w. in P. fucoides and F. lumbricalis, respectively. 57Co also exhibited similar behaviour in both species of macroalgae, but see more the concentrations were much lower – 846 and 886 Bq kg−1 d.w., respectively. The lowest activity concentration was determined for 85Sr (58 Bq kg−1 d.w.) in F. lumbricalis, whereas in P. fucoides the level of this radionuclide was below the limit of detection. A possible explanation of this fact is the passive adsorption of strontium cations by negatively charged polysaccharides present in the cell wall, which in F. lumbricalis is much thicker. F. lumbricalis belongs

to the buy BAY 73-4506 coarsely branched group of macroalgae with a corticated internal anatomy, according to the Littler functional-form model ( Littler & Littler 1980, Lobban & Harrison 1997), and its external walls form a type of skeleton in which strontium ions may be trapped more efficiently. An index commonly used to compare the bioaccumulation properties of the species under scrutiny

here is the concentration factor (CF), calculated as the ratio of the radionuclide concentration found in an organism to its concentration in seawater (Szefer 2002b). However, the concentration factor can only be related to the steady state conditions found in the natural environment. In the present study, it was not possible to calculate concentration factors, because a steady state was not attained during the experiment, and conditions changed, especially with regard to radionuclide concentrations in the algal

thalli and in the seawater. Hence, it seemed reasonable to suggest another factor, named the ‘interspecific diversity factor’ (ISDFP/F) for the purposes of this study. ISDFP/F is defined as the ratio of the radionuclide concentration in one species (P. fucoides) to its corresponding concentration in another species (F. lumbricalis), as described by the following formula: equation(1) ISDFP/F=APolysiphonia/AFurcellaria.ISDFP/F=APolysiphonia/AFurcellaria. FER This factor enables the bioaccumulation abilities of two species towards a single radionuclide to be compared. In this case, the term ‘bioaccumulation ability’ should be understood as the relationship between the rate of bioaccumulation during a given time interval and the bioaccumulative capacity. However, the simple measurement of radionuclide concentrations does not suffice to distinguish which of these two components is the most influential on the final result.