Bioaccumulation, toxicity and physico-chemical speciation of silver in bivalve molluscs: ecotoxicological and health consequences

Abstract The toxicity and bioaccumulation of silver have been studied comparatively in the freshwater bivalve Dreissena polymorpha and in four marine species: the oyster Crassostrea gigas , the mussel Mytilus galloprovincialis , the scallop Chlamys varia and the clam Scrobicularia plana . In the freshwater and marine mussels, the silver absorption was very limited but M. galloprovincialis was more susceptible than D. polymorpha . The oysters and scallops were silver accumulators but the effect of the metal was much more noxious in the second species. These data have demonstrated that no direct relationships exist between the global concentration in soft tissues and the susceptibility of the different bivalves. Thus the physico-chemical forms of storage of silver (silver sulphide, metal-binding proteinic compounds) were determined in each species and related to the high variability of biological responses. The modes of exposure (through food or water) influenced the binding of silver with cytosolic compounds (in oysters) and its biological effects (in scallops). Changes in salinity had only a moderate effect on silver bioaccumulation in oysters, a fact which is interesting since pollutions due to this metal often affect estuarine and coastal areas. In the light of these data, the potential injuries due to silver pollution may be attributable: (1) to noxious effects on susceptible species with a resulting imbalance of biocoenosis structure; and (2) to the existence of silver accumulation with a risk of transfer to the food web. However, the knowledge of the chemical speciation of silver in organisms permit to predict the importance of this risk.