Investigating the mechanisms of silver nanoparticle toxicity in Daphnia magna: a multi-omics approach

The work presented in this thesis tests the hypothesis that AgNP toxicity is induced through the release of ionic silver (Ag) and therefore, that the mechanism of AgNP and Ag+ toxicity is identical. This hypothesis was tested through the comparison of molecular-level changes in Daphnia magna, a global keystone species of freshwater ecosystems, induced by AgNP and AgN03. Through use of Agilent microarray transcriptomics and direct-infusion mass spectrometry metabolomics, the same molecular profile changes were observed in D. magna exposed to AgNPs and to the dissolved Ag fraction alone. However, a greater magnitude of effect was observed in AgNP exposures. The measurement of the uptake and depuration of both forms of silver in D. magna suggested the increased magnitude of molecular response to AgNP exposure fit a Trojan-horse type mechanism. Whereby AgNPs absorbed by D. magna, resulted in higher internal concentration of toxic Ag+. Further investigation into the mechanism of AgNP toxicity revealed significant changes to constituents of the purine metabolism pathway and an absence of a traditional oxidative stress response. Overall, this research advances the mechanistic understanding of AgNP toxicity to aquatic organisms, and highlights the ability of omics technologies to provide unique insights into mechanisms of toxicity.