EXPERIMENTAL-STUDY OF THE EFFECTS OF VARIOUS FACTORS ON THE UPTAKE OF CO-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 accumulation of Co-60 by freshwater mosses. Three species were compared from the point of view of their value as bioindicators. Two opposite seasons were simulated, through lighting and water temperature. To better understand the mechanisms involved in cobalt fixation by mosses, the respective 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 mineral suspended matter and mosses was evaluated. These experiments demonstrate that two successive phases occurs in the contamination of aquatic mosses by Co-60, i.e., the first one to surface adsorption and the second one to biological absorption. As regards the studied factors, only season and temporary emersion have a marked influence on the mosses contamination by Co-60. Under the experimental conditions, the presence 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.