The stability of nanoparticles in soil and water environments is a key factor controlling their environmental fate. In order to accurately predict the fate of these emerging contaminants a much deeper understanding of the chemical modifications of nanoparticle surfaces, how they interact with organic matter, dissolve, precipitate, and agglomerate are required.  Therefore, the purpose of this topical session is to generate discussion on how recent advances in the area of chemical and physical alterations of nanoparticles will impact their transport in soil, water, and organisms.