Long-term variations of man-made radionuclide concentrations in a bio-indicator Mytilus gallopro¨incialis from the French Mediterranean coast

Results from a 14-year monitoring 1984]1997. of man-made radionuclide 137Cs and 106Ru. levels in Mytilus gallopro¨incialis collected monthly on the French Mediterranean coast are presented. In this area sources of man-made radionuclides are on the one hand atmospheric fallout from both the past nuclear testings and the Chernobyl accident and on the other hand discharges from nuclear installations located on the Rhˆone River banks, especially those from the spent nuclear fuel reprocessing plant in Marcoule. Long-term variations of radionuclide concentrations in Mytilus demonstrated seasonal variations which are linked to the reproductive cycle of these organisms as well as to variations in land-based inputs of man-made radionuclides. A comparative study of these seasonal variations has been carried out with the aid of spectral analysis. Due to differences in released activities and discharge patterns, flow rates appear to govern mainly the 137Cs variations in the Rhˆone waters, whereas 106Ru variations are driven by the discharges. In the area under the influence of the Rhˆone outflow, 137Cs variations in mussels are characterized by seasonal variations which are themselves inversely correlated with variations of 137Cs concentrations in Rhˆone waters. This cyclic component seems to be closely linked to the mussel reproductive cycle. The possible influence of other parameters is discussed.