In the first days of June, most activity in shallow water sediments was due to Ruthenium isotopes; 6-12 months later about 10% of Cesium isotopes deposited at the sea surface was found in the upper 2-4 cm of sediment. Maximum radionuclide concentrations in the soft parts of mussels (137Cs: 8 Bqkg-1, 103Ru: 235 Bqkg-1) were found 2-4 days after the maximum radionuclide deposition. From the radionuclide elimination curves, a two compartment system was identified, with biological half lives of 2 and 63 days for Cesium and 2 and 14 days for Ruthenium. -from English summary