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

摘要

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 1 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.