The Uptake and Distribution of Radionuclides in Marine Organisms

McDonald, Paul (1989) The Uptake and Distribution of Radionuclides in Marine Organisms. PhD thesis, University of Glasgow.

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The behaviour and distribution of alpha-emitting radionuclides in the mussel (Mytilus edulis), winkle (Littorina littorea) and Dublin Bay prawn (Nephrops norvegicus) have been investigated under both environmental and laboratory conditions using alpha-autoradiography in conjunction with conventional radio- analytical techniques. Of the samples exposed to environmental levels of radioactivity, Ravenglass mussels, collected between 1983 and 1984, exhibited 239+240 Pu concentrations ranging from 43Bqkg (dry) in muscle tissue to 1658Bqkg-1 in byssal threads, the corresponding 137Cs range being 131Bqkg to 1340Bqkg-1 . Although 210Po concentrations were not determined in byssal threads, muscle tissue still displayed the lowest nuclide concentration (124Bqkg -1), whilst the viscera (containing digestive gland, stomach and kidneys) contained the highest (596Bqkg -1). Subsequent concentration factor calculations for 137 Cs,210 Po and 239+240 Pu in the total soft parts of Ravenglass mussels were, respectively, 9, 25800 and 1400. In Cumbrian winkles, nuclide concentrations ranged a) for 239 Pu, from 18.5Bqkg -1(muscle tissue) to 457Bqkg -1(pallial complex), b) for 137Cs, from 103Bqkg (foot tissue) to 1495Bqkg (pallial complex) and c) for Po, from 12.2Bqkg-1 (muscle tissue) to 145Bqkg (digestive gland). Total soft parts CFs were calculated at 16 for 137Cs, 5500 for Po and 5700 for 239+240 Pu. The magnitude of these CFs, as for those of the mussel is consistent with the respective CF values recommended by IAEA (IAEA, 1985) for molluscs. Radionuclide concentrations in Whitehaven-landed prawns were much lower than those observed in mussels or winkles; no artificial y-emitter activities were present above detection limits and the highest 238+240 Pu concentration was 5.96Bqkg-1 in the carapace. Po activities, however, were more readily detectable throughout the prawn's tissues, concentrations ranging from 2.7Bqkg -1(abdomen muscle) to 144Bqkg (cardiac foregut), producing CFs of the order of 2x10 4 in tissues associated with feeding and digestion. Previous studies have attempted to determine the principal nuclide source to marine organisms by comparing nuclide activity quotients in their tissues, sea water and particulate material. From the environmental samples here, no single transport medium appears to dominate such uptake. Under laboratory conditions, mussels, winkles and prawns all exhibited the ability to accumulate 237 Np, 239Pu and 241 Am from both sea water and food media. Up to 90% of the accumulated activity was located in the hard protective shells of the organisms. In general, of the soft tissues studied, those associated with feeding and digestion accumulated radionuclides most effectively. In digestive glands/hepatopancreas, the site of nuclide uptake was in the digestive tubules. Other active tissues were the gill and heart of the Dublin Bay prawn and the pallial complex and operculum of the winkle. The prawn's gill was the only tissue to exhibit a clear preference between food and sea water labelling media - with higher accumulation via sea water. Heart tissue contained enhanced levels of 239 Pu relative to 237 Np and 241Am. This unusual observation may be associated with metal-detoxification processes. The various glandular and secretory functions of the winkle's pallial complex may account for the comparable magnitude of nuclide activities in this tissue and of those in the digestive gland. Other mucous secretions, on the external layers of the winkle's head and foot tissues, have been observed to accumulate radionuclides but not as efficiently as the pallial complex. The most intense a-track distributions encountered in the project were found in the winkle's operculum. These observations can be attributed to the chitinous nature of the tissue. Laboratory experiments therefore have shown that the accumulation and distribution of transuranic nuclides in marine invertebrates are highly influenced by the presence of scleroproteins, chitinous material and mucous secretions. Despite the relatively low activities present in Ravenglass mussels and winkles, their alpha-autoradiographs exhibited tissue activity trends in general accordance with those obtained experimentally. This finding provides some support for the validity of laboratory-derived information and for its extrapolation to environmental conditions. From radiochemical analysis, it is apparent that the Po contributes significantly to the total alpha-activity of the environmental marine organisms. Because of the decreasing concentrations of a-emitting transuranic nuclides (mainly 238 Pu,239+240 Pu and 241 Am) in the Ravenglass environment, the influence of natural Po in any future a-autoradiographic studies will become increasingly dominant. The primary radiological implication of the observed radionuclide concentrations in Ravenglass mussels and winkles is that, from seafood ingestion, the critical group receives only a small percentage of the ICRP-recommended dose limit. Dose contributions from Po are higher than those from 239+240Pu in mussels but are less than those from 239+240 Pu in winkles.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Biogeochemistry, Nuclear chemistry, Biological oceanography
Date of Award: 1989
Depositing User: Enlighten Team
Unique ID: glathesis:1989-77945
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09

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