The rapid and unregulated introduction of silver nanoparticles (AgNPs) to the consumer market has raised concerns over their potential to impair essential biological processes within wastewater treatment plants (WWTPs). This work examines the toxicity and adsorption of 20 nm citrate capped AgNPs to Nitrosomonas europaea, a model ammonia oxidizing bacteria found in WWTPs, in the presence and absence of surrogate wastewater and natural water constituents, including bovine serum albumin (BSA), alginate, and Suwannee River Humic Acid (SRHA).  In the presence of NH3, AgNPs rapidly dissolved to form Ag(NH3)2+, which increased their toxicity towards N. europaea. BSA prevented this NH3-dependent dissolution by binding to the surface of the AgNPs blocking its interaction with NH3. Interestingly, AgNP dissolution became BSA-dependent with higher concentrations of BSA leading to higher dissolution rates. However, lower toxicity was observed with increasing BSA concentrations and was attributed to a two-fold mechanism: 1) the binding of dissolved Ag+ by the BSA and 2) decreased AgNP adsorption to N. europaeacells through electrosteric hindrances of the surface-sorbed BSA molecules.  Unlike BSA, alginate did not completely prevent NH3-dependent dissolution and did not bind dissolved Ag+, due to a lack of silver ligands. Alginate did interact with the AgNP surface which resulted in reduced dissolution rates and decreased adsorption to N. europaeathrough electrosteric hindrances. These interactions led to a decreased AgNP toxicity in the presence of high alginate concentrations.  SRHA followed a similar trend to alginate in which NH3-dependent dissolution was not completely prevented and SRHA did not bind dissolved Ag+ due to a lack of silver-binding ligands. Similar to alginate, SRHA did reduce toxicity by interacting with the AgNP surface and reducing the dissolution rates. SRHA also prevented AgNPs from adsorbing to N. europaea cells. However, unlike BSA and alginate, electrostatic repulsion was the main stabilization mechanism.

Influence of ammonia and macromolecules on the toxicity and adsorption of silver nanoparticles to <i>Nitrosomonas europaea</i>

248th National Meeting (2014)

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Influence of ammonia and macromolecules on the toxicity and adsorption of silver nanoparticles to Nitrosomonas europaea