The objective of this thesis was to evaluate the toxicity of silver nanoparticles at predicted environmentally relevant concentrations (i.e. 0.01, 0.1, 0.5 and 1.0 mg/L by mass of nanoparticles). One concentration of silver nitrate (0.01 mg/L) was included to compare the effects of silver ions (from AgNO3) with effects of the same concentration of nanoparticles. Zebrafish (Danio rerio) larvae were exposed in a critical window of larval development (i.e. 6 dpf – 21 dpf) to quantify effects on survival, growth and changes in gene expression.
Suspended nanoparticles were found to be polydispersed and there was a tendency towards broader size distributions and bigger agglomerates with increasing concentration. No negative effects were observed in survival or growth. However, exposure to the highest concentration of silver nanoparticles (1.0 mg/L) resulted in a significant positive effect on survival. Microbiological analysis of water samples from the exposure tanks showed that there were more microorganisms in the sample collected from the highest exposure concentration, indicating that increased survival was most likely not explained by antibacterial properties of silver nanoparticles. Changes in gene expression following exposure to equal concentrations of silver nanoparticles and silver nitrate (i.e. 0.01 mg/L) resulted in distinctive gene expression profiles, with silver nanoparticles inducing changes in a much higher number of genes than silver nitrate. Both gene expression profiles were identified by Ingenuity Pathway analysis to associate with the visual system and cardiovascular health. Silver nanoparticles induced changes in several genes involved in the negative feedback-loop of the circadian rhythm system and pathways associated with the activation of nuclear receptors. It could be interesting to investigate if these effects on the gene level will manifest itself on a later stage of development.