Oyster radionuclide concentrations

Whole Body Radionuclide Concentration Factors and Turnover Rates. A series of experiments were performed to determine the turnover rates and concentration factors of Co, Cs, Mn, and Zn in the marine clam Mya arenaria and the oyster Crassostrea gigas. 

Tissue Turnover of Radionuclides. Oysters and clams that had accumulated either Mn and Zn or Co and Cs for about Ih mo in the laboratory were transferred to unfiltered oceanic water, and changes in concentrations of the radionuclides in the tissues were followed for about 5 mo. Large differences were found in the rates of radionuclides loss from the tissues of both the oysters (Figure l)and the clams (Figure 2). Three patterns of loss during the experimental period were observed. From many tissues, the loss was monophasic, from others it was biphasic, but in some there was an increase or a period of little change before the loss occurred. The last pattern was seen for Zn in some tissues of oysters and clams and indicates that zinc may be mobilized from some tissues for accumulation in others. 

The concentration in the soft tissues of oysters on an ash weight basis was Zn - Fe > Mn > Co (Table II). The concentration factors of the stable elements, Co, Mn, and Zn were higher than those determined by radionuclide studies in the laboratory (cf. Tables I and II). 

Concentrations in postrelease oysters in nonfiltered seawater were higher than those in filtered seawater for all radionuclides. The amounts accumulated per hour in animals in filtered water compared to those in nonfiltered water were lower by 95% for Co, by 78% for Mn, by 52% for Zn, and by 40% for 13 >137cs. 

On December 4, 1973, the prerelease oysters were removed at 0900 h, and the postrelease were removed at 1230 h animals were placed in the discharge canal water at 1530 h on December 3. Compared with the expected concentrations in the water, the amounts of most radionuclides accumulated per hour during the release were lower in December than in July (Table IV). 

Animals were removed from the test solutions, dissected, weighed, and the radionuclides quantified. After a 24 h exposure, the concentration factors in the oysters differed both with the test material and with the element (Table V). In the tissues, concentration factors of both elements generally were high in the gills and the digestive gland and stomach and low in the muscle and the blood. 

Concentration factors and rate constants determined experimentally in the oyster Crassostrea gigas and the clam Mya arenaria differ widely with species and element. The physical form of the element in the water affects turnover also accumulation of radionuclides of Co, Cs, Mn, and Zn is greater in water containing suspended particles. The chemical form of the element in the water affects its accumulation. When glycine, ethylenediaminetetraacetate (EDTA), yellow stuff , or clay are added to seawater, the accumulation of Cu and Zn by the oyster differs with each test material glycine increases and EDTA decreases the accumulation of both elements. 

This group of radionuclides is most likely to be of concern in terrestrially produced foods. Biological concentration processes in freshwater and marine systems can result in very rapid transfer and enrichment of specific radionuclides. The radionuclides which enter such systems can in certain cases be rapidly accumulated by plankton and algae. These organisms serve as food for higher trophic levels and thus the radionuclides become concentrated in organisms such as oysters, clams and shrimps. Radionuclides of particular concern in freshwater and marine food chains include Mn, Fe, Fe, Co, Zn, "Zr, Nb, Ru, °"Ru, " " Ag, " Sb, " l, " Cs, "Cs, Ce and some of the transuranic elements. 

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