Bioaccumulation of Heavy Metals in the Tissue of the Clam Galatea paradoxa and Sediments from the Volta Estuary, Ghana

The concentrations of heavy metals, Mn, Zn, Fe and Hg were determined in sediments and in the whole soft tissue of the clam Galatea paradoxa from two clam fishing locations, Ada and Aveglo at the Volta estuary in Ghana from March to September 2008. Thirty clams were obtained from each sampling location monthly and grouped into three size classes of 10 individuals each based on shell lengths as follows: small (25 -40mm), medium (41-55mm), and large (above 55mm). Metal concentrations in the tissues of the different clam size-classes from the two stations were similar and did not vary significantly.A comparative evaluation of the metal concentrations in the clams and sediments however, revealed significant variations in concentrations for Zn, Fe and, Hg. Concentration of Fe in the sediment from Ada for June was 18 times higher than the concentration in the clams similarly, Hg concentrations were approximately 5 times higher in the clam tissues than in the sediments. On the basis of calculated BSAFs the metal enrichment in the tissues of the clams rank in the following order Hg > Mn > Fe. The BSAFs indicated a significant accumulation of Hg in the clam tissues relative to the concentrations of other metals in the sediments. The concentrations of the studied metal in the clam and sediment samples are similar to those observed in areas under low pollution impact and the current the levels of contamination of these metals in the estuary do not exceed the clams’ capacity of regulation.