Mercury speciation and mobility at the sediment-water interface in Pialassa Baiona (Ravenna, Italy). Flux benthiques de mercure et de méthylmercure dans la région de Pialassa Baiona (Ravenne, Italie). Speciazione e mobilità del mercurio all’interfaccia acqua-sedimento in Pialassa Baiona (Ravenna, Italia)

Coastal marine environment represent areas of great natural, economic and touristic value. Among them, coastal lagoons are characterized by elevated ecological importance, but they are also particularly vulnerable to sediment contamination by a variety of pollutants. Previous research on mercury (Hg) showed strong contamination of the Pialassa Baiona (P.B.) Lagoon, near ravenna (Northern Adriatic Sea). The lagoon received between 100 and 200 tons of Hg generated by an acetaldheyde factory in 1957-1977. In this study Hg cycling at the sediment-water interface in the P.B. lagoon was investigated by means of an in situ benthic chamber. The in situ flux of Hg accounted for a comparable amount to that observed in the Grado lagoon (Northern Adriatic), a similar coastal environment where Hg contents in the sediments are almost 50% lower then in the P.B. lagoon. On the other hand, the 8-h integrated flux for the methylated form was extremely low and estimated to be only 7% of the corresponding flux in the Grado Lagoon. Despite the high contents of Hg buried in bottom sediments, the extemely anoxic conditions found in P.B. seem to limit Hg mobilization and bioavailability, mitigating the adverse effects of its accumulation in this environment.