Evidence for the Remobilization of Sellafield Waste Radionuclides in an Intertidal Salt Marsh, West Cumbria, U.K.

Intertidal sediments in north-west England contain enhanced levels of artificial radionuclides due to the authorized release of lowlevel liquid waste from the Sellafield reprocessing site. In this paper, the behaviour of99Tc,137Cs,237Np,238Pu,239Pu,240Pu,239+ 240Pu and241Am in an intertidal marsh sediment is described. The radionuclide data, together with stable element data, allow detailed interpretation of the behaviour of these artificial radionuclides in a natural environment. For241Am and239+240Pu, for which the Sellafield discharge history is well known, the distributions down the sediment core show a high correlation with the Sellafield discharge history. The sediment profiles for other less widely studied radionuclides,99Tc and237Np, have been examined in relation to both the post-1978 published discharge histories and the behaviour of other Sellafield-derived radionuclides in the core. There is strong evidence that significant post-depositional remobilization of a proportion of the most labile elements,237Np,137Cs and99Tc, is occurring at the marsh.