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

Abstract Time series of 137 Cs and 99 Tc activity concentrations in the brown seaweed Fucus vesiculosus and seawater, gathered at three locations on the eastern Irish coastline during the period 1988–2008, have been modelled using a novel approach incorporating a variable uptake rate in the seaweed. Seasonal variations in the time series, identified using spectral analysis, were incorporated into the model which was used to determine transfer kinetic parameters and to predict 137 Cs and 99 Tc concentrations in seaweed, as influenced by levels in ambient seawater. An optimisation method combining evolutionary and grid search minimisation techniques was adopted to determine the best values for the model parameters, from which concentration factors ( CF ) and biological half-lives ( tb 1/2 ) for 137 Cs and 99 Tc in F. vesiculosus were calculated. CF values of 170–179 and 1.1 × 105 l kg −1 (dry weight) were obtained for 137 Cs and 99 Tc, respectively, while the corresponding tb 1/2 values were 39–47 and 32 days, respectively.