Metallothionein induction and bioaccumulation kinetics of Cd and Ag in the marine fish Terapon jarbua challenged with dietary or waterborne Ag and Cu

A series of experiments were conducted to determine the effects of sublethal pre-exposure of dissolved and dietary silver (Ag) and copper (Cu) on the subsequent Ag and cadmium (Cd) bioaccumulation by the marine 3-line theraponids Terapon jarbua. Parameters measured in this study included the accumulated metal concentration and metallothionein (MT) induction in different fish tissues, and the dietary assimilation efficiency (AE) and dissolved uptake of Ag and Cd. An obvious increase in the Ag (up to 4-fold) or Cu (up to 2-fold) body concentration and MT induction (up to 2-fold) in fish was observed following 1 wk waterborne or dietary exposure. However, MT induction was not sufficient to bind with the accumulated metals, and the accumulated Cu and Ag were also bound with ligands other than MT. There was a significant correlation between the accumulated Ag or Cu concentration and the MT induction. However, MT induction in the muscle was more responsive to dietary Ag exposure than to waterborne Ag exposure. The AE and the dissolved uptake rate constant of Ag and Cd both increased in response to waterborne and dietary Cu or Ag pre-exposure. In contrast, the efflux rate constant for Ag and Cd decreased in response to Cu or Ag pre-exposure. The quantified biokinetic parameters of Ag or Cd were significantly correlated with the accumulated body burdens of Ag and Cu, and the induced MT concentration. Such a relationship may also be dependent on the route of metal pre-exposure. For Ag, the biokinetic modification was obvious when Ag exceeded 1.5 mu g g(-1) dry weight. Our study also demonstrated that simultaneous exposure to dissolved Ag and Cu had an antagonistic effect on Cu and Ag bioaccumulation, probably as a result of competition between Cu+ and Ag+ for binding sites.