text: The silver nanoparticles that pass through wastewater treatment plants undergo transformations in the environment through changes in aggregation state, oxidation state, precipitation of secondary phases, or sorption of organic species. These transformations can result in the formation of colloidal solutions. Each of these new species potentially have toxic effects which have yet to be fully examined.
  Most silver nanoparticles in products have an organic shell structure around a core of Ag. This shell is often created with carboxylic acids functional groups, usually using citrate, leading to stabilization through adsorption or covalent attachment of organic compounds. In seawater, glutathione reacts with citrate to form a thioester via esterification.  
  Thioesters exhibit electrosteric repulsive forces due to amine functional groups and their size, which prevents aggregation. These electrostatic repulsive forces are weakened by counterions in solution, such as Ca found in seawater. Ca ions are naturally found in seawater due to the weathering of calcareous rocks, and allow for dissolution of the oxide-coated particle at low electrolyte concentrations.
  This leads to the aggregation of silver nanoparticles onto thioesters in seawater. When aggregation occurs, the silver nanoparticles lose microbial toxicity, but have greater exposure in the environment for larger organisms. These effects have not been completely identified, but may be hazardous to an organism’s health via biological magnification.