Relative content of radionuclides in aquatic components  <B>Relative content of radionuclides in aquatic components</B><P>V. Patrascu</B><I><P> Romanian Marine Research Institute, Blvd. Mamaia 300, Constantza, Romania</I><P> Abstract<P> This paper is a coherent appreciation of the concentration factors (CF) from the radioactivity data of the RMRI Constantza for 19831991 on the Romanian Black Sea littoral between the Danube mouths and Mangalia. The results are indications on the relative multiyearly average level of the radionuclides K40, Ac228, Ra226, Cs134, Cs137 etc. Maximum probability intervals of values are identified and extremes of the CF are defined. The radionuclides are classified according to the level of the CF in a component and the components according to the concentration capacity of a nuclid. The results of using the two criteria are as follows: by components Submerged sediment: Cs > Ra, Ac, Ru > K Macroalgae Ra, Ac > Cs > K Mollusca soft part: Co > Cs > Ac, Ra, Ag, Ru > K shell: Co > Ac > Cs > K and by radionuclidesK: Submerged sediment > Macroalgae > Fish > Mollusca soft > Mollusca shell Ac, Ra: Bryopsis > Submerged sediment > Macroalgea > Mollusca > Fish Cs: Submerged sediment > Fish > Macroalgae > Mollusca > Shell<P> Radiocesium is mainly found in substratum (CF of the order of 1000), the vegetal and animal organisms have a moderate behaviour (CF of the order of tens)<P>