Mercury in the bivalves Anadara ( Senilia) senilis, Perna perna and Crassostrea tulipa from Ghana

Three bivalves: Anadara ( Senilia) senilis ( n=220), Crassostrea tulipa ( n=260) from two ‘open’ lagoons (Benya and Ningo) and a ‘closed’ lagoon (Sakumo), and Perna perna ( n=170) from rocky shores adjacent to Benya and Sakumo, were analyzed for their total and organic Hg concentrations and total body burden. Median concentrations for cockles were 0.20 μg/g dw for the wet season and 0.36 μg/g dw for the dry season. Total mercury concentration for both mussels and oysters ranged from 0.04 to 0.84 μg/g dw. Seasonal variations and age effect were detected in all the species but no significant spatial variation was found along the coast. Organic (methyl) mercury concentration ranged from 0.03 to 0.55 μg/g dw was stable without age effect. The median relative organic mercury varied between 30 and 80% depending on the season, location, species and the type of lagoon. The lower concentrations in the wet season were due to primary production and dilution effect. Log-transformed regression relationships between body burden and size were used to compare the species.