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

Abstract

Loss of 10 radionuclides by Mytdus edulis was studled near its salinity minimum in the Bothnian Sea (northern Baltic Sea) by labelling mussels in the laboratory and then allowing them to depurate during a 10 mo period in the field at 2 locations: one with normal temperatures, the other with temperatures 8 to 10 C" above normal. During winter, the clearest effect of heating was accelerated loss of silver. Also zinc was apparently lost more rapidly in warm water, whereas none of the remaining nuclides showed loss rates significantly different from zero at either temperature. At normal temperatures during spring and summer all analysed elements were lost faster than in the heated winter experiment despite similar average temperature conditions. It is concluded that temperature differences play only a minor role In the observed seasonal effect on long-term loss rates. Food availabhty appears to be a key factor. Loss rates are apparently faster than in full-salinity waters. Possible reasons for this are discussed. Plutonium to americium ratlos decreased during depuration. The pluton~un~ fraction lost after 300d was estimated to be twice the corresponding fraction of americium. Europium to americium ratios remained unchanged during all seasons and temperatures. whereas cerium to americium ratios decreased to half during the initial loss phase, after which they remained unaltered. It is concluded that europium behaved as an ideal analogue to americium in this experiment.

Exploring New Frontiers in Marine Radioisotope Tracing – Adapting to New Opportunities and Challenges

“…One problem in working with radioisotopes is the difficulty in obtaining permits to conduct experiments in field situations. While some studies have taken advantage of using radioisotopes to explore how metals behave in natural settings (Dahlgaard, 1986;Fisher et al, 1996), increasingly, such studies have become difficult due to legal and administrative constraints. The few experiments that have compared lab and field behaviors of radionuclide processing by marine biota have indicated small differences, so laboratory simulations may be generally applicable to field situations.…”

Trophic transfer of silver to marine herbivores: A review of recent studies

“…A maximum of 56% of Ag variation could be attributed to the seasonal change in weight of the clams, while the remaining variation is unexplained (44%). In the Baltic, Ag is released from mussels faster in the spring and summer than in winter, and it is likely that this release is associated with spawning [37]. Silver concentrations in oysters ( Crassostrea virginica ) are much lower after spawning in summer, allowing oysters to rapidly reduce Ag body burden through spawning activity [38].…”

“…There is surprisingly little information of Ag efflux in aquatic animals. Depuration of Ag from marine bivalves is generally faster than that of other metals, with biological half‐lives in the range of 20 to 60 d. Dahlgaard [37] attributed a much longer biological half‐life of Ag in Baltic mussels ( Mytilus edulis ) during winter to lower food availability rather than to lower temperature. Binding of Ag with different ligands may directly affect Ag depuration (or physiological efflux).…”