The role of the bacterial community in the radionuclide transfers in freshwater ecosystems

This chapter investigates the radionuclide fluxes between the bacteria and the water in aquatic ecosystem by examining the bulk transfers mediated by a bacterial community isolated from the river sediments. A comparison of the aerobic bacterial communities colonizing the sediments and the water column shows that the bacterial community of the sediments is composed of two sub-communities. The first one is similar to the water column community by its biochemical features; the other one displays quite different characteristics and appears to be more representative of the sediments. An important part of 60Co and 134Cs can be immobilized by the bacterial biomass that constitutes a pool of radionuclides, their transfers to the water column being controlled by temperature and pH. The uptake of 60Co and 134Cs by bacteria is described by the Michaelis–Menten model. The uptake kinetics depend on the type of radionuclide and the level of radiocontamination in the water column. The highest affinity uptake system is observed for 60Co at low radiocontamination levels. The decontamination of bacterial biomass develops in two phases. The first phase is characterized by a very short biological half-life, a few seconds or minutes, while the second phase is longer; the biological half-lives reach between 15 h to 461 h for 60Co and between 39 h and 8,976 h for 134C