EFFECTS OF SOME FACTORS ON UPTAKE AND RELEASE OF RU-106 BY A FRESH-WATER MOSS, PLATHYPNIDIUM-RIPARIOIDES

In order to correctly interpret field data related to bioindicators, laboratory experiments were carried out to study Ru-106 accumulation and release by mosses, as a function of experimental procedures and conditions, aimed to reproduce ecological realities. Mosses were exposed to Ru-106 during 5 to 7 days and then transferred to an inactive, daily-renewed medium. Results were expressed mathematically by a sum of two exponential functions for fixation, which was shown to be a two-phase rapid and intense phenomenon, and by a simple exponential function for elimination, which was slower and regular. Three rhythms of contaminant release were simulated, and they were found to have little effect on fixation extent as measured by concentration factor, while the speed of fixation was affected slightly. Accumulation was also studied under two opposite seasons, simulated by modifying temperature, illumination and daylight period. It occured with very different kinetics, suggesting an important intervention of adsorption processes, whose speed is conditioned by temperature. This hypothesis was supported by the considerable effect the size of the exchange surface had on extent and speed of fixation, shown by comparison of accumulation in two species. Nevertheless, reduced uptake in darkness indicated the probable role of physiological processes. As far as desorption is concerned, the studied factors had little effect. The most significant differences in retention were due to the previous average exposure time and to exchange surface size.