Cs-137 accumulation and elimination by Gracilaria caudata alga and Abudefduf saxatilis fish. Compartmental analysis

From the ecological point of view, 137Cs is a critical radionuclide because its physical half-life is long (30 years), and it has a high fission yield. Besides, it presents similar characteristics to sodium and potassium, fundamental elements for the living organisms, in great concentration in all cells. This work has as aim to study the 137Cs accumulation and elimination by the alga Gracilaria caudata and by the fish Abudefduf saxatilis as well as to obtain the transfer constants of the137Cs from the water into the organisms. The concentration factor found for the fish was 5.6 +- 0.2 and for the alga, 13.0 +- 0,6. With 7 and 22 days, the fish and alga respectively had already eliminated half of the accumulated radionuclide. The 137Cs ingestion efficiency by the fish was also studied and it was verified that the fish assimilated only 47.6 % of the cesium content in the food; and within of 4 days it had eliminated more than half of ingested cesium. A compartmental model was proposed to explain the distribution of cesium in the compartments (water - alga and water - fish). Data obtained from the experiments of 137Cs accumulation and elimination were applied in the Ana Comp Program. This program permits the compartmental analysis, and quantifies the cesium distribution from the sea-water to the organisms, and vice versa, through the transfer constants (k). The Ana Comp Program also allowed to calculate the dose that one would receive by the consumption of fish contaminated by cesium. Levels of 137Cs from the global fallout in environmental samples, from Sao Sebastiao, northern coast of Sao Paulo, (where the 'Centro de Biologia Marinha da Universidade de Sao Paulo - CEBIMar - USP' is located), were verified. (author)