Acute toxicity, bioaccumulation and effects of dietary transfer of silver from Artemia exposed to PVP/PEI-coated silver nanoparticles to zebrafish

Supervisor: Amaia Orbea (UPV/EHU)
Over the past decades until our days, there has been a continuous increase in the use of nanotechnologies and nanomaterials due to the great advances that science is experiencing in this field. Brand new types on engineered nanomaterials entail brand new properties with interesting commercial purposes. This is the case of nanosilver, which usage keeps growing, increasing its potential input into the ecosystems. This could lead to unforeseen health or environmental hazards. Up to now, there are few ecotoxicological studies that test concentrations of contaminants considered, according to prediction models, as environmentally relevant. Furthermore, the fate of nanosilver in the aquatic environment is largely unknown. Silver can be bioaccumulated by lower trophic level organisms, and then incorporated into the food chain, reaching higher level predators, which experience a silver transfer and also might experience a biomagnification process. Thus, in this study we have especially focused in these two aspects: (1) to test an environmentally relevant concentration in parallel with a likely effective dose, and (2) to test bioaccumulation and effects of silver transferred by the diet. For this, the small crustacean brine shrimp (Artemia sp.) and the vertebrate model zebrafish (Danio rerio) were used to simulate two trophic levels of a simplified food web. With the aim of quantifying silver bioaccumulation in both species, chemical analyses by ICP-MS were performed. Also, with the aim to localize the fate of silver in fish tissues, autometallography was employed. The greatest silver accumulation, amount of black silver deposits and biological effects were observed in organisms exposed to the highest dose of silver. Nevertheless, silver bioaccumulation was also detected by autometallography in the tissues of fish fed with brine shrimps exposed to the environmental dose of Ag nanoparticles and this silver transfer was enough to impair fish health as reflected by the reduction of the lysosomal membrane stability. In conclusion, in addition to being bioaccumulated and transferred through the food web, silver is able to exert toxic effects on organisms in a dose-dependent way, even at an environmentally relevant concentration, which should act as concern of the need of studies in further detail about real impact of nanomaterials in the environment and the need of usage regulations.