Ecotoxicological impact of engineered nanomaterials in bivalve molluscs: An overview

The increasing production and application of engineered nanomaterials (ENMs) in consumer products over the past decade will inevitably lead to their release into aquatic systems and thereby cause the exposure to aquatic organisms, resulting in growing environmental and human health concern. Since bivalves are widely used in the monitoring of aquatic pollution, the aim of this review was to compile and analyse data concerning the ecotoxicity of ENMs using bivalve molluscs. The state of the art regarding the experimental approach, characterization, behaviour, fate, bioaccumulation, tissue and subcellular distribution and mechanisms of toxicity of ENMs in marine and freshwater bivalve molluscs is summarized to achieve a new insight into the mode of action of these nanoparticles in invertebrate organisms. This review shows that the studies about the toxic effects of ENMs in bivalves were conducted mainly with seawater species compared to freshwater ones and that the genus Mytilus is the main taxa used as a model system. There is no standardization of experimental approaches for toxicity testing and reviewed data indicate the need to develop standard protocols for ENMs ecotoxicological testing. In general, the main organ for ENM accumulation is the digestive gland and their cellular fate differs according to nano-specific properties, experimental conditions and bivalve species. Endosomal-lysosomal system and mitochondria are the major cellular targets of ENMs. Metal based ENMs mode of action is related mainly to the dissolution and/or release of the chemical component of the particle inducing immunotoxicity, oxidative stress and cellular injury to proteins, membrane and DNA damage. This review indicates that the aquatic environment is the potential ultimate fate for ENMs and confirms that bivalve molluscs are key model species for monitoring aquatic pollution by ENMs.