Studies of the speciation, colloidal association and remobilisation of plutonium in the marine environment

The physico-chemical speciation of plutonium in diverse marine environments such as the Irish Sea, the English Channel, the Mediterranean and the high Arctic is reviewed in some detail. Emphasis is given to the oxidation-state distribution of plutonium in the water column and to the proportion of plutonium present in colloidal form. The seabed sediment compartment is also examined and the capacity for plutonium to he remobilised from sediments demonstrated by reference to recent studies carried out in the Irish Sea. Specifically, the development of a low-resolution compartmental model fur the prediction of future plutonium concentrations in seawater and sediment in the Irish Sea is discussed and interpreted in terms of the processes controlling the desorption, remobilisation and dispersion of plutonium in this zone. The requirement to quantify its speciation locally and to identify the by processes involved in its transfer, before attempting to conceptualise a model in any detail, is stressed. Further, the value of the modelling approach in predicting long-term trends in plutonium levels and estimating likely mean availability times is highlighted. Finally, the form(s) in and extent to which plutonium can he advected over large distances in the marine environment are discussed in the context of a case study of current interest.