Concentration and Distribution of the Transuranium Radionuclides 239 + 240Pu, 238Pu and 241Am in Mytilus edulis, Fucus vesiculosus and Surface Sediment of Esk Estuary

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Abstract
Concentrations and distributions are reported for 239 + 240Pu, 238Pu and 241Am in M. edulis L., F. vesiculosus L. and surface sediment from the Esk estuary, Cumbria, England, UK, which is subjected to effluents from the British Nuclear Fuel Limited U reprocessing plant at Windscale, Cumbria. For M. edulis, data was obtained on total soft tissues, shell and for 11 organs and tissues. The distribution of alpha particle activity for thin sections of the mussels was obtained by autoradiography using a new thermoset dielectric detector CR-39. Evidence is presented which indicates that uptake of transuranium radionuclides is probably from seawater rather than from ingested sediment. Pu and Am retained within the intestinal tract is excreted in feces; that which enters the systemic circulation gives rise to a diffuse distribution. No significant enrichment of Pu and Am occurs in kidney granules, but in the pericardial gland as a result of ultrafiltration processes localized enhanced levels of alpha radioactivity were observed. Highest enrichment of Pu and Am occurs in byssal threads and periostracum, lowest in the shell when the periostracum has been removed. Alpha particle distribution for byssal threads and periostracum is diffuse, hot-spots are absent and uptake is probably direct from conservative species present in the seawater. In situ dialysis studies in surface silty sediments of the area provide evidence of conservative species for Pu and Am. Differences in concentration of Pu and Am for 1977, 1978 and 1979 are described; in 1979 there was an increase in levels of Pu in the mussel and sediment. F. vesiculosus contained more Pu than Am. The Am/Pu ratio for F. vesiculosus is similar to that in byssal threads of M. edulis.