Metallothionein Levels in Gills and Visceral Mass of Ruditapes Philippinarum Exposed to Sublethal Doses of Cadmium and Copper

Metallothioneins (MTs) are widespread in various organisms, being suggested as specific biomarkers of heavy metal pollution, because their induction is obviously elevated by heavy metal exposure. Marine bivalves are suitable organisms for evaluating the impact of marine metal pollution. In this study we compare short-term, sub-lethal responses of one marine clam, Ruditapes philippinarum, exposed to Cu and Cd under laboratory conditions. MT concentrations are analyzed by mercury-saturation assay in gills and visceral mass of Ruditapes philippinarum collected from one control group and five experimental groups which differ by metal concentrations. Furthermore, MT concentrations are also studied in a time-series experiment after exposure to both metals. The visceral mass shows higher background values of MT than the gills. MT concentrations increase significantly in gills and visceral mass after Cu or Cd treatment for 5 days and the two metals show similar induced regulations in different organs after short-term exposure. But MT induced trend differs by Cu and Cd during the whole exposure time. In addition, it is also revealed that the ratio of MT inducement differs in gills and visceral mass. The inducible capacity of MT in visceral mass is greater than gills, therefore, MT in the visceral mass may combine great majority of the ingested heavy metals and prevent them from transferring to other organisms. We suggest that the MT in visceral mass of Ruditapes philippinarum be considered as a potential biomarker to indicate heavy metal pollution in marine system.