Assimilation and bioconcentration of Ag and Cd by the marine black bream after waterborne and dietary metal exposure.

We determined the aqueous uptake and dietary assimilation of Cd and Ag by the marine black bream Acanthopagrus schlegeli following one to four weeks' exposure (or conditioning) to waterborne or dietary Cd or Ag at different concentrations. The concentrations of metals and metallothioneins (MT) in different tissues also were determined. The viscera contained the highest Ag, Cd, and MT concentrations after metal exposure. After exposure to waterborne metals, the metal and MT concentrations in the gills were higher than those in the remaining tissues (mainly muscles and bones), but this pattern was reversed following exposure to dietary metals. The assimilation efficiencies (AEs) of Cd and Ag ranged from 6 to 24% and 15 to 30%, respectively. The rate constant of uptake from the dissolved phase (ku) of Cd and Ag ranged from 2.2 to 7.5 and 8.0 to 31.7 L kg(-1) d(-l), respectively. In all the exposure experiments, the ku and AE increased with induced MT concentration and tissue metal concentration. Increasing metal accumulation may have been due to the increased available binding sites following the induction of MT in the fish. Furthermore, the MT induced by either Cd or Ag was not specific, but was able to bind with both metals and enhance bioaccumulation. Exposure to dissolved and dietary metals may increase metal accumulation, which potentially may lead to metal toxicity, although the fish may develop a tolerance to metals due to the apparent induction of MT.