All of these requirements were met in our experiment. The calculated ISDFP/F values of nine radionuclides are illustrated graphically in Figure 3. The values close to 1.0, as determined in the cases of three radioisotopes – 57Co, 60Co and 241Am (Table 3) – mean that no great diversity was observed between F. lumbricalis and P. fucoides and that the bioaccumulation of these radionuclides proceeded according to a very similar pattern in both species. A value slightly

in excess of 1.0 was found in the case of 51Cr, and only in one case – 54Mn – was ISDFP/F markedly < 1.0. This may indicate that bioaccumulation proceeds more easily and faster in F. lumbricalis. Considerably higher values, exceeding 3.0, were calculated in the cases of zinc (65Zn) and tin (113Sn) isotopes, while the highest Etoposide ISDFP/F value of 6.7 was recorded for silver (110mAg), indicating the preference of P. fucoides for the bioaccumulation of 110mAg. The estimated value of ISDFP/F for radioactive

caesium isotopes, which showed the lowest concentrations in both species, was almost 2.0, again indicating that bioaccumulation was more effective in P. fucoides. It should be stressed that the interspecific diversity factor obtained for 137Cs accumulation under steady-state environmental BAY 73-4506 clinical trial conditions, calculated using concentration levels in plants prior to exposure (the black bar in Figure 3), was very close to this value (1.9). This could indicate that the bioaccumulative efficiencies in both red algae during the laboratory experiment remained in the same proportion to their efficiencies in the marine environment. In both species, bioaccumulation was achieved by foliar uptake; the surface exchange area was therefore one of the most important parameters during this process (Lobban & Harrison 1997). For this reason, the higher concentrations of most of the radionuclides found in P. fucoides can be related primarily to the extensive

surface exchange area specific to this species. According to the Littler functional-form group model ( Littler & Littler 1980), in which those authors divide macroalgae into six different groups based upon external morphology and internal anatomy, P. fucoides belongs to the filamentous group. This group is characterized by a delicately-branched external morphology, uniseriate, multiseriate or lightly-corticated internal anatomy, and a soft texture that may also facilitate ID-8 bioaccumulation. Additionally, the specific internal construction of the genus Polysiphonia consisting of a central axis, elongated cells, surrounded by pericentral cells of the same length to create a semi-pneumatic construction, may influence the bioaccumulative capacity to a large extent ( Szweykowska & Szweykowski 1979). The activity changes of eight radionuclides in F. lumbricalis thalli during the time of exposure are presented in Figure 4, Figure 5 and Figure 6. The curves enable five stages in the process of radionuclide accumulation by the macroalgae to be identified.