sites closest to the Cumbrian coastline. Activity, from equivalent sampling sites, remained similar between surveys carried out in 1995 and 1998. The muted response of the seabed sediments, to fluctuations in the Sellafield discharges, compared with the water column is to be expected given that they reflect the integrated radionuclide discharge history.