Stability of nanoparticles in water.

Aqueous systems represent a likely carrier for manufactured nanoparticles upon their introduction into the natural environment. Their behavior in water, and in turn the risk that is posed by these materials to environmental and human communities, is a top concern. In terms of risk assessment, nanoparticle exposure to organisms is largely driven by their dispersion and behavior in aqueous systems, while their potential hazard, although not always well understood, is often related to their surface speciation. Both of these characteristics arise from the reactions that occur at the solid/liquid interface. The objective of this article is to establish the current state of the science with regard to the possible changes in surface properties and/or behavior of manufactured nanoparticles in different aqueous solutions of model and inorganic composition. The general reactions occurring at the nanoparticle/water interface, or between nanoparticles themselves, are first introduced. Following this, metal oxides, pure metals and carbon nanoparticles are considered on a case-by-case basis.