Spatial Distribution of Uranium and Radium in the Sediments, Mussels (mytilus Sp.) and Sea Water in Port of Sibenik

The purpose of this study is to assess the response of the aquatic environment (sediment, sea water and mussels Mytilus sp.) on uranium and radium activity and concentration following the decrease of phosphate discharges from a technologically improved transhipment terminal, situated at the CroatianAdriatic coast in the port of Sibenik. The highest U activities (485±16 Bq kg" dry weight) and Ra activities (662±6 Bq kg" 1 dry weight) were found in the sediment sample collected from the sampling site closest to the terminal. The maximum concentrations in the sediment samples are above the natural ranges and are clearly indicative of technologica I influence. Mussel samples from the port of Sibenik showed levels of U activities in the range from 12.1 ±2.9 to 19.4±7.2 Bq kg" dry weight and 226 Ra activities from 1. 9 ± 0. 5 to 5. 9 ± 1.1 Bq kg" dry weight, which is somewhat higher than in consume mussels. Only the sea water sample at the sampling site, taken just above the bottom sediment, shows higher uranium concentration (3.1±0.2 f.Lg L ) comparing to the samples taken in upper sea water layers (2.1 ±0.2 f.Lg L ). Higher concentration is in the range of the concentration level of uranium in natural seawater. Since the transhipment terminal in the port of Sibenik was modernised in the eighties, the discharge of the phosphate ore into the seawater was drastically reduced and, consequently, uranium concentration levels in the seawater decreased. The enhanced uranium and radium activity levels are found only in the sediment near operational docks, and in the mussels which live on this docks.