Laboratory and field studies of polonium and plutonium in marine plankton

Uptake experiments were successfully undertaken for polonium and plutonium in the marine diatom Skeletonema costatum. Experiments were complemented with a field study which yielded concentration factors for these radionuclides for plankton samples collected in the eastern Irish Sea. The uptake experiment produced uptake half times of 0.8 and 0.6 days for plutonium and polonium, respectively. Concentration factors of 3.1 x 105 l kg-1 for plutonium and 2.4 x 105 l kg-1 for polonium were consistent with those suggested by the IAEA for phytoplankton. Concentration factors derived from the field study were 2 x 103 l kg-1 for plutonium and 1.4 x 104 l kg-1 for polonium and were more consistent with IAEA values for zooplankton rather than phytoplankton. The maximum calculated dose rate due to Po and Pu in plankton sampled in the field was 0.12 μGy h-1. In applying the laboratory-derived phytoplankton CF values for Po and Pu, higher dose rates, in the range 6-11 μGy h-1, were calculated. The latter values are well below the UNSCEAR and IAEA review value of 400 μGy h-1, and are also below the Environment Agency marine action level of 40 μGy h-1.