Anthropogenic radionuclides in biota samples from the Caspian Sea

Samples of fish flesh collected in 1999 in the south-western Caspian Sea in the Baku area, important for caviar production (sturgeon – russkyi osyotr, sevruga and beluga), as well as for consumption (roach and carp) were analysed for anthropogenic strontium, caesium, plutonium and americium, and natural polonium. The highest massic activities of 137 Cs were found in sevruga and beluga flesh (1.2–1.8 Bq/kg wet weight (ww)), while 90 Sr levels were between 5–12 mBq/kg ww, and plutonium and americium levels were close to limits of detection (∼0.2 mBq/kg ww). The observed plutonium and strontium levels are in the same range as in the Mediterranean Sea, whereas caesium has been accumulated in conditions of lower salinity in larger proportions. The 210 Po levels in fish were between 0.2–3 mBq/kg ww, in a fresh caviar (spawn) sample they were higher by a factor of 4 than in sturgeons, but comparable with levels observed in other species. The highest radionuclide levels, by one to two orders of magnitude, were measured in a macroalgae sample. The distribution of radionuclides seems to be more related to the species than to environmental conditions. The estimated concentration factors (CFs) for strontium and plutonium in fish and algae are in a reasonable agreement with IAEA recommended values. Caesium in the same species has been accumulated in larger quantities, so that the resulting CF is higher by a factor of two. The highest CFs were found for macroalgae, documenting that algae are suitable biomonitors of radioactive contamination. The measured activities of radionuclides in biota samples do not represent any radiological risk from their consumption.