Modelling temporal trends of 137Cs and 99Tc concentrations in Fucus vesiculosus from the eastern Irish coastline

► 137Cs and 99Tc activity concentrations in brown seaweed measured during 1988-2008. ► Significant seasonal variations in time series identified using spectral analysis. ► Novel transfer kinetic model using variable uptake rate applied. ► Evolutionary and grid search minimisation techniques used to fit model. ► Concentration factor and biological half-life values determined.