Engineered nanoparticles (ENPs) undergo physicochemical transformations in aquatic environments that influence their stability, dissolution, and toxicity. Silver nanoparticles (nAg) are of particular concern because they release bioavailable Ag⁺ ions. Phytoplankton-derived extracellular polymeric substances (EPS) and exometabolites can adsorb onto nanoparticle surfaces, forming an ecocorona that modifies their environmental behavior. However, the respective roles of these biomolecules remain insufficiently understood.
This thesis investigated how extracellular biomolecules released by the freshwater phytoplankton Cyclotella meneghiniana and Chlamydomonas reinhardtii influence nAg fate, transformations, and toxicity. Advanced analytical techniques, mechanistic experiments, and theoretical modeling were used to characterize nanoparticle–biomolecule interactions.
A critical review established the conceptual framework, while asymmetrical flow field-flow fractionation (AF4) coupled with multiple detectors demonstrated its potential for characterizing nAg interactions with phytoplankton-derived EPS in complex matrices.
Experimental results showed that EPS form ecocoronas that modify nAg colloidal stability and dissolution. Diatom-derived EPS enhanced stability through steric repulsion and reduced dissolution. Extended DLVO modeling further demonstrated that C. reinhardtii EPS increased energy barriers to particle collision, enhancing colloidal stability.
The effects on toxicity depended on nanoparticle surface chemistry. EPS reduced dissolution and mitigated the toxicity of citrate-coated nAg toward phytoplankton, whereas interactions with lipoic-acid-coated nAg promoted dissolution and increased toxicity.
Finally, targeted metabolomics identified extracellular metabolites from C. reinhardtii that associated with nAg surfaces. Comparisons between EPS-containing exudates and low-molecular-weight metabolites revealed matrix-dependent interactions, indicating that EPS modulate metabolite association with nanoparticles.
Overall, this thesis demonstrates that phytoplankton-derived EPS and exometabolites regulate nAg aggregation, stability, dissolution, and toxicity. These findings provide mechanistic insights into nanoparticle transformations at the nano–bio interface and highlight the importance of ecocorona formation in the environmental risk assessment of engineered nanomaterials.
