Screening methodology for dose assessment to seawater organisms in baltic sea

Determination of radionuclides in Baltic Sea environment in the frame of MORS programme gives opportunity to evaluate doses for aquatic organisms from the Southern Baltic Sea. The available environmental data from the last few years included concentrations of 137Cs (bomb-tests-fallout and Chernobyl origin), 226Ra (natural radionuclide) and 239,240Pu (bomb-tests-fallout) in biota, bottom sediment and water. The doses assessment of 137Cs, 226Ra and 239,240Pu for aquatic animals was performed, based on the screening methodology elaborated by U.S. Department of Energy. Baltic Sea fish (cod, sprat, herring, plaice) and crustaceans (Sanduria entomon and Mytilus edulis) were taken in to consideration and the annual doses from 137Cs, 226Ra and 239Pu to organisms were calculated at average concentrations of these radionuclides observed in water, concentration of radionuclides determined in bottom sediments from two sub-areas (Gdansk Basin and Bornholm Basin) and average concentrations of radionuclides in animal tissues. The total maximal annual doses for seawater organisms do not exceed a one percent of recommended dose limits however, the dominate contribution to the total dose depends on analysed radionuclide. For 137Cs a maximum contribution to the total dose gives external dose from bottom sediment (about 0.5 mGy y-1). Only about 1% of the total 137Cs dose is derived from internal dose however animal-water ratio obtained from measurements is much lower (in a range 30-300 L kg-1) comparing with recommended by DOE Standard value (22000 L kg-1). For 226Ra internal doses for fish and Mytilus are similar (0.2 mGy y-1, 0.6 mGy y-1 respectively) and they are comparable with external doses from sediment (0.3 mGy y-1) whereas internal dose for Sanduria is about 10 times higher (7 mGy y-1). A measured animal- water ratios (20 - 500 L kg-1) differs remarkably from default DOE Standard value (3200 L kg-1). For plutonium 239Pu the maximum contribution to the total dose gives internal dose and external dose from sediment contributes less then 1%. The contribution of external dose from water is negligible for all analysed radionuclides. A measured animal-water ratios for Mytilus edulis (2600 L kg-1) is much higher then default DOE Standard value (1000 L kg-1) and it suggests careful verification parameters used in the screening methodology. The default animal-water bioaccumulation ratios that are provided by screening methodology can be used with caution when they are applied to dose evaluation for biota. (author)