Marine bivalves, such as mussels and clams, have been extensively used as biological monitors of metal pollution in the coastal waters worldwide. Previous studies showed that the past history of metal contamination in the ambient environments can affect subsequent metal bioaccumulation, due to the modification of the animals’ physiological or biochemical processes under metal stress conditions. The metal binding protein, metallothioneins (MTs), can be induced by exposures of many metals (e.g., Cd, Zn and Hg) in various marine invertebrates, and thereby has a close relationship with metal body burden and plays an important role in metal detoxification, storage, and homeostasis in the aquatic animals....[ Read more ]

Marine bivalves, such as mussels and clams, have been extensively used as biological monitors of metal pollution in the coastal waters worldwide. Previous studies showed that the past history of metal contamination in the ambient environments can affect subsequent metal bioaccumulation, due to the modification of the animals’ physiological or biochemical processes under metal stress conditions. The metal binding protein, metallothioneins (MTs), can be induced by exposures of many metals (e.g., Cd, Zn and Hg) in various marine invertebrates, and thereby has a close relationship with metal body burden and plays an important role in metal detoxification, storage, and homeostasis in the aquatic animals.

In this study, a series of metal pre-exposures were carried out with the green mussel Perna viridis. Additionally, the clams Ruditapes philippinarum and Mactra veneriformis were collected from both metal contaminated and relatively unpolluted sites. By means of the sensitive radiotracer techniques, the indices of metal bioavailability, namely, assimilation efficiency (AE), dissolved uptake rate and efflux rate, were quantified to examine the controls of metal body burden and MT level on metal bioavailability in the bivalves pre-exposed to different metal stresses.

The results indicate that generally metal pre-exposure can influence subsequent metal bioaccumulation in the bivalves. The metal binding and storage strategies involved in this process are metal specific. The assimilation of Cd increases with the elevated Cd tissue burden, in correlation with an increase in the Cd associated with the MTLP fraction as well as a higher MT concentration. The increased AE and decreased dissolved uptake of Hg are likely caused by the induction of MT by Cd pre-exposure. The dietary uptake of Zn is enhanced when the MT is significantly induced by Cd. Contrarily, Ag biovailability is mainly controlled by sulfide binding, which can increase Ag accumulation from both solution and food and decrease efflux of the metal. Information presented in this study is important in understanding biomonitoring data of metal pollution in marine environment.