Depuration and bioaccumulation of heavy metals by clams from Tolo Harbour, Hong Kong

The concentrations of 6 heavy metals (Cd, Cr, Cu, Pb, Zn and Ni) in 3 species of clams collected from 2 sites of Tolo Harbour, Hong Kong (Circe sinensis and Gafrarium fumidum from Sha Lan, and Tapes philippinarum from Lok Wo Sha;) were determined. In general, the contents of all the metals were rather low, except Zn (44, 58, and 98 mg/g dry weight basis respectively, for the 3 clam species) The 3 species of clams were placed in artificial seawater, the metal concentrations in their soft tissues were monitored daily for 7 days and the final metal concentrations were compared with the initial concentrations. Levels of Zn, Cr and Ni decreased, Cd and Pb increased significantly (p < 0.05), while Cu did not differ significantly (p > 0.05) in C. sinensis. As to G. fumidum, no significant differences were noted for most metals (Cd, Cr, Cu and Zn) and significant increases were observed for Pb and Ni. T. philippinarum showed a significant decline in Zn level but significant increases in Ni and Cd levels, while Cu, Cd and Cr levels remained more or less the same. By placing the clams in artificial seawater added with Yau Ma Tei Typhoon Shelter sediment, one of the most polluted sediments in Hong Kong for 12 days, significant increases (p < 0.05) in Zn, Pb, Cd and Cu levels were detected in C. sinensis whereas G. fumidum had significant increases (p < 0.05) in Cu and Pb, and T. philippinarum showed a significant rise (p < 0.05) in Cd level.