Bioaccumulation of 110mAg, 60Co, 137Cs and 54Mn by the Freshwater Crustacean Daphnia magna from Dietary sources (Scenedesmus obliquus and Cyclotella meneghiana)

Abstract

The importance of food as radionuclide source for the crustaceanDaphnia magna was investigated using a planktonic food chain composed of young pre-adult daphnids and two algal species(Scenedesmus obliquus and Cyclotella meneghiana). Daphnids placed in a tank containing natural 0.45 μm filteredwater were fed on algae previously kept during 4 days in natural water contaminated by 110mAg, 60Co, 137Cs and 54Mn. After about one week of exposure, daphnids wereplaced in non-contaminated water on a diet of non-labelled algae,in order to monitor radionuclide release. The results suggest that the Trophic Transfer Factor (TTF) of radionuclides in daphnids was generally greater for the transfer via Scenedesmus than via Cyclotella> and that it could be linked to the intracellular fraction of accumulated radionuclidesand consequently to their biochemical behaviour. For theradionuclide transfer via Cyclotella meneghiana, the biological periods ranged, for the first compartment, from 7 to 30 min and for the second, from 10 h to 1.8 d. As regards thetransfer via the green algae Scenedesmus obliquus the biological half-lives were longer, since Tb1 characterizing the first compartment, ranged from 11 min to 5.2 h, whereas Tb2 ranged from 1.2 to 2.1 d. From an operational point of view, this paper underlines the importanceof considering the food contamination in the models of radionuclide transfer through trophic chains, in order to widentheir applications in different seasons or ecosystems.