EXPERIMENTAL-STUDY OF THE EFFECTS OF VARIOUS FACTORS ON THE UPTAKE OFCO-60 BY FRESH-WATER MOSSES

Laboratory experiments were conducted to study the effects of several biotic and abiotic factors likely to intervene in situ on the accumula tion of Co-60 by freshwater mosses. Three species were compared from t he point of view of their value as bioindicators. Two opposite seasons were simulated, through lighting and water temperature. To better und erstand the mechanisms involved in cobalt fixation by mosses, the resp ective roles of light and temperature were studied separately. As the watercourses know seasonal fluctuations, the possibility of temporary emersion of plants was considered. Finally, the competition between mi neral suspended matter and mosses was evaluated. These experiments dem onstrate that two successive phases occurs in the contamination of aqu atic mosses by Co-60, i.e., the first one to surface adsorption and th e second one to biological absorption. As regards the studied factors, only season and temporary emersion have a marked influence on the mos ses contamination by Co-60. Under the experimental conditions, the pre sence of mineral suspended matter modify little the Co-60 accumulation by mosses, but, in this scope, extrapolating experimental findings to the natural environment was difficult.