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

Results from a 14-year monitoring (1984-1997) of man-made radionuclide (Cs-137 and Ru-106) levels in Mytilus galloprovincialis 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 Rhone 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 Cs-137 variations in the Rhone waters, whereas Ru-106 variations are driven by the discharges. In the area under the intluence of the Rhone outflow Cs-137 variations in mussels are characterized by seasonal variations which are themselves inversely correlated with variations of Cs-137 concentrations in Rhone waters. This cyclic component seems to be closely linked to the mussel reproductive cycle. The possible influence of other parameters is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.