Continuing contamination of north Atlantic and Arctic waters by Sellafield radionuclides.

Discharges of 99Tc and 129I from the reprocessing plant at Sellafield have increased significantly since the mid-1990s, against the overall trend of most other radionuclides. The 'pulsed' release of 99Tc has provided an opportunity to study transport pathways and transit times in UK waters, the North Sea and beyond. Transit times estimated from the 99Tc data are signifcantly shorter than rates reported previously using other radiotracers. The possible reasons for this are discussed. A comparison is made between the response of seawater concentrations and those in the brown seaweed Fucus vesiculosus to variations in the release rates. Current discharges of plutonium are very low compared with the 1970s and 1980s. However, the seabed sediments of the Irish Sea represent a substantial source and remobilisation into the water column results in the continuing export of plutonium from the Irish Sea and its transport to Arctic waters.