Concentration and depuration of some radionuclides present in a chronically exposed population of mussels (Mytilus edulis)

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.

Effects of season and temperature on longterm in situ loss rates of Pu, Am, Np, Eu, Ce, Ag, Tc, Zn, Co and Mn in a Baltic Mytilus edulis population

“…This gives 318 and 267 d for the cold and warm experiments, respectively; in other words, after -300 d, the fraction lost of plutonium is ca twice that of americium. Clifton et al (1983) observed a slower loss of 239* 2 4 0~~ (but not 2 3 8 P~) than of 241Am. These differences could be an effect of different oxidation states.…”

“…Furthermore, Wallace (1980) found that mussels feeding on fish-farm debris maintained a high growth rate throughout the North-Norwegian winter, whereas comparable mussels that had no access to this food source ceased growing and formed distinct winter-rings. Therefore, the seasonal loss pattern observed in the present work is probably due to a lack Clifton et al (1983). 3: Guary & Fowler (1977), 4: Beasley et al (1982), 5: Guary & Fowler (1981), 6: Dahlgaard (1981), 7: Fowler et al (1981), 8: Van Weers (1973.…”

“…It could probably also explain why Cahfornia mussels do not show the same seasonal variation in trace element levels as those from Rhode Island in the US mussel watch (Goldberg et al 1983, Palmieri et al 1984. Furthermore, reduced energy metabolism and slow growth (Seed 1980) might explain the higher concentrations of plutonium and cadmium observed in mussels sampled highest up in the tidal zone (Clifton et al 1983, Goldberg et al 1983, Palmieri et al 1984.…”

“…Among these, the results of Young & Folsom (1967) on 65Zn, Clifton et al (1983) on americium, plutonium, caesium, cerium and ruthenium, and Guary & Fowler (1977) on neptunium, applied specifically to Mytilus soft parts, whereas several others (Table 5) were obtained simply by repeated whole-body countings.…”

Modelling in situ mussel ruthemum-106 concentration dynamics due to fluctuating seawater radionuclide concentrations

“…Very few experiments have been carried out on the in situ elimination of ruthenium by mussels. Two have been selected for consideration: Clifton et al (1983) describe an experiment on the accumulation and elimination by Mytilus edulis of several radionuclides (including ' 0 6~u ) discharged by the fuel reprocessing plant at Sellafield (U.K.). This experiment was carried out between 1980 and 1981.…”