No abstract

No abstract

Factors are described which affect the concentration (p Ci g-' dry wt) and loss of ^Am, 239 + 240Pur 2 3 8~u r 144Ce, 13?Cs, '^Cs, lo6Ru, ^Zr and ^Nb in an exposed population of mussels Mytilus edulis L. from Ravenglass on the Esk estuary, Cumbria, UK which receives radioeffluents from the British Nuclear Fuels Ltd. (BNFL) plant at Sellafield, some 10 km to the north. Tidal position and mussel body size have a negligible influence on the concentration of 241Am, l3?Cs and ^Ru in the total soft tissue, but variation in soft tissue weight throughout the year has a considerable influence on the apparent concentration and depuration times of these radionuclides. Apart from the clearance (ti,, biol, 1 to 3 h) of sediment-associated activity from the digestive tract, the depuration rate profiles follow a single component clearance curve with a biological half-life in excess of 200 d for ^'Am, 239 + ^OPU, 23%and l4Ve, and of 40 d for 13'Cs. The clearance of Io6Ru is more complex and consists of a 3 component depuration profile with biological half-lives of 6 h, 12 d and 260 d. The depuration profiles presented in this work are for chronically ingested isotopes under natural conditions; acute exposure will most likely result in different profiles, especially those derived from laboratory spiking experiments. Isotope ratio data support the hypothesis that the main route of entry into the mussel for the majority of the radionuclides studied is from the water. Differences in the biological half-lives observed between 239 + ^OPu and both and 241Am could be related to their different physico-chemical forms rather than a biological mechanism differentiating between these isotopes; as there are no suitable data available for the composition (chemical or physical) of the BNFL effluent it is not possible to determine whether these differences reflect procedures employed during fuel reprocessing or sediment-water interactions after discharge. This paucity of information also makes it difficult to determine the degree to which the Ravenglass mussels reflect recent discharges from BNFL.

No abstract

Concentrations and distributions are reported for 239 + 240h, 2 3 8 P~ and 2 4 1~m in Mytilus edulisL., Fucus vesiculosus L. and surface sediment from the Esk estuary Cumbria UK, which is subjected to effluents from the British Nuclear Fuel Ltd uranium 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 und Am retained within the intestinal tract is excreted in faeces; that which enters the systemic circulation gives rise to a diffuse distribution. No significant enr~chment of Pu and Am occurs in kidney granules, but in the pericardial gland as a result of ultrafiltration processes localised 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 hence uptake is probably direct form conservative species present in the seawater. In situ dialysis studies in surface silty sediments of the area provide evidence of conservative species for both Pu and Am. Differences in concentration of Pu and Am for 1977in 1979 there was an increase in levels of h in the mussel and sediment. F. vesiculosus contained more h than Am. However, the Am/Pu ratio for F. vesiculosus is similar to that in byssal threads of M. edulis.