Biomonitoring of mercury in polluted coastal area using transplanted mussels

The Kastela Bay is heavily polluted with inorganic mercury originated from direct discharges from the chlor-alkali plant, which operated in the period from 1950 to 1990. Even though the plant was closed 15 years ago, elevated levels of total mercury are still evident in surface sediments of the bay. In order to assess the availability of remobilized mercury to marine organisms, cultured mussels (M. galloprovincialis) were transplanted from pristine area to Kastela Bay, in the period from September 2000 to March 2001. Mussel samples were collected for the analysis of THg and MeHg in whole soft tissue, gills and digestive gland. Surface sediments and suspended matter were collected for the analysis of THg. Digestive gland was the target organ for the accumulation of THg, while concentrations of MeHg were similar in all analyzed tissues. The percentage of MeHg in mussel tissues (4-27%) was characteristic for the areas contaminated with inorganic mercury. A significant negative correlation was observed between the THg concentration in the tissues and the percentage of MeHg. Concentrations of THg in mussel tissues, which were decreasing from the source of contamination in an anticlockwise direction towards the exit of the bay, were significantly positively correlated to THg content in sediment and suspended particles. Spatial distribution of mercury species (THg and MeHg) in different environmental compartments was in accordance with the prevailing circulation in the bay. Data obtained through 6 months of biomonitoring experiment indicated that digestive gland was more sensitive indicator of THg concentrations in the environment than the whole organism or gills. As for MeHg, all tissues were equally suitable as biomonitors of MeHg concentrations in the environment.