The Loss of Radionuclides in Marine Organisms during Thermal Decomposition

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The losses of ¹³⁷Cs, ¹⁰⁶Ru-¹⁰⁶Rh, ⁶⁵Zn, ⁶⁰Co, ⁵⁹Fe, ⁵⁴Mn, ⁹⁵Zr-⁹⁵Nb and ¹⁴⁴Ce from the tissues of bivalves and green algae during dry ashing were investigated under the conditions of the temperature of 450, 550 or 800°C and the ignition time of 12, 24, or 48 hours.
Samples were prepared by rearing the organisms in sea water containing each radionuclide described above.
Biological tissues were decomposed in an electric muffle furnace. Recoveries of individual radionuclides in the tissues were calculated by the radioactivity ratio of pre and post-ashing of samples. Under the condition of 450°C, ignition was not complete in 24 hours for bivalves and in 12 hours for green algae.
The results of this investigation indicated that ¹³⁷Cs, ¹⁰⁶Ru-¹⁰⁶Rh, ⁶⁵Zn and ⁶⁰Co showed the loss in some ashing conditions and that the manners of the loss of these radionuclides were different between the organisms. ⁵⁹Fe, ⁵⁴Mn, ⁹⁵Zr-⁹⁵Nb and ¹⁴⁴Ce were not significantly lost under any condition used in this experiment. Accordingly, the loss of ¹³⁷Cs, ¹⁰⁶Ru-¹⁰⁶Rh, ⁶⁵Zn and ⁶⁰Co might be correlated with the biological matrix in which these radionuclides were incorporated, while there seemed to be no effect of biological matrix to the ashing loss of ⁵⁹Fe, ⁵⁴Mn, ⁹⁵Zr-⁹⁵Nb and ¹⁴⁴Ce.
The most desirable ashing condition in our investigation was 450°C, 48 hours for ¹³⁷Cs and 550°C, 12 hours for other radionuclides in bivalves, and 450°C, 24 hours for ¹³⁷Cs, ¹⁰⁶Ru-¹⁰⁶Rh and ⁶⁵Zn, and 550°C, 12 hours for other radionuclides in green algae.