Dispersion of mercury pollution from the point pollution source in the semi-enclosed coastal area – Kastela bay, Eastern Adriatic coast

Dispersion of mercury pollution from the point pollution source in the semi-enclosed coastal area – Kastela bay, Eastern Adriatic coast N. Mikac1, D. Barisic1, N.Cukrov1, S. Kozar1, G. Kniewald1, B. Ouddane2 1 Division for Marine and Environmental Research, Rudjer Boskovic Institute, Zagreb, Croatia 2 Université des Sciences et Technologies de Lille, UMR CNRS 8110 (PBDS), Equipe Chimie Analytique et Marine Bat C8, 59655 Villeneuve d’Ascq Cedex, France The greatest environmental problem of local pollution by mercury in Croatia has occurred in Kaštela Bay following 40 years activity (1950-1990) of the chlor-alkali plant located on the northeastern coast of the Bay. It was estimated that about 50 tons of mercury has been introduced into the bay. Elevated mercury concentrations in sediments and bioaccumulation of total and methyl mercury in marine organisms of this area were demonstrated. The most recent study (2002) still showed very high concentrations of total mercury (up to 70 mg/kg) in sediments in front of the factory and favorable conditions for mercury methylation (up to 50 μg/kg of MeHg). High concentration of mercury in sediments in the different parts of the bay indicated that mercury is efficiently transported from the pollution source. In this work attempt was made to quantify dispersion of mercury from the point pollution source over the whole bay and the export of mercury from the bay into the coastal area. More than 80 sediment cores (up to 100 cm long) were sampled over the entire surface of the bay. Cores were sliced into 5 or 10 cm layers and concentration of total mercury, as well as level of radionuclides (natural U and its decay series products and artificial 137Cs) were determined in sediment sub-samples. It was recently shown that the sediments in front of the factory are also contaminated by uranium originating from the coal burning products of the thermoelectric factory unit. Therefore, comparing distributions of these two pollutants may help to elucidate the mechanism of transport of mercury from the pollution source. Data showed that generally the first 15 cm of the sediment over the whole bay are contaminated by mercury and that, in most of the sites, this contamination is still evident at depths greater than 50 cm. Principal pathways of mercury transport by sediment and its quantification will be discussed in the paper.