Anthropogenically derived mercury in sediments of Pialassa Baiona, Ravenna, Italy

Pialassa Baiona, a coastal wetland near the city of Ravenna, has been impacted for two decades (1958-1978) by industrial discharges containing mercury and floating agglomerates of residues of polymerization processes. Although the industrial use of mercury completely ceased in the early 90's, surface sediments are still highly contaminated, mercury concentrations decreasing from the southern sub-basin, close to the discharge point, to the farthest northern border. Concentrations of total mercury, synthetic polymers (determined by pyrolysis-GC/MS), total organic carbon, C/N ratio, total sulfur and 210Pb dating, were determined in sediment cores collected in the southern and northern sub-basins. Mercury and polymers exhibited parallel profiles with a peak corresponding to the historic emission record in the southern core, while in northern cores peaks of maximum concentration display a delay reflecting the time required for the pollutants to migrate. A recently developed mercury sequential extraction procedure was applied to the most polluted layers to study inorganic mercury speciation. Results indicate differences between the southern and northern areas, suggesting a more efficient binding of mercury to sediments in the southern sub-basin.