same period as the Norwegian study 1 . Our results for vegetation and water contamination (examples in Fig. 1) show the same two-component exponential decline (Q t ǃQ 1 e ǁk,t +Q 2 e ǁk,t ) observed for immature fish 1 . The decline in 137 Cs in mature fish was influenced by slower biological uptake rates during the initial period after Chernobyl 1,3 , so only the second component of the decline is shown for our fish data (Fig. 1).Our results show that the effective ecological half-life (T eff , the time for the 137 Cs concentration to reduce by 50%) in young fish, water and terrestrial vegetation has increased from 1-4 years during the first five years after Chernobyl 1,4 to 6-30 years in recent years. The common rate of decline in 137

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A multi-compartmental box model of the Irish Sea has been developed to predict the distribution and radiological consequences of radionuclides discharged from the Sellafield reprocessing plant. The box structure was based on observations of radionuclide distributions in the sea bed and the water circulation was generated from extensive time-series data on 137Cs concentrations in seawater. Measurements of naturally-occurring nuclides provided both data on the extent and rate of these processes and a means to validate the model assumptions.The model structure is briefly outlined, comparisons are made between model predictions and field observation, and some of the difficulties in making such comparisons are discussed.

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