Bioaccumulation of mercury by clams (Meretrix meretrix) collected from the Saudi Coast of the Arabian Gulf

The objective of this study was to investigate Hg bioaccumulation in clams living in different salinities. Several hundred clams and samples of sediment were collected from 12 locations on the Saudi coast of the Arabian Gulf. To investigate size dependency of Hg accumulation, clams size was intentionally varied as much as possible. Soft tissue from each clam was removed carefully and wet digested separately. The collected sediment samples were air dried, sieved and wet digested. Concentrations of Hg in the digests were determined by cold vapor technique. Concentrations of Hg in the clam soft tissues ranged between 5 and 160 µg kg^-1 wet tissue weight. Analysis of variance revealed that inter-and intra-station differences in Hg concentrations in clams were significant (p <0.05). The maximum mean concentration of Hg was found in the clams collected from sampling station 1BA-a hypersaline relatively pristine location. In general (in 7 out of 11 locations), accumulation of Hg by clams was dependent on their size. It was found that Hg concentrations in sediments were poorly correlated to Hg accumulation by clams (p <0.05). The mean Hg concentrations in clams showed a positive correlation with seawater salinity. Thermodynamic calculations suggest that Hg-chloro complexes might be responsible for increased Hg bioaccumulation. It is proposed that size of clam and seawater salinity influence Hg bioaccumulation by clams from the Saudi coastal areas of the Arabian Gulf.